report the working directory to the terminal with OSC 7

Before each prompt gosh sends ESC ] 7 ; file://host/path BEL (host and
path percent-encoded), so terminals like GNOME Terminal open new tabs
and windows in the directory of the shell instead of the one gosh was
started in. Nothing is sent if stdout is not a terminal or TERM=dumb.

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>

README.md

@@ -11,18 +11,32 @@ Built-in commands:
   exit [code]   - Exit shell with status code (default: $?)
   quit [code]   - Quit shell with status code (default: $?)
   set VAR=val   - Set environment variable
+  set [-ex] [-o pipefail] [--] [args] - Options: -e exit when a command
+                  fails, -x print commands, -o pipefail; args are $1, ...
+                  (set: show variables, set -o: show options)
   export VAR=val - Export environment variable
-  unset VAR     - Remove a variable
+  unset VAR     - Remove a variable (unset -f name: a function)
-  source file   - Run the commands of file in this shell (also: . file)
+  source file [args] - Run the commands of file in this shell (also: . file)
   jobs          - List background and stopped jobs
   fg [%n]       - Continue job n (default: current job) in the foreground
   bg [%n]       - Continue stopped job n in the background
-  wait [%n]     - Wait for job n or all background jobs
+  wait [%n|pid] - Wait for job n (or process pid, e.g. $!) or all jobs
   alias [name[=value] ...] - Define or show aliases (alias ll='ls -l')
   unalias name  - Remove an alias (unalias -a: all aliases)
   :             - Do nothing (exit status 0)
   break [n]     - Leave the innermost (or n-th) for/while/until loop
   continue [n]  - Continue with the next iteration of a loop
+  return [n]    - Leave a function or sourced file with status n
+  local VAR[=val] - Variable that gets its old value back when the
+                  function returns
+  shift [n]     - Remove the first n positional parameters (default 1)
+  read [-r] [-p prompt] [VAR ...] - Read a line into variables (split
+                  at $IFS; the last one gets the rest; default $REPLY)
+  eval args     - Run the arguments as a command in this shell
+  exec [cmd]    - Replace the shell with cmd; without cmd, its
+                  redirections apply to the shell (exec > log)
+  trap [cmd] SIG... - Run cmd on a signal (INT, TERM, HUP, USR1, ...)
+                  or on EXIT; trap '' SIG ignores it, trap - SIG resets
   help          - Show this help
 
 Features:
@@ -45,11 +59,23 @@ Features:
     GOSH_COLORS='user=1;33:path=36' (keys user, root, path, error; values
     are ANSI SGR codes, empty = no color); disabled with $NO_COLOR,
     TERM=dumb or when output is not a terminal
+  - Reports the working directory to the terminal (OSC 7) before each
+    prompt, so new tabs/windows open in the same directory
   - Variables: name=value sets a variable (like set), name=value command
     sets it only for that command; the value is not split or expanded as
     a pattern
   - Environment variable expansion ($VAR, ${VAR}, ${VAR:-default});
     using an unset variable is an error, use ${VAR:-} for an empty default
+  - Parameter expansion: ${#VAR} (length), ${VAR#pat} ${VAR##pat}
+    ${VAR%pat} ${VAR%%pat} (remove prefix/suffix), ${VAR/pat/rep}
+    ${VAR//pat/rep}, ${VAR:offset:length}, ${VAR-x} ${VAR:=x} ${VAR:+x}
+    ${VAR:?msg}
+  - Arithmetic: $((expression)) with integers and the C operators
+    (+ - * / % ** << >> < == && || ?: = += ++ ...)
+  - Positional parameters: $0, $1 ... $9, ${10}, $# (count), "$@" (one
+    word each), "$*" (one word), $$ (process ID), $! (process ID of the
+    last background job); set by gosh script
+    args, gosh -c command name args, functions, set -- and source
   - Command substitution: $(command) is replaced by the output of command
     (run in a subshell); unquoted it is split into words, "$(command)"
     stays one word
@@ -57,9 +83,16 @@ Features:
     a || b (b only if a failed); $? is the exit status of the last command
   - Control structures: if cmd; then ...; elif cmd; then ...; else ...; fi,
     for x in words; do ...; done, while cmd; do ...; done, until ...,
-    ! cmd negates the status; they can span several lines (prompt "> ")
+    case word in pattern|pattern) ...;; esac, { cmd; cmd; } groups,
+    ( cmd; cmd ) subshells; ! cmd negates the status; they can span
+    several lines (prompt "> "), have redirections (done < file) and can
+    be used in pipes (| while read l; do ...; done) and with &
+  - Functions: name() { ...; } (or function name { ...; }); the arguments
+    are $1, $2, ...; in pipes, & and $(...) they run in a subshell
   - Pipes (a | b) and redirections: < file, > file, >> file, 2> file,
-    2>> file, 2>&1, >&2, &> file (stdout and stderr), &>> file
+    2>> file, 2>&1, >&2, &> file (stdout and stderr), &>> file,
+    <<EOF here-documents (<<-EOF strips tabs, <<'EOF' expands nothing),
+    <<<word here-strings
   - Job control: command & runs in the background, Ctrl+Z stops the
     foreground job; jobs, fg, bg and wait manage the jobs
   - Aliases replace the first word of a command in interactive shells
@@ -75,8 +108,8 @@ Features:
 ### Aufruf
 
 ```
-gosh [-l] [-i] [--norc] [--noprofile] [script]
+gosh [-l] [-i] [-ex] [-o option] [--norc] [--noprofile] [script [args ...]]
-gosh [-l] [--noprofile] -c command
+gosh [-l] [-ex] [-o option] [--noprofile] -c command [name [args ...]]
 gosh -version
 ```
 
@@ -84,12 +117,14 @@ gosh -version
 |------------------------|------------------------------------------------------------------|
 | `gosh`                 | interaktive Shell (wenn stdin ein Terminal ist)                  |
 | `gosh -c 'befehl'`     | führt den Befehl aus und beendet sich                            |
-| `gosh skript.gosh`     | führt das Skript Zeile für Zeile aus                             |
+| `gosh -c 'befehl' name a b` | wie oben, mit `$0` = `name`, `$1` = `a`, `$2` = `b`         |
+| `gosh skript.gosh a b` | führt das Skript Zeile für Zeile aus, `$1` = `a`, `$2` = `b`     |
 | `befehle \| gosh`      | liest die Befehle von stdin                                      |
 | `-i`                   | erzwingt den interaktiven Modus, auch ohne Terminal              |
 | `-l`, `--login`        | Login-Shell, liest die Profil-Dateien (siehe unten)              |
 | `--norc`               | `goshrc`-Dateien nicht lesen                                     |
 | `--noprofile`          | `profile`-Dateien nicht lesen                                    |
+| `-e`, `-x`, `-o option` | Optionen wie bei `set` (z. B. `gosh -e skript`, `-o pipefail`)  |
 
 Ohne Terminal bricht gosh bei einem fehlgeschlagenen Befehl nicht ab und beendet sich mit dem Exit-Status des letzten Befehls: `127`, wenn ein Befehl nicht gefunden wurde, `126`, wenn er nicht ausführbar ist, `128+n`, wenn er durch Signal `n` beendet wurde. Leere Zeilen und Zeilen, die mit `#` beginnen, werden übersprungen, Skripte können also mit `#!/usr/bin/gosh` beginnen.
 
@@ -137,7 +172,7 @@ export PATH=$HOME/bin:$PATH
 
 ### Kontrollstrukturen
 
-gosh kennt `if`, `for`, `while` und `until` wie `sh`, auf einer Zeile oder über mehrere Zeilen:
+gosh kennt `if`, `for`, `while`, `until`, `case`, `{ …; }` und `( … )` wie `sh`, auf einer Zeile oder über mehrere Zeilen:
 
 ```bash
 if [ -f ~/.goshrc ]; then
@@ -157,10 +192,19 @@ for i in {1..5}; do echo "Durchlauf $i"; done
 n=3
 while [ $n -gt 0 ]; do
   echo $n
-  n=$(expr $n - 1)
+  n=$((n - 1))
 done
 
 until ping -c1 -W1 server >/dev/null; do sleep 1; done
+
+case "$1" in
+  start|run) echo "starte" ;;
+  stop)      echo "stoppe" ;;
+  *.tar.gz)  tar xzf "$1" ;;
+  *)         echo "unbekannt: $1" ;;
+esac
+
+test -d build || { echo "kein build-Verzeichnis"; exit 1; }
 ```
 
 | Konstrukt                                   | Bedeutung                                                         |
@@ -169,17 +213,156 @@ until ping -c1 -W1 server >/dev/null; do sleep 1; done
 | `for x in wörter; do …; done`               | setzt `x` nacheinander auf jedes Wort                             |
 | `while befehl; do …; done`                  | wiederholt, solange `befehl` erfolgreich ist                      |
 | `until befehl; do …; done`                  | wiederholt, bis `befehl` erfolgreich ist                          |
+| `case wort in muster\|muster) …;; esac`     | führt den ersten Zweig aus, dessen Muster auf `wort` passt        |
+| `{ befehl; befehl; }`                       | fasst Befehle zusammen (z. B. nach `\|\|`)                         |
+| `( befehl; befehl )`                        | führt die Befehle in einer Subshell aus                           |
 | `! befehl`                                  | kehrt den Exit-Status um                                          |
 | `break [n]`, `continue [n]`                 | verlässt die (n-te) Schleife bzw. springt zum nächsten Durchlauf  |
 | `:`                                         | tut nichts, Exit-Status 0 (z. B. `while :; do …; done`)           |
 
 - Bedingungen sind normale Befehle (auch Listen mit `&&`/`||`), meist `test` bzw. `[ … ]` (z. B. `[ -f datei ]`, `[ "$a" = b ]`, `[ $n -lt 3 ]`).
-- Die Wörter nach `for … in` werden wie Argumente expandiert: `*.go`, `{1..10}`, `$VAR`, `$(befehl)`. Ohne `in` läuft die Schleife nicht (Positionsparameter gibt es nicht).
+- Die Wörter nach `for … in` werden wie Argumente expandiert: `*.go`, `{1..10}`, `$VAR`, `$(befehl)`, `"$@"`. Ohne `in` läuft die Schleife über die Positionsparameter (`for a; do …` ist `for a in "$@"; do …`).
+- `case`: Die Muster sind Wildcards wie bei Dateinamen (`*`, `?`, `[…]`), nur passen `*` und `?` hier auch auf `/`. Mehrere Muster werden mit `|` getrennt, das `(` vor dem Muster ist optional, das `;;` im letzten Zweig auch. Zeichen in Anführungszeichen passen nur wörtlich (`"*")` passt nur auf `*`). Wie überall in gosh sind Werte von Variablen keine Muster: Nach `p='*.go'` passt `$p)` nur auf den Text `*.go`. Passt kein Muster, ist der Status 0.
+- `{ …; }`: `{` und `}` sind nur am Anfang eines Befehls Schlüsselwörter, vor dem `}` muss deshalb ein `;` oder ein Zeilenumbruch stehen. Die Befehle laufen in der Shell selbst (keine Subshell).
 - Variablen, `$(...)` und Wildcards im Rumpf werden bei jedem Durchlauf neu ersetzt.
 - Ist ein Befehl noch nicht vollständig (z. B. nach `if …; then` oder `for …` + Enter, nach `&&`, `|` oder einem `\` am Zeilenende), zeigt gosh den Fortsetzungs-Prompt `> `; Ctrl+C verwirft die angefangene Eingabe. Skripte und Startdateien lesen entsprechend weiter.
 - Ctrl+C bricht die ganze Befehlszeile ab, also auch eine Schleife (`while true; do sleep 1; done`).
 - Der Exit-Status ist der des zuletzt ausgeführten Befehls; ein `if` ohne passenden Zweig und eine Schleife ohne Durchlauf haben den Status 0.
-- Nicht unterstützt: Kontrollstrukturen in Pipes (`for …; done | sort`), mit Umleitung (`done > datei`) oder im Hintergrund (`done &`), außerdem `case`, Funktionen und `read`. Arithmetik geht z. B. mit `n=$(expr $n + 1)`.
+- Zum Rechnen in Bedingungen und Schleifen siehe [Arithmetik](#arithmetik): `while [ $i -lt 10 ]; do i=$((i + 1)); done`.
+
+### Umleitungen, Pipes und Hintergrund bei Kontrollstrukturen
+
+Kontrollstrukturen lassen sich wie einfache Befehle umleiten, in Pipes verwenden und im Hintergrund starten:
+
+```bash
+# Datei Zeile für Zeile lesen
+while read -r name rest; do
+  echo "Name: $name"
+done < /etc/passwd
+
+# Ausgabe einer Schleife sortieren bzw. umleiten
+for f in *.log; do wc -l < "$f"; done | sort -n
+if make; then echo ok; else echo kaputt; fi > build.status 2>&1
+{ date; uptime; } >> status.log
+
+# Zeilen aus einer Pipe verarbeiten
+git ls-files | while read -r f; do echo "== $f"; done
+
+# Schleife im Hintergrund
+for host in a b c; do ping -c1 $host; done > ping.log &
+```
+
+- Umleitungen nach `done`, `fi`, `esac`, `}` und `)` gelten für alle Befehle darin. Die Kontrollstruktur läuft dabei in der Shell selbst, Variablen aus `while read x; do …; done < datei` sind danach also gesetzt.
+- In einer Pipe und im Hintergrund (`&`) läuft eine Kontrollstruktur (wie in `sh`) in einer Subshell, einem eigenen gosh-Prozess, weil alle Teile einer Pipe gleichzeitig laufen. Variablen, die dort gesetzt werden, gelten danach nicht mehr: Nach `ls | while read f; do n=$f; done` ist `n` nicht gesetzt. Die Subshell kennt die Funktionen und Positionsparameter der Shell.
+- Auch Listen lassen sich in den Hintergrund schicken: `make && make install &` läuft als ein Job in einer Subshell.
+- Mit Ctrl+C wird die ganze Pipe abgebrochen, auch eine Endlosschleife wie `while true; do date; sleep 1; done | tee log`.
+
+### Subshells
+
+`( befehle )` führt Befehle in einer Subshell aus, einem eigenen gosh-Prozess. Änderungen an Verzeichnis, Variablen und Funktionen gelten nur dort:
+
+```bash
+(cd /tmp && tar xzf ~/paket.tar.gz)    # danach ist man noch im alten Verzeichnis
+(export LANG=C; sort datei)
+(exit 3); echo $?                      # 3
+(cd build && make) > build.log 2>&1
+```
+
+- `exit` beendet nur die Subshell, ihr Exit-Status ist der des letzten Befehls bzw. von `exit`.
+- Die Subshell bekommt alle Variablen (in gosh sind alle exportiert), die Funktionen und die Positionsparameter. Aliase gelten dort nicht (wie in Skripten).
+- `{ …; }` fasst dagegen Befehle zusammen, ohne eine Subshell zu starten.
+- `(` und `)` sind Operatoren: Ein Wort wie `a(b)` ist ein Syntaxfehler, Klammern als Text brauchen Anführungszeichen oder `\` (`echo "(a)"`, `find . \( -name x \)`).
+
+### Funktionen
+
+```bash
+# Definition (auch: function gruss { … })
+gruss() {
+  local name=${1:-Welt}       # local: nur in der Funktion
+  echo "Hallo $name"
+}
+
+gruss                       # Hallo Welt
+gruss Flo                   # Hallo Flo
+gruss Flo > datei           # Umleitungen gelten für alle Befehle der Funktion
+gruss Flo | tr a-z A-Z      # auch in Pipes
+x=$(gruss Flo)
+
+ist_root() {
+  [ "$(id -u)" = 0 ] && return 0
+  return 1
+}
+ist_root || echo "kein root"
+
+# Die Funktion liest von stdin
+zeilen() {
+  while read -r zeile; do echo "> $zeile"; done
+}
+zeilen < /etc/hostname
+ls | zeilen
+```
+
+- Eine Funktion wird mit `name() { …; }`, `name () { …; }` oder `function name { …; }` definiert. Der Rumpf ist ein zusammengesetzter Befehl, meist `{ …; }`, aber auch `if`, `for`, `while` oder `case` sind möglich. Die Definition darf über mehrere Zeilen gehen.
+- Die Argumente des Aufrufs sind in der Funktion `$1`, `$2`, …, `$#` und `"$@"`; danach haben die Positionsparameter wieder ihre alten Werte. `$0` bleibt der Name des Skripts.
+- `return [n]` beendet die Funktion mit dem Status `n` (ohne `n`: der Status des letzten Befehls). Ohne `return` ist der Status der des letzten Befehls.
+- Funktionen laufen in der Shell selbst: Variablen, die sie setzen, und `cd` gelten danach weiter. `local name[=wert]` macht eine Variable lokal, sie bekommt beim Verlassen der Funktion ihren alten Wert zurück (Funktionen, die von dort aufgerufen werden, sehen den lokalen Wert).
+- `name=wert funktion` setzt die Variable nur während des Aufrufs.
+- In einer Pipeline, im Hintergrund (`funktion &`) und in `$(...)` läuft eine Funktion in einer Subshell, Änderungen an Variablen gehen dort also verloren (wie in `sh`). Die Subshell kennt alle Funktionen.
+- Eine Funktion hat Vorrang vor Built-ins und Programmen gleichen Namens. Weil es noch kein `command` gibt, kann eine Funktion `ls` das Programm `ls` aber nicht aufrufen. Mit `\ls` umgeht man nur Aliase. Besser ist ein anderer Name, z. B. `ll() { ls -l "$@"; }`.
+- `unset -f name` entfernt eine Funktion. Rekursion ist erlaubt, aber nur bis zu einer Tiefe von 1000.
+- Namen dürfen aus Buchstaben, Ziffern, `_`, `-` und `.` bestehen (nicht mit einer Ziffer oder `-` beginnend). Funktionen werden auch mit Tab vervollständigt.
+
+### Positionsparameter
+
+| Parameter          | Bedeutung                                                        |
+|--------------------|------------------------------------------------------------------|
+| `$0`               | Name des Skripts (bzw. `name` bei `gosh -c befehl name`)         |
+| `$1` … `$9`, `${10}` | die Argumente                                                  |
+| `$#`               | Anzahl der Argumente                                             |
+| `"$@"`             | alle Argumente, jedes als eigenes Wort                           |
+| `"$*"`             | alle Argumente als ein Wort, durch Leerzeichen getrennt          |
+| `$$`               | Prozess-ID der Shell                                             |
+| `$!`               | Prozess-ID des letzten Hintergrund-Jobs (`wait $!`, `kill $!`)   |
+
+```bash
+#!/usr/bin/gosh
+# aufruf: skript.gosh [-v] datei ...
+if [ $# -eq 0 ]; then
+  echo "usage: $0 [-v] datei ..." >&2
+  exit 2
+fi
+verbose=no
+case $1 in
+  -v) verbose=yes; shift ;;
+esac
+for f in "$@"; do
+  test $verbose = yes && echo "verarbeite $f"
+  wc -l "$f"
+done
+```
+
+- Gesetzt werden sie von `gosh skript a b`, `gosh -c befehl name a b`, beim Aufruf einer Funktion, mit `source datei a b` (nur während die Datei läuft) und mit `set -- a b c`.
+- `shift [n]` entfernt die ersten `n` (Standard: 1) Parameter, `$2` wird zu `$1` usw.
+- Wie bei Variablen ist ein nicht gesetzter Parameter ein Fehler: `$1` ohne Argumente meldet `1: unbound variable`. Für optionale Argumente `${1:-}` bzw. `${1:-standard}` verwenden oder vorher `$#` prüfen.
+- `"$@"` ohne Argumente ergibt kein Wort (auch nicht das leere). Ohne Anführungszeichen verhalten sich `$@` und `$*` wie `"$@"`, da gosh Werte nie an Leerzeichen teilt.
+
+### read
+
+`read` liest eine Zeile von stdin und verteilt sie auf Variablen:
+
+```bash
+read -p "Name? " name                  # Eingabe vom Terminal mit Prompt
+read vorname nachname < name.txt       # erste Zeile einer Datei
+read -r zeile                          # Backslashes nicht auswerten
+while read -r zeile; do echo "$zeile"; done   # in einem Skript: alle Zeilen von stdin
+```
+
+- `read name1 name2 …` teilt die Zeile an den Zeichen von `$IFS` (Standard: Leerzeichen, Tab, Zeilenumbruch). Jede Variable bekommt ein Feld, die letzte den Rest der Zeile. Bei zu wenigen Feldern werden die übrigen Variablen leer. Leerzeichen am Anfang und Ende werden entfernt. Andere `IFS`-Zeichen trennen genau ein Feld (`IFS=:` macht aus `a::b` die Felder `a`, ``, `b`).
+- Ohne Namen landet die ganze Zeile unverändert in `$REPLY`.
+- Ohne `-r` maskiert `\` das nächste Zeichen (`a\ b` bleibt ein Feld), und ein `\` am Zeilenende setzt die Zeile fort. `-p prompt` gibt den Prompt auf stderr aus, wenn stdin ein Terminal ist.
+- Der Status ist 0, oder 1 am Ende der Eingabe (die Variablen werden trotzdem mit dem Rest gesetzt). So endet `while read …` nach der letzten Zeile.
+- `read` liest Byte für Byte und damit nie mehr als eine Zeile, den Rest bekommen die nächsten Befehle. Ctrl+C bricht `read` in der interaktiven Shell ab (Status 130).
+- `read` verändert die Shell und lässt sich deshalb nicht als einfacher Befehl in einer Pipeline verwenden (`echo a | read x`, in `sh` wirkungslos). Umleitungen funktionieren: `read x < datei`, `read x <<< "$text"`, `while read l; do …; done < datei`. In einer Schleife in einer Pipe (`… | while read l; do …; done`) geht es auch, da die ganze Schleife in einer Subshell läuft.
 
 ### Variablen
 
@@ -202,6 +385,60 @@ echo $name ${name:-standard}
 - Variablen in den Argumenten werden ersetzt, bevor die Zuweisung davor gilt: `x=1 echo $x` gibt nicht `1` aus, sondern meldet `x: unbound variable` (wenn `x` vorher nicht gesetzt war).
 - In einer Pipeline (`x=1 | cat`) ändert eine Zuweisung die Shell nicht.
 
+### Parameter-Expansion
+
+```bash
+datei=/home/flo/bilder/urlaub.tar.gz
+echo ${#datei}            # 30        Länge
+echo ${datei##*/}         # urlaub.tar.gz   wie basename
+echo ${datei%/*}          # /home/flo/bilder  wie dirname
+echo ${datei%%.*}         # /home/flo/bilder/urlaub
+echo ${datei#*.}          # tar.gz
+echo ${datei/flo/anna}    # /home/anna/bilder/urlaub.tar.gz
+echo ${datei//\//:}       # :home:flo:bilder:urlaub.tar.gz
+echo ${datei:0:5}         # /home
+echo ${port:-8080}        # Standardwert, wenn port leer oder nicht gesetzt
+: ${EDITOR:=vim}          # Standardwert setzen
+echo ${1:?datei fehlt}    # Fehler, wenn kein Argument
+```
+
+| Ausdruck              | ergibt                                                              |
+|-----------------------|---------------------------------------------------------------------|
+| `${#name}`            | Länge des Werts in Zeichen                                          |
+| `${name#muster}`      | Wert ohne das kürzeste passende Präfix (`##`: das längste)          |
+| `${name%muster}`      | Wert ohne das kürzeste passende Suffix (`%%`: das längste)          |
+| `${name/muster/neu}`  | ersetzt den ersten (längsten) Treffer, `//` alle, `/#` nur am Anfang, `/%` nur am Ende |
+| `${name:anfang}`, `${name:anfang:länge}` | Teilstring; negativer Anfang zählt vom Ende (`${x: -2}`), negative Länge lässt Zeichen am Ende weg |
+| `${name:-wort}`       | `wort`, wenn `name` nicht gesetzt oder leer ist, sonst der Wert     |
+| `${name:=wort}`       | wie `:-`, setzt `name` aber auch auf `wort`                         |
+| `${name:+wort}`       | `wort`, wenn `name` gesetzt und nicht leer ist, sonst nichts        |
+| `${name:?meldung}`    | Fehler mit `meldung`, wenn `name` nicht gesetzt oder leer ist       |
+| `${name-wort}` usw.   | ohne `:`: nur „nicht gesetzt“ zählt, ein leerer Wert nicht          |
+
+- Das Wort bzw. Muster wird expandiert (Variablen, `$(…)`, `$((…))`, Anführungszeichen, `~`), aber nicht in Wörter geteilt. Verschachteln geht: `${a:-${b:-c}}`.
+- Muster sind Wildcards wie bei Dateinamen (`*`, `?`, `[…]`), nur passen `*` und `?` auch auf `/`. Zeichen in Anführungszeichen und Werte von Variablen passen nur wörtlich (wie überall in gosh): `${x%"*"}` entfernt einen `*` am Ende, `${x%$suffix}` den Text von `$suffix`.
+- Mit `+`, `-`, `?` und `=` gibt es keinen Fehler für nicht gesetzte Variablen, alle anderen Formen melden `unbound variable`.
+- Längen und Teilstrings zählen Zeichen, nicht Bytes (`${#x}` für `Grüße` ist 5).
+- `${name:?…}` bricht nur den Befehl ab (wie eine nicht gesetzte Variable), mit `set -e` endet damit das Skript.
+
+### Arithmetik
+
+```bash
+echo $((1 + 2 * 3))              # 7
+n=$((n + 1))                     # hochzählen
+: $((n++))                       # dasselbe mit ++
+echo $(( (a + b) / 2 ))
+echo $((x > 5 ? 1 : 0))
+echo $((0x1F)) $((2 ** 10)) $((7 % 3))
+i=0; while [ $i -lt 10 ]; do i=$((i + 1)); done
+```
+
+- `$((ausdruck))` rechnet mit ganzen 64-Bit-Zahlen. Es gibt die Operatoren aus C: `+ - * / %`, `**` (Potenz), `<< >>`, `< <= > >= == !=`, `& | ^ ~`, `! && ||`, `? :`, Zuweisungen `= += -= *= /= %= <<= >>= &= |= ^=`, `++` und `--` (davor und danach) sowie `,`.
+- Variablen lassen sich mit und ohne `$` verwenden (`$((n + 1))`, `$(($n + 1))`). Ist ihr Wert selbst ein Ausdruck, wird er ausgerechnet; ein leerer Wert zählt als 0, eine nicht gesetzte Variable ist ein Fehler.
+- Zahlen sind dezimal, `0x…` hexadezimal oder mit führender `0` oktal (`010` ist 8).
+- Division durch 0 ist ein Fehler. Bei `&&`, `||` und `? :` wird die nicht benötigte Seite nicht ausgerechnet.
+- Das Ergebnis ist ein Wort (auch ohne Anführungszeichen). `((…))` als eigener Befehl und `let` gibt es nicht, `: $((…))` tut das Gleiche.
+
 ### Befehlsersetzung
 
 `$(befehl)` wird durch die Ausgabe von `befehl` ersetzt:
@@ -215,12 +452,12 @@ $ vim $(grep -l TODO *.go)
 $ echo "Dateien: $(ls | wc -l)"
 ```
 
-- Der Befehl läuft in einer eigenen Subshell (einem neuen gosh-Prozess): `cd`, `set` oder `export` darin ändern die laufende Shell nicht. Er darf alles enthalten, was gosh kann (Pipes, `;`, `&&`, Umleitungen, verschachtelte `$(...)`), und liest von der gleichen Eingabe, Fehlermeldungen gehen auf stderr.
+- Der Befehl läuft in einer eigenen Subshell (einem neuen gosh-Prozess): `cd`, `set` oder `export` darin ändern die laufende Shell nicht. Die Subshell kennt die Funktionen und Positionsparameter der Shell. Er darf alles enthalten, was gosh kann (Pipes, `;`, `&&`, Umleitungen, verschachtelte `$(...)`), und liest von der gleichen Eingabe, Fehlermeldungen gehen auf stderr.
 - Abschließende Zeilenumbrüche der Ausgabe werden entfernt.
 - Ohne Anführungszeichen wird die Ausgabe an Leerzeichen, Tabs und Zeilenumbrüchen in mehrere Wörter geteilt, `"$(befehl)"` bleibt ein einziges Wort (mit den Zeilenumbrüchen darin).
 - Anders als in `sh` werden Wildcards in der Ausgabe nicht expandiert, und Zeichen wie `;` oder `|` darin sind normaler Text: Die Ausgabe ist immer nur Daten.
 - Besteht ein Befehl nur aus einer Ersetzung (`$(false)`), ist ihr Exit-Status `$?`, sonst zählt der Status des Befehls. Ctrl+C während der Ersetzung bricht die ganze Zeile ab.
-- In `'...'` oder mit `\$(` wird nichts ersetzt. Die alte Schreibweise mit Backticks (`` `befehl` ``) und Arithmetik `$((1+2))` gibt es nicht.
+- In `'...'` oder mit `\$(` wird nichts ersetzt. Die alte Schreibweise mit Backticks (`` `befehl` ``) gibt es nicht. `$((…))` ist keine Befehlsersetzung, sondern [Arithmetik](#arithmetik); eine Subshell darin braucht ein Leerzeichen: `$( (befehl) )`.
 
 ### Befehlslisten und Exit-Status
 
@@ -246,6 +483,65 @@ Status 127
 
 Schlägt ein Programm fehl, gibt gosh selbst keine Meldung mehr aus (das Programm meldet den Fehler selbst), nur bei Fehlern von gosh, z. B. wenn ein Befehl nicht gefunden wird.
 
+### Fehlerbehandlung: set -e, set -x, trap
+
+```bash
+#!/usr/bin/gosh
+set -euo pipefail                # abbrechen bei Fehlern, auch in Pipes
+
+tmp=$(mktemp -d)
+trap 'rm -rf "$tmp"' EXIT        # aufräumen, auch bei Fehlern oder Ctrl+C
+
+cd "$tmp"
+curl -fsSO https://example.org/paket.tar.gz
+tar xzf paket.tar.gz
+```
+
+| Option                     | Bedeutung                                                         |
+|----------------------------|-------------------------------------------------------------------|
+| `set -e` (`-o errexit`)    | beendet die Shell, wenn ein Befehl fehlschlägt                     |
+| `set -x` (`-o xtrace`)     | gibt jeden Befehl nach der Expansion mit `+ ` davor auf stderr aus |
+| `set -o pipefail`          | Status einer Pipe ist der des letzten fehlgeschlagenen Befehls     |
+| `set -u` (`-o nounset`)    | ist in gosh immer an, `set +u` gibt es nicht                       |
+| `set +e`, `set +x`, …      | schaltet die Option wieder aus                                     |
+| `set -o` / `set +o`        | zeigt die Optionen an (`set +o` als Befehle zum Wiederherstellen)  |
+
+- `set -e` gilt nicht für Bedingungen von `if`, `while` und `until`, für Befehle mit `!` und für alle Befehle einer `&&`/`||`-Liste außer dem letzten: `test -f x || echo fehlt` bricht nicht ab. Es gilt auch in Funktionen, Schleifen, Subshells und `$(…)`, ein fehlgeschlagenes `x=$(befehl)` beendet das Skript also.
+- Die Optionen lassen sich auch beim Aufruf setzen (`gosh -ex skript`, `gosh -o pipefail -c '…'`) und gelten in Subshells weiter.
+- `set` ohne Argumente zeigt alle Variablen an. `set a b c` und `set -e a b` setzen außerdem die Positionsparameter, `set VAR=wert` setzt wie bisher eine Variable.
+
+`trap befehl signal …` führt `befehl` aus, wenn das Signal kommt:
+
+| Aufruf                     | Bedeutung                                                         |
+|----------------------------|-------------------------------------------------------------------|
+| `trap 'befehl' EXIT`       | beim Beenden der Shell (Ende des Skripts, `exit`, Fehler mit `set -e`, Ctrl+C, `kill`) |
+| `trap 'befehl' INT TERM`   | bei den Signalen (`HUP`, `INT`, `QUIT`, `TERM`, `USR1`, `USR2`, `ALRM`, `WINCH`, auch mit `SIG` davor oder als Nummer) |
+| `trap '' INT`              | ignoriert das Signal, auch in gestarteten Programmen               |
+| `trap - INT`               | stellt das normale Verhalten wieder her                            |
+| `trap`, `trap -p [sig]`    | zeigt die Traps an                                                 |
+| `trap -l`                  | listet die Signale                                                 |
+
+- Der Befehl läuft in der Shell (er kann Variablen sehen und `exit` aufrufen), und zwar nach dem Befehl, der gerade läuft, wie in `sh`. `$?` ist im Trap der Status davor, beim `EXIT`-Trap der Exit-Status der Shell.
+- Ein Skript mit `EXIT`-Trap führt ihn auch aus, wenn es durch Ctrl+C, `SIGTERM` oder `SIGHUP` beendet wird, und endet danach mit diesem Signal. Mit einem eigenen Trap für das Signal (`trap 'echo abgebrochen; exit 1' INT`) läuft stattdessen dieser Trap. Endet er nicht mit `exit`, läuft das Skript nach dem abgebrochenen Befehl weiter.
+- In der interaktiven Shell geht Ctrl+C mit Job-Control nur an den laufenden Befehl, ein `INT`-Trap wird dabei nicht ausgelöst.
+- Subshells (`( … )`, `$(…)`, Pipes) erben keine Traps, ignorierte Signale bleiben aber ignoriert.
+
+### eval und exec
+
+```bash
+cmd="ls -l | head -3"
+eval "$cmd"                      # führt den Text als Befehl aus
+eval "wert_$name=42"             # Variablennamen zusammensetzen
+
+exec > build.log 2>&1            # ab hier geht alle Ausgabe in die Datei
+exec < eingabe.txt               # stdin der Shell umleiten
+exec ssh server                  # gosh durch ssh ersetzen
+```
+
+- `eval` fügt seine Argumente mit Leerzeichen zusammen und führt das Ergebnis in der laufenden Shell aus, mit allen Expansionen ein zweites Mal. In einer Pipe oder im Hintergrund läuft es in einer Subshell.
+- `exec befehl` ersetzt gosh durch `befehl` (gleiche Prozess-ID, Variablen vor dem Befehl gelten für ihn). Wird der Befehl nicht gefunden, beendet sich ein Skript mit Status 127, die interaktive Shell meldet nur den Fehler.
+- `exec` ohne Befehl wendet seine Umleitungen dauerhaft auf die Shell an: `exec > log` leitet ab dort alle Ausgaben um, `exec >&2` bzw. `exec > /dev/tty` wieder zurück.
+
 ### Klammer-Expansion
 
 Wie in bash erzeugt `{…}` aus einem Wort mehrere Wörter:
@@ -319,13 +615,47 @@ $ grep -c error < build.log
 | `2>&1`          | stderr dorthin, wohin stdout gerade geht                   |
 | `>&2`           | stdout dorthin, wohin stderr gerade geht                   |
 | `&> datei`      | stdout und stderr in `datei` (`&>>` hängt an)              |
+| `<<EOF`         | Here-Doc: die folgenden Zeilen bis `EOF` sind stdin         |
+| `<<< wort`      | Here-String: `wort` (und ein Zeilenumbruch) ist stdin      |
 | `> datei`       | ohne Befehl: legt `datei` an bzw. leert sie                |
 
 - Umleitungen werden von links nach rechts ausgewertet: `befehl > log 2>&1` schreibt beides in `log`, `befehl 2>&1 > log` schickt stderr dorthin, wo stdout vorher hinging (z. B. in eine Pipe).
 - Unterstützt werden die Dateideskriptoren 0, 1 und 2. Vor `>` und `<` zählt nur eine Zahl ohne Anführungszeichen als Deskriptor (`2>f`, aber nicht `x2>f` oder `"2">f`).
 - Operatoren in Anführungszeichen oder mit `\` davor sind normale Zeichen: `echo "a|b" 'c>d' e\>f`.
 - Der Exit-Status einer Pipeline ist der des letzten Befehls. Beendet sich ein Befehl am Ende (z. B. `head`), bekommt der schreibende Befehl davor `SIGPIPE`, `yes | head -1` endet also sofort.
-- Die Built-ins `pwd` und `help` lassen sich umleiten und in Pipes verwenden (`help | less`). `cd`, `set`, `export`, `exit` und `quit` verändern die Shell selbst und sind in einer Pipeline nicht erlaubt.
+- Die Built-ins `pwd` und `help` lassen sich umleiten und in Pipes verwenden (`help | less`). `cd`, `set`, `export`, `exit` und `quit` verändern die Shell selbst und sind in einer Pipeline nicht erlaubt. Umleitungen von `source datei > log` gelten für alle Befehle der Datei.
+- Zu Kontrollstrukturen mit Umleitungen und in Pipes siehe oben.
+
+### Here-Docs und Here-Strings
+
+```bash
+cat <<EOF > config.ini
+[server]
+host = $HOSTNAME
+started = $(date +%F)
+EOF
+
+cat <<'EOF' > script.sh       # 'EOF': nichts wird ersetzt
+echo "$HOME bleibt wörtlich stehen"
+EOF
+
+if true; then
+	cat <<-EOF                # <<-: Tabs am Zeilenanfang werden entfernt
+	eingerückt
+	EOF
+fi
+
+grep -c x <<< "$text"         # Here-String
+read a b <<< "1 2"
+```
+
+- Nach `<<WORT` folgen ab der nächsten Zeile die Eingabezeilen, bis zu einer Zeile, die genau `WORT` ist. In der interaktiven Shell zeigt gosh dafür den Fortsetzungs-Prompt `> `.
+- Ohne Anführungszeichen am Wort werden `$VAR`, `${VAR}`, `$(…)` und `\` vor `$`, `` ` ``, `\` und dem Zeilenende ersetzt (wie in `"…"`, nur dass `"` ein normales Zeichen ist). Wildcards, `~` und `{a,b}` werden nicht ersetzt. Ist das Wort ganz oder teilweise in Anführungszeichen (`'EOF'`, `"EOF"`, `\EOF`), wird nichts ersetzt.
+- `<<-WORT` entfernt Tabs (keine Leerzeichen) am Anfang jeder Zeile und der Endzeile, damit sich Here-Docs in Skripten einrücken lassen.
+- Mehrere Here-Docs in einer Zeile (`cat <<A; cat <<B`) folgen nacheinander. Here-Docs gehen auch an Funktionen, Schleifen (`done <<EOF`) und in Pipes.
+- `<<< wort` übergibt `wort` mit einem Zeilenumbruch als Eingabe. Das Wort wird wie ein Argument expandiert (Variablen, `$(…)`), aber nicht als Wildcard.
+- Die Eingabe steht in einer temporären Datei, die sofort wieder gelöscht wird, deshalb sind auch große Here-Docs kein Problem.
+- Ein Here-Doc in einer Befehlsersetzung (`x=$(cat <<EOF … EOF)`) funktioniert, solange der Text darin keine unpaarigen Anführungszeichen wie `it's` enthält.
 
 ### Aliase
 
@@ -390,7 +720,8 @@ $ bg %2                       # oder: angehaltenen Job im Hintergrund weiterlauf
 - `cd`, `set`, `export`, `exit`, `source`, `fg`, `bg` und `wait` lassen sich nicht mit `&` im Hintergrund starten.
 - In Skripten und mit `gosh -c` gibt es keine Job-Control (kein Ctrl+Z, kein `fg`/`bg`), `&` und `wait` funktionieren aber. Hintergrund-Jobs lesen dort von `/dev/null`.
 - Wird ein angehaltener Job von außen fortgesetzt (`kill -CONT`), zeigt `jobs` ihn weiter als `Stopped`, bis er endet oder erneut angehalten wird; `fg` und `bg` funktionieren trotzdem.
-- Einen Job beenden lässt sich mit `kill` über die Prozess-ID (z. B. `kill 12345`); `kill %1` versteht gosh noch nicht.
+- Einen Job beenden lässt sich mit `kill` über die Prozess-ID (z. B. `kill 12345` oder `kill $!` für den letzten Hintergrund-Job); `kill %1` versteht gosh noch nicht.
+- `wait` wartet auch auf eine Prozess-ID: `befehl & pid=$!; …; wait $pid` liefert den Exit-Status von `befehl`. Eine Zahl ohne `%` ist zuerst eine Prozess-ID, sonst eine Job-Nummer.
 
 ### Prompt
 

arith.go

@@ -0,0 +1,458 @@
+package main
+
+// Arithmetic expansion $((expression)) with 64-bit integers and the
+// operators of C (and ** for powers), in the order of precedence:
+//
+//	x++ x--, ++x --x, + - ! ~ (unary), **, * / %, + -, << >>,
+//	< <= > >=, == !=, &, ^, |, &&, ||, ?:, = += -= *= /= %= <<= >>= &= ^= |=, ","
+//
+// Variables can be used with or without $; their values are evaluated as
+// expressions, an empty value is 0, an unset variable is an error (like
+// everywhere in gosh). Numbers are decimal, 0x... hexadecimal or 0...
+// octal.
+
+import (
+	"errors"
+	"fmt"
+	"os"
+	"strconv"
+	"strings"
+)
+
+// arithEnd returns the index of the last ) of $((...)) at s[i], or -1 if
+// there is no arithmetic expansion (e.g. $( (cmd) ), a command substitution
+// of a subshell).
+func arithEnd(s string, i int) int {
+	if !strings.HasPrefix(s[i:], "$((") {
+		return -1
+	}
+	end := substEnd(s, i)
+	if end < 0 {
+		return -1
+	}
+	// The inner ( must end right before the outer )
+	if inner := substEnd(s, i+1); inner != end-1 {
+		return -1
+	}
+	return end
+}
+
+// evalArithText expands an arithmetic expression (variables, $(...), quotes)
+// and evaluates it.
+func evalArithText(text string) (int64, error) {
+	expr, err := expandWordText(text)
+	if err != nil {
+		return 0, err
+	}
+	return evalArith(expr, 0)
+}
+
+// maxArithDepth limits the recursion of variables whose values are
+// expressions with variables.
+const maxArithDepth = 32
+
+func evalArith(expr string, depth int) (int64, error) {
+	if depth > maxArithDepth {
+		return 0, errors.New("arithmetic: expression recursion level exceeded")
+	}
+	toks, err := lexArith(expr)
+	if err != nil {
+		return 0, err
+	}
+	a := &arith{toks: toks, depth: depth, expr: expr}
+	if len(toks) == 0 {
+		return 0, nil
+	}
+	v, err := a.comma()
+	if err != nil {
+		return 0, err
+	}
+	if a.pos < len(a.toks) {
+		return 0, a.syntaxErr()
+	}
+	return v, nil
+}
+
+type arithToken struct {
+	kind byte // 'n' number, 'v' variable, 'o' operator
+	text string
+	num  int64
+}
+
+var arithOps = []string{
+	"<<=", ">>=", "**", "++", "--", "<<", ">>", "<=", ">=", "==", "!=", "&&", "||",
+	"+=", "-=", "*=", "/=", "%=", "&=", "^=", "|=",
+	"+", "-", "*", "/", "%", "<", ">", "&", "|", "^", "!", "~", "?", ":", "=", "(", ")", ",",
+}
+
+func lexArith(s string) ([]arithToken, error) {
+	var toks []arithToken
+	for i := 0; i < len(s); {
+		ch := s[i]
+		switch {
+		case ch == ' ' || ch == '\t' || ch == '\n':
+			i++
+		case ch >= '0' && ch <= '9':
+			j := i
+			for j < len(s) && (isVarNameByte(s[j], false)) {
+				j++
+			}
+			n, err := strconv.ParseInt(s[i:j], 0, 64)
+			if err != nil {
+				return nil, fmt.Errorf("%s: value too great for base (error token is \"%s\")", strings.TrimSpace(s), s[i:j])
+			}
+			toks = append(toks, arithToken{kind: 'n', text: s[i:j], num: n})
+			i = j
+		case isVarNameByte(ch, true):
+			j := i
+			for j < len(s) && isVarNameByte(s[j], false) {
+				j++
+			}
+			toks = append(toks, arithToken{kind: 'v', text: s[i:j]})
+			i = j
+		default:
+			found := false
+			for _, op := range arithOps {
+				if strings.HasPrefix(s[i:], op) {
+					toks = append(toks, arithToken{kind: 'o', text: op})
+					i += len(op)
+					found = true
+					break
+				}
+			}
+			if !found {
+				return nil, fmt.Errorf("%s: syntax error: invalid arithmetic operator (error token is \"%s\")", strings.TrimSpace(s), sanitize(s[i:]))
+			}
+		}
+	}
+	return toks, nil
+}
+
+type arith struct {
+	toks  []arithToken
+	pos   int
+	skip  int // > 0 while a branch is evaluated that has no effect (&&, ||, ?:)
+	depth int
+	expr  string
+}
+
+func (a *arith) peekOp(ops ...string) string {
+	if a.pos < len(a.toks) && a.toks[a.pos].kind == 'o' {
+		for _, op := range ops {
+			if a.toks[a.pos].text == op {
+				return op
+			}
+		}
+	}
+	return ""
+}
+
+func (a *arith) syntaxErr() error {
+	token := "end of expression"
+	if a.pos < len(a.toks) {
+		token = a.toks[a.pos].text
+	}
+	return fmt.Errorf("%s: arithmetic syntax error (error token is \"%s\")", strings.TrimSpace(a.expr), sanitize(token))
+}
+
+// variable returns the value of a variable in an expression.
+func (a *arith) variable(name string) (int64, error) {
+	if a.skip > 0 {
+		return 0, nil
+	}
+	value, ok := os.LookupEnv(name)
+	if !ok {
+		return 0, fmt.Errorf("%s: unbound variable", name)
+	}
+	if strings.TrimSpace(value) == "" {
+		return 0, nil
+	}
+	if n, err := strconv.ParseInt(strings.TrimSpace(value), 0, 64); err == nil {
+		return n, nil
+	}
+	return evalArith(value, a.depth+1)
+}
+
+func (a *arith) setVariable(name string, v int64) {
+	if a.skip == 0 {
+		os.Setenv(name, strconv.FormatInt(v, 10))
+	}
+}
+
+func (a *arith) comma() (int64, error) {
+	v, err := a.assign()
+	for err == nil && a.peekOp(",") != "" {
+		a.pos++
+		v, err = a.assign()
+	}
+	return v, err
+}
+
+func (a *arith) assign() (int64, error) {
+	if a.pos+1 < len(a.toks) && a.toks[a.pos].kind == 'v' && a.toks[a.pos+1].kind == 'o' {
+		name, op := a.toks[a.pos].text, a.toks[a.pos+1].text
+		if op == "=" || len(op) >= 2 && strings.HasSuffix(op, "=") && op != "==" && op != "!=" && op != "<=" && op != ">=" {
+			a.pos += 2
+			rhs, err := a.assign()
+			if err != nil {
+				return 0, err
+			}
+			v := rhs
+			if op != "=" {
+				old, err := a.variable(name)
+				if err != nil {
+					return 0, err
+				}
+				if v, err = a.apply(strings.TrimSuffix(op, "="), old, rhs); err != nil {
+					return 0, err
+				}
+			}
+			a.setVariable(name, v)
+			return v, nil
+		}
+	}
+	return a.ternary()
+}
+
+func (a *arith) ternary() (int64, error) {
+	cond, err := a.binary(0)
+	if err != nil || a.peekOp("?") == "" {
+		return cond, err
+	}
+	a.pos++
+	if cond == 0 {
+		a.skip++
+	}
+	yes, err := a.assign()
+	if cond == 0 {
+		a.skip--
+	}
+	if err != nil {
+		return 0, err
+	}
+	if a.peekOp(":") == "" {
+		return 0, a.syntaxErr()
+	}
+	a.pos++
+	if cond != 0 {
+		a.skip++
+	}
+	no, err := a.assign()
+	if cond != 0 {
+		a.skip--
+	}
+	if err != nil {
+		return 0, err
+	}
+	if cond != 0 {
+		return yes, nil
+	}
+	return no, nil
+}
+
+// binaryLevels are the binary operators from the lowest precedence on.
+var binaryLevels = [][]string{
+	{"||"}, {"&&"}, {"|"}, {"^"}, {"&"}, {"==", "!="}, {"<", "<=", ">", ">="},
+	{"<<", ">>"}, {"+", "-"}, {"*", "/", "%"},
+}
+
+func (a *arith) binary(level int) (int64, error) {
+	if level == len(binaryLevels) {
+		return a.power()
+	}
+	lhs, err := a.binary(level + 1)
+	if err != nil {
+		return 0, err
+	}
+	for {
+		op := a.peekOp(binaryLevels[level]...)
+		if op == "" {
+			return lhs, nil
+		}
+		a.pos++
+		// && and || do not evaluate the right side if the result is known
+		short := op == "&&" && lhs == 0 || op == "||" && lhs != 0
+		if short {
+			a.skip++
+		}
+		rhs, err := a.binary(level + 1)
+		if short {
+			a.skip--
+		}
+		if err != nil {
+			return 0, err
+		}
+		if lhs, err = a.apply(op, lhs, rhs); err != nil {
+			return 0, err
+		}
+	}
+}
+
+func boolInt(b bool) int64 {
+	if b {
+		return 1
+	}
+	return 0
+}
+
+// apply applies a binary operator.
+func (a *arith) apply(op string, x, y int64) (int64, error) {
+	switch op {
+	case "||":
+		return boolInt(x != 0 || y != 0), nil
+	case "&&":
+		return boolInt(x != 0 && y != 0), nil
+	case "|":
+		return x | y, nil
+	case "^":
+		return x ^ y, nil
+	case "&":
+		return x & y, nil
+	case "==":
+		return boolInt(x == y), nil
+	case "!=":
+		return boolInt(x != y), nil
+	case "<":
+		return boolInt(x < y), nil
+	case "<=":
+		return boolInt(x <= y), nil
+	case ">":
+		return boolInt(x > y), nil
+	case ">=":
+		return boolInt(x >= y), nil
+	case "<<":
+		return x << uint64(y&63), nil
+	case ">>":
+		return x >> uint64(y&63), nil
+	case "+":
+		return x + y, nil
+	case "-":
+		return x - y, nil
+	case "*":
+		return x * y, nil
+	case "/", "%":
+		if y == 0 {
+			if a.skip > 0 {
+				return 0, nil
+			}
+			return 0, fmt.Errorf("%s: division by 0", strings.TrimSpace(a.expr))
+		}
+		if op == "/" {
+			return x / y, nil
+		}
+		return x % y, nil
+	case "**":
+		if y < 0 {
+			if a.skip > 0 {
+				return 0, nil
+			}
+			return 0, fmt.Errorf("%s: exponent less than 0", strings.TrimSpace(a.expr))
+		}
+		result := int64(1)
+		for ; y > 0; y-- {
+			result *= x
+		}
+		return result, nil
+	}
+	return 0, a.syntaxErr()
+}
+
+// power parses x ** y (right associative, binds tighter than * but less
+// than the unary operators).
+func (a *arith) power() (int64, error) {
+	base, err := a.unary()
+	if err != nil || a.peekOp("**") == "" {
+		return base, err
+	}
+	a.pos++
+	exp, err := a.power()
+	if err != nil {
+		return 0, err
+	}
+	return a.apply("**", base, exp)
+}
+
+func (a *arith) unary() (int64, error) {
+	switch op := a.peekOp("+", "-", "!", "~", "++", "--"); op {
+	case "":
+		return a.postfix()
+	case "++", "--":
+		a.pos++
+		if a.pos >= len(a.toks) || a.toks[a.pos].kind != 'v' {
+			return 0, a.syntaxErr()
+		}
+		name := a.toks[a.pos].text
+		a.pos++
+		v, err := a.variable(name)
+		if err != nil {
+			return 0, err
+		}
+		if op == "++" {
+			v++
+		} else {
+			v--
+		}
+		a.setVariable(name, v)
+		return v, nil
+	default:
+		a.pos++
+		v, err := a.unary()
+		if err != nil {
+			return 0, err
+		}
+		switch op {
+		case "-":
+			return -v, nil
+		case "!":
+			return boolInt(v == 0), nil
+		case "~":
+			return ^v, nil
+		}
+		return v, nil
+	}
+}
+
+func (a *arith) postfix() (int64, error) {
+	if a.pos < len(a.toks) && a.toks[a.pos].kind == 'v' {
+		name := a.toks[a.pos].text
+		a.pos++
+		v, err := a.variable(name)
+		if err != nil {
+			return 0, err
+		}
+		if op := a.peekOp("++", "--"); op != "" {
+			a.pos++
+			n := v + 1
+			if op == "--" {
+				n = v - 1
+			}
+			a.setVariable(name, n)
+		}
+		return v, nil
+	}
+	return a.primary()
+}
+
+func (a *arith) primary() (int64, error) {
+	if a.pos >= len(a.toks) {
+		return 0, a.syntaxErr()
+	}
+	t := a.toks[a.pos]
+	switch {
+	case t.kind == 'n':
+		a.pos++
+		return t.num, nil
+	case t.kind == 'o' && t.text == "(":
+		a.pos++
+		v, err := a.comma()
+		if err != nil {
+			return 0, err
+		}
+		if a.peekOp(")") == "" {
+			return 0, a.syntaxErr()
+		}
+		a.pos++
+		return v, nil
+	}
+	return 0, a.syntaxErr()
+}

brace.go

@@ -94,8 +94,8 @@ func wordEnd(s string, i int) int {
 				i = j
 			}
 		case ch == '$' && i+1 < len(s) && s[i+1] == '{':
-			if j := strings.IndexByte(s[i:], '}'); j >= 0 {
+			if j := paramEnd(s, i); j >= 0 {
-				i += j
+				i = j
 			}
 		case quote == '"':
 			if ch == '"' {
@@ -134,8 +134,8 @@ func braceScan(s string, fn func(i, depth int) bool) {
 			}
 			continue
 		case ch == '$' && i+1 < len(s) && s[i+1] == '{':
-			if j := strings.IndexByte(s[i:], '}'); j >= 0 {
+			if j := paramEnd(s, i); j >= 0 {
-				i += j
+				i = j
 			}
 			continue
 		case quote == '"':

compound_test.go

@@ -0,0 +1,274 @@
+package main
+
+import (
+	"errors"
+	"os"
+	"reflect"
+	"strings"
+	"testing"
+	"time"
+)
+
+func TestExec_CompoundRedirections(t *testing.T) {
+	resetShell(t)
+	for _, name := range []string{"GOSH_A", "GOSH_N"} {
+		os.Unsetenv(name)
+		defer os.Unsetenv(name)
+	}
+	tests := []struct {
+		input string
+		want  string
+	}{
+		{"if true; then echo yes; fi > out", "yes\n"},
+		{"for x in a b; do echo $x; done > out", "a\nb\n"},
+		{"for x in a b; do echo $x; done >> out; echo c >> out", "a\nb\nc\n"},
+		{"{ echo out; echo err >&2; } > out 2>&1", "out\nerr\n"},
+		{"{ echo err >&2; } 2> out", "err\n"},
+		{"case x in x) echo case;; esac > out", "case\n"},
+		// The redirections apply to all commands, also nested ones
+		{"{ echo a; { echo b; }; } > out", "a\nb\n"},
+		{"{ echo a; echo b > other; echo c; } > out", "a\nc\n"},
+		{"f() { echo from-f; }; { f; } > out", "from-f\n"},
+		// Reading a file line by line in the shell itself
+		{"printf 'l1\\nl2 x\\n' > in; while read -r l; do echo \"<$l>\" >> out; done < in", "<l1>\n<l2 x>\n"},
+		{"printf 'a b\\nc d\\n' > in; while read x y; do echo $y$x >> out; done < in", "ba\ndc\n"},
+		{"printf '1\\n2\\n3\\n' > in; GOSH_N=0; while read l; do GOSH_N=$(expr $GOSH_N + $l); done < in; echo $GOSH_N > out", "6\n"},
+		// ... with the loop's variables changed in the shell
+		{"printf 'v\\n' > in; while read GOSH_A; do :; done < in; echo ${GOSH_A:-empty} > out", "empty\n"},
+		{"printf 'v\\n' > in; { read GOSH_A; } < in; echo $GOSH_A > out", "v\n"},
+		// Redirections are expanded
+		{"GOSH_A=out; { echo var; } > $GOSH_A", "var\n"},
+		// Files are closed and stdout is restored afterwards
+		{"{ echo a; } > out; echo b >> out", "a\nb\n"},
+	}
+	for _, tc := range tests {
+		if got := runIn(t, tc.input); got != tc.want {
+			t.Errorf("%q: out = %q, want %q", tc.input, got, tc.want)
+		}
+		if ioOverride != [3]*os.File{} {
+			t.Fatalf("%q: ioOverride not restored", tc.input)
+		}
+	}
+
+	for input, want := range map[string]string{
+		"{ :; } < gosh-no-such-file": "gosh-no-such-file: no such file or directory",
+		"{ :; } > {a,b}":             "{a,b}: ambiguous redirect",
+	} {
+		if err := runInErr(t, input); err == nil || err.Error() != want {
+			t.Errorf("%q: err = %v, want %q", input, err, want)
+		}
+	}
+}
+
+// runInErr runs input in a temporary directory and returns its error.
+func runInErr(t *testing.T, input string) error {
+	t.Helper()
+	origDir, _ := os.Getwd()
+	defer os.Chdir(origDir)
+	os.Chdir(t.TempDir())
+	return execInput(input)
+}
+
+func TestExec_CompoundPipelines(t *testing.T) {
+	resetShell(t)
+	os.Unsetenv("GOSH_A")
+	defer os.Unsetenv("GOSH_A")
+	tests := []struct {
+		input string
+		want  string
+	}{
+		{"for x in 3 1 2; do echo $x; done | sort > out", "1\n2\n3\n"},
+		{"printf 'a b\\nc d\\n' | while read x y; do echo $y$x; done > out", "ba\ndc\n"},
+		{"echo hi | { read l; echo got $l; } > out", "got hi\n"},
+		{"if true; then echo yes; fi | tr a-z A-Z > out", "YES\n"},
+		{"echo x | case y in y) cat;; esac | tr x X > out", "X\n"},
+		{"for x in a b; do echo $x; done > /dev/null | cat > out", ""},
+		{"{ echo b; echo a; } | sort | head -1 > out", "a\n"},
+		// The parts of a pipeline run in subshells: the shell is not changed
+		{"echo v | while read GOSH_A; do :; done; echo ${GOSH_A:-unset} > out", "unset\n"},
+		// Functions and positional parameters are known in the subshell
+		{"f() { echo f-$1; }; set -- p; for x in 1; do f $1; done | cat > out", "f-p\n"},
+		// The status is the one of the last command
+		{"echo | while read l; do false; done; echo $? > out", "1\n"},
+		{"true | if false; then :; else sh -c 'exit 3'; fi; echo $? > out", "3\n"},
+		{"for x in 1; do sh -c 'exit 4'; done | true; echo $? > out", "0\n"},
+		{"! echo | while read l; do false; done; echo $? > out", "0\n"},
+	}
+	for _, tc := range tests {
+		if got := runIn(t, tc.input); got != tc.want {
+			t.Errorf("%q: out = %q, want %q", tc.input, got, tc.want)
+		}
+	}
+}
+
+func TestExec_Subshells(t *testing.T) {
+	resetShell(t)
+	os.Unsetenv("GOSH_A")
+	defer os.Unsetenv("GOSH_A")
+	tests := []struct {
+		input string
+		want  string
+	}{
+		{"(echo a; echo b) > out", "a\nb\n"},
+		{"(echo sub) | tr a-z A-Z > out", "SUB\n"},
+		// Changes stay in the subshell
+		{"mkdir d; (cd d; pwd > ../in); cd d 2>/dev/null && echo still-outside > out", "still-outside\n"},
+		{"GOSH_A=1; (GOSH_A=2; echo $GOSH_A > out); echo $GOSH_A >> out", "2\n1\n"},
+		{"(exit 3); echo $? > out", "3\n"},
+		{"(exit 3) || echo failed > out", "failed\n"},
+		{"(f() { echo in-sub; }; f) > out; f 2>> out || echo no-f >> out", "in-sub\nno-f\n"},
+		{"(echo a; (echo b)) > out", "a\nb\n"},
+		{"( echo spaced ) > out", "spaced\n"},
+		{"(\n  echo multi\n  echo line\n) > out", "multi\nline\n"},
+		// The subshell knows the functions and positional parameters
+		{"f() { echo f-$1; }; set -- p; (f $1) > out", "f-p\n"},
+	}
+	for _, tc := range tests {
+		if got := runIn(t, tc.input); got != tc.want {
+			t.Errorf("%q: out = %q, want %q", tc.input, got, tc.want)
+		}
+	}
+}
+
+func TestExec_CompoundBackground(t *testing.T) {
+	resetShell(t)
+	tests := []struct {
+		input string
+		want  string
+	}{
+		{"for x in a b; do echo $x; done > out & wait", "a\nb\n"},
+		{"true && echo and > out & wait", "and\n"},
+		{"false || echo or > out & wait", "or\n"},
+		{"(echo sub > out) & wait", "sub\n"},
+		{"{ echo group; } > out & wait", "group\n"},
+		{"! false && echo negated > out & wait", "negated\n"},
+		{"for x in 3 1; do echo $x; done | sort > out & wait", "1\n3\n"},
+	}
+	for _, tc := range tests {
+		if got := runIn(t, tc.input); got != tc.want {
+			t.Errorf("%q: out = %q, want %q", tc.input, got, tc.want)
+		}
+	}
+	// The shell does not wait for a background loop
+	start := time.Now()
+	runIn(t, "for x in 1; do sleep 1; done & echo $? > out")
+	if lastStatus != 0 || time.Since(start) > 500*time.Millisecond {
+		t.Errorf("background loop: $? = %d after %v", lastStatus, time.Since(start))
+	}
+	execInput("wait")
+}
+
+func TestExtractHeredocs(t *testing.T) {
+	tests := []struct {
+		input string
+		want  string
+	}{
+		{"cat <<EOF\nhello\nEOF\n", "cat <<<\"hello\"\n"},
+		{"cat <<EOF\nhello\nEOF", "cat <<<\"hello\"\n"},
+		{"cat << EOF\na\nb\nEOF\necho x\n", "cat <<<\"a\nb\"\necho x\n"},
+		{"cat <<'EOF'\n$x \"q\" it's\nEOF\n", "cat <<<'$x \"q\" it'\\''s'\n"},
+		{"cat <<\"EOF\"\n$x\nEOF\n", "cat <<<'$x'\n"},
+		{"cat <<\\EOF\n$x\nEOF\n", "cat <<<'$x'\n"},
+		{"cat <<E\"O\"F\n$x\nEOF\n", "cat <<<'$x'\n"},
+		{"cat <<EOF\n\"q\" \\\" \\$x \\a\nEOF\n", "cat <<<\"\\\"q\\\" \\\\\\\" \\$x \\\\a\"\n"},
+		{"cat <<EOF\n$(echo \"a\")\nEOF\n", "cat <<<\"$(echo \"a\")\"\n"},
+		{"cat <<-EOF\n\t\ttabs\n\tEOF\n", "cat <<<\"tabs\"\n"},
+		{"cat <<EOF\nEOF\n", "cat </dev/null\n"},
+		{"cat <<A; cat <<B\na\nA\nb\nB\n", "cat <<<\"a\"; cat <<<\"b\"\n"},
+		{"cat <<EOF | sort\nb\nEOF\n", "cat <<<\"b\" | sort\n"},
+		// The delimiter must be the whole line
+		{"cat <<EOF\n EOF\nEOFX\nEOF\n", "cat <<<\" EOF\nEOFX\"\n"},
+		// Not here-documents
+		{"echo '<<EOF'\n", "echo '<<EOF'\n"},
+		{"echo \"<<EOF\"\n", "echo \"<<EOF\"\n"},
+		{"echo \\<<x\n", "echo \\<<x\n"},
+		{"echo # <<EOF\n", "echo # <<EOF\n"},
+		{"cat <<<word\n", "cat <<<word\n"},
+		{"echo $(echo a <<<b)\n", "echo $(echo a <<<b)\n"},
+	}
+	for _, tc := range tests {
+		got, err := extractHeredocs(tc.input)
+		if err != nil {
+			t.Errorf("%q: %v", tc.input, err)
+			continue
+		}
+		if got != tc.want {
+			t.Errorf("%q:\n got %q\nwant %q", tc.input, got, tc.want)
+		}
+	}
+
+	for _, input := range []string{"cat <<EOF", "cat <<EOF\n", "cat <<EOF\nbody\n", "cat <<'EOF\n"} {
+		if _, err := extractHeredocs(input); !errors.Is(err, errIncomplete) {
+			t.Errorf("%q: err = %v, want incomplete", input, err)
+		}
+	}
+	for _, input := range []string{"cat <<\n", "cat << ;\n"} {
+		if _, err := extractHeredocs(input); err == nil || errors.Is(err, errIncomplete) {
+			t.Errorf("%q: err = %v, want syntax error", input, err)
+		}
+	}
+}
+
+func TestExec_Heredocs(t *testing.T) {
+	resetShell(t)
+	t.Setenv("GOSH_A", "value")
+	tests := []struct {
+		input string
+		want  string
+	}{
+		{"cat <<EOF > out\nhello\nworld\nEOF", "hello\nworld\n"},
+		{"cat <<EOF > out\n$GOSH_A ${GOSH_A} $(echo sub) \\$GOSH_A\nEOF", "value value sub $GOSH_A\n"},
+		{"cat <<'EOF' > out\n$GOSH_A $(echo sub)\nEOF", "$GOSH_A $(echo sub)\n"},
+		{"cat <<EOF > out\n\"quotes\" 'single' back\\slash\nEOF", "\"quotes\" 'single' back\\slash\n"},
+		{"cat <<EOF > out\nline \\\ncontinued\nEOF", "line continued\n"},
+		{"cat <<'EOF' > out\nline \\\nkept\nEOF", "line \\\nkept\n"},
+		{"cat <<-EOF > out\n\tindented\n\t\tmore\n\tEOF", "indented\nmore\n"},
+		{"cat <<EOF > out\n  *.go {a,b} ~\nEOF", "  *.go {a,b} ~\n"},
+		{"cat <<EOF > out\nEOF", ""},
+		{"cat <<EOF | tr a-z A-Z > out\npiped\nEOF", "PIPED\n"},
+		{"cat > out <<EOF\nredirect first\nEOF", "redirect first\n"},
+		{"cat <<A > out; cat <<B >> out\na\nA\nb\nB", "a\nb\n"},
+		{"while read l; do echo \"<$l>\" >> out; done <<EOF\none\ntwo\nEOF", "<one>\n<two>\n"},
+		{"f() { cat; }; f <<EOF > out\nto f\nEOF", "to f\n"},
+		{"set -- a 'b c'; cat <<EOF > out\n$# $1 $@\nEOF", "2 a a b c\n"},
+		{"for x in 1 2; do\n  cat <<EOF >> out\nx=$x\nEOF\ndone", "x=1\nx=2\n"},
+		{"echo \"$(cat <<EOF\nin subst\nEOF\n)\" > out", "in subst\n"},
+		// Here-strings
+		{"cat <<<word > out", "word\n"},
+		{"cat <<< \"two words $GOSH_A\" > out", "two words value\n"},
+		{"cat <<<'*.go' > out", "*.go\n"},
+		{"read x y <<<'a b c'; echo $y > out", "b c\n"},
+	}
+	for _, tc := range tests {
+		if got := runIn(t, tc.input); got != tc.want {
+			t.Errorf("%q: out = %q, want %q", tc.input, got, tc.want)
+		}
+	}
+}
+
+// TestRunScript_Heredoc checks that a script reads a here-document and
+// continues after it, with correct line numbers in error messages.
+func TestRunScript_Heredoc(t *testing.T) {
+	resetShell(t)
+	got := runIn(t, `printf 'cat <<EOF > out\nbody\nEOF\necho after >> out\n' > s; . ./s`)
+	if got != "body\nafter\n" {
+		t.Errorf("script with here-document: out = %q", got)
+	}
+	got = runIn(t, `printf 'cat <<EOF\nbody\n' > s; . ./s 2> out`)
+	if !strings.Contains(got, "s:1: syntax error: unexpected end of file") {
+		t.Errorf("unterminated here-document: %q", got)
+	}
+}
+
+// TestTokenize_UTF8 checks that non-ASCII characters survive quoting and
+// escaping (each byte used to be converted to a rune of its own).
+func TestTokenize_UTF8(t *testing.T) {
+	got, err := splitWords(`echo 'wörtlich' "für" über \ä 'a'"ö"`)
+	want := []string{"echo", "wörtlich", "für", "über", "ä", "aö"}
+	if err != nil || !reflect.DeepEqual(got, want) {
+		t.Errorf("got %q, %v, want %q", got, err, want)
+	}
+	if got := runIn(t, "cat <<'EOF' > out\nGrüße\nEOF"); got != "Grüße\n" {
+		t.Errorf("here-document: %q", got)
+	}
+}

dup_linux.go

@@ -0,0 +1,16 @@
+package main
+
+import (
+	"os"
+
+	"golang.org/x/sys/unix"
+)
+
+// dupTo makes file descriptor fd refer to f (dup2; linux/arm64 only has
+// dup3).
+func dupTo(f *os.File, fd int) error {
+	if int(f.Fd()) == fd {
+		return nil // dup3 fails for the same descriptor
+	}
+	return unix.Dup3(int(f.Fd()), fd, 0)
+}

dup_other.go

@@ -0,0 +1,14 @@
+//go:build !linux
+
+package main
+
+import (
+	"os"
+
+	"golang.org/x/sys/unix"
+)
+
+// dupTo makes file descriptor fd refer to f.
+func dupTo(f *os.File, fd int) error {
+	return unix.Dup2(int(f.Fd()), fd)
+}

expand.go

@@ -0,0 +1,458 @@
+package main
+
+// Parameter expansion ${...}: ${name}, ${#name} and the operators
+//
+//	${name:-word} ${name-word}   word if name is unset (or empty with :)
+//	${name:=word} ${name=word}   ... and assign it to name
+//	${name:+word} ${name+word}   word if name is set (and not empty with :)
+//	${name:?word} ${name?word}   error if name is unset (or empty)
+//	${name#pat} ${name##pat}     remove the shortest/longest matching prefix
+//	${name%pat} ${name%%pat}     remove the shortest/longest matching suffix
+//	${name/pat/rep}              replace the first (//: every) match
+//	${name/#pat/rep}             ... at the start, /% at the end
+//	${name:offset[:length]}      substring (arithmetic expressions)
+//
+// The word is expanded (variables, $(...), $((...)), quotes, ~), but not
+// split. In patterns, quoted characters and values of variables match
+// literally, like everywhere in gosh.
+
+import (
+	"errors"
+	"fmt"
+	"os"
+	"path"
+	"strconv"
+	"strings"
+	"unicode/utf8"
+)
+
+// paramEnd returns the index of the } that ends the ${ at s[i], or -1.
+// Nested ${...}, $(...), quotes and escapes are skipped.
+func paramEnd(s string, i int) int {
+	var quote byte
+	for j := i + 2; j < len(s); j++ {
+		ch := s[j]
+		switch {
+		case quote == '\'':
+			if ch == '\'' {
+				quote = 0
+			}
+		case ch == '\\':
+			j++
+		case isSubstStart(s, j):
+			end := substEnd(s, j)
+			if end < 0 {
+				return -1
+			}
+			j = end
+		case ch == '$' && j+1 < len(s) && s[j+1] == '{':
+			end := paramEnd(s, j)
+			if end < 0 {
+				return -1
+			}
+			j = end
+		case quote == '"':
+			if ch == '"' {
+				quote = 0
+			}
+		case ch == '"' || ch == '\'':
+			quote = ch
+		case ch == '}':
+			return j
+		}
+	}
+	return -1
+}
+
+// paramNameLen returns the length of the parameter name at the start of
+// expr: a variable name, a number or a special parameter.
+func paramNameLen(expr string) int {
+	switch {
+	case expr == "":
+		return 0
+	case isSpecialParam(expr[:1]):
+		return 1
+	case expr[0] >= '0' && expr[0] <= '9':
+		n := 1
+		for n < len(expr) && expr[n] >= '0' && expr[n] <= '9' {
+			n++
+		}
+		return n
+	}
+	n := 0
+	for n < len(expr) && isVarNameByte(expr[n], n == 0) {
+		n++
+	}
+	return n
+}
+
+// expandParam expands the inside of ${...}.
+func expandParam(expr string) (string, error) {
+	bad := func() (string, error) { return "", fmt.Errorf("bad substitution: ${%s}", expr) }
+	unbound := func(name string) (string, error) { return "", fmt.Errorf("%s: unbound variable", name) }
+
+	// ${#name}: the length in characters (${#} alone is $#)
+	if len(expr) > 1 && expr[0] == '#' {
+		name := expr[1:]
+		if paramNameLen(name) != len(name) {
+			return bad()
+		}
+		value, ok := lookupParam(name)
+		if !ok {
+			return unbound(name)
+		}
+		return strconv.Itoa(utf8.RuneCountInString(value)), nil
+	}
+
+	n := paramNameLen(expr)
+	if n == 0 {
+		return bad()
+	}
+	name, op := expr[:n], expr[n:]
+	if op != "" && strings.IndexByte(":-=+?#%/", op[0]) < 0 {
+		return bad()
+	}
+	value, set := lookupParam(name)
+	if op == "" {
+		if !set {
+			return unbound(name)
+		}
+		return value, nil
+	}
+
+	// ${name:-word} and friends
+	colon := strings.HasPrefix(op, ":")
+	if kind := strings.TrimPrefix(op, ":"); kind != "" && strings.IndexByte("-=+?", kind[0]) >= 0 {
+		word := kind[1:]
+		missing := !set || colon && value == ""
+		switch kind[0] {
+		case '-':
+			if missing {
+				return expandWordText(word)
+			}
+		case '=':
+			if missing {
+				if !isVarName(name) {
+					return "", fmt.Errorf("$%s: cannot assign in this way", name)
+				}
+				w, err := expandWordText(word)
+				if err != nil {
+					return "", err
+				}
+				os.Setenv(name, w)
+				return w, nil
+			}
+		case '+':
+			if missing {
+				return "", nil
+			}
+			return expandWordText(word)
+		case '?':
+			if missing {
+				msg, err := expandWordText(word)
+				if err != nil {
+					return "", err
+				}
+				if msg == "" {
+					msg = "parameter null or not set"
+				}
+				return "", fmt.Errorf("%s: %s", name, msg)
+			}
+		}
+		return value, nil
+	}
+
+	if !set {
+		return unbound(name)
+	}
+	switch {
+	case colon:
+		return substring(value, op[1:])
+	case strings.HasPrefix(op, "#"), strings.HasPrefix(op, "%"):
+		longest := strings.HasPrefix(op[1:], op[:1])
+		word := op[1:]
+		if longest {
+			word = op[2:]
+		}
+		pattern, err := expandPattern(word)
+		if err != nil {
+			return "", err
+		}
+		if op[0] == '#' {
+			return removePrefix(value, pattern, longest), nil
+		}
+		return removeSuffix(value, pattern, longest), nil
+	case strings.HasPrefix(op, "/"):
+		spec := op[1:]
+		all := strings.HasPrefix(spec, "/")
+		var anchor byte
+		switch {
+		case all:
+			spec = spec[1:]
+		case strings.HasPrefix(spec, "#"), strings.HasPrefix(spec, "%"):
+			anchor, spec = spec[0], spec[1:]
+		}
+		patText, repText := spec, ""
+		if i := unquotedSlash(spec); i >= 0 {
+			patText, repText = spec[:i], spec[i+1:]
+		}
+		pattern, err := expandPattern(patText)
+		if err != nil {
+			return "", err
+		}
+		rep, err := expandWordText(repText)
+		if err != nil {
+			return "", err
+		}
+		return replacePattern(value, pattern, rep, all, anchor), nil
+	}
+	return bad()
+}
+
+// unquotedSlash returns the index of the first / in s that is not quoted,
+// escaped or inside $(...) or ${...}, or -1.
+func unquotedSlash(s string) int {
+	var quote byte
+	for i := 0; i < len(s); i++ {
+		ch := s[i]
+		switch {
+		case quote == '\'':
+			if ch == '\'' {
+				quote = 0
+			}
+		case ch == '\\':
+			i++
+		case isSubstStart(s, i):
+			if end := substEnd(s, i); end >= 0 {
+				i = end
+			}
+		case ch == '$' && i+1 < len(s) && s[i+1] == '{':
+			if end := paramEnd(s, i); end >= 0 {
+				i = end
+			}
+		case quote == '"':
+			if ch == '"' {
+				quote = 0
+			}
+		case ch == '"' || ch == '\'':
+			quote = ch
+		case ch == '/':
+			return i
+		}
+	}
+	return -1
+}
+
+// substring implements ${name:offset[:length]}; offset and length are
+// arithmetic expressions, a negative offset counts from the end.
+func substring(value, spec string) (string, error) {
+	offText, lenText, hasLen := strings.Cut(spec, ":")
+	runes := []rune(value)
+	off, err := evalArithText(offText)
+	if err != nil {
+		return "", err
+	}
+	if off < 0 {
+		off += int64(len(runes))
+	}
+	if off < 0 || off > int64(len(runes)) {
+		return "", nil
+	}
+	end := int64(len(runes))
+	if hasLen {
+		n, err := evalArithText(lenText)
+		if err != nil {
+			return "", err
+		}
+		if n < 0 {
+			end += n // a negative length counts from the end
+		} else {
+			end = min(off+n, end)
+		}
+	}
+	if end < off {
+		return "", errors.New(strings.TrimSpace(lenText) + ": substring expression < 0")
+	}
+	return string(runes[off:end]), nil
+}
+
+// expandWordText expands the word of a parameter expansion (or of $((...)))
+// to a single string: quotes are removed, $..., $(...) and $((...)) are
+// expanded and a leading ~ is replaced by the home directory.
+func expandWordText(word string) (string, error) {
+	value, _, err := expandWordParts(word)
+	return value, err
+}
+
+// expandPattern expands a word like expandWordText, but returns it as a glob
+// pattern: quoted characters and expanded values are escaped.
+func expandPattern(word string) (string, error) {
+	_, pattern, err := expandWordParts(word)
+	return pattern, err
+}
+
+func expandWordParts(word string) (value, pattern string, err error) {
+	var v, p strings.Builder
+	literal := func(s string) {
+		v.WriteString(s)
+		p.WriteString(escapeGlob(s))
+	}
+	var quote byte
+	for i := 0; i < len(word); i++ {
+		ch := word[i]
+		switch {
+		case quote == '\'':
+			if ch == '\'' {
+				quote = 0
+			} else {
+				literal(word[i : i+1])
+			}
+		case ch == '\\' && i+1 < len(word):
+			i++
+			if quote == '"' && strings.IndexByte("$\"\\`", word[i]) < 0 {
+				literal("\\")
+			}
+			literal(word[i : i+1])
+		case ch == '$':
+			value, n, err := expandDollar(word[i:])
+			if err != nil {
+				return "", "", err
+			}
+			literal(value)
+			i += n - 1
+		case quote == '"':
+			if ch == '"' {
+				quote = 0
+			} else {
+				literal(word[i : i+1])
+			}
+		case ch == '"' || ch == '\'':
+			quote = ch
+		case ch == '~' && i == 0 && (len(word) == 1 || word[1] == '/'):
+			if home := getHomeDir(); home != "" {
+				literal(home)
+			} else {
+				literal("~")
+			}
+		default:
+			v.WriteByte(ch)
+			if ch == '!' && strings.HasSuffix(p.String(), "[") && !strings.HasSuffix(p.String(), "\\[") {
+				p.WriteByte('^') // POSIX [!...] is [^...] in Go
+			} else {
+				p.WriteByte(ch)
+			}
+		}
+	}
+	if quote != 0 {
+		return "", "", fmt.Errorf("unterminated %c quote", quote)
+	}
+	return v.String(), p.String(), nil
+}
+
+// expandDollar expands the $ expression at the start of s ($name, ${...},
+// $(...) or $((...))) and returns its value and length.
+func expandDollar(s string) (string, int, error) {
+	if end := arithEnd(s, 0); end >= 0 {
+		value, err := evalArithText(s[3 : end-1])
+		if err != nil {
+			return "", 0, err
+		}
+		return strconv.FormatInt(value, 10), end + 1, nil
+	}
+	if isSubstStart(s, 0) {
+		end := substEnd(s, 0)
+		if end < 0 {
+			return "", 0, errors.New("missing ) in command substitution")
+		}
+		out, err := commandSubst(s[2:end])
+		return out, end + 1, err
+	}
+	return expandVar(s)
+}
+
+// globMatch reports whether s matches the glob pattern (in which escaped
+// characters match literally). Unlike for file names, * and ? also match a
+// /. An invalid pattern matches only itself.
+func globMatch(pattern, s string) bool {
+	// path.Match does not let * match a /; NUL can be in neither string
+	toNUL := strings.NewReplacer("/", "\x00")
+	ok, err := path.Match(toNUL.Replace(pattern), toNUL.Replace(s))
+	if err != nil {
+		return unescapeGlob(pattern) == s
+	}
+	return ok
+}
+
+// runeBounds returns the indexes in s where characters start, and len(s).
+func runeBounds(s string) []int {
+	bounds := make([]int, 0, len(s)+1)
+	for i := range s {
+		bounds = append(bounds, i)
+	}
+	return append(bounds, len(s))
+}
+
+func removePrefix(value, pattern string, longest bool) string {
+	bounds := runeBounds(value)
+	for k := range bounds {
+		i := bounds[k]
+		if longest {
+			i = bounds[len(bounds)-1-k]
+		}
+		if globMatch(pattern, value[:i]) {
+			return value[i:]
+		}
+	}
+	return value
+}
+
+func removeSuffix(value, pattern string, longest bool) string {
+	bounds := runeBounds(value)
+	for k := range bounds {
+		i := bounds[len(bounds)-1-k]
+		if longest {
+			i = bounds[k]
+		}
+		if globMatch(pattern, value[i:]) {
+			return value[:i]
+		}
+	}
+	return value
+}
+
+// replacePattern replaces the longest match of pattern at the first (or
+// every) position by rep. anchor '#' only matches at the start, '%' only at
+// the end. Empty matches are not replaced.
+func replacePattern(value, pattern, rep string, all bool, anchor byte) string {
+	if pattern == "" {
+		return value
+	}
+	bounds := runeBounds(value)
+	var b strings.Builder
+	for k := 0; k < len(bounds)-1; k++ {
+		i := bounds[k]
+		match := -1
+		if anchor != '#' || i == 0 {
+			for m := len(bounds) - 1; m > k; m-- {
+				if anchor == '%' && m != len(bounds)-1 {
+					break
+				}
+				if globMatch(pattern, value[i:bounds[m]]) {
+					match = m
+					break
+				}
+			}
+		}
+		if match < 0 {
+			b.WriteString(value[i:bounds[k+1]])
+			continue
+		}
+		b.WriteString(rep)
+		if !all {
+			b.WriteString(value[bounds[match]:])
+			return b.String()
+		}
+		k = match - 1
+	}
+	return b.String()
+}

expand_test.go

@@ -0,0 +1,375 @@
+package main
+
+import (
+	"os"
+	"os/exec"
+	"strings"
+	"testing"
+)
+
+func TestExpandParam(t *testing.T) {
+	resetShell(t)
+	t.Setenv("P", "/usr/local/lib/libfoo.so.1")
+	t.Setenv("F", "archive.tar.gz")
+	t.Setenv("H", "hello")
+	t.Setenv("E", "")
+	t.Setenv("U8", "Grüße")
+	t.Setenv("SP", "a b  c")
+	t.Setenv("GLOB", "*.go")
+	os.Unsetenv("UNSET")
+	positional = []string{"one", "two"}
+
+	tests := []struct {
+		input string
+		want  string
+	}{
+		{"${#P}", "26"},
+		{"${#U8}", "5"},
+		{"${#1}", "3"},
+		{"${#}", "2"},
+		{"${P#*/}", "usr/local/lib/libfoo.so.1"},
+		{"${P##*/}", "libfoo.so.1"},
+		{"${P%/*}", "/usr/local/lib"},
+		{"${P%%.*}", "/usr/local/lib/libfoo"},
+		{"${F%.gz}", "archive.tar"},
+		{"${F#*.}", "tar.gz"},
+		{"${F##*.}", "gz"},
+		{"${F%.zip}", "archive.tar.gz"},
+		{"${U8%e}", "Grüß"},
+		{"${U8#?}", "rüße"},
+		{"${H/l/L}", "heLlo"},
+		{"${H//l/L}", "heLLo"},
+		{"${H//l}", "heo"},
+		{"${H/#h/H}", "Hello"},
+		{"${H/#e/E}", "hello"},
+		{"${H/%o/O}", "hellO"},
+		{"${H/l*/X}", "heX"},
+		{"${SP// /_}", "a_b__c"},
+		{"${H/[aeiou]/_}", "h_llo"},
+		{"${H:1}", "ello"},
+		{"${H:1:3}", "ell"},
+		{"${H: -2}", "lo"},
+		{"${H:0:-1}", "hell"},
+		{"${H:1+1:2*1}", "ll"},
+		{"${H:10}", ""},
+		{"${U8:1:3}", "rüß"},
+		{"${UNSET-dflt}", "dflt"},
+		{"${UNSET:-dflt}", "dflt"},
+		{"${E-dflt}", ""},
+		{"${E:-dflt}", "dflt"},
+		{"${H:-dflt}", "hello"},
+		{"${UNSET+alt}", ""},
+		{"${E+alt}", "alt"},
+		{"${E:+alt}", ""},
+		{"${H:+alt}", "alt"},
+		{"${UNSET:-${H}}", "hello"},
+		{"${UNSET:-${UNSET:-deep}}", "deep"},
+		{`${UNSET:-"a  b"}`, "a  b"},
+		{"${UNSET:-a  b}", "a  b"},
+		{"${UNSET:-$(echo sub)}", "sub"},
+		{"${UNSET:-$((1+2))}", "3"},
+		{"${UNSET:-}", ""},
+		{"${2:-x}", "two"},
+		{"${3:-three}", "three"},
+		// Quoted characters and values of variables are no patterns
+		{"${GLOB#*.}", "go"},
+		{`${GLOB#"*"}`, ".go"},
+		{"${GLOB%$GLOB}", ""},
+		{"${F%$GLOB}", "archive.tar.gz"},
+		{`${P//\//:}`, ":usr:local:lib:libfoo.so.1"},
+	}
+	for _, tc := range tests {
+		got, err := splitWords(`"` + tc.input + `"`)
+		if err != nil {
+			t.Errorf("%s: %v", tc.input, err)
+			continue
+		}
+		if len(got) != 1 || got[0] != tc.want {
+			t.Errorf("%s = %q, want %q", tc.input, got, tc.want)
+		}
+	}
+
+	// := assigns
+	defer os.Unsetenv("GOSH_ASSIGN")
+	os.Unsetenv("GOSH_ASSIGN")
+	if got, _ := splitWords("${GOSH_ASSIGN:=set} $GOSH_ASSIGN"); strings.Join(got, " ") != "set set" {
+		t.Errorf(":= gives %q", got)
+	}
+
+	for input, want := range map[string]string{
+		"${UNSET}":              "UNSET: unbound variable",
+		"${#UNSET}":             "UNSET: unbound variable",
+		"${UNSET%x}":            "UNSET: unbound variable",
+		"${UNSET:?is required}": "UNSET: is required",
+		"${E:?}":                "E: parameter null or not set",
+		"${1x}":                 "bad substitution: ${1x}",
+		"${H!}":                 "bad substitution: ${H!}",
+		"${3:=x}":               "$3: cannot assign in this way",
+		"${H:3:-5}":             "-5: substring expression < 0",
+		"${H":                   "missing } in variable reference",
+	} {
+		if _, err := splitWords(input); err == nil || !strings.Contains(err.Error(), want) {
+			t.Errorf("%s: err = %v, want %q", input, err, want)
+		}
+	}
+}
+
+func TestArith(t *testing.T) {
+	t.Setenv("N", "5")
+	t.Setenv("EXPR", "N*2")
+	t.Setenv("EMPTY", "")
+	os.Unsetenv("UNSET")
+	tests := []struct {
+		expr string
+		want int64
+	}{
+		{"1+2*3", 7},
+		{"(1+2)*3", 9},
+		{"7/2", 3},
+		{"-7/2", -3},
+		{"7%3", 1},
+		{"2**10", 1024},
+		{"-2**2", 4},
+		{"2**3**2", 512},
+		{"1<<4", 16},
+		{"256>>4", 16},
+		{"~0", -1},
+		{"!0", 1},
+		{"!5", 0},
+		{"3 > 2 && 2 > 1", 1},
+		{"0 || 0", 0},
+		{"5 & 3", 1},
+		{"5 | 3", 7},
+		{"5 ^ 3", 6},
+		{"1 ? 10 : 20", 10},
+		{"0 ? 10 : 20", 20},
+		{"0x1F", 31},
+		{"010", 8},
+		{"N", 5},
+		{"N * N", 25},
+		{"EXPR + 1", 11},
+		{"EMPTY + 1", 1},
+		{"1, 2, 3", 3},
+		{"", 0},
+		{"  42  ", 42},
+		// Short-circuit: no error and no assignment on the other side
+		{"0 && 1/0", 0},
+		{"1 || UNSET", 1},
+		{"1 ? 2 : 1/0", 2},
+	}
+	for _, tc := range tests {
+		got, err := evalArith(tc.expr, 0)
+		if err != nil || got != tc.want {
+			t.Errorf("$((%s)) = %d, %v, want %d", tc.expr, got, err, tc.want)
+		}
+	}
+
+	for expr, want := range map[string]string{
+		"1/0":     "division by 0",
+		"1%0":     "division by 0",
+		"2**-1":   "exponent less than 0",
+		"UNSET+1": "UNSET: unbound variable",
+		"1 +":     "arithmetic syntax error",
+		"(1":      "arithmetic syntax error",
+		"1 2":     "arithmetic syntax error",
+		"1 @ 2":   "invalid arithmetic operator",
+		"09":      "value too great for base",
+		"5 = 3":   "arithmetic syntax error",
+	} {
+		if _, err := evalArith(expr, 0); err == nil || !strings.Contains(err.Error(), want) {
+			t.Errorf("$((%s)): err = %v, want %q", expr, err, want)
+		}
+	}
+}
+
+func TestExec_Arith(t *testing.T) {
+	resetShell(t)
+	for _, name := range []string{"I", "J"} {
+		os.Unsetenv(name)
+		defer os.Unsetenv(name)
+	}
+	tests := []struct {
+		input string
+		want  string
+	}{
+		{"echo $((1 + 2)) > out", "3\n"},
+		{"I=5; echo $((I + 1)) $(($I * 2)) > out", "6 10\n"},
+		{"I=5; echo $((I++)) $I $((++I)) $((I += 10)) $I > out", "5 6 7 17 17\n"},
+		{"I=1; : $((I = I * 3)); echo $I > out", "3\n"},
+		{"I=0; while [ $I -lt 3 ]; do I=$((I + 1)); done; echo $I > out", "3\n"},
+		{"echo $(( $(echo 3) + ${J:-4} )) > out", "7\n"},
+		{`echo "$((2 * 21))" > out`, "42\n"},
+		{"echo x$((1+1))y > out", "x2y\n"},
+		{"set -- 3 4; echo $(($1 * $2)) $(($# + 1)) > out", "12 3\n"},
+		// $( ( ... ) ) is a command substitution of a subshell
+		{"echo $( (echo sub) ) > out", "sub\n"},
+		{"cat <<EOF > out\n$((6 * 7))\nEOF", "42\n"},
+		{"case $((1 + 1)) in 2) echo two > out;; esac", "two\n"},
+	}
+	for _, tc := range tests {
+		if got := runIn(t, tc.input); got != tc.want {
+			t.Errorf("%q: out = %q, want %q", tc.input, got, tc.want)
+		}
+	}
+}
+
+// goshOutput runs gosh -c script in a new process and returns its combined
+// output and exit status.
+func goshOutput(t *testing.T, script string, args ...string) (string, int) {
+	t.Helper()
+	cmd := exec.Command(subshellPath, append([]string{"-c", script, "gosh"}, args...)...)
+	cmd.Dir = t.TempDir()
+	out, err := cmd.CombinedOutput()
+	return string(out), exitStatus(err)
+}
+
+func TestShell_Errexit(t *testing.T) {
+	tests := []struct {
+		script string
+		want   string
+		status int
+	}{
+		{"set -e; echo a; false; echo never", "a\n", 1},
+		{"set -e; sh -c 'exit 3'; echo never", "", 3},
+		{"set -e; gosh-no-such-cmd; echo never", "gosh: gosh-no-such-cmd: command not found\n", 127},
+		// Not for conditions, negated commands and && || lists (except the last)
+		{"set -e; if false; then :; fi; while false; do :; done; until true; do :; done; echo ok", "ok\n", 0},
+		{"set -e; false || echo or; false && echo no; ! true; echo ok", "or\nok\n", 0},
+		{"set -e; true && false; echo never", "", 1},
+		{"set -e; false || false; echo never", "", 1},
+		{"set -e; f() { false; echo never; }; if f; then :; fi; echo cond-ok", "never\ncond-ok\n", 0},
+		// Also in functions, loops, subshells, pipelines and $(...)
+		{"set -e; f() { false; echo never; }; f; echo never", "", 1},
+		{"set -e; for x in 1; do false; echo never; done", "", 1},
+		{"set -e; (false; echo never); echo never", "", 1},
+		{"set -e; (exit 4); echo never", "", 4},
+		{"set -e; true | false; echo never", "", 1},
+		{"set -e; x=$(false); echo never", "", 1},
+		{"set -e; set +e; false; echo off", "off\n", 0},
+		// gosh -e
+		{"false; echo never", "", 1},
+	}
+	for i, tc := range tests {
+		script := tc.script
+		var out string
+		var status int
+		if i == len(tests)-1 {
+			cmd := exec.Command(subshellPath, "-e", "-c", script)
+			b, err := cmd.CombinedOutput()
+			out, status = string(b), exitStatus(err)
+		} else {
+			out, status = goshOutput(t, script)
+		}
+		if out != tc.want || status != tc.status {
+			t.Errorf("%q: %q, status %d, want %q, %d", tc.script, out, status, tc.want, tc.status)
+		}
+	}
+}
+
+func TestShell_Options(t *testing.T) {
+	tests := []struct {
+		script string
+		want   string
+	}{
+		{"set -x; x=1; echo \"a b\" $x", "+ x=1\n+ echo 'a b' 1\na b 1\n"},
+		{"set -x; f() { echo f; }; f", "+ f\n+ echo f\nf\n"},
+		// Each command once, also a function in a pipeline (in any order)
+		{"f() { echo f; }; (set -x; f | cat) 2>&1 | sort", "+ cat\n+ echo f\n+ f\nf\n"},
+		{"set -x; set +x; echo quiet", "+ set +x\nquiet\n"},
+		{"false | true; echo $?; set -o pipefail; false | true; echo $?; sh -c 'exit 3' | false | true; echo $?", "0\n1\n1\n"},
+		{"set -o pipefail; true | true; echo $?", "0\n"},
+		{"set -euo pipefail; set -o", "errexit         on\nnounset         on\npipefail        on\nxtrace          off\n"},
+		{"set -e; set +o | grep errexit", "set -o errexit\n"},
+		{"set -- a b; set -e x y z; echo $# $1", "3 x\n"},
+		{"set -e; (set -o | grep errexit)", "errexit         on\n"},
+		{"set +u", "gosh: set: +u: unset variables are always an error in gosh\n"},
+		{"set -k", "gosh: set: -k: invalid option\n"},
+	}
+	for _, tc := range tests {
+		if out, _ := goshOutput(t, tc.script); out != tc.want {
+			t.Errorf("%q: %q, want %q", tc.script, out, tc.want)
+		}
+	}
+}
+
+func TestShell_EvalExec(t *testing.T) {
+	tests := []struct {
+		script string
+		want   string
+		status int
+	}{
+		{`cmd="echo a; echo b"; eval "$cmd"`, "a\nb\n", 0},
+		{`eval x=5; echo $x`, "5\n", 0},
+		{`x=y; y=deep; eval echo \$$x`, "deep\n", 0},
+		{`eval "f() { echo from-eval; }"; f`, "from-eval\n", 0},
+		{`eval "echo piped" | tr a-z A-Z`, "PIPED\n", 0},
+		{`eval 'exit 3'; echo never`, "", 3},
+		{`eval; echo empty`, "empty\n", 0},
+		{`eval "if"`, "gosh: eval: syntax error: unexpected end of input\n", 1},
+		{`for i in 1 2; do eval "v$i=$i"; done; echo $v1$v2`, "12\n", 0},
+		{`exec echo replaced; echo never`, "replaced\n", 0},
+		{`X=1 exec sh -c 'echo $X'`, "1\n", 0},
+		{`exec > out; echo to-file; exec >&2; cat out`, "to-file\n", 0},
+		{`exec 2> err; ls /gosh-no-such-dir; exec 2>&1; grep -c gosh-no-such-dir err`, "1\n", 0},
+		{`printf 'l1\nl2\n' > in; exec < in; read a; read b; echo $b $a`, "l2 l1\n", 0},
+		{`exec gosh-no-such-cmd; echo never`, "gosh: gosh-no-such-cmd: command not found\n", 127},
+		{`exec echo a | tr a A`, "A\n", 0},
+	}
+	for _, tc := range tests {
+		if out, status := goshOutput(t, tc.script); out != tc.want || status != tc.status {
+			t.Errorf("%q: %q, status %d, want %q, %d", tc.script, out, status, tc.want, tc.status)
+		}
+	}
+}
+
+func TestShell_Trap(t *testing.T) {
+	tests := []struct {
+		script string
+		want   string
+		status int
+	}{
+		{`trap "echo bye" EXIT; echo running`, "running\nbye\n", 0},
+		{`trap 'echo "bye $?"' EXIT; exit 3`, "bye 3\n", 3},
+		{`trap 'echo "bye $?"' EXIT; false`, "bye 1\n", 1},
+		{`trap 'echo bye; exit 5' EXIT; true`, "bye\n", 5},
+		{`trap 'echo exit-trap' 0; f() { exit 2; }; f`, "exit-trap\n", 2},
+		{`trap 'echo set-e' EXIT; set -e; false; echo never`, "set-e\n", 1},
+		{`trap "echo bye" EXIT; trap - EXIT; echo no-trap`, "no-trap\n", 0},
+		{`trap 'echo got USR1' USR1; kill -USR1 $$; sleep 0.2; echo after`, "got USR1\nafter\n", 0},
+		// The trap runs after the current command (the signal arrives
+		// asynchronously, hence the sleep)
+		{`trap 'echo got $?' SIGUSR2; false; kill -USR2 $$; sleep 0.2; echo status $?`, "got 0\nstatus 0\n", 0},
+		{`trap '' USR1; kill -USR1 $$; echo ignored`, "ignored\n", 0},
+		{`trap '' USR1; sh -c 'kill -USR1 $$; echo child-ignores'`, "child-ignores\n", 0},
+		{`trap 'echo t' INT TERM; trap - INT; trap`, "trap -- 'echo t' TERM\n", 0},
+		{`trap 'echo t' INT; trap -p INT | cat`, "trap -- 'echo t' INT\n", 0},
+		{`trap 'echo cleanup' EXIT; kill -TERM $$; echo never`, "cleanup\n", 128 + 15},
+		{`trap 'echo term; exit 9' TERM; kill $$; echo never`, "term\n", 9},
+		{`trap 'echo x' BOGUS`, "gosh: trap: BOGUS: invalid signal specification\n", 1},
+		{`trap -l | grep -c TERM`, "1\n", 0},
+		// Traps are not inherited by subshells, ignored signals are
+		{`trap 'echo parent' EXIT; (echo sub)`, "sub\nparent\n", 0},
+	}
+	for _, tc := range tests {
+		if out, status := goshOutput(t, tc.script); out != tc.want || status != tc.status {
+			t.Errorf("%q: %q, status %d, want %q, %d", tc.script, out, status, tc.want, tc.status)
+		}
+	}
+}
+
+func TestShell_LastBackgroundPid(t *testing.T) {
+	tests := []struct {
+		script string
+		want   string
+	}{
+		{`sleep 0.1 & pid=$!; case $pid in *[!0-9]*) echo bad;; *) echo pid;; esac; wait $pid; echo $?`, "pid\n0\n"},
+		{`sh -c 'exit 7' & wait $!; echo $?`, "7\n"},
+		{`echo ${!:-none}`, "none\n"},
+		{`sleep 0.1 & sleep 0.2 & first=$!; wait %1; echo $?; wait $first; echo $?`, "0\n0\n"},
+	}
+	for _, tc := range tests {
+		if out, _ := goshOutput(t, tc.script); out != tc.want {
+			t.Errorf("%q: %q, want %q", tc.script, out, tc.want)
+		}
+	}
+}

funcs.go

@@ -0,0 +1,240 @@
+package main
+
+// Functions and positional parameters. A function runs in the shell itself
+// (it can change variables and the directory), with its arguments as the
+// positional parameters $1, $2, ... In a pipeline, in the background and in
+// $(...) it runs in a subshell, which gets the definitions of all functions.
+
+import (
+	"errors"
+	"fmt"
+	"os"
+	"slices"
+	"sort"
+	"strconv"
+	"strings"
+)
+
+// funcDef is a function defined with name() { ...; }.
+type funcDef struct {
+	name string
+	body node
+	text string // the source of the definition, passed to subshells
+}
+
+var (
+	functions = map[string]*funcDef{}
+
+	// scriptName is $0: the script, the name given after gosh -c command,
+	// or the name gosh was started with.
+	scriptName = "gosh"
+	// positional are the positional parameters $1, $2, ...
+	positional []string
+
+	// lastBackgroundPid is $!: the process ID of the last background job
+	// (of its last process).
+	lastBackgroundPid int
+
+	// funcDepth is the number of functions that are currently running.
+	funcDepth int
+	// localFrames holds, for every running function, the previous values
+	// of the variables it declared with local.
+	localFrames []map[string]savedVar
+
+	// ioOverride replaces stdin, stdout and stderr of the shell while a
+	// function with redirections runs (f > file), so that the commands in
+	// it use the redirected files.
+	ioOverride [3]*os.File
+)
+
+// maxFuncDepth limits the nesting of function calls, so that endless
+// recursion ends with an error.
+const maxFuncDepth = 1000
+
+type savedVar struct {
+	value string
+	ok    bool
+}
+
+// returnSignal is returned by the return builtin and ends the running
+// function or sourced file with the given status.
+type returnSignal struct {
+	status int
+}
+
+func (r returnSignal) Error() string { return "return" }
+
+// stdio returns stdin (0), stdout (1) or stderr (2) of the shell, which are
+// redirected while a function with redirections runs.
+func stdio(fd int) *os.File {
+	if f := ioOverride[fd]; f != nil {
+		return f
+	}
+	return [3]*os.File{os.Stdin, os.Stdout, os.Stderr}[fd]
+}
+
+// isFuncName reports whether name can be the name of a function: letters,
+// digits, _, - and ., not starting with a digit or -.
+func isFuncName(name string) bool {
+	if name == "" || name[0] == '-' || name[0] >= '0' && name[0] <= '9' || terminators[name] || compoundStarts[name] {
+		return false
+	}
+	for i := 0; i < len(name); i++ {
+		if c := name[i]; !isVarNameByte(c, false) && c != '-' && c != '.' {
+			return false
+		}
+	}
+	return true
+}
+
+func defineFunction(def *funcDef) {
+	functions[def.name] = def
+}
+
+// functionNames returns the names of all functions, sorted.
+func functionNames() []string {
+	names := make([]string, 0, len(functions))
+	for name := range functions {
+		names = append(names, name)
+	}
+	sort.Strings(names)
+	return names
+}
+
+// functionDefs returns the definitions of all functions as source text, to
+// run them in a subshell.
+func functionDefs() string {
+	var b strings.Builder
+	for _, name := range functionNames() {
+		b.WriteString(functions[name].text)
+		b.WriteByte('\n')
+	}
+	return b.String()
+}
+
+// callFunction runs a function in the shell with args[1:] as positional
+// parameters, the files fds as stdin, stdout and stderr and the assignments
+// that came before the call set while it runs.
+func callFunction(fn *funcDef, args []string, fds [3]*os.File, assigns []string) error {
+	if funcDepth >= maxFuncDepth {
+		return fmt.Errorf("%s: maximum function nesting level exceeded (%d)", sanitize(fn.name), maxFuncDepth)
+	}
+	defer setTemporarily(assigns)()
+
+	savedIO, savedPositional, savedLoopDepth := ioOverride, positional, loopDepth
+	ioOverride, positional, loopDepth = fds, slices.Clone(args[1:]), 0
+	funcDepth++
+	localFrames = append(localFrames, map[string]savedVar{})
+	defer func() {
+		// Restore the variables declared with local
+		for name, v := range localFrames[len(localFrames)-1] {
+			if v.ok {
+				os.Setenv(name, v.value)
+			} else {
+				os.Unsetenv(name)
+			}
+		}
+		localFrames = localFrames[:len(localFrames)-1]
+		funcDepth--
+		ioOverride, positional, loopDepth = savedIO, savedPositional, savedLoopDepth
+	}()
+
+	err := fn.body.exec()
+	var ret returnSignal
+	if errors.As(err, &ret) {
+		if ret.status == 0 {
+			return nil
+		}
+		return statusError(ret.status)
+	}
+	return err
+}
+
+// lookupParam returns the value of a special or positional parameter ($?,
+// $#, $$, $0, $1, ..., $@ and $* joined with blanks) or of a variable.
+func lookupParam(name string) (string, bool) {
+	switch {
+	case name == "?":
+		return strconv.Itoa(lastStatus), true
+	case name == "#":
+		return strconv.Itoa(len(positional)), true
+	case name == "$":
+		return strconv.Itoa(os.Getpid()), true
+	case name == "!":
+		if lastBackgroundPid == 0 {
+			return "", false
+		}
+		return strconv.Itoa(lastBackgroundPid), true
+	case name == "@" || name == "*":
+		return strings.Join(positional, " "), true
+	case name == "0":
+		return scriptName, true
+	case isDigits(name):
+		n, err := strconv.Atoi(name)
+		if err != nil || n > len(positional) {
+			return "", false
+		}
+		return positional[n-1], true
+	}
+	return os.LookupEnv(name)
+}
+
+// builtinReturn implements return [n].
+func builtinReturn(args []string) error {
+	if funcDepth == 0 && sourceDepth == 0 {
+		return errors.New("return: can only `return' from a function or sourced script")
+	}
+	status := lastStatus
+	if len(args) > 1 {
+		n, err := strconv.Atoi(args[1])
+		if err != nil {
+			return fmt.Errorf("return: %s: numeric argument required", sanitize(args[1]))
+		}
+		status = n & 0xff
+	}
+	return returnSignal{status}
+}
+
+// builtinLocal implements local name[=value] ...: the variables get their
+// previous values back when the function returns. Without a value the
+// variable is unset in the function.
+func builtinLocal(args []string) error {
+	if funcDepth == 0 {
+		return errors.New("local: can only be used in a function")
+	}
+	frame := localFrames[len(localFrames)-1]
+	var err error
+	for _, arg := range args[1:] {
+		name, value, hasValue := strings.Cut(arg, "=")
+		if !isVarName(name) {
+			err = fmt.Errorf("local: `%s': not a valid identifier", sanitize(arg))
+			continue
+		}
+		if _, saved := frame[name]; !saved {
+			old, ok := os.LookupEnv(name)
+			frame[name] = savedVar{old, ok}
+		}
+		if hasValue {
+			os.Setenv(name, value)
+		} else {
+			os.Unsetenv(name)
+		}
+	}
+	return err
+}
+
+// builtinShift implements shift [n].
+func builtinShift(args []string) error {
+	n := 1
+	if len(args) > 1 {
+		var err error
+		if n, err = strconv.Atoi(args[1]); err != nil || n < 0 {
+			return fmt.Errorf("shift: %s: numeric argument required", sanitize(args[1]))
+		}
+	}
+	if n > len(positional) {
+		return fmt.Errorf("shift: %d: shift count out of range", n)
+	}
+	positional = positional[n:]
+	return nil
+}

funcs_test.go

@@ -0,0 +1,367 @@
+package main
+
+import (
+	"os"
+	"os/exec"
+	"path/filepath"
+	"reflect"
+	"strings"
+	"testing"
+)
+
+// resetShell removes functions and positional parameters after a test.
+func resetShell(t *testing.T) {
+	t.Helper()
+	t.Cleanup(func() {
+		functions = map[string]*funcDef{}
+		positional, scriptName = nil, "gosh"
+		errexit, xtrace, pipefail = false, false, false
+		for name := range traps {
+			setTrap(name, "-")
+		}
+	})
+}
+
+func TestTokenize_PositionalParameters(t *testing.T) {
+	resetShell(t)
+	scriptName, positional = "prog", []string{"a", "b c", ""}
+
+	tests := []struct {
+		input string
+		want  []string
+	}{
+		{"echo $0 $1 $2", []string{"echo", "prog", "a", "b c"}},
+		{"echo $# ${#}", []string{"echo", "3", "3"}},
+		{`echo "$@"`, []string{"echo", "a", "b c", ""}},
+		{`echo x"$@"y`, []string{"echo", "xa", "b c", "y"}},
+		{`echo $@`, []string{"echo", "a", "b c", ""}},
+		{`echo "$*"`, []string{"echo", "a b c "}},
+		{`echo ${2}x $10`, []string{"echo", "b cx", "a0"}},
+		{`echo ${4:-four}`, []string{"echo", "four"}},
+		{`echo '$1' \$1`, []string{"echo", "$1", "$1"}},
+	}
+	for _, tc := range tests {
+		got, err := splitWords(tc.input)
+		if err != nil {
+			t.Errorf("%q: %v", tc.input, err)
+			continue
+		}
+		if !reflect.DeepEqual(got, tc.want) {
+			t.Errorf("%q: got %q, want %q", tc.input, got, tc.want)
+		}
+	}
+
+	// An unset positional parameter is an error, like an unset variable
+	if _, err := splitWords("echo $4"); err == nil || !strings.Contains(err.Error(), "4: unbound variable") {
+		t.Errorf("$4: err = %v", err)
+	}
+
+	// "$@" without parameters is no word at all
+	positional = nil
+	for input, want := range map[string][]string{
+		`echo "$@"`:   {"echo"},
+		`echo "$@" x`: {"echo", "x"},
+		`echo "x$@"`:  {"echo", "x"},
+		`echo "$*"`:   {"echo", ""},
+		`echo $#`:     {"echo", "0"},
+	} {
+		if got, _ := splitWords(input); !reflect.DeepEqual(got, want) {
+			t.Errorf("%q without parameters: got %q, want %q", input, got, want)
+		}
+	}
+}
+
+func TestExec_Functions(t *testing.T) {
+	resetShell(t)
+	for _, name := range []string{"GOSH_A", "GOSH_L"} {
+		os.Unsetenv(name)
+		defer os.Unsetenv(name)
+	}
+	tests := []struct {
+		input string
+		want  string
+	}{
+		{"f() { echo hi > out; }; f", "hi\n"},
+		{"f () { echo $1-$2-$# >> out; }; f a b", "a-b-2\n"},
+		{"f(){ echo braces >> out; }; f", "braces\n"},
+		{"function f { echo keyword >> out; }; f", "keyword\n"},
+		{"function f() { echo both >> out; }; f", "both\n"},
+		{"f() {\n  echo multi >> out\n  echo line >> out\n}\nf", "multi\nline\n"},
+		{"f()\n{\n  echo next-line >> out\n}\nf", "next-line\n"},
+		{"f() if true; then echo if-body >> out; fi; f", "if-body\n"},
+		{`f() { for a in "$@"; do echo "<$a>" >> out; done; }; f x "y z"`, "<x>\n<y z>\n"},
+		// The positional parameters are restored after the call
+		{`set -- outer; f() { echo $1 >> out; }; f inner; echo $1 >> out`, "inner\nouter\n"},
+		// Functions change the shell (variables, directory)
+		{"f() { GOSH_A=set; }; f; echo $GOSH_A > out", "set\n"},
+		// return
+		{"f() { echo a >> out; return; echo b >> out; }; f", "a\n"},
+		{"f() { return 3; }; f; echo $? > out", "3\n"},
+		{"f() { false; return; }; f; echo $? > out", "1\n"},
+		{"f() { for x in 1 2 3; do if [ $x = 2 ]; then return 7; fi; echo $x >> out; done; }; f; echo $? >> out", "1\n7\n"},
+		{"f() { sh -c 'exit 4'; }; f; echo $? > out", "4\n"},
+		// local
+		{"GOSH_L=global; f() { local GOSH_L=local; echo $GOSH_L >> out; }; f; echo $GOSH_L >> out", "local\nglobal\n"},
+		{"f() { local GOSH_L; GOSH_L=x; }; f; echo ${GOSH_L:-unset} > out", "unset\n"},
+		{"f() { local GOSH_L=1; g; echo $GOSH_L >> out; }; g() { GOSH_L=2; }; f", "2\n"},
+		// Assignments before a call apply only while it runs
+		{"f() { echo $GOSH_A >> out; }; GOSH_A=temp f; echo ${GOSH_A:-unset} >> out", "temp\nunset\n"},
+		// Redirections of a call apply to all commands in the function
+		{"f() { echo one; echo two; }; f > out", "one\ntwo\n"},
+		{"f() { echo err >&2; }; f 2> out", "err\n"},
+		{"echo input > in; f() { cat; }; f < in > out", "input\n"},
+		{"f() { echo nested > out; }; g() { f; }; g", "nested\n"},
+		// Functions run before builtins and commands of the same name
+		{"echo() { printf 'own\\n' > out; }; echo x; unset -f echo", "own\n"},
+		{"f() { echo x > out; }; unset -f f; f", ""},
+		// In pipelines, in the background and in $(...) they run in a subshell
+		{"f() { echo piped; }; f | tr a-z A-Z > out", "PIPED\n"},
+		{"f() { tr a-z A-Z; }; echo lower | f > out", "LOWER\n"},
+		{"f() { echo bg > out; }; f & wait", "bg\n"},
+		{`f() { echo "sub $1"; }; echo "$(f arg)" > out`, "sub arg\n"},
+		{`f() { g; }; g() { echo g-in-sub; }; echo $(f) > out`, "g-in-sub\n"},
+		{`set -- p1; echo "$(echo $1)" > out`, "p1\n"},
+		{"f() { GOSH_A=changed; }; f | cat; echo ${GOSH_A:-unchanged} > out", "unchanged\n"},
+	}
+	for _, tc := range tests {
+		os.Unsetenv("GOSH_A")
+		os.Unsetenv("GOSH_L")
+		if got := runIn(t, tc.input); got != tc.want {
+			t.Errorf("%q: out = %q, want %q", tc.input, got, tc.want)
+		}
+		if funcDepth != 0 || len(localFrames) != 0 || ioOverride != [3]*os.File{} {
+			t.Fatalf("%q: function state not restored", tc.input)
+		}
+	}
+
+	for input, want := range map[string]string{
+		"return":               "return: can only `return' from a function or sourced script",
+		"local x":              "local: can only be used in a function",
+		"f() { f; }; f":        "f: maximum function nesting level exceeded (1000)",
+		"f() echo x":           "f: the body of a function must be a compound command like { ...; }",
+		"f() { return x; }; f": "return: x: numeric argument required",
+	} {
+		if err := execInput(input); err == nil || err.Error() != want {
+			t.Errorf("%q: err = %v, want %q", input, err, want)
+		}
+	}
+}
+
+func TestExec_Case(t *testing.T) {
+	resetShell(t)
+	tests := []struct {
+		input string
+		want  string
+	}{
+		{"case abc in a*) echo a > out;; b*) echo b > out;; esac", "a\n"},
+		{"case bcd in a*) echo a > out;; b*) echo b > out;; esac", "b\n"},
+		{"case xyz in a*) echo a > out;; esac", ""},
+		{"case stop in start|run) echo s > out;; stop|halt) echo h > out;; esac", "h\n"},
+		{"case x in (x) echo paren > out;; esac", "paren\n"},
+		{"case x in x)echo tight > out;;esac", "tight\n"},
+		{"case x in x ) echo blank > out ;; esac", "blank\n"},
+		{"case x in\n  y) echo y > out ;;\n  x)\n    echo x1 >> out\n    echo x2 >> out\n    ;;\nesac", "x1\nx2\n"},
+		// The last clause needs no ;;
+		{"case x in x) echo last > out; esac", "last\n"},
+		{"case x in x) ;; esac; echo empty > out", "empty\n"},
+		{"case x in esac; echo none > out", "none\n"},
+		// Patterns: wildcards, also across /, quoted characters are literal
+		{"case a/b/c in *) echo star > out;; esac", "star\n"},
+		{"case a/b in a?b) echo q > out;; esac", "q\n"},
+		{"case b in [abc]) echo class > out;; esac", "class\n"},
+		{"case d in [!abc]) echo neg > out;; esac", "neg\n"},
+		{`case '*' in "*") echo quoted > out;; *) echo glob > out;; esac`, "quoted\n"},
+		{`case abc in "*") echo quoted > out;; *) echo glob > out;; esac`, "glob\n"},
+		{`case 'a b' in "a b") echo space > out;; esac`, "space\n"},
+		{`case 'x)' in 'x)') echo paren-in-quotes > out;; esac`, "paren-in-quotes\n"},
+		// Variables in the word and in patterns
+		{`set -- --help; case $1 in -h|--help) echo help > out;; esac`, "help\n"},
+		// Values of variables are no patterns (like everywhere in gosh)
+		{`P='b*'; case bar in $P) echo pattern > out;; *) echo literal > out;; esac`, "literal\n"},
+		{`P='b*'; case 'b*' in $P) echo same > out;; esac`, "same\n"},
+		{`case $(echo hi) in hi) echo subst > out;; esac`, "subst\n"},
+		{`case "" in "") echo empty-word > out;; esac`, "empty-word\n"},
+		// Only the first matching clause runs
+		{"case a in a) echo 1 >> out;; *) echo 2 >> out;; esac", "1\n"},
+		// Nested in other structures
+		{"for x in a b; do case $x in a) echo A >> out;; *) echo other >> out;; esac; done", "A\nother\n"},
+		{"f() { case $1 in y) return 0;; *) return 1;; esac; }; f y && echo yes > out", "yes\n"},
+	}
+	for _, tc := range tests {
+		if got := runIn(t, tc.input); got != tc.want {
+			t.Errorf("%q: out = %q, want %q", tc.input, got, tc.want)
+		}
+	}
+
+	for input, status := range map[string]int{
+		"case x in y) false;; esac": 0,
+		"case x in x) false;; esac": 1,
+		"case x in x) true;; esac":  0,
+		"case x in x) echo;":        2,
+		"case x y in x) ;; esac":    2,
+		"echo a;; echo b":           2,
+	} {
+		runIn(t, input)
+		if lastStatus != status {
+			t.Errorf("%q: $? = %d, want %d", input, lastStatus, status)
+		}
+	}
+}
+
+func TestExec_Group(t *testing.T) {
+	tests := []struct {
+		input string
+		want  string
+	}{
+		{"{ echo a >> out; echo b >> out; }", "a\nb\n"},
+		{"{\n  echo multi >> out\n}", "multi\n"},
+		{"false || { echo fallback >> out; }", "fallback\n"},
+		{"echo { } > out", "{ }\n"},
+	}
+	for _, tc := range tests {
+		if got := runIn(t, tc.input); got != tc.want {
+			t.Errorf("%q: out = %q, want %q", tc.input, got, tc.want)
+		}
+	}
+}
+
+func TestExec_PositionalBuiltins(t *testing.T) {
+	resetShell(t)
+	tests := []struct {
+		input string
+		want  string
+	}{
+		{"set -- a b c; echo $# $1 $3 > out", "3 a c\n"},
+		{"set -- a b c; shift; echo $# $1 > out", "2 b\n"},
+		{"set -- a b c; shift 2; echo $# $1 > out", "1 c\n"},
+		{"set -- a b; shift 3; echo $# $? > out", "2 1\n"},
+		{"set --; echo $# > out", "0\n"},
+		{"set -- a b; for x; do echo $x >> out; done", "a\nb\n"},
+		{"set -- 1 2 3; while [ $# -gt 0 ]; do echo $1 >> out; shift; done", "1\n2\n3\n"},
+		// source with arguments
+		{"echo 'echo $# $1 > out' > lib; set -- x; . ./lib a b", "2 a\n"},
+		{"echo 'echo $1 > out' > lib; set -- x; . ./lib a b; echo $1 >> out", "a\nx\n"},
+		// return ends a sourced file
+		{"printf 'echo one >> out\\nreturn 3\\necho two >> out\\n' > lib; . ./lib; echo $? >> out", "one\n3\n"},
+	}
+	for _, tc := range tests {
+		positional = nil
+		if got := runIn(t, tc.input); got != tc.want {
+			t.Errorf("%q: out = %q, want %q", tc.input, got, tc.want)
+		}
+	}
+}
+
+func TestRead(t *testing.T) {
+	for _, name := range []string{"GOSH_A", "GOSH_B", "GOSH_C", "REPLY", "IFS"} {
+		os.Unsetenv(name)
+		defer os.Unsetenv(name)
+	}
+	tests := []struct {
+		input string
+		data  string
+		want  string
+	}{
+		{"read GOSH_A", "hello world\n", "[hello world]"},
+		{"read GOSH_A GOSH_B", "  one   two  three  \n", "[one][two  three]"},
+		{"read GOSH_A GOSH_B GOSH_C", "one\n", "[one][][]"},
+		{"read GOSH_A", "no newline", "[no newline]"},
+		{"read GOSH_A GOSH_B", `a\ b c` + "\n", "[a b][c]"},
+		{"read -r GOSH_A GOSH_B", `a\ b c` + "\n", `[a\][b c]`},
+		{"read GOSH_A", "con\\\ntinued\n", "[continued]"},
+		{"read", "  reply  \n", "[  reply  ]"},
+		{"IFS=:; read GOSH_A GOSH_B GOSH_C", "a::b:c\n", "[a][][b:c]"},
+		{"IFS=:; read GOSH_A GOSH_B", "a b:c d\n", "[a b][c d]"},
+		{"IFS=; read GOSH_A", "  keep  \n", "[  keep  ]"},
+		{"read GOSH_A; read GOSH_B", "first\nsecond\n", "[first][second]"},
+	}
+	for _, tc := range tests {
+		for _, name := range []string{"GOSH_A", "GOSH_B", "GOSH_C", "REPLY", "IFS"} {
+			os.Unsetenv(name)
+		}
+		dir := t.TempDir()
+		in := filepath.Join(dir, "in")
+		os.WriteFile(in, []byte(tc.data), 0644)
+		f, _ := os.Open(in)
+		saved := os.Stdin
+		os.Stdin = f
+		execInput(tc.input)
+		os.Stdin = saved
+		f.Close()
+
+		var got strings.Builder
+		names := []string{"GOSH_A", "GOSH_B", "GOSH_C"}
+		if !strings.Contains(tc.input, "GOSH_") {
+			names = []string{"REPLY"}
+		}
+		for _, name := range names {
+			if v, ok := os.LookupEnv(name); ok {
+				got.WriteString("[" + v + "]")
+			}
+		}
+		if got.String() != tc.want {
+			t.Errorf("%q with %q: got %s, want %s", tc.input, tc.data, got.String(), tc.want)
+		}
+	}
+
+	// Status 1 at the end of the input, also after a last line without newline
+	for data, want := range map[string]int{"line\n": 0, "partial": 1, "": 1} {
+		dir := t.TempDir()
+		os.WriteFile(filepath.Join(dir, "in"), []byte(data), 0644)
+		runIn(t, "read GOSH_A < "+filepath.Join(dir, "in"))
+		if lastStatus != want {
+			t.Errorf("read from %q: $? = %d, want %d", data, lastStatus, want)
+		}
+	}
+
+	if err := execInput("read 1x"); err == nil || err.Error() != "read: `1x': not a valid identifier" {
+		t.Errorf("read 1x: %v", err)
+	}
+	if err := execInput("echo a | read GOSH_A"); err == nil || !strings.Contains(err.Error(), "cannot be used in a pipeline") {
+		t.Errorf("read in a pipeline: %v", err)
+	}
+}
+
+// TestShell_Arguments checks $0 and the positional parameters of scripts and
+// gosh -c, and that a script reads lines from stdin with read.
+func TestShell_Arguments(t *testing.T) {
+	dir := t.TempDir()
+	script := filepath.Join(dir, "script.gosh")
+	os.WriteFile(script, []byte(`echo "$# [$1] [$2]"
+usage() {
+  echo "usage: $1" >&2
+  return 2
+}
+case ${1:-} in
+  -h) usage x; exit $? ;;
+esac
+while read -r line; do
+  echo "line: $line"
+done
+`), 0644)
+
+	tests := []struct {
+		args  []string
+		stdin string
+		want  string
+	}{
+		{[]string{"-c", `echo $0 $# "$@"`}, "", subshellPath + " 0\n"},
+		{[]string{"-c", `echo $0 $# "$@"`, "name", "a", "b c"}, "", "name 2 a b c\n"},
+		{[]string{"-c", `for a; do echo "<$a>"; done`, "n", "x y", "z"}, "", "<x y>\n<z>\n"},
+		{[]string{script, "one", "two words"}, "l1\nl2\n", "2 [one] [two words]\nline: l1\nline: l2\n"},
+	}
+	for _, tc := range tests {
+		cmd := exec.Command(subshellPath, tc.args...)
+		cmd.Stdin = strings.NewReader(tc.stdin)
+		out, _ := cmd.Output()
+		if string(out) != tc.want {
+			t.Errorf("gosh %q: got %q, want %q", tc.args, out, tc.want)
+		}
+	}
+
+	cmd := exec.Command(subshellPath, script, "-h")
+	out, err := cmd.CombinedOutput()
+	if exitStatus(err) != 2 || !strings.Contains(string(out), "usage: x") {
+		t.Errorf("script -h: status %d, output %q", exitStatus(err), out)
+	}
+}

heredoc.go

@@ -0,0 +1,268 @@
+package main
+
+// Here-documents: cmd <<WORD, followed by lines up to a line WORD, is the
+// same as a here-string cmd <<<"lines" (without the last newline, which the
+// here-string adds). extractHeredocs rewrites the source that way before it
+// is parsed, so that the rest of gosh (and subshells, which get the source
+// text) only has to know here-strings.
+
+import (
+	"strings"
+)
+
+// hereDoc is a here-document whose body has not been read yet.
+type hereDoc struct {
+	seg       int // the index of its placeholder in the output segments
+	delim     string
+	quoted    bool // the delimiter was quoted: the body is not expanded
+	stripTabs bool // <<-: leading tabs are removed from the lines
+}
+
+// extractHeredocs replaces every here-document operator in src by a
+// here-string with its body and removes the body and delimiter lines. The
+// body starts after the end of the line with the operator. If the input
+// ends before the delimiter line, it returns errIncomplete (an interactive
+// shell then reads more lines).
+//
+// The body is expanded like "..." if the delimiter is unquoted ($VAR, $(...),
+// \ before $ ` \ and newline), and taken literally if any part of the
+// delimiter is quoted ('EOF', "EOF", \EOF).
+func extractHeredocs(src string) (string, error) {
+	if !strings.Contains(src, "<<") {
+		return src, nil
+	}
+	var (
+		segs      []string
+		cur       strings.Builder
+		pending   []hereDoc
+		wordStart = true
+	)
+	copyTo := func(i, end int) int {
+		if end < 0 || end > len(src) {
+			end = len(src)
+		}
+		cur.WriteString(src[i:end])
+		return end
+	}
+
+	for i := 0; i < len(src); {
+		ch := src[i]
+		switch {
+		case ch == '\\':
+			i = copyTo(i, i+2)
+			wordStart = false
+		case ch == '\'':
+			end := strings.IndexByte(src[i+1:], '\'')
+			if end >= 0 {
+				end += i + 2
+			}
+			i = copyTo(i, end)
+			wordStart = false
+		case ch == '"':
+			end := dquoteEnd(src, i)
+			if end >= 0 {
+				end++
+			}
+			i = copyTo(i, end)
+			wordStart = false
+		case isSubstStart(src, i):
+			end := substEnd(src, i)
+			if end >= 0 {
+				end++
+			}
+			i = copyTo(i, end)
+			wordStart = false
+		case ch == '#' && wordStart:
+			// A comment, until the end of the line
+			end := strings.IndexByte(src[i:], '\n')
+			if end >= 0 {
+				end += i
+			}
+			i = copyTo(i, end)
+		case strings.HasPrefix(src[i:], "<<<"):
+			i = copyTo(i, i+3)
+			wordStart = false
+		case strings.HasPrefix(src[i:], "<<"):
+			h, n, err := parseHereOp(src[i:])
+			if err != nil {
+				return "", err
+			}
+			segs = append(segs, cur.String())
+			cur.Reset()
+			h.seg = len(segs)
+			segs = append(segs, "") // filled in when the body has been read
+			pending = append(pending, h)
+			i += n
+			wordStart = false
+		case ch == '\n':
+			cur.WriteByte(ch)
+			i++
+			wordStart = true
+			// The bodies of the here-documents of this line follow
+			for _, h := range pending {
+				body, n, ok := readHereBody(src[i:], h)
+				if !ok {
+					return "", errIncomplete
+				}
+				segs[h.seg] = hereString(body, h.quoted)
+				i += n
+			}
+			pending = nil
+		default:
+			cur.WriteByte(ch)
+			i++
+			wordStart = strings.IndexByte(" \t;&|()<>", ch) >= 0
+		}
+	}
+	if len(pending) > 0 {
+		return "", errIncomplete
+	}
+	segs = append(segs, cur.String())
+	return strings.Join(segs, ""), nil
+}
+
+// dquoteEnd returns the index of the " that ends the double-quoted string
+// starting at s[i], or -1.
+func dquoteEnd(s string, i int) int {
+	for j := i + 1; j < len(s); j++ {
+		switch {
+		case s[j] == '\\':
+			j++
+		case isSubstStart(s, j):
+			end := substEnd(s, j)
+			if end < 0 {
+				return -1
+			}
+			j = end
+		case s[j] == '"':
+			return j
+		}
+	}
+	return -1
+}
+
+// parseHereOp parses a here-document operator <<WORD or <<-WORD at the
+// start of s and returns it and its length.
+func parseHereOp(s string) (hereDoc, int, error) {
+	h := hereDoc{}
+	i := 2
+	if i < len(s) && s[i] == '-' {
+		h.stripTabs = true
+		i++
+	}
+	for i < len(s) && (s[i] == ' ' || s[i] == '\t') {
+		i++
+	}
+	var delim strings.Builder
+	start := i
+	for i < len(s) && strings.IndexByte(" \t\n;&|()<>", s[i]) < 0 {
+		switch c := s[i]; c {
+		case '\'', '"':
+			end := strings.IndexByte(s[i+1:], c)
+			if end < 0 {
+				return h, 0, errIncomplete
+			}
+			delim.WriteString(s[i+1 : i+1+end])
+			i += end + 2
+			h.quoted = true
+		case '\\':
+			if i+1 < len(s) {
+				delim.WriteByte(s[i+1])
+			}
+			i += 2
+			h.quoted = true
+		default:
+			delim.WriteByte(c)
+			i++
+		}
+	}
+	if i == start {
+		if i == len(s) || s[i] == '\n' {
+			return h, 0, syntaxError("newline")
+		}
+		return h, 0, syntaxError(s[i : i+1])
+	}
+	h.delim = delim.String()
+	return h, min(i, len(s)), nil
+}
+
+// readHereBody reads the lines of a here-document from s up to the
+// delimiter line. It returns the body (each line with its newline) and the
+// number of bytes consumed, or ok == false if there is no delimiter line yet.
+func readHereBody(s string, h hereDoc) (body string, n int, ok bool) {
+	var b strings.Builder
+	for pos := 0; ; {
+		end := strings.IndexByte(s[pos:], '\n')
+		last := end < 0
+		if last {
+			end = len(s) - pos
+		}
+		line := s[pos : pos+end]
+		if h.stripTabs {
+			line = strings.TrimLeft(line, "\t")
+		}
+		next := min(pos+end+1, len(s))
+		if line == h.delim {
+			return b.String(), next, true
+		}
+		if last {
+			return "", 0, false
+		}
+		b.WriteString(line)
+		b.WriteByte('\n')
+		pos = next
+	}
+}
+
+// hereString returns the here-string (or redirection) that has the effect of
+// a here-document with the given body.
+func hereString(body string, quoted bool) string {
+	if body == "" {
+		return "</dev/null"
+	}
+	body = strings.TrimSuffix(body, "\n")
+	if quoted {
+		return "<<<'" + strings.ReplaceAll(body, "'", `'\''`) + "'"
+	}
+	return `<<<"` + escapeHereBody(body) + `"`
+}
+
+// escapeHereBody quotes the body of an unquoted here-document for "...":
+// " becomes \", a backslash that only escapes $ ` \ and newline in a
+// here-document stays one, others become \\. $(...) and ${...} are kept as
+// they are, "$@" becomes "$*" (one word, as in a here-document).
+func escapeHereBody(body string) string {
+	var b strings.Builder
+	for i := 0; i < len(body); i++ {
+		c := body[i]
+		switch {
+		case isSubstStart(body, i):
+			end := substEnd(body, i)
+			if end < 0 {
+				end = len(body) - 1
+			}
+			b.WriteString(body[i : end+1])
+			i = end
+		case strings.HasPrefix(body[i:], "$@"):
+			b.WriteString("$*")
+			i++
+		case strings.HasPrefix(body[i:], "${"):
+			end := paramEnd(body, i)
+			if end < 0 {
+				end = len(body) - 1
+			}
+			b.WriteString(strings.Replace(body[i:end+1], "${@", "${*", 1))
+			i = end
+		case c == '\\' && i+1 < len(body) && strings.IndexByte("$`\\\n", body[i+1]) >= 0:
+			b.WriteString(body[i : i+2])
+			i++
+		case c == '\\':
+			b.WriteString(`\\`)
+		case c == '"':
+			b.WriteString(`\"`)
+		default:
+			b.WriteByte(c)
+		}
+	}
+	return b.String()
+}

jobs.go

@@ -286,7 +286,16 @@ func (j *job) result() error {
 	for _, p := range j.procs[:len(j.procs)-1] {
 		printError(p.err)
 	}
-	return j.procs[len(j.procs)-1].err
+	last := j.procs[len(j.procs)-1].err
+	if pipefail && exitStatus(last) == 0 {
+		// The status of the last command that failed
+		for i := len(j.procs) - 2; i >= 0; i-- {
+			if err := j.procs[i].err; exitStatus(err) != 0 {
+				return silent(err)
+			}
+		}
+	}
+	return last
 }
 
 // waitForeground waits for a job in the foreground. If it is stopped, it is
@@ -504,9 +513,12 @@ func builtinBg(args []string, stdout io.Writer) error {
 func builtinWait(args []string) error {
 	jobs := append([]*job(nil), jobTable...)
 	if len(args) > 1 {
-		j, err := findJob("wait", args)
+		j := jobByPid(args[1])
-		if err != nil {
+		if j == nil {
-			return err
+			var err error
+			if j, err = findJob("wait", args); err != nil {
+				return err
+			}
 		}
 		jobs = []*job{j}
 	}
@@ -523,6 +535,23 @@ func builtinWait(args []string) error {
 	return err
 }
 
+// jobByPid returns the job with a process with the ID in spec (wait $!), or
+// nil.
+func jobByPid(spec string) *job {
+	pid, err := strconv.Atoi(spec)
+	if err != nil {
+		return nil
+	}
+	for _, j := range jobTable {
+		for _, p := range j.procs {
+			if p.cmd != nil && p.cmd.Process.Pid == pid {
+				return j
+			}
+		}
+	}
+	return nil
+}
+
 // exitShell exits the shell, unless there are stopped jobs and the user was
 // not warned yet (like bash).
 func exitShell(code int) error {
@@ -530,6 +559,8 @@ func exitShell(code int) error {
 		exitWarned = true
 		return errors.New("there are stopped jobs")
 	}
+	lastStatus = code // $? in the EXIT trap
+	runExitTrap()
 	releaseTerminal()
 	os.Exit(code)
 	return nil

main.go

@@ -12,6 +12,7 @@ import (
 	"os/user"
 	"path/filepath"
 	"runtime/debug"
+	"slices"
 	"sort"
 	"strconv"
 	"strings"
@@ -152,18 +153,20 @@ func tokenize(input string) ([]token, error) {
 		plain    = true          // the word so far has no quotes, escapes or expansions
 		assign   bool            // the word is an assignment name=value
 		tildeOK  bool            // ~ may be expanded here (after = or : of an assignment)
+		noParams bool            // the word contains "$@" without positional parameters
 		quote    byte
 		escaped  bool
 		rawStart = -1 // start of the current word in input
 	)
 
 	endWord := func() {
-		if inWord {
+		// "$@" without parameters is no word at all, unlike ""
+		if inWord && !(noParams && b.Len() == 0) {
 			tokens = append(tokens, token{word: b.String(), pattern: pat.String(), glob: glob, assign: assign})
 		}
 		b.Reset()
 		pat.Reset()
-		glob, assign, plain = false, false, true
+		glob, assign, plain, noParams = false, false, true, false
 		inWord = false
 		rawStart = -1
 	}
@@ -188,18 +191,28 @@ func tokenize(input string) ([]token, error) {
 			if quote == '"' && !strings.ContainsRune("$\"\\`", rune(ch)) {
 				literal("\\")
 			}
-			literal(string(ch))
+			literal(input[i : i+1])
 			inWord = true
 			escaped = false
 		case quote == '\'':
 			if ch == '\'' {
 				quote = 0
 			} else {
-				literal(string(ch))
+				literal(input[i : i+1])
 			}
 		case ch == '\\':
 			startRaw(i)
 			escaped = true
+		case arithEnd(input, i) >= 0:
+			// $((expression)): the value is one word
+			startRaw(i)
+			value, n, err := expandDollar(input[i:])
+			if err != nil {
+				return nil, err
+			}
+			literal(value)
+			inWord = true
+			i += n - 1
 		case isSubstStart(input, i):
 			startRaw(i)
 			end := substEnd(input, i)
@@ -227,6 +240,20 @@ func tokenize(input string) ([]token, error) {
 				}
 			}
 			i = end
+		case ch == '$' && !assign && positionalWords(input[i:], quote == '"') > 0:
+			// $@ and "$@": one word per positional parameter
+			startRaw(i)
+			if len(positional) == 0 && quote == '"' {
+				noParams = true
+			}
+			for k, param := range positional {
+				if k > 0 {
+					endWord()
+				}
+				literal(param)
+				inWord = true
+			}
+			i += positionalWords(input[i:], quote == '"') - 1
 		case ch == '$':
 			startRaw(i)
 			value, n, err := expandVar(input[i:])
@@ -246,7 +273,7 @@ func tokenize(input string) ([]token, error) {
 			if ch == '"' {
 				quote = 0
 			} else {
-				literal(string(ch))
+				literal(input[i : i+1])
 			}
 		case ch == '"' || ch == '\'':
 			startRaw(i)
@@ -289,6 +316,10 @@ func tokenize(input string) ([]token, error) {
 			}
 			t := token{op: string(ch), fd: fd}
 			switch {
+			case strings.HasPrefix(input[i:], "<<<"):
+				// <<<word: the word (and a newline) is the input
+				t.op = "<<<"
+				i += 2
 			case ch == '>' && i+1 < len(input) && input[i+1] == '>':
 				t.op = ">>"
 				i++
@@ -501,29 +532,21 @@ func splitWords(input string) ([]string, error) {
 // is not followed by a variable name is returned literally.
 func expandVar(s string) (string, int, error) {
 	if len(s) > 1 && s[1] == '{' {
-		end := strings.IndexByte(s, '}')
+		end := paramEnd(s, 0)
 		if end < 0 {
 			return "", 0, errors.New("missing } in variable reference")
 		}
-		name, def, hasDef := strings.Cut(s[2:end], ":-")
+		value, err := expandParam(s[2:end])
-		if name == "?" {
+		return value, end + 1, err
-			return strconv.Itoa(lastStatus), end + 1, nil
-		}
-		if !isVarName(name) {
-			return "", 0, fmt.Errorf("bad substitution: %s", s[:end+1])
-		}
-		value, ok := os.LookupEnv(name)
-		if hasDef && value == "" {
-			return def, end + 1, nil
-		}
-		if !ok {
-			return "", 0, fmt.Errorf("%s: unbound variable", name)
-		}
-		return value, end + 1, nil
 	}
 
-	if len(s) > 1 && s[1] == '?' {
+	// $?, $#, $$, $!, $@, $*, $0 and $1 to $9 ($10 is $1 followed by 0)
-		return strconv.Itoa(lastStatus), 2, nil
+	if len(s) > 1 && (isSpecialParam(s[1:2]) || isDigits(s[1:2])) {
+		value, ok := lookupParam(s[1:2])
+		if !ok {
+			return "", 0, fmt.Errorf("%s: unbound variable", s[1:2])
+		}
+		return value, 2, nil
 	}
 
 	n := 1
@@ -540,6 +563,25 @@ func expandVar(s string) (string, int, error) {
 	return value, n, nil
 }
 
+// isSpecialParam reports whether name is one of the special parameters ?,
+// #, $, !, @ and *.
+func isSpecialParam(name string) bool {
+	return len(name) == 1 && strings.Contains("?#$!@*", name)
+}
+
+// positionalWords returns the number of bytes of $@ or ${@} at the start of
+// s, which expands to one word per positional parameter (also in double
+// quotes). Unquoted, $* and ${*} do the same (gosh never splits values).
+// It returns 0 for anything else.
+func positionalWords(s string, quoted bool) int {
+	for _, p := range []string{"$@", "${@}", "$*", "${*}"} {
+		if strings.HasPrefix(s, p) && (strings.Contains(p, "@") || !quoted) {
+			return len(p)
+		}
+	}
+	return 0
+}
+
 func isVarName(name string) bool {
 	if name == "" {
 		return false
@@ -753,6 +795,49 @@ func useColor() bool {
 	return readline.IsTerminal(int(os.Stdout.Fd()))
 }
 
+// reportCwd tells the terminal the current working directory with the OSC 7
+// escape sequence, so that new tabs or windows open in the same directory
+// (VTE terminals like GNOME Terminal, kitty, WezTerm, foot, iTerm2, ...).
+// Terminals without support ignore it. Nothing is written if stdout is not a
+// terminal or TERM is "dumb".
+func reportCwd() {
+	if os.Getenv("TERM") == "dumb" || !readline.IsTerminal(int(os.Stdout.Fd())) {
+		return
+	}
+	wd, err := os.Getwd()
+	if err != nil {
+		return
+	}
+	hostname, _ := os.Hostname()
+	fmt.Fprint(os.Stdout, osc7Sequence(hostname, wd))
+}
+
+// osc7Sequence returns ESC ] 7 ; file://host/path BEL. Host and path are
+// percent-encoded, so control characters in a directory name cannot end the
+// sequence early or inject other escape sequences.
+func osc7Sequence(hostname, dir string) string {
+	return "\x1b]7;file://" + percentEncode(hostname, false) + percentEncode(dir, true) + "\a"
+}
+
+// percentEncode encodes every byte except unreserved URI characters (and '/'
+// if keepSlash) as %XX.
+func percentEncode(s string, keepSlash bool) string {
+	const hex = "0123456789ABCDEF"
+	var b strings.Builder
+	for i := 0; i < len(s); i++ {
+		c := s[i]
+		if c >= 'a' && c <= 'z' || c >= 'A' && c <= 'Z' || c >= '0' && c <= '9' ||
+			c == '-' || c == '.' || c == '_' || c == '~' || c == '/' && keepSlash {
+			b.WriteByte(c)
+		} else {
+			b.WriteByte('%')
+			b.WriteByte(hex[c>>4])
+			b.WriteByte(hex[c&15])
+		}
+	}
+	return b.String()
+}
+
 // shellCompleter implements readline.AutoCompleter for contextual completion
 type shellCompleter struct {
 	commands []string
@@ -760,7 +845,7 @@ type shellCompleter struct {
 
 func newShellCompleter() *shellCompleter {
 	return &shellCompleter{
-		commands: []string{"cd", "pwd", "echo", "exit", "quit", "set", "export", "source", "jobs", "fg", "bg", "wait", "alias", "unalias", "break", "continue", "unset", "help"},
+		commands: []string{"cd", "pwd", "echo", "exit", "quit", "set", "export", "source", "jobs", "fg", "bg", "wait", "alias", "unalias", "break", "continue", "unset", "help", "return", "local", "shift", "read"},
 	}
 }
 
@@ -777,7 +862,7 @@ func (c *shellCompleter) Do(line []rune, pos int) ([][]rune, int) {
 	// ... and after if, then, do etc.
 	if fields := strings.Fields(before); len(fields) > 0 {
 		switch fields[len(fields)-1] {
-		case "if", "then", "elif", "else", "do", "while", "until", "!":
+		case "if", "then", "elif", "else", "do", "while", "until", "!", "{", ";;":
 			isFirstWord = true
 		}
 	}
@@ -791,7 +876,7 @@ func (c *shellCompleter) Do(line []rune, pos int) ([][]rune, int) {
 		// Complete commands
 		var candidates [][]rune
 		seen := make(map[string]bool)
-		names := append(append(append([]string(nil), c.commands...), aliasNames()...), pathExecutables(word)...)
+		names := append(append(append(append([]string(nil), c.commands...), aliasNames()...), functionNames()...), pathExecutables(word)...)
 		for _, cmd := range names {
 			if strings.HasPrefix(cmd, word) && !seen[cmd] {
 				seen[cmd] = true
@@ -935,8 +1020,8 @@ func completeFilePath(line, prefix string) []string {
 	return matches
 }
 
-const usage = `usage: gosh [-l] [-i] [--norc] [--noprofile] [script]
+const usage = `usage: gosh [-l] [-i] [-ex] [-o option] [--norc] [--noprofile] [script [args ...]]
-       gosh [-l] [--noprofile] -c command
+       gosh [-l] [-ex] [-o option] [--noprofile] -c command [name [args ...]]
        gosh -version`
 
 // sysConfDir holds the system-wide startup files.
@@ -949,6 +1034,7 @@ func main() {
 	if strings.HasPrefix(os.Args[0], "-") {
 		args = append([]string{"-l"}, args...)
 	}
+	scriptName = os.Args[0]
 	os.Exit(run(args))
 }
 
@@ -968,7 +1054,25 @@ flags:
 			noRC = true
 		case "--noprofile":
 			noProfile = true
+		case "-o", "+o":
+			// -o pipefail etc., like set
+			if len(args) < 2 {
+				fmt.Fprintln(os.Stderr, "gosh: -o: option requires an argument")
+				return 2
+			}
+			if err := setOption(0, args[1], args[0] == "-o"); err != nil {
+				fmt.Fprintln(os.Stderr, "gosh:", err)
+				return 2
+			}
+			args = args[1:]
 		default:
+			// -e, -x and combinations like -ex, like set
+			if len(args[0]) > 1 && args[0][0] == '-' && strings.Trim(args[0][1:], "ex") == "" {
+				for _, c := range []byte(args[0][1:]) {
+					setOption(c, "", true)
+				}
+				break
+			}
 			break flags
 		}
 		args = args[1:]
@@ -986,21 +1090,26 @@ flags:
 			fmt.Println(usage)
 			return 0
 		case arg == "-c":
-			// Like sh, further arguments are allowed (they would become $0,
+			// gosh -c command [name [args ...]]: name is $0, args are $1, ...
-			// $1, ...), but gosh has no positional parameters yet.
 			if len(args) < 2 {
 				fmt.Fprintln(os.Stderr, "gosh: -c: option requires an argument")
 				fmt.Fprintln(os.Stderr, usage)
 				return 2
 			}
+			if len(args) > 2 {
+				scriptName, positional = args[2], args[3:]
+			}
 			script = func() int { return runScript(strings.NewReader(args[1]), "") }
 		case strings.HasPrefix(arg, "-") && arg != "-":
 			fmt.Fprintf(os.Stderr, "gosh: %s: invalid option\n", arg)
 			fmt.Fprintln(os.Stderr, usage)
 			return 2
 		case arg == "-":
+			positional = args[1:]
 			script = func() int { return runScript(os.Stdin, "") }
 		default:
+			// gosh script [args ...]
+			scriptName, positional = arg, args[1:]
 			f, err := os.Open(arg)
 			if err != nil {
 				fmt.Fprintln(os.Stderr, "gosh:", err)
@@ -1024,9 +1133,12 @@ flags:
 	}
 
 	if !interactiveMode {
-		return script()
+		status := script()
+		runExitTrap()
+		return status
 	}
 	interactive()
+	runExitTrap()
 	return 0
 }
 
@@ -1064,6 +1176,8 @@ func sourceStartupFile(path string) {
 		return
 	}
 	defer f.Close()
+	sourceDepth++
+	defer func() { sourceDepth-- }()
 	runScript(bufio.NewReader(f), path)
 }
 
@@ -1127,12 +1241,19 @@ func runScript(r io.Reader, name string) int {
 				goto next // read the rest of the command
 			}
 			buf.Reset()
-			if err != nil {
+			if err == nil {
-				lastStatus = exitStatus(err)
+				err = tree.exec()
-				report(err, startLine)
+				var ret returnSignal
+				if errors.As(err, &ret) {
+					// return in a sourced file
+					lastStatus = ret.status
+					return lastStatus
+				}
 			} else {
-				report(tree.exec(), startLine)
+				lastStatus = exitStatus(err)
 			}
+			report(err, startLine)
+			runPendingTraps()
 		}
 	next:
 		if readErr != nil {
@@ -1192,6 +1313,10 @@ func exitStatus(err error) int {
 	if errors.As(err, &lc) {
 		return 0
 	}
+	var ret returnSignal
+	if errors.As(err, &ret) {
+		return ret.status
+	}
 	var exitErr *exec.ExitError
 	if errors.As(err, &exitErr) {
 		if ws, ok := exitErr.Sys().(syscall.WaitStatus); ok && ws.Signaled() {
@@ -1218,7 +1343,7 @@ func interactive() {
 	// Ctrl+C sends SIGINT to the whole foreground process group. Catch it so
 	// that it only stops the running command and not the shell. (signal.Ignore
 	// would be inherited by the child processes.)
-	signal.Notify(make(chan os.Signal, 1), os.Interrupt)
+	signal.Notify(interruptChan, os.Interrupt)
 
 	histFile := historyFile()
 	if histFile != "" {
@@ -1248,9 +1373,11 @@ func interactive() {
 	var buf strings.Builder
 	for {
 		if buf.Len() == 0 {
+			runPendingTraps()
 			// Report finished and stopped background jobs
 			reapJobs(true)
 			// Update prompt dynamically (in case directory changed)
+			reportCwd()
 			l.SetPrompt(getPrompt())
 		} else {
 			l.SetPrompt("> ")
@@ -1339,11 +1466,12 @@ func printError(err error) {
 		exitErr   *exec.ExitError
 		statusErr statusError
 		lc        loopControl
+		ret       returnSignal
 	)
-	if err == nil || errors.As(err, &exitErr) || errors.As(err, &statusErr) || errors.As(err, &lc) {
+	if err == nil || errors.As(err, &exitErr) || errors.As(err, &statusErr) || errors.As(err, &lc) || errors.As(err, &ret) {
 		return
 	}
-	fmt.Fprintln(os.Stderr, "gosh:", err)
+	fmt.Fprintln(stdio(2), "gosh:", err)
 }
 
 // execInput parses and executes input: a command line or a whole script.
@@ -1361,27 +1489,8 @@ func execInput(input string) error {
 // execCommand executes a pipeline of simple commands with redirections, in
 // the background if background is set.
 func execCommand(input string, background bool) error {
-	// Brace expansion comes first, so that its results are expanded further
 	substStatus = 0
-	input, err := expandBraceWords(input)
+	stages, err := expandStages(input)
-	if err != nil {
-		return err
-	}
-
-	// Split the input into words and operators, expanding variables and ~ on
-	// the way.
-	tokens, err := tokenize(input)
-	var (
-		synErr    syntaxError
-		statusErr statusError
-	)
-	if errors.As(err, &synErr) || errors.As(err, &statusErr) {
-		return err
-	}
-	if err != nil {
-		return fmt.Errorf("invalid input: %w", err)
-	}
-	stages, err := parsePipeline(tokens)
 	if err != nil {
 		return err
 	}
@@ -1399,19 +1508,62 @@ func execCommand(input string, background bool) error {
 	return runPipeline(stages, strings.TrimSpace(input), background)
 }
 
-// redirect is a redirection of a simple command, e.g. 2>>file or 2>&1.
+// expandStages expands the text of a pipeline of simple commands and splits
-type redirect struct {
+// it into its stages.
-	op   string // <, >, >>, &>, &>>, >& or <&
+func expandStages(input string) ([]stage, error) {
-	fd   int    // the redirected file descriptor
+	// Brace expansion comes first, so that its results are expanded further
-	dup  int    // the target file descriptor of >& and <&
+	input, err := expandBraceWords(input)
-	file string // the file name for all other operators
+	if err != nil {
+		return nil, err
+	}
+
+	// Split the input into words and operators, expanding variables and ~ on
+	// the way.
+	tokens, err := tokenize(input)
+	var (
+		synErr    syntaxError
+		statusErr statusError
+	)
+	if errors.As(err, &synErr) || errors.As(err, &statusErr) {
+		return nil, err
+	}
+	if err != nil {
+		return nil, fmt.Errorf("invalid input: %w", err)
+	}
+	return parsePipeline(tokens)
 }
 
-// stage is a simple command of a pipeline.
+// openRedirections expands and opens the redirections of a compound command
+// and returns the resulting stdin, stdout and stderr, and the files to close
+// afterwards.
+func openRedirections(text string) ([3]*os.File, []*os.File, error) {
+	fds := [3]*os.File{stdio(0), stdio(1), stdio(2)}
+	stages, err := expandStages(text)
+	if err != nil {
+		return fds, nil, err
+	}
+	if len(stages) != 1 || len(stages[0].args) > 0 || len(stages[0].assigns) > 0 {
+		return fds, nil, syntaxError(text)
+	}
+	opened, err := applyRedirects(&fds, stages[0].redirects)
+	return fds, opened, err
+}
+
+// redirect is a redirection of a simple command, e.g. 2>>file or 2>&1.
+type redirect struct {
+	op   string // <, >, >>, &>, &>>, >&, <& or <<<
+	fd   int    // the redirected file descriptor
+	dup  int    // the target file descriptor of >& and <&
+	file string // the file name for all other operators (the text for <<<)
+}
+
+// stage is a simple command of a pipeline, or a script that runs in a
+// subshell (a compound command in a pipeline or in the background).
 type stage struct {
 	assigns   []string // name=value before the command name
 	args      []string
 	redirects []redirect
+	script    string
 }
 
 // parsePipeline groups tokens into the stages of a pipeline.
@@ -1448,6 +1600,11 @@ func parsePipeline(tokens []token) ([]stage, error) {
 				return nil, syntaxError(next.op)
 			}
 			i++
+			if t.op == "<<<" {
+				// A here-string is not expanded as a pattern
+				cur.redirects = append(cur.redirects, redirect{op: t.op, fd: t.fd, file: tokens[i].word})
+				continue
+			}
 			files := expandWord(tokens[i])
 			if len(files) > 1 {
 				return nil, fmt.Errorf("%s: ambiguous redirect", sanitize(tokens[i].word))
@@ -1476,7 +1633,7 @@ func runPipeline(stages []stage, text string, background bool) error {
 		shellTTY, _ = readline.GetState(ttyFd)
 	}
 
-	stdin := os.Stdin
+	stdin := stdio(0)
 	if background && !jobControl {
 		// Without job control background jobs must not read from the
 		// terminal, like in sh
@@ -1486,12 +1643,12 @@ func runPipeline(stages []stage, text string, background bool) error {
 	}
 	var startErr error
 	for i, st := range stages {
-		stdout := os.Stdout
+		stdout := stdio(1)
 		var next *os.File
 		if i < len(stages)-1 {
 			r, w, err := os.Pipe()
 			if err != nil {
-				if stdin != os.Stdin {
+				if stdin != stdio(0) {
 					stdin.Close()
 				}
 				startErr = err
@@ -1521,6 +1678,11 @@ func runPipeline(stages []stage, text string, background bool) error {
 			}
 			fmt.Fprintf(os.Stderr, "[%d] %d\n", j.id, pid)
 		}
+		for _, p := range j.procs {
+			if p.cmd != nil {
+				lastBackgroundPid = p.cmd.Process.Pid
+			}
+		}
 		return nil
 	}
 	return waitForeground(j)
@@ -1530,11 +1692,26 @@ func runPipeline(stages []stage, text string, background bool) error {
 // stdout. Pipe ends passed in are closed by startStage once the stage no
 // longer needs them, so that the neighbors see EOF or get SIGPIPE.
 func startStage(st stage, stdin, stdout *os.File, j *job, inPipeline, background bool) *proc {
+	if (inPipeline || background) && st.script == "" {
+		// eval and exec in a pipeline or in the background run in a
+		// subshell, like in sh
+		switch firstArg(st.args) {
+		case "eval":
+			st.script, st.args = strings.Join(st.args[1:], " "), nil
+		case "exec":
+			st.args = st.args[1:]
+		}
+	}
+	if _, isFunc := functions[firstArg(st.args)]; xtrace && st.script == "" && !(isFunc && (inPipeline || background)) {
+		// (a function in a pipeline is shown by its subshell)
+		traceCommand(st)
+	}
+
 	var owned []*os.File
-	if stdin != os.Stdin {
+	if stdin != stdio(0) {
 		owned = append(owned, stdin)
 	}
-	if stdout != os.Stdout {
+	if stdout != stdio(1) {
 		owned = append(owned, stdout)
 	}
 	closeOwned := func() {
@@ -1547,7 +1724,7 @@ func startStage(st stage, stdin, stdout *os.File, j *job, inPipeline, background
 	// the command would read from /dev/null, so interactive programs (su,
 	// vim, ssh, ...) would get EOF right away. readline only reads from stdin
 	// while a line is being edited, so it does not steal input.
-	fds := [3]*os.File{stdin, stdout, os.Stderr}
+	fds := [3]*os.File{stdin, stdout, stdio(2)}
 	opened, err := applyRedirects(&fds, st.redirects)
 	owned = append(owned, opened...)
 	if err == nil && len(st.args) == 0 && len(st.assigns) > 0 {
@@ -1564,25 +1741,39 @@ func startStage(st stage, stdin, stdout *os.File, j *job, inPipeline, background
 			err = statusError(substStatus)
 		}
 	}
-	if err != nil || len(st.args) == 0 {
+	if err != nil || len(st.args) == 0 && st.script == "" {
 		// A command without arguments only creates or truncates the files
 		closeOwned()
 		return finishedProc(err)
 	}
 
-	if builtin, ok := builtins[st.args[0]]; ok {
+	var fn *funcDef
+	isFunc := false
+	if st.script == "" {
+		fn, isFunc = functions[st.args[0]]
+	}
+	if isFunc && !inPipeline && !background {
+		defer closeOwned()
+		return finishedProc(callFunction(fn, st.args, fds, st.assigns))
+	}
+	if !isFunc && st.script == "" && st.args[0] == "exec" && !inPipeline && !background {
+		defer closeOwned()
+		return finishedProc(builtinExec(st.args, fds, st.assigns))
+	}
+	if builtin, ok := builtins[firstArg(st.args)]; !isFunc && st.script == "" && ok {
 		switch {
-		case inPipeline && builtin.changesState:
+		case inPipeline && builtin.changesState && !onlyShows(st.args):
 			closeOwned()
 			return finishedProc(fmt.Errorf("%s: cannot be used in a pipeline", st.args[0]))
-		case background && builtin.changesState:
+		case background && builtin.changesState && !onlyShows(st.args):
 			closeOwned()
 			return finishedProc(fmt.Errorf("%s: cannot be run in the background", st.args[0]))
 		}
+		shellStderr := stdio(2)
 		run := func() error {
 			defer closeOwned()
-			err := runBuiltin(st.args, fds[1])
+			err := runBuiltin(st.args, fds[0], fds[1])
-			if err != nil && fds[2] != os.Stderr {
+			if err != nil && fds[2] != shellStderr {
 				// Report the error where stderr is redirected to
 				fmt.Fprintln(fds[2], "gosh:", err)
 				return statusError(1)
@@ -1590,8 +1781,12 @@ func startStage(st stage, stdin, stdout *os.File, j *job, inPipeline, background
 			return err
 		}
 		if !inPipeline && !background {
-			// name=value before a builtin applies only while it runs
+			// name=value before a builtin applies only while it runs, its
+			// redirections also to the commands it runs (source file > out)
 			defer setTemporarily(st.assigns)()
+			saved := ioOverride
+			ioOverride = fds
+			defer func() { ioOverride = saved }()
 			return finishedProc(run())
 		}
 		p := &proc{done: make(chan error, 1)}
@@ -1599,7 +1794,23 @@ func startStage(st stage, stdin, stdout *os.File, j *job, inPipeline, background
 		return p
 	}
 
-	cmd := exec.Command(st.args[0], st.args[1:]...)
+	var cmd *exec.Cmd
+	if st.script != "" {
+		cmd, err = subshellCommand(st.script, positional)
+		if err != nil {
+			closeOwned()
+			return finishedProc(err)
+		}
+	} else if isFunc {
+		// A function in a pipeline or in the background runs in a subshell
+		cmd, err = subshellCommand(`"$@"`, st.args)
+		if err != nil {
+			closeOwned()
+			return finishedProc(err)
+		}
+	} else {
+		cmd = exec.Command(st.args[0], st.args[1:]...)
+	}
 	cmd.Stdin, cmd.Stdout, cmd.Stderr = fds[0], fds[1], fds[2]
 	if len(st.assigns) > 0 {
 		// name=value before a command is only in its environment (the
@@ -1623,7 +1834,7 @@ func startStage(st stage, stdin, stdout *os.File, j *job, inPipeline, background
 	// The child has its own copies of the files now
 	closeOwned()
 	if errors.Is(err, exec.ErrNotFound) {
-		err = fmt.Errorf("%s: %w", sanitize(st.args[0]), errCommandNotFound)
+		err = fmt.Errorf("%s: %w", sanitize(firstArg(st.args)), errCommandNotFound)
 	}
 	if err != nil {
 		return finishedProc(err)
@@ -1638,6 +1849,13 @@ func startStage(st stage, stdin, stdout *os.File, j *job, inPipeline, background
 	return &proc{cmd: cmd}
 }
 
+func firstArg(args []string) string {
+	if len(args) == 0 {
+		return ""
+	}
+	return args[0]
+}
+
 // setTemporarily sets the variables of the assignments and returns a
 // function that restores the previous values.
 func setTemporarily(assigns []string) func() {
@@ -1686,6 +1904,16 @@ func applyRedirects(fds *[3]*os.File, redirects []redirect) ([]*os.File, error)
 			continue
 		}
 
+		if r.op == "<<<" {
+			f, err := hereFile(r.file + "\n")
+			if err != nil {
+				return fail(err)
+			}
+			opened = append(opened, f)
+			fds[r.fd] = f
+			continue
+		}
+
 		flags := os.O_WRONLY | os.O_CREATE | os.O_TRUNC
 		switch r.op {
 		case "<":
@@ -1711,6 +1939,26 @@ func applyRedirects(fds *[3]*os.File, redirects []redirect) ([]*os.File, error)
 	return opened, nil
 }
 
+// hereFile returns a file to read content from: a temporary file that is
+// already removed (like bash does for here-documents), so that large inputs
+// work and nothing is left behind.
+func hereFile(content string) (*os.File, error) {
+	f, err := os.CreateTemp("", "gosh-here-*")
+	if err != nil {
+		return nil, err
+	}
+	os.Remove(f.Name())
+	if _, err := f.WriteString(content); err != nil {
+		f.Close()
+		return nil, err
+	}
+	if _, err := f.Seek(0, io.SeekStart); err != nil {
+		f.Close()
+		return nil, err
+	}
+	return f, nil
+}
+
 // builtins lists the built-in commands. Commands that change the state of
 // the shell cannot be used in a pipeline, since there they would run
 // concurrently (sh runs them in a subshell where they have no effect).
@@ -1734,10 +1982,18 @@ var builtins = map[string]struct{ changesState bool }{
 	"unset":    {changesState: true},
 	"break":    {changesState: true},
 	"continue": {changesState: true},
+	"return":   {changesState: true},
+	"local":    {changesState: true},
+	"shift":    {changesState: true},
+	"read":     {changesState: true},
+	"trap":     {changesState: true},
+	"eval":     {changesState: true},
+	"exec":     {changesState: true},
 }
 
-// runBuiltin executes a built-in command, writing its output to stdout.
+// runBuiltin executes a built-in command, reading from stdin and writing its
-func runBuiltin(args []string, stdout io.Writer) error {
+// output to stdout.
+func runBuiltin(args []string, stdin *os.File, stdout io.Writer) error {
 	switch args[0] {
 	case "cd":
 		// Save current directory before changing (for 'cd -')
@@ -1790,17 +2046,11 @@ func runBuiltin(args []string, stdout io.Writer) error {
 		}
 		return exitShell(lastStatus)
 	case "set":
-		// set VAR=value - set environment variable
+		return builtinSet(args, stdout)
-		if len(args) < 2 {
+	case "trap":
-			return fmt.Errorf("usage: set VAR=value")
+		return builtinTrap(args, stdout)
-		}
+	case "eval":
-		// Parse VAR=value
+		return builtinEval(args)
-		parts := strings.SplitN(args[1], "=", 2)
-		if len(parts) != 2 {
-			return fmt.Errorf("usage: set VAR=value")
-		}
-		os.Setenv(parts[0], parts[1])
-		return nil
 	case "export":
 		// export VAR=value - same as set but also marks for child processes
 		if len(args) < 2 {
@@ -1817,12 +2067,21 @@ func runBuiltin(args []string, stdout io.Writer) error {
 		// Does nothing, successfully (e.g. while :; do ...)
 		return nil
 	case "unset":
-		// unset NAME ... - remove variables
+		// unset [-v] NAME ... - remove variables, unset -f NAME ... - functions
-		if len(args) < 2 {
+		names := args[1:]
-			return fmt.Errorf("usage: unset NAME ...")
+		funcs := len(names) > 0 && names[0] == "-f"
+		if len(names) > 0 && (names[0] == "-f" || names[0] == "-v") {
+			names = names[1:]
+		}
+		if len(names) == 0 {
+			return fmt.Errorf("usage: unset [-f|-v] NAME ...")
 		}
 		var err error
-		for _, name := range args[1:] {
+		for _, name := range names {
+			if funcs {
+				delete(functions, name)
+				continue
+			}
 			if !isVarName(name) {
 				err = fmt.Errorf("unset: `%s': not a valid identifier", sanitize(name))
 				continue
@@ -1832,6 +2091,14 @@ func runBuiltin(args []string, stdout io.Writer) error {
 		return err
 	case "break", "continue":
 		return builtinLoopControl(args)
+	case "return":
+		return builtinReturn(args)
+	case "local":
+		return builtinLocal(args)
+	case "shift":
+		return builtinShift(args)
+	case "read":
+		return builtinRead(args, stdin)
 	case "alias":
 		return builtinAlias(args, stdout)
 	case "unalias":
@@ -1845,9 +2112,15 @@ func runBuiltin(args []string, stdout io.Writer) error {
 	case "wait":
 		return builtinWait(args)
 	case "source", ".":
-		// source file - run the commands of file in the current shell
+		// source file [args] - run the commands of file in the current shell
 		if len(args) < 2 {
-			return fmt.Errorf("usage: %s file", args[0])
+			return fmt.Errorf("usage: %s file [args ...]", args[0])
+		}
+		if len(args) > 2 {
+			// The arguments are the positional parameters while it runs
+			saved := positional
+			positional = slices.Clone(args[2:])
+			defer func() { positional = saved }()
 		}
 		return sourceFile(args[0], args[1])
 	case "help":
@@ -1860,18 +2133,32 @@ Built-in commands:
   exit [code]   - Exit shell with status code (default: $?)
   quit [code]   - Quit shell with status code (default: $?)
   set VAR=val   - Set environment variable
+  set [-ex] [-o pipefail] [--] [args] - Options: -e exit when a command
+                  fails, -x print commands, -o pipefail; args are $1, ...
+                  (set: show variables, set -o: show options)
   export VAR=val - Export environment variable
-  unset VAR     - Remove a variable
+  unset VAR     - Remove a variable (unset -f name: a function)
-  source file   - Run the commands of file in this shell (also: . file)
+  source file [args] - Run the commands of file in this shell (also: . file)
   jobs          - List background and stopped jobs
   fg [%n]       - Continue job n (default: current job) in the foreground
   bg [%n]       - Continue stopped job n in the background
-  wait [%n]     - Wait for job n or all background jobs
+  wait [%n|pid] - Wait for job n (or process pid, e.g. $!) or all jobs
   alias [name[=value] ...] - Define or show aliases (alias ll='ls -l')
   unalias name  - Remove an alias (unalias -a: all aliases)
   :             - Do nothing (exit status 0)
   break [n]     - Leave the innermost (or n-th) for/while/until loop
   continue [n]  - Continue with the next iteration of a loop
+  return [n]    - Leave a function or sourced file with status n
+  local VAR[=val] - Variable that gets its old value back when the
+                  function returns
+  shift [n]     - Remove the first n positional parameters (default 1)
+  read [-r] [-p prompt] [VAR ...] - Read a line into variables (split
+                  at $IFS; the last one gets the rest; default $REPLY)
+  eval args     - Run the arguments as a command in this shell
+  exec [cmd]    - Replace the shell with cmd; without cmd, its
+                  redirections apply to the shell (exec > log)
+  trap [cmd] SIG... - Run cmd on a signal (INT, TERM, HUP, USR1, ...)
+                  or on EXIT; trap '' SIG ignores it, trap - SIG resets
   help          - Show this help
 
 Features:
@@ -1894,11 +2181,23 @@ Features:
     GOSH_COLORS='user=1;33:path=36' (keys user, root, path, error; values
     are ANSI SGR codes, empty = no color); disabled with $NO_COLOR,
     TERM=dumb or when output is not a terminal
+  - Reports the working directory to the terminal (OSC 7) before each
+    prompt, so new tabs/windows open in the same directory
   - Variables: name=value sets a variable (like set), name=value command
     sets it only for that command; the value is not split or expanded as
     a pattern
   - Environment variable expansion ($VAR, ${VAR}, ${VAR:-default});
     using an unset variable is an error, use ${VAR:-} for an empty default
+  - Parameter expansion: ${#VAR} (length), ${VAR#pat} ${VAR##pat}
+    ${VAR%pat} ${VAR%%pat} (remove prefix/suffix), ${VAR/pat/rep}
+    ${VAR//pat/rep}, ${VAR:offset:length}, ${VAR-x} ${VAR:=x} ${VAR:+x}
+    ${VAR:?msg}
+  - Arithmetic: $((expression)) with integers and the C operators
+    (+ - * / % ** << >> < == && || ?: = += ++ ...)
+  - Positional parameters: $0, $1 ... $9, ${10}, $# (count), "$@" (one
+    word each), "$*" (one word), $$ (process ID), $! (process ID of the
+    last background job); set by gosh script
+    args, gosh -c command name args, functions, set -- and source
   - Command substitution: $(command) is replaced by the output of command
     (run in a subshell); unquoted it is split into words, "$(command)"
     stays one word
@@ -1906,9 +2205,16 @@ Features:
     a || b (b only if a failed); $? is the exit status of the last command
   - Control structures: if cmd; then ...; elif cmd; then ...; else ...; fi,
     for x in words; do ...; done, while cmd; do ...; done, until ...,
-    ! cmd negates the status; they can span several lines (prompt "> ")
+    case word in pattern|pattern) ...;; esac, { cmd; cmd; } groups,
+    ( cmd; cmd ) subshells; ! cmd negates the status; they can span
+    several lines (prompt "> "), have redirections (done < file) and can
+    be used in pipes (| while read l; do ...; done) and with &
+  - Functions: name() { ...; } (or function name { ...; }); the arguments
+    are $1, $2, ...; in pipes, & and $(...) they run in a subshell
   - Pipes (a | b) and redirections: < file, > file, >> file, 2> file,
-    2>> file, 2>&1, >&2, &> file (stdout and stderr), &>> file
+    2>> file, 2>&1, >&2, &> file (stdout and stderr), &>> file,
+    <<EOF here-documents (<<-EOF strips tabs, <<'EOF' expands nothing),
+    <<<word here-strings
   - Job control: command & runs in the background, Ctrl+Z stops the
     foreground job; jobs, fg, bg and wait manage the jobs
   - Aliases replace the first word of a command in interactive shells

main_test.go

@@ -631,12 +631,11 @@ func TestExecInput_ExportEnvVar(t *testing.T) {
 }
 
 func TestExecInput_SetNoArgs(t *testing.T) {
-	err := execInput("set")
+	// set without arguments shows the variables, quoted for the shell
-	if err == nil {
+	t.Setenv("GOSH_SHOWN", "a b")
-		t.Error("expected error for set with no args, got nil")
+	got := runIn(t, "set > out")
-	}
+	if !strings.Contains(got, "GOSH_SHOWN='a b'\n") {
-	if !strings.Contains(err.Error(), "usage: set VAR=value") {
+		t.Errorf("set: GOSH_SHOWN missing in %q", got)
-		t.Errorf("expected usage error, got: %v", err)
 	}
 }
 
@@ -941,7 +940,7 @@ func TestSplitWords(t *testing.T) {
 		{`echo x${GOSH_A}y`, []string{"echo", "xa by"}},
 		// Escaped and lone dollar signs stay literal
 		{`echo \$GOSH_A "\$GOSH_A"`, []string{"echo", "$GOSH_A", "$GOSH_A"}},
-		{`echo $ 5$ $1`, []string{"echo", "$", "5$", "$1"}},
+		{`echo $ 5$ $%`, []string{"echo", "$", "5$", "$%"}},
 		// Backslash in double quotes only escapes $ " \ and `
 		{`echo "a\nb\\c"`, []string{"echo", `a\nb\c`}},
 		// Defaults
@@ -1134,6 +1133,31 @@ func TestBuildPrompt_ColorEscapesControlCharacters(t *testing.T) {
 	}
 }
 
+func TestOSC7Sequence(t *testing.T) {
+	tests := []struct{ host, dir, want string }{
+		{"host", "/home/flow", "\x1b]7;file://host/home/flow\a"},
+		{"host", "/tmp/a b/ä", "\x1b]7;file://host/tmp/a%20b/%C3%A4\a"},
+		{"host", "/x%y#z?", "\x1b]7;file://host/x%25y%23z%3F\a"},
+		{"", "/", "\x1b]7;file:///\a"},
+	}
+	for _, tt := range tests {
+		if got := osc7Sequence(tt.host, tt.dir); got != tt.want {
+			t.Errorf("osc7Sequence(%q, %q) = %q, want %q", tt.host, tt.dir, got, tt.want)
+		}
+	}
+}
+
+func TestOSC7Sequence_EscapesControlCharacters(t *testing.T) {
+	got := osc7Sequence("ho/st\x07", "/evil\x07\x1b]0;title\x1b\\")
+	body := strings.TrimSuffix(strings.TrimPrefix(got, "\x1b]7;"), "\a")
+	if strings.ContainsAny(body, "\x07\x1b") {
+		t.Errorf("sequence contains control characters: %q", got)
+	}
+	if !strings.HasPrefix(body, "file://ho%2Fst%07/evil%07%1B") {
+		t.Errorf("unexpected encoding: %q", got)
+	}
+}
+
 func TestUseColor_NoColor(t *testing.T) {
 	t.Setenv("NO_COLOR", "1")
 	if useColor() {
@@ -1366,7 +1390,7 @@ func TestRun_Options(t *testing.T) {
 		{[]string{"-c", "false"}, 1},
 		{[]string{"-l", "--noprofile", "-c", "sh -c 'exit 5'"}, 5},
 		{[]string{"-c"}, 2},
-		{[]string{"-x"}, 2},
+		{[]string{"-z"}, 2},
 		{[]string{"/gosh/no/such/script"}, 127},
 	}
 	for _, tc := range tests {
@@ -1437,6 +1461,26 @@ func pipelineString(pl *pipelineNode) string {
 			s += "while "
 		}
 		s += treeString(n.cond) + " do " + treeString(n.body) + " done"
+	case *caseNode:
+		s += "case " + n.word + " in"
+		for _, c := range n.clauses {
+			s += " (" + strings.Join(c.patterns, "|") + ") " + treeString(c.body) + " ;;"
+		}
+		s += " esac"
+	case *groupNode:
+		s += "{ " + treeString(n.body) + " }"
+	case *subshellNode:
+		s += "(" + n.text + ")"
+	case *redirNode:
+		s += pipelineString(&pipelineNode{cmd: n.cmd}) + " <" + n.redirs + ">"
+	case *pipeNode:
+		var elems []string
+		for _, e := range n.elems {
+			elems = append(elems, "<"+e.text+">")
+		}
+		s += strings.Join(elems, " | ")
+	case *funcDefNode:
+		s += n.def.name + "() " + pipelineString(&pipelineNode{cmd: n.def.body})
 	}
 	return s
 }
@@ -1504,6 +1548,27 @@ func TestParse_ControlStructures(t *testing.T) {
 		{"while a; do if b; then break; fi; done", "while [a] do if [b] then [break] fi done"},
 		{"for i in 1 2; do for j in 3 4; do echo $i$j; done; done", "for i in (1 2) do for j in (3 4) do [echo $i$j] done done"},
 		{"if a; then if b; then c; fi fi", "if [a] then if [b] then [c] fi fi"},
+		// Compound commands in pipelines, with redirections, in the background
+		{"for x in a; do b; done | cat", "<for x in a; do b; done> | <cat>"},
+		{"a | while b; do c; done | d", "<a> | <while b; do c; done> | <d>"},
+		{"if a; then b; fi > out 2>&1", "if [a] then [b] fi <> out 2>&1>"},
+		{"while read l; do b; done < in", "while [read l] do [b] done << in>"},
+		{"{ a; b; } 2> err", "{ [a]; [b] } <2> err>"},
+		{"for x in a; do b; done &", "for x in (a) do [b] done &"},
+		{"a && b &", "[a] && [b] &"},
+		// Subshells
+		{"(a; b)", "(a; b)"},
+		{"( a ) | b", "<( a )> | <b>"},
+		{"(a) > f", "(a) <> f>"},
+		{"(a; (b)) && c", "(a; (b)) && [c]"},
+		// case, groups and functions
+		{"case $x in a|b) c;; (d) e; f;; esac", "case $x in (a|b) [c] ;; (d) [e]; [f] ;; esac"},
+		{"case x in\n  a)\n    b\n    ;;\nesac", "case x in (a) [b] ;; esac"},
+		{"{ a; }", "{ [a] }"},
+		{"f() { a; }", "f() { [a] }"},
+		{"f ( ) { a; }", "f() { [a] }"},
+		{"function f { a; }", "f() { [a] }"},
+		{"f() (a)", "f() (a)"},
 	}
 	for _, tc := range tests {
 		tree, err := parse(tc.input)
@@ -1522,6 +1587,8 @@ func TestParse_Incomplete(t *testing.T) {
 		"if a", "if a; then", "if a; then b", "if a; then b; else", "if a; then b; elif c",
 		"for x", "for x in a b", "for x in a; do", "for x in a; do b",
 		"while a", "while a; do b", "until a; do",
+		"(a", "(a; b", "{ a;", "case x in", "case x in a) b;;", "f() {", "f()",
+		"cat <<EOF", "cat <<EOF\nbody", "cat <<'EOF'\nbody\nEO",
 		"a &&", "a ||", "a |", "echo 'open", `echo "open`, "echo $(a", "echo a \\",
 	} {
 		if _, err := parse(input); !errors.Is(err, errIncomplete) {
@@ -1536,6 +1603,9 @@ func TestParse_SyntaxErrors(t *testing.T) {
 		"fi", "then", "done", "if a; then fi", "if ; then a; fi", "while a; do done",
 		"if a; then b; done", "for 1x in a; do b; done", "for x in a do b; done; x",
 		"a | | b", "| a",
+		"()", "a (", "a )", "echo (a)", ")", "(a) b", "if a; then b; fi c", "{ a; } b",
+		"case x in a b) c;; esac", "case x in ) a;; esac", "cat <<", "cat << ;",
+		"f() { a; } | b",
 	} {
 		_, err := parse(input)
 		if err == nil || errors.Is(err, errIncomplete) {
@@ -1543,11 +1613,9 @@ func TestParse_SyntaxErrors(t *testing.T) {
 		}
 	}
 	for input, want := range map[string]string{
-		"for x in a; do b; done | cat": "control structures in pipelines are not supported",
+		"f() { a; } | b":     "function definitions in pipelines are not supported",
-		"echo | while a; do b; done":   "control structures in pipelines are not supported",
+		"f() { a; } > out":   "redirections of function definitions are not supported",
-		"if a; then b; fi > out":       "redirections of control structures are not supported (near `>')",
+		"if a; then b; fi c": "syntax error near unexpected token `c'",
-		"for x in a; do b; done &":     "only simple commands and pipelines can run in the background",
-		"a && b &":                     "only simple commands and pipelines can run in the background",
 	} {
 		if _, err := parse(input); err == nil || err.Error() != want {
 			t.Errorf("parse(%q) = %v, want %q", input, err, want)

options.go

@@ -0,0 +1,284 @@
+package main
+
+// Shell options (set -e, set -x, set -o pipefail) and the builtins eval and
+// exec.
+
+import (
+	"errors"
+	"fmt"
+	"io"
+	"os"
+	"os/exec"
+	"slices"
+	"sort"
+	"strings"
+	"syscall"
+)
+
+var (
+	// errexit (set -e): exit when a command fails
+	errexit bool
+	// xtrace (set -x): print commands before they run
+	xtrace bool
+	// pipefail (set -o pipefail): the status of a pipeline is the one of
+	// the last command that failed
+	pipefail bool
+
+	// errexitOff is > 0 while commands run whose failure does not end the
+	// shell with set -e: conditions of if, while and until, commands
+	// negated with ! and all but the last command of && and || lists.
+	errexitOff int
+)
+
+// shellOptions are the long names of the options for set -o.
+var shellOptions = []struct {
+	name   string
+	letter byte
+	value  *bool
+}{
+	{"errexit", 'e', &errexit},
+	{"nounset", 'u', nil}, // always on in gosh
+	{"pipefail", 0, &pipefail},
+	{"xtrace", 'x', &xtrace},
+}
+
+// setOption sets an option by letter or long name.
+func setOption(letter byte, name string, on bool) error {
+	for _, o := range shellOptions {
+		if letter != 0 && o.letter == letter || name != "" && o.name == name {
+			if o.value == nil {
+				if !on {
+					return errors.New("set: +u: unset variables are always an error in gosh")
+				}
+				return nil
+			}
+			*o.value = on
+			return nil
+		}
+	}
+	if name != "" {
+		return fmt.Errorf("set: %s: invalid option name", sanitize(name))
+	}
+	return fmt.Errorf("set: -%c: invalid option", letter)
+}
+
+// optionFlags returns the command line flags of gosh that pass the options
+// on to a subshell.
+func optionFlags() []string {
+	var flags []string
+	if errexit {
+		flags = append(flags, "-e")
+	}
+	if xtrace {
+		flags = append(flags, "-x")
+	}
+	if pipefail {
+		flags = append(flags, "-o", "pipefail")
+	}
+	return flags
+}
+
+// builtinSet implements set: set [-+ex] [-+o name] [--] [args], set -o and
+// set +o (show the options), set without arguments (show the variables) and
+// gosh's set VAR=value.
+func builtinSet(args []string, stdout io.Writer) error {
+	args = args[1:]
+	if len(args) == 0 {
+		env := os.Environ()
+		sort.Strings(env)
+		for _, kv := range env {
+			name, value, _ := strings.Cut(kv, "=")
+			if isVarName(name) {
+				fmt.Fprintf(stdout, "%s=%s\n", name, shellQuote(value))
+			}
+		}
+		return nil
+	}
+	if len(args) == 1 && isAssignment(args[0]) {
+		// set VAR=value
+		name, value, _ := strings.Cut(args[0], "=")
+		os.Setenv(name, value)
+		return nil
+	}
+
+	for len(args) > 0 {
+		arg := args[0]
+		if arg == "--" {
+			positional = slices.Clone(args[1:])
+			return nil
+		}
+		if len(arg) < 2 || arg[0] != '-' && arg[0] != '+' {
+			break
+		}
+		on := arg[0] == '-'
+		args = args[1:]
+		if arg[1:] == "o" {
+			if len(args) == 0 {
+				printOptions(stdout, on)
+				return nil
+			}
+			if err := setOption(0, args[0], on); err != nil {
+				return err
+			}
+			args = args[1:]
+			continue
+		}
+		for k := 1; k < len(arg); k++ {
+			if arg[k] == 'o' {
+				// set -euo pipefail: the name is the next argument
+				if len(args) == 0 {
+					return fmt.Errorf("set: %co: option requires an argument", arg[0])
+				}
+				if err := setOption(0, args[0], on); err != nil {
+					return err
+				}
+				args = args[1:]
+				continue
+			}
+			if err := setOption(arg[k], "", on); err != nil {
+				return err
+			}
+		}
+	}
+	if len(args) > 0 {
+		positional = slices.Clone(args)
+	}
+	return nil
+}
+
+// onlyShows reports whether a builtin that changes the shell is called in a
+// way that only shows something (trap -p, set -o), so that it can be used in
+// a pipeline.
+func onlyShows(args []string) bool {
+	switch args[0] {
+	case "trap":
+		return len(args) == 1 || args[1] == "-p" || args[1] == "-l"
+	case "set":
+		return len(args) == 1 || len(args) == 2 && (args[1] == "-o" || args[1] == "+o")
+	}
+	return false
+}
+
+// printOptions shows the options like set -o (human readable) or set +o
+// (as commands).
+func printOptions(w io.Writer, human bool) {
+	for _, o := range shellOptions {
+		on := o.value == nil || *o.value
+		switch {
+		case human && on:
+			fmt.Fprintf(w, "%-15s on\n", o.name)
+		case human:
+			fmt.Fprintf(w, "%-15s off\n", o.name)
+		case on:
+			fmt.Fprintf(w, "set -o %s\n", o.name)
+		default:
+			fmt.Fprintf(w, "set +o %s\n", o.name)
+		}
+	}
+}
+
+// shellQuote quotes s for the shell if it contains special characters.
+func shellQuote(s string) string {
+	if s != "" && strings.Trim(s, "abcdefghijklmnopqrstuvwxyzABCDEFGHIJKLMNOPQRSTUVWXYZ0123456789_-+=.,:/@%") == "" {
+		return s
+	}
+	return "'" + strings.ReplaceAll(s, "'", `'\''`) + "'"
+}
+
+// traceCommand prints a simple command for set -x.
+func traceCommand(st stage) {
+	var words []string
+	for _, a := range st.assigns {
+		name, value, _ := strings.Cut(a, "=")
+		words = append(words, name+"="+shellQuote(value))
+	}
+	for _, arg := range st.args {
+		words = append(words, shellQuote(arg))
+	}
+	if len(words) > 0 {
+		fmt.Fprintln(stdio(2), "+", sanitize(strings.Join(words, " ")))
+	}
+}
+
+// checkErrexit ends the shell with set -e if the pipeline pl, the last one
+// of its and-or list, failed. Compound commands are not checked themselves
+// (the failing command in them is), but subshells and pipelines are.
+func checkErrexit(pl *pipelineNode, err error) {
+	status := exitStatus(err)
+	if !errexit || errexitOff > 0 || pl.negate || status == 0 {
+		return
+	}
+	var (
+		lc  loopControl
+		ret returnSignal
+	)
+	if errors.As(err, &lc) || errors.As(err, &ret) {
+		return
+	}
+	cmd := pl.cmd
+	if r, ok := cmd.(*redirNode); ok {
+		cmd = r.cmd
+	}
+	switch cmd.(type) {
+	case *simpleNode, *pipeNode, *subshellNode:
+		printError(err)
+		exitShell(status)
+	}
+}
+
+// builtinEval implements eval: the arguments, joined with blanks, run as a
+// command in the shell.
+func builtinEval(args []string) error {
+	text := strings.Join(args[1:], " ")
+	if strings.TrimSpace(text) == "" {
+		return nil
+	}
+	tree, err := parse(text)
+	if errors.Is(err, errIncomplete) {
+		return errors.New("eval: syntax error: unexpected end of input")
+	}
+	if err != nil {
+		return err
+	}
+	return tree.exec()
+}
+
+// builtinExec implements exec: without a command its redirections apply to
+// the shell itself (exec > log), otherwise the command replaces the shell.
+func builtinExec(args []string, fds [3]*os.File, assigns []string) error {
+	for fd, f := range fds {
+		if f != stdio(fd) {
+			if err := dupTo(f, fd); err != nil {
+				return fmt.Errorf("exec: %w", err)
+			}
+		}
+	}
+	if len(args) == 1 {
+		for _, a := range assigns {
+			name, value, _ := strings.Cut(a, "=")
+			os.Setenv(name, value)
+		}
+		return nil
+	}
+
+	path, err := exec.LookPath(args[1])
+	if err != nil {
+		err = fmt.Errorf("%s: %w", sanitize(args[1]), errCommandNotFound)
+		return execFailed(err)
+	}
+	releaseTerminal()
+	err = syscall.Exec(path, args[1:], append(os.Environ(), assigns...))
+	// Exec only returns if it failed
+	return execFailed(fmt.Errorf("exec: %s: %w", sanitize(args[1]), err))
+}
+
+// execFailed reports a failed exec. A non-interactive shell exits then, like
+// sh.
+func execFailed(err error) error {
+	if interactiveShell {
+		return err
+	}
+	printError(err)
+	exitShell(exitStatus(err))
+	return err
+}

packaging/man/gosh.1

@@ -9,13 +9,16 @@ gosh \- a simple shell written in Go
 .RB [ \-i ]
 .RB [ \-\-norc ]
 .RB [ \-\-noprofile ]
-.RI [ script ]
+.RI [ script
+.RI [ args " ...]]"
 .br
 .B gosh
 .RB [ \-l ]
 .RB [ \-\-noprofile ]
 .B \-c
 .I command
+.RI [ name
+.RI [ args " ...]]"
 .br
 .B gosh
 .B \-version
@@ -23,9 +26,10 @@ gosh \- a simple shell written in Go
 .B gosh
 is a small command interpreter with a syntax close to
 .BR sh (1).
-It supports command history, tab completion, variables, command
+It supports command history, tab completion, variables, positional
-substitution, command lists, control structures, pipes, redirections,
+parameters, command substitution, command lists, control structures,
-wildcards, brace expansion, aliases and job control.
+functions, pipes, redirections, wildcards, brace expansion, aliases and job
+control.
 .PP
 Without arguments and with a terminal on standard input,
 .B gosh
@@ -34,20 +38,44 @@ starts an interactive shell. With a
 argument it runs the commands of that file, with
 .B \-c
 the given command string, and otherwise it reads commands from standard
-input.
+input. The
+.I args
+after the script, or after the
+.I name
+of
+.BR \-c ,
+become the positional parameters
+.BR $1 ,
+.BR $2 ", ..."
 .PP
 .B gosh
 is a proof of concept and not meant for production use.
 .SH OPTIONS
 .TP
-.B \-c \fIcommand\fP
+.B \-c \fIcommand\fP [\fIname\fP [\fIargs\fP ...]]
 Run
 .I command
 and exit.
+.I name
+becomes
+.BR $0 ,
+the
+.I args
+become
+.BR $1 ,
+.BR $2 ", ..."
 .TP
 .B \-i
 Force interactive mode, even if standard input is not a terminal.
 .TP
+.BR \-e ", " \-x ", " "\-o \fIoption\fP"
+Set options like
+.BR set ,
+e.g.
+.B gosh \-e script
+or
+.BR "gosh \-o pipefail \-c" " ...".
+.TP
 .BR \-l ", " \-\-login
 Act as a login shell and read the profile files (see
 .BR "STARTUP FILES" ).
@@ -168,6 +196,119 @@ for an empty default.
 .TP
 .B $?
 The exit status of the last command.
+.SS Parameter expansion
+.TP
+.B ${#VAR}
+The length of the value in characters.
+.TP
+.BR ${VAR#\fIpattern\fP} ", " ${VAR##\fIpattern\fP}
+The value without the shortest (longest) prefix matching
+.IR pattern .
+.TP
+.BR ${VAR%\fIpattern\fP} ", " ${VAR%%\fIpattern\fP}
+The value without the shortest (longest) suffix matching
+.IR pattern .
+.TP
+.BR ${VAR/\fIpattern\fP/\fIstring\fP} ", " ${VAR//\fIpattern\fP/\fIstring\fP}
+The value with the first (every) longest match of
+.I pattern
+replaced by
+.IR string ;
+.B /#
+and
+.B /%
+only match at the start and at the end.
+.TP
+.BR ${VAR:\fIoffset\fP} ", " ${VAR:\fIoffset\fP:\fIlength\fP}
+A substring; offset and length are arithmetic expressions, negative values
+count from the end.
+.TP
+.BR ${VAR:\-\fIword\fP} ", " ${VAR:=\fIword\fP} ", " ${VAR:+\fIword\fP} ", " ${VAR:?\fIword\fP}
+.I word
+if
+.B VAR
+is unset or empty (and assign it with
+.BR := ),
+.I word
+if it is set and not empty, or an error with the message
+.IR word .
+Without the colon, only an unset variable counts.
+.PP
+The word is expanded but not split. In patterns,
+.BR * ,
+.B ?
+and
+.B [...]
+are wildcards that also match
+.BR / ;
+quoted characters and values of variables match literally.
+.SS Arithmetic expansion
+.B $((\fIexpression\fP))
+is replaced by the value of
+.IR expression ,
+computed with 64-bit integers. The operators of C are supported,
+in order of precedence:
+.BR "++ \-\-" ,
+unary
+.BR "+ \- ! ~" ,
+.B **
+(power),
+.BR "* / %" ,
+.BR "+ \-" ,
+.BR "<< >>" ,
+.BR "< <= > >=" ,
+.BR "== !=" ,
+.BR & ,
+.BR ^ ,
+.BR | ,
+.BR && ,
+.BR || ,
+.BR "? :" ,
+the assignments
+.B = += \-= *= /= %= <<= >>= &= ^= |=
+and
+.BR , .
+Variables can be used with or without
+.BR $ ;
+an unset variable is an error, an empty one is 0. Numbers can be
+hexadecimal
+.RB ( 0x1F )
+or octal
+.RB ( 017 ).
+.SS Positional parameters
+.TP
+.B $0
+The name of the script, or the
+.I name
+given after
+.BR "gosh \-c" .
+.TP
+.BR $1 " ... " $9 ", " ${10}
+The arguments of the script, of
+.BR "gosh \-c" ,
+of a function call or of
+.BR source ,
+or the words set with
+.BR "set \-\-" .
+An unset parameter is an error like an unset variable; use
+.B ${1:\-}
+for an optional argument.
+.TP
+.B $#
+The number of positional parameters.
+.TP
+.B \(dq$@\(dq
+All positional parameters, each as a separate word. Without parameters it
+expands to no word at all.
+.TP
+.B \(dq$*\(dq
+All positional parameters as one word, separated by blanks.
+.TP
+.B $$
+The process ID of the shell.
+.TP
+.B $!
+The process ID of the last background job.
 .SS Command substitution
 .B $(\fIcommand\fP)
 is replaced by the output of
@@ -175,7 +316,7 @@ is replaced by the output of
 which runs in a subshell. Trailing newlines are removed. Unquoted, the
 output is split into words at blanks and newlines; inside double quotes it
 stays one word. Wildcards and operators in the output are not interpreted.
-Backticks and arithmetic expansion are not supported.
+Backticks are not supported.
 .SS Tilde and brace expansion
 .B ~
 and
@@ -269,6 +410,24 @@ Redirect standard output to where standard error goes.
 .BR &> " \fIfile\fP, " &>> " \fIfile\fP"
 Write (or append) standard output and standard error to
 .IR file .
+.TP
+.BI << word
+Here-document: the lines after the command, up to a line that is exactly
+.IR word ,
+are standard input. If no part of
+.I word
+is quoted, variables, command substitutions and backslashes before
+.BR $ ,
+.BR \(ga ,
+.B \e
+and newline are expanded in the lines.
+.BI <<\- word
+also removes leading tabs from the lines and the delimiter line.
+.TP
+.BI <<< " word"
+Here-string:
+.I word
+and a newline are standard input.
 .PP
 Redirections are evaluated from left to right. Only file descriptors 0, 1
 and 2 are supported.
@@ -278,6 +437,9 @@ and 2 are supported.
 \fBfor\fP \fIname\fP \fBin\fP \fIwords\fP; \fBdo\fP \fIlist\fP; \fBdone\fP
 \fBwhile\fP \fIlist\fP; \fBdo\fP \fIlist\fP; \fBdone\fP
 \fBuntil\fP \fIlist\fP; \fBdo\fP \fIlist\fP; \fBdone\fP
+\fBcase\fP \fIword\fP \fBin\fP [\fB(\fP]\fIpattern\fP[\fB|\fP\fIpattern\fP]...\fB)\fP \fIlist\fP \fB;;\fP ... \fBesac\fP
+\fB{\fP \fIlist\fP; \fB}\fP
+\fB(\fP \fIlist\fP \fB)\fP
 \fB!\fP \fIcommand\fP
 .fi
 .PP
@@ -285,10 +447,64 @@ Control structures may span several lines; an incomplete command shows
 the continuation prompt
 .BR "> " .
 .B !
-negates the exit status of a command. Control structures cannot be used
+negates the exit status of a command.
-in pipes, with redirections or in the background.
+.B for
+without
+.B in
+loops over the positional parameters.
+.PP
 .B case
-and functions are not supported.
+runs the list of the first clause with a pattern that matches
+.IR word .
+Patterns are wildcards as for file names, but
+.B *
+and
+.B ?
+also match a
+.BR / ;
+quoted characters match literally, and values of variables are not
+patterns. The
+.B ;;
+of the last clause may be omitted.
+.PP
+.B {
+.IR list ;
+.B }
+groups commands; they run in the current shell.
+.B (
+.I list
+.B )
+runs the commands in a subshell, a new
+.B gosh
+process, so that changes of the directory, variables and functions only
+apply there.
+.PP
+Redirections after a control structure
+.RB ( "done < file" ,
+.BR "fi > log 2>&1" )
+apply to all commands in it, which still run in the current shell. In a
+pipe and in the background
+.RB ( & ),
+a control structure runs in a subshell, like in
+.BR sh (1).
+The subshell knows the functions and positional parameters of the shell.
+.SS Functions
+.nf
+\fIname\fP\fB() {\fP \fIlist\fP; \fB}\fP
+\fBfunction\fP \fIname\fP \fB{\fP \fIlist\fP; \fB}\fP
+.fi
+.PP
+defines a function; the body can be any compound command. When the
+function is called, its arguments are the positional parameters, which get
+their old values back afterwards. Functions run in the current shell, so
+variables they set stay set; use
+.B local
+for variables that belong to the function. Redirections of a call apply to
+all commands of the function. In pipes, in the background and in
+.B $(...)
+a function runs in a subshell that knows all functions. Functions take
+precedence over builtins and programs of the same name. Calls can be nested
+up to a depth of 1000.
 .SS Aliases
 In interactive shells, the first word of a command is replaced by its
 alias. If the alias value ends with a blank, the next word is checked for
@@ -318,16 +534,52 @@ Exit the shell with status
 .BI set " VAR" = value
 Set a variable.
 .TP
+.BR set " [\fB\-+ex\fP] [\fB\-+o\fP \fIoption\fP] [\fB\-\-\fP] [\fIargs\fP ...]"
+Set
+.RB ( \- )
+or unset
+.RB ( + )
+options and set the positional parameters to
+.IR args .
+.B \-e
+.RB ( errexit )
+exits the shell when a command fails, except in conditions of
+.BR if ,
+.B while
+and
+.BR until ,
+negated commands and all but the last command of
+.B &&
+and
+.B ||
+lists.
+.B \-x
+.RB ( xtrace )
+prints every simple command after expansion.
+.B \-o pipefail
+makes the status of a pipeline the one of the last command that failed.
+.B \-u
+.RB ( nounset )
+is always on.
+.B set \-o
+and
+.B set +o
+show the options,
+.B set
+without arguments shows the variables.
+.TP
 .BI export " VAR" = value
 Export a variable.
 .TP
-.BI unset " VAR"
+.BR unset " [\fB\-v\fP] \fIVAR\fP ..., " "unset \-f" " \fIname\fP ..."
-Remove a variable.
+Remove variables, or functions.
 .TP
-.BI source " file\fR, \fP" ". " file
+.BR source " \fIfile\fP [\fIargs\fP ...], " . " \fIfile\fP [\fIargs\fP ...]"
 Run the commands of
 .I file
-in the current shell.
+in the current shell, with
+.I args
+as positional parameters if given.
 .TP
 .B jobs
 List background and stopped jobs.
@@ -342,9 +594,13 @@ Continue stopped job
 .I n
 in the background.
 .TP
-.BR wait " [\fB%\fP\fIn\fP]"
+.BR wait " [\fB%\fP\fIn\fP | \fIpid\fP]"
 Wait for job
-.I n
+.IR n ,
+the job with process
+.I pid
+(e.g.
+.BR $! ),
 or for all background jobs.
 .TP
 .BR alias " [\fIname\fP[\fB=\fP\fIvalue\fP] ...]"
@@ -361,6 +617,81 @@ Leave the innermost (or
 .IR n -th)
 loop, or continue with its next iteration.
 .TP
+.BR return " [\fIn\fP]"
+Leave a function or sourced file with status
+.I n
+(default:
+.BR $? ).
+.TP
+.BR local " \fIVAR\fP[\fB=\fP\fIvalue\fP] ..."
+In a function: the variable gets its previous value back when the function
+returns. Without a value it is unset.
+.TP
+.BR shift " [\fIn\fP]"
+Remove the first
+.I n
+(default 1) positional parameters.
+.TP
+.BR read " [\fB\-r\fP] [\fB\-p\fP \fIprompt\fP] [\fIVAR\fP ...]"
+Read a line from standard input and split it into fields at the
+characters of
+.B IFS
+(default blank, tab and newline). Each
+.I VAR
+gets one field, the last one the rest of the line; without
+.I VAR
+the whole line is stored in
+.BR REPLY .
+Without
+.BR \-r ,
+a backslash escapes the next character and continues the line at its end.
+.B \-p
+prints
+.I prompt
+if the input is a terminal. The exit status is 1 at the end of the input.
+.TP
+.BR eval " [\fIargs\fP ...]"
+Join the arguments with blanks and run the result as a command in the
+current shell.
+.TP
+.BR exec " [\fIcommand\fP [\fIargs\fP ...]]"
+Replace the shell with
+.IR command .
+Without a command, the redirections of
+.B exec
+apply to the shell itself
+.RB ( "exec > log 2>&1" ).
+.TP
+.BR trap " [\fB\-lp\fP] [[\fIaction\fP] \fIsignal\fP ...]"
+Run
+.I action
+in the shell when
+.I signal
+arrives (after the running command) or, for
+.B EXIT
+.RB ( 0 ),
+when the shell exits; a script with an EXIT trap also runs it when it is
+ended by SIGINT, SIGTERM or SIGHUP. Signals:
+.BR HUP ,
+.BR INT ,
+.BR QUIT ,
+.BR TERM ,
+.BR USR1 ,
+.BR USR2 ,
+.BR ALRM ,
+.BR WINCH .
+An empty
+.I action
+ignores the signal (also in started programs),
+.B \-
+restores the default.
+.B trap
+and
+.B trap \-p
+show the traps,
+.B trap \-l
+the signals.
+.TP
 .B help
 Show a summary of builtins and features.
 .SH JOB CONTROL
@@ -408,6 +739,13 @@ If the last command failed, its exit status is shown as
 .BI [ N ]
 before the
 .BR $ .
+.PP
+Before each prompt, gosh reports the working directory to the terminal with
+the OSC 7 escape sequence
+.RB ( "ESC ] 7 ; file://" \fIhost\fP/\fIpath\fP " BEL" ),
+so terminals like GNOME Terminal open new tabs and windows in the same
+directory. Nothing is sent if the output is not a terminal or
+.BR TERM=dumb .
 .SH ENVIRONMENT
 .TP
 .B GOSH_HISTFILE
@@ -448,6 +786,10 @@ without argument.
 .TP
 .B PATH
 Directories searched for commands.
+.TP
+.B IFS
+Field separators for
+.BR read .
 .SH FILES
 .TP
 .I /etc/gosh/profile
@@ -493,6 +835,14 @@ cp config.yaml{,.bak}
 make > build.log 2>&1 || echo "failed: $?"
 LANG=C sort file
 alias ll=\(aqls \-l\(aq
+greet() { echo "Hello ${1:\-World}"; }
+set \-euo pipefail; trap \(aqrm \-rf "$tmp"\(aq EXIT
+echo ${file##*/} $((n + 1))
+git ls\-files | while read \-r f; do wc \-l "$f"; done
+while read \-r user rest; do echo "$user"; done < /etc/passwd
+(cd build && make) > build.log 2>&1
+case "$1" in start|stop) echo "$1ing" ;; *) echo "usage: $0 start|stop" ;; esac
+read \-r \-p \(aqName? \(aq name
 chsh \-s /usr/bin/gosh
 .fi
 .SH SEE ALSO

parser.go

@@ -1,8 +1,8 @@
 package main
 
 // Parser and executor for command lines and scripts: lists (; & && || and
-// newlines), pipelines, ! and the control structures if, for, while and
+// newlines), pipelines, ! and the compound commands if, for, while, until,
-// until. Simple commands (with their pipes and redirections) are kept as
+// case, { ...; } and ( ... ), and function definitions. Simple commands (with their pipes and redirections) are kept as
 // text; they are expanded and run by execCommand only when they are
 // executed, so that e.g. the variable of a for loop is expanded anew in
 // every iteration.
@@ -11,6 +11,7 @@ import (
 	"errors"
 	"fmt"
 	"os"
+	"slices"
 	"strconv"
 	"strings"
 	"syscall"
@@ -48,7 +49,13 @@ var aliasExpansion = true
 
 // reserved words that end a list; they are only recognized as the first word
 // of a command.
-var terminators = map[string]bool{"then": true, "elif": true, "else": true, "fi": true, "do": true, "done": true}
+var terminators = map[string]bool{
+	"then": true, "elif": true, "else": true, "fi": true, "do": true, "done": true,
+	"esac": true, "}": true,
+}
+
+// compoundStarts are the reserved words that start a compound command.
+var compoundStarts = map[string]bool{"if": true, "for": true, "while": true, "until": true, "case": true, "{": true}
 
 // ---------------------------------------------------------------------------
 // Lexer
@@ -57,7 +64,7 @@ type tokenKind int
 
 const (
 	tWord tokenKind = iota
-	tOp             // ; & && || | or newline
+	tOp             // ; ;; & && || | ( ) or newline
 )
 
 type rawToken struct {
@@ -126,6 +133,9 @@ func lex(src string) ([]rawToken, error) {
 		switch {
 		case ch == ' ' || ch == '\t':
 			i++
+		case ch == ';' && next == ';':
+			op(";;", i)
+			i += 2
 		case ch == '\n' || ch == ';':
 			op(string(ch), i)
 			i++
@@ -137,7 +147,7 @@ func lex(src string) ([]rawToken, error) {
 		case ch == '|' && next == '|', ch == '&' && next == '&':
 			op(src[i:i+2], i)
 			i += 2
-		case ch == '|', ch == '&' && next != '>':
+		case ch == '|', ch == '&' && next != '>', ch == '(', ch == ')':
 			op(string(ch), i)
 			i++
 		default:
@@ -167,6 +177,12 @@ func lexWord(src string, i int) (int, error) {
 				return 0, errIncomplete
 			}
 			j++
+			if isSubstStart(src, j) {
+				// \$(...) is literal text, but its ( and ) belong to the word
+				if end := substEnd(src, j); end >= 0 {
+					j = end
+				}
+			}
 		case isSubstStart(src, j):
 			end := substEnd(src, j)
 			if end < 0 {
@@ -174,8 +190,8 @@ func lexWord(src string, i int) (int, error) {
 			}
 			j = end
 		case ch == '$' && j+1 < len(src) && src[j+1] == '{':
-			if k := strings.IndexByte(src[j:], '}'); k >= 0 {
+			if end := paramEnd(src, j); end >= 0 {
-				j += k
+				j = end
 			}
 		case quote == '"':
 			if ch == '"' {
@@ -183,7 +199,7 @@ func lexWord(src string, i int) (int, error) {
 			}
 		case ch == '"' || ch == '\'':
 			quote = ch
-		case ch == ' ' || ch == '\t' || ch == '\n' || ch == ';' || ch == '|':
+		case ch == ' ' || ch == '\t' || ch == '\n' || ch == ';' || ch == '|' || ch == '(' || ch == ')':
 			return j, nil
 		case ch == '&':
 			// &>, >& and <& are redirections, not the & operator
@@ -221,6 +237,7 @@ type listEntry struct {
 type andOrNode struct {
 	first *pipelineNode
 	rest  []andOrPart
+	text  string // the source, to run it in a subshell in the background
 }
 
 type andOrPart struct {
@@ -228,8 +245,8 @@ type andOrPart struct {
 	pipeline *pipelineNode
 }
 
-// pipelineNode is a simple command (whose text may contain a pipeline) or a
+// pipelineNode is a pipeline (a simpleNode or pipeNode) or a single
-// control structure, optionally negated with !.
+// compound command, optionally negated with !.
 type pipelineNode struct {
 	negate bool
 	cmd    node
@@ -240,6 +257,33 @@ type simpleNode struct {
 	text string
 }
 
+// pipeNode is a pipeline that contains compound commands. Like all commands
+// of a pipeline in sh, they run in subshells (new gosh processes), since
+// the commands of a pipeline run concurrently.
+type pipeNode struct {
+	elems []pipeElem
+	text  string
+}
+
+type pipeElem struct {
+	text     string // the source of the command, with its redirections
+	compound bool
+	subshell string // for ( list ): the list, which runs in the subshell directly
+}
+
+// redirNode is a compound command with redirections; they apply to all
+// commands in it.
+type redirNode struct {
+	cmd    node
+	redirs string // the source text of the redirections
+}
+
+// subshellNode is ( list ): the list runs in a new gosh process, so that it
+// cannot change the shell.
+type subshellNode struct {
+	text string // the source of the list
+}
+
 type ifNode struct {
 	conds    []*listNode
 	bodies   []*listNode
@@ -259,6 +303,27 @@ type whileNode struct {
 	body  *listNode
 }
 
+// caseNode is case word in pattern|pattern) list ;; ... esac.
+type caseNode struct {
+	word    string // expanded when the case command runs
+	clauses []caseClause
+}
+
+type caseClause struct {
+	patterns []string // expanded when they are tried
+	body     *listNode
+}
+
+// groupNode is { list; }.
+type groupNode struct {
+	body *listNode
+}
+
+// funcDefNode is a function definition name() compound-command.
+type funcDefNode struct {
+	def *funcDef
+}
+
 // singleSimple returns the simple command if the list is just that.
 func (l *listNode) singleSimple() *simpleNode {
 	if len(l.items) != 1 || l.items[0].background {
@@ -284,6 +349,10 @@ type parser struct {
 // parse parses a command line or script. It returns errIncomplete if the
 // input ends inside a construct.
 func parse(src string) (*listNode, error) {
+	src, err := extractHeredocs(src)
+	if err != nil {
+		return nil, err
+	}
 	src, continued := joinContinuationLines(src)
 	if continued {
 		return nil, errIncomplete
@@ -356,7 +425,7 @@ func (p *parser) parseList(terms map[string]bool) (*listNode, error) {
 	for {
 		p.skipNewlines()
 		t := p.peek()
-		if t == nil || t.kind == tWord && terms[t.text] {
+		if t == nil || terms[t.text] {
 			return list, nil
 		}
 		ao, err := p.parseAndOr()
@@ -371,16 +440,12 @@ func (p *parser) parseList(terms map[string]bool) (*listNode, error) {
 		case t.kind == tOp && (t.text == ";" || t.text == "&" || t.text == "\n"):
 			p.pos++
 			entry.background = t.text == "&"
-		case t.kind == tWord && terms[t.text]:
+		case terms[t.text]:
-			// e.g. "fi" right after the end of a nested control structure
+			// e.g. "fi" right after the end of a nested control structure,
+			// or ;; after a command in a case clause
 		default:
 			return nil, p.unexpected(t)
 		}
-		if entry.background {
-			if _, ok := ao.first.cmd.(*simpleNode); !ok || len(ao.rest) > 0 || ao.first.negate {
-				return nil, errors.New("only simple commands and pipelines can run in the background")
-			}
-		}
 		list.items = append(list.items, entry)
 	}
 }
@@ -397,6 +462,7 @@ func (p *parser) nonEmpty(list *listNode) error {
 }
 
 func (p *parser) parseAndOr() (*andOrNode, error) {
+	start := p.peek().start
 	first, err := p.parsePipeline()
 	if err != nil {
 		return nil, err
@@ -405,6 +471,7 @@ func (p *parser) parseAndOr() (*andOrNode, error) {
 	for {
 		t := p.peek()
 		if t == nil || t.kind != tOp || (t.text != "&&" && t.text != "||") {
+			ao.text = p.src[start:p.toks[p.pos-1].end]
 			return ao, nil
 		}
 		p.pos++
@@ -420,79 +487,188 @@ func (p *parser) parseAndOr() (*andOrNode, error) {
 	}
 }
 
+// parsePipeline parses [!] command [| command]... A pipeline of simple
+// commands stays one simpleNode (its text is split into the commands when it
+// runs); a pipeline with compound commands becomes a pipeNode.
 func (p *parser) parsePipeline() (*pipelineNode, error) {
 	pl := &pipelineNode{}
 	if p.peekWord("!") {
 		pl.negate = true
 		p.pos++
 	}
-	t := p.peek()
+	var (
-	if t == nil {
+		elems []pipeElem
-		return nil, errIncomplete
+		cmds  []node
-	}
+		start = -1
-	if t.kind == tOp || terminators[t.text] {
+	)
-		return nil, p.unexpected(t)
+	for {
-	}
+		t := p.peek()
-
+		if t == nil {
-	var err error
+			return nil, errIncomplete
-	compound := true
-	switch t.text {
-	case "if":
-		pl.cmd, err = p.parseIf()
-	case "for":
-		pl.cmd, err = p.parseFor()
-	case "while", "until":
-		pl.cmd, err = p.parseWhile()
-	default:
-		compound = false
-		pl.cmd, err = p.parseSimple()
-	}
-	if err != nil {
-		return nil, err
-	}
-
-	if compound {
-		if t := p.peek(); t != nil {
-			switch {
-			case t.kind == tOp && t.text == "|":
-				return nil, errors.New("control structures in pipelines are not supported")
-			case t.kind == tWord && !terminators[t.text]:
-				return nil, fmt.Errorf("redirections of control structures are not supported (near `%s')", t.text)
-			}
 		}
+		if t.kind == tOp && t.text != "(" || t.kind == tWord && terminators[t.text] {
+			return nil, p.unexpected(t)
+		}
+		if start < 0 {
+			start = t.start
+		}
+		cmd, compound, err := p.parseCommand()
+		if err != nil {
+			return nil, err
+		}
+		elem := pipeElem{text: p.src[t.start:p.toks[p.pos-1].end], compound: compound}
+		if sub, ok := cmd.(*subshellNode); ok {
+			elem.subshell = sub.text
+		}
+		elems = append(elems, elem)
+		cmds = append(cmds, cmd)
+
+		if t := p.peek(); t == nil || t.kind != tOp || t.text != "|" {
+			break
+		}
+		p.pos++
+		p.skipNewlines()
+		if p.peek() == nil {
+			return nil, errIncomplete
+		}
+	}
+
+	text := p.src[start:p.toks[p.pos-1].end]
+	compound := false
+	for i, e := range elems {
+		if _, ok := cmds[i].(*funcDefNode); ok && len(elems) > 1 {
+			return nil, errors.New("function definitions in pipelines are not supported")
+		}
+		compound = compound || e.compound
+	}
+	switch {
+	case len(elems) == 1:
+		pl.cmd = cmds[0]
+	case !compound:
+		pl.cmd = &simpleNode{text: text}
+	default:
+		pl.cmd = &pipeNode{elems: elems, text: text}
 	}
 	return pl, nil
 }
 
-// parseSimple parses a pipeline of simple commands and returns its text.
+// parseCommand parses a simple command, a compound command with its
+// redirections or a function definition, and reports whether it is not a
+// simple command.
+func (p *parser) parseCommand() (node, bool, error) {
+	t := p.peek()
+	start := t.start
+	if name, ok := p.funcDefName(); ok {
+		def, err := p.parseFuncDef(name, start)
+		if err != nil {
+			return nil, true, err
+		}
+		if t := p.peek(); t != nil && t.kind == tWord && !terminators[t.text] {
+			return nil, true, errors.New("redirections of function definitions are not supported")
+		}
+		return def, true, nil
+	}
+	if !isCompoundStart(t) {
+		cmd, err := p.parseSimple()
+		return cmd, false, err
+	}
+	cmd, err := p.parseCompound()
+	if err != nil {
+		return nil, true, err
+	}
+	redirs, err := p.parseRedirections()
+	if err != nil {
+		return nil, true, err
+	}
+	if redirs != "" {
+		cmd = &redirNode{cmd: cmd, redirs: redirs}
+	}
+	return cmd, true, nil
+}
+
+// isCompoundStart reports whether a compound command starts at t.
+func isCompoundStart(t *rawToken) bool {
+	return t.kind == tWord && compoundStarts[t.text] || t.kind == tOp && t.text == "("
+}
+
+// parseRedirections parses the redirections after a compound command and
+// returns their source text (expanded when the command runs).
+func (p *parser) parseRedirections() (string, error) {
+	start, end := -1, -1
+	for t := p.peek(); t != nil && t.kind == tWord && !terminators[t.text]; t = p.peek() {
+		needsTarget, ok := redirectionWord(t.text)
+		if !ok {
+			return "", syntaxError(t.text)
+		}
+		if start < 0 {
+			start = t.start
+		}
+		end = t.end
+		p.pos++
+		if needsTarget {
+			t = p.peek()
+			if t == nil || t.kind != tWord {
+				if t == nil {
+					return "", syntaxError("newline")
+				}
+				return "", p.unexpected(t)
+			}
+			end = t.end
+			p.pos++
+		}
+	}
+	if start < 0 {
+		return "", nil
+	}
+	return p.src[start:end], nil
+}
+
+// redirectionWord reports whether word starts with a redirection operator
+// (optionally after a file descriptor), and whether the target is the next
+// word (2> file instead of 2>file).
+func redirectionWord(word string) (needsTarget, ok bool) {
+	w := strings.TrimLeft(word, "0123456789")
+	for _, op := range []string{"&>>", "&>", "<<<", ">>", ">&", "<&", ">", "<"} {
+		if strings.HasPrefix(w, op) {
+			if op[0] == '&' && len(w) != len(word) {
+				return false, false
+			}
+			return w == op, true
+		}
+	}
+	return false, false
+}
+
+// parseSimple parses a simple command (without pipes) and returns its text.
 func (p *parser) parseSimple() (*simpleNode, error) {
 	start := p.toks[p.pos].start
 	end := start
-	for t := p.peek(); t != nil; t = p.peek() {
+	for t := p.peek(); t != nil && t.kind == tWord; t = p.peek() {
-		if t.kind == tWord {
-			end = t.end
-			p.pos++
-			continue
-		}
-		if t.text != "|" {
-			break
-		}
-		p.pos++
 		end = t.end
-		p.skipNewlines()
+		p.pos++
-		next := p.peek()
-		switch {
-		case next == nil:
-			return nil, errIncomplete
-		case next.kind == tOp || terminators[next.text]:
-			return nil, p.unexpected(next)
-		case next.text == "if" || next.text == "for" || next.text == "while" || next.text == "until":
-			return nil, errors.New("control structures in pipelines are not supported")
-		}
 	}
 	return &simpleNode{text: p.src[start:end]}, nil
 }
 
+// parseCompound parses the compound command that starts at the current
+// token.
+func (p *parser) parseCompound() (node, error) {
+	switch p.peek().text {
+	case "if":
+		return p.parseIf()
+	case "for":
+		return p.parseFor()
+	case "while", "until":
+		return p.parseWhile()
+	case "case":
+		return p.parseCase()
+	case "(":
+		return p.parseSubshell()
+	default: // {
+		return p.parseGroup()
+	}
+}
+
 func (p *parser) parseIf() (*ifNode, error) {
 	p.pos++ // if
 	n := &ifNode{}
@@ -604,6 +780,167 @@ func (p *parser) parseWhile() (*whileNode, error) {
 	return n, nil
 }
 
+// parseGroup parses { list; }.
+func (p *parser) parseGroup() (*groupNode, error) {
+	p.pos++ // {
+	body, err := p.parseList(map[string]bool{"}": true})
+	if err == nil {
+		err = p.nonEmpty(body)
+	}
+	if err == nil {
+		err = p.expect("}")
+	}
+	if err != nil {
+		return nil, err
+	}
+	return &groupNode{body: body}, nil
+}
+
+// parseSubshell parses ( list ).
+func (p *parser) parseSubshell() (*subshellNode, error) {
+	p.pos++ // (
+	start := p.toks[p.pos-1].end
+	body, err := p.parseList(map[string]bool{")": true})
+	if err == nil {
+		err = p.nonEmpty(body)
+	}
+	if err != nil {
+		return nil, err
+	}
+	t := p.peek()
+	if t == nil {
+		return nil, errIncomplete
+	}
+	if t.kind != tOp || t.text != ")" {
+		return nil, p.unexpected(t)
+	}
+	p.pos++
+	return &subshellNode{text: p.src[start:t.start]}, nil
+}
+
+// parseCase parses case word in [(]pattern[|pattern]...) list ;; ... esac.
+// The last clause may omit the ;;.
+func (p *parser) parseCase() (*caseNode, error) {
+	p.pos++ // case
+	t := p.peek()
+	if t == nil {
+		return nil, errIncomplete
+	}
+	if t.kind != tWord {
+		return nil, p.unexpected(t)
+	}
+	n := &caseNode{word: t.text}
+	p.pos++
+	p.skipNewlines()
+	if err := p.expect("in"); err != nil {
+		return nil, err
+	}
+	for {
+		p.skipNewlines()
+		t := p.peek()
+		if t == nil {
+			return nil, errIncomplete
+		}
+		if t.kind == tWord && t.text == "esac" {
+			p.pos++
+			return n, nil
+		}
+		patterns, err := p.parsePatterns()
+		if err != nil {
+			return nil, err
+		}
+		body, err := p.parseList(map[string]bool{";;": true, "esac": true})
+		if err != nil {
+			return nil, err
+		}
+		n.clauses = append(n.clauses, caseClause{patterns: patterns, body: body})
+		if t := p.peek(); t == nil {
+			return nil, errIncomplete
+		} else if t.text == ";;" {
+			p.pos++
+		}
+	}
+}
+
+// parsePatterns parses the patterns of a case clause up to and including the
+// ).
+func (p *parser) parsePatterns() ([]string, error) {
+	if t := p.peek(); t.kind == tOp && t.text == "(" {
+		p.pos++ // the optional ( before the first pattern
+	}
+	var patterns []string
+	for {
+		t := p.peek()
+		if t == nil {
+			return nil, errIncomplete
+		}
+		if t.kind != tWord {
+			return nil, p.unexpected(t)
+		}
+		patterns = append(patterns, t.text)
+		p.pos++
+		t = p.peek()
+		switch {
+		case t == nil:
+			return nil, errIncomplete
+		case t.kind == tOp && t.text == "|":
+			p.pos++
+		case t.kind == tOp && t.text == ")":
+			p.pos++
+			return patterns, nil
+		default:
+			return nil, p.unexpected(t)
+		}
+	}
+}
+
+// funcDefName reports whether a function definition starts at the current
+// token: name(), or function name [()]. It consumes the tokens up to the
+// body.
+func (p *parser) funcDefName() (string, bool) {
+	start := p.pos
+	if t := p.peek(); t.kind != tWord {
+		return "", false
+	} else if t.text == "function" {
+		p.pos++
+		if t := p.peek(); t == nil || t.kind != tWord || !isFuncName(t.text) {
+			p.pos = start
+			return "", false
+		}
+	}
+	name := p.peek().text
+	isOp := func(i int, text string) bool {
+		return i < len(p.toks) && p.toks[i].kind == tOp && p.toks[i].text == text
+	}
+	switch {
+	case isOp(p.pos+1, "(") && isOp(p.pos+2, ")") && isFuncName(name):
+		p.pos += 3
+	case p.pos > start:
+		p.pos++ // function name
+	default:
+		return "", false
+	}
+	return name, true
+}
+
+// parseFuncDef parses the body of a function definition that started at
+// src[start]: a compound command.
+func (p *parser) parseFuncDef(name string, start int) (*funcDefNode, error) {
+	p.skipNewlines()
+	t := p.peek()
+	if t == nil {
+		return nil, errIncomplete
+	}
+	if !isCompoundStart(t) {
+		return nil, fmt.Errorf("%s: the body of a function must be a compound command like { ...; }", sanitize(name))
+	}
+	body, err := p.parseCompound()
+	if err != nil {
+		return nil, err
+	}
+	return &funcDefNode{def: &funcDef{name: name, body: body, text: p.src[start:p.toks[p.pos-1].end]}}, nil
+}
+
 // parseLoopBody parses "do list done".
 func (p *parser) parseLoopBody() (*listNode, error) {
 	if err := p.expect("do"); err != nil {
@@ -623,11 +960,14 @@ func (p *parser) parseLoopBody() (*listNode, error) {
 // Execution
 
 // isAbort reports whether err stops the execution of the enclosing lists:
-// break, continue, or a command that was interrupted with Ctrl+C (like in
+// break, continue, return, or a command that was interrupted with Ctrl+C
-// bash, Ctrl+C aborts the whole command line, e.g. a loop).
+// (like in bash, Ctrl+C aborts the whole command line, e.g. a loop).
 func isAbort(err error) bool {
-	var lc loopControl
+	var (
-	return errors.As(err, &lc) || exitStatus(err) == 128+int(syscall.SIGINT)
+		lc  loopControl
+		ret returnSignal
+	)
+	return errors.As(err, &lc) || errors.As(err, &ret) || exitStatus(err) == 128+int(syscall.SIGINT)
 }
 
 // silent returns an error with only the exit status of err, for errors that
@@ -644,11 +984,12 @@ func (l *listNode) exec() error {
 	for _, entry := range l.items {
 		printError(err)
 		if entry.background {
-			err = entry.andOr.first.cmd.(*simpleNode).run(true)
+			err = entry.andOr.runBackground()
 		} else {
 			err = entry.andOr.exec()
 		}
 		lastStatus = exitStatus(err)
+		runPendingTraps()
 		if isAbort(err) {
 			return err
 		}
@@ -656,9 +997,18 @@ func (l *listNode) exec() error {
 	return err
 }
 
+// exec runs the and-or list. With set -e, only a failure of the last
+// pipeline ends the shell.
 func (a *andOrNode) exec() error {
+	last := a.first
+	if len(a.rest) > 0 {
+		errexitOff++
+	}
 	err := a.first.exec()
-	for _, part := range a.rest {
+	if len(a.rest) > 0 {
+		errexitOff--
+	}
+	for i, part := range a.rest {
 		lastStatus = exitStatus(err)
 		if isAbort(err) {
 			return err
@@ -667,12 +1017,50 @@ func (a *andOrNode) exec() error {
 			continue
 		}
 		printError(err)
+		isLast := i == len(a.rest)-1
+		if !isLast {
+			errexitOff++
+		}
 		err = part.pipeline.exec()
+		if !isLast {
+			errexitOff--
+		}
+		last = part.pipeline
+	}
+	if last == a.lastPipeline() {
+		checkErrexit(last, err)
 	}
 	return err
 }
 
+func (a *andOrNode) lastPipeline() *pipelineNode {
+	if len(a.rest) == 0 {
+		return a.first
+	}
+	return a.rest[len(a.rest)-1].pipeline
+}
+
+// runBackground starts the and-or list as a background job. Pipelines run
+// like in the foreground, everything else in a subshell.
+func (a *andOrNode) runBackground() error {
+	if len(a.rest) == 0 && !a.first.negate {
+		switch cmd := a.first.cmd.(type) {
+		case *simpleNode:
+			return cmd.run(true)
+		case *pipeNode:
+			return cmd.run(true)
+		case *subshellNode:
+			return runPipeline([]stage{{script: cmd.text}}, a.text, true)
+		}
+	}
+	return runPipeline([]stage{{script: a.text}}, a.text, true)
+}
+
 func (pl *pipelineNode) exec() error {
+	if pl.negate {
+		errexitOff++
+		defer func() { errexitOff-- }()
+	}
 	err := pl.cmd.exec()
 	if !pl.negate || isAbort(err) {
 		return err
@@ -716,7 +1104,9 @@ func (s *simpleNode) run(background bool) error {
 
 func (n *ifNode) exec() error {
 	for i, cond := range n.conds {
+		errexitOff++
 		err := cond.exec()
+		errexitOff--
 		if isAbort(err) {
 			return err
 		}
@@ -759,7 +1149,9 @@ func (n *whileNode) exec() error {
 
 	var result error
 	for {
+		errexitOff++
 		err := n.cond.exec()
+		errexitOff--
 		if isAbort(err) {
 			return err
 		}
@@ -779,7 +1171,8 @@ func (n *whileNode) exec() error {
 }
 
 func (n *forNode) exec() error {
-	var words []string
+	// Without "in", the loop runs over the positional parameters
+	words := slices.Clone(positional)
 	if n.hasIn {
 		var err error
 		if words, err = expandWordList(n.words); err != nil {
@@ -804,6 +1197,137 @@ func (n *forNode) exec() error {
 	return result
 }
 
+func (n *groupNode) exec() error {
+	return n.body.exec()
+}
+
+func (n *subshellNode) exec() error {
+	return runPipeline([]stage{{script: n.text}}, "("+strings.TrimSpace(n.text)+")", false)
+}
+
+// exec runs the compound command with stdin, stdout and stderr of the shell
+// redirected.
+func (n *redirNode) exec() error {
+	fds, opened, err := openRedirections(n.redirs)
+	if err != nil {
+		return err
+	}
+	saved := ioOverride
+	ioOverride = fds
+	defer func() {
+		ioOverride = saved
+		for _, f := range opened {
+			f.Close()
+		}
+	}()
+	return n.cmd.exec()
+}
+
+func (n *pipeNode) exec() error {
+	return n.run(false)
+}
+
+// run builds the stages of the pipeline: simple commands are expanded,
+// compound commands run in subshells.
+func (n *pipeNode) run(background bool) error {
+	substStatus = 0
+	var stages []stage
+	for _, e := range n.elems {
+		switch {
+		case e.subshell != "":
+			stages = append(stages, stage{script: e.subshell})
+		case e.compound:
+			stages = append(stages, stage{script: e.text})
+		default:
+			text := e.text
+			if interactiveShell && aliasExpansion {
+				if tree, err := parse(expandAliases(text)); err == nil {
+					if simple := tree.singleSimple(); simple != nil {
+						text = simple.text
+					}
+				}
+			}
+			st, err := expandStages(text)
+			if err != nil {
+				return err
+			}
+			if len(st) == 0 {
+				st = []stage{{}}
+			}
+			stages = append(stages, st...)
+		}
+	}
+	return runPipeline(stages, n.text, background)
+}
+
+func (n *funcDefNode) exec() error {
+	defineFunction(n.def)
+	return nil
+}
+
+// exec runs the body of the first clause with a pattern that matches the
+// word. The status is 0 if no pattern matches.
+func (n *caseNode) exec() error {
+	word, err := expandCaseWord(n.word)
+	if err != nil {
+		return err
+	}
+	for _, clause := range n.clauses {
+		for _, pattern := range clause.patterns {
+			ok, err := caseMatch(pattern, word)
+			if err != nil {
+				return err
+			}
+			if ok {
+				return clause.body.exec()
+			}
+		}
+	}
+	lastStatus = 0
+	return nil
+}
+
+// expandCaseWord expands the word of a case command: like an argument, but
+// without brace expansion, wildcards and splitting.
+func expandCaseWord(text string) (string, error) {
+	tokens, err := tokenize(text)
+	if err != nil {
+		return "", fmt.Errorf("invalid input: %w", err)
+	}
+	var words []string
+	for _, t := range tokens {
+		if t.op != "" {
+			return "", syntaxError(t.op)
+		}
+		words = append(words, t.word)
+	}
+	return strings.Join(words, " "), nil
+}
+
+// caseMatch reports whether word matches the pattern of a case clause. The
+// pattern is expanded first; quoted characters in it match literally. Unlike
+// for file names, * and ? also match a /.
+func caseMatch(pattern, word string) (bool, error) {
+	tokens, err := tokenize(pattern)
+	if err != nil {
+		return false, fmt.Errorf("invalid input: %w", err)
+	}
+	var literal, glob []string
+	isGlob := false
+	for _, t := range tokens {
+		if t.op != "" {
+			return false, syntaxError(t.op)
+		}
+		literal = append(literal, t.word)
+		glob = append(glob, t.pattern)
+		isGlob = isGlob || t.glob
+	}
+	if !isGlob {
+		return word == strings.Join(literal, " "), nil
+	}
+	return globMatch(strings.Join(glob, " "), word), nil
+}
+
 // expandWordList expands the words of a for loop like the arguments of a
 // command (braces, ~, variables, $(...), wildcards).
 func expandWordList(text string) ([]string, error) {

read.go

@@ -0,0 +1,219 @@
+package main
+
+// The read builtin: read [-r] [-p prompt] [name ...] reads a line and splits
+// it into fields at the characters of $IFS (default: blank, tab, newline).
+
+import (
+	"errors"
+	"fmt"
+	"io"
+	"os"
+	"os/signal"
+	"strings"
+	"syscall"
+
+	"github.com/chzyer/readline"
+	"golang.org/x/sys/unix"
+)
+
+// builtinRead implements read. Each name gets one field, the last one the
+// rest of the line; without names the whole line is stored in $REPLY. The
+// status is 1 at the end of the input.
+func builtinRead(args []string, stdin *os.File) error {
+	raw := false
+	prompt := ""
+	args = args[1:]
+	for len(args) > 0 && strings.HasPrefix(args[0], "-") && args[0] != "-" {
+		opt := args[0]
+		args = args[1:]
+		if opt == "--" {
+			break
+		}
+		for k := 1; k < len(opt); k++ {
+			switch opt[k] {
+			case 'r':
+				raw = true
+			case 'p':
+				switch {
+				case k+1 < len(opt):
+					prompt = opt[k+1:]
+				case len(args) > 0:
+					prompt, args = args[0], args[1:]
+				default:
+					return errors.New("read: -p: option requires an argument")
+				}
+				k = len(opt)
+			default:
+				return fmt.Errorf("read: -%c: invalid option\nusage: read [-r] [-p prompt] [name ...]", opt[k])
+			}
+		}
+	}
+	for _, name := range args {
+		if !isVarName(name) {
+			return fmt.Errorf("read: `%s': not a valid identifier", sanitize(name))
+		}
+	}
+
+	terminal := readline.IsTerminal(int(stdin.Fd()))
+	if prompt != "" && terminal {
+		fmt.Fprint(stdio(2), prompt)
+	}
+	// Ctrl+C or a trapped signal ends a read from the terminal
+	line, literal, eof, err := readInputLine(stdin, raw, terminal && (interactiveShell || len(trapChans) > 0))
+	if err != nil {
+		return err
+	}
+
+	if len(args) == 0 {
+		os.Setenv("REPLY", line)
+	} else {
+		ifs, ok := os.LookupEnv("IFS")
+		if !ok {
+			ifs = " \t\n"
+		}
+		fields := splitFields(line, literal, ifs, len(args))
+		for i, name := range args {
+			value := ""
+			if i < len(fields) {
+				value = fields[i]
+			}
+			os.Setenv(name, value)
+		}
+	}
+	if eof {
+		return statusError(1)
+	}
+	return nil
+}
+
+// readInputLine reads a line from f, byte by byte so that nothing after the
+// line is consumed. Unless raw is set, a backslash escapes the next
+// character (literal marks the escaped characters, which never split
+// fields) and backslash-newline continues the line. eof reports that the
+// input ended before a newline. If interruptible is set, Ctrl+C aborts the
+// read with status 130.
+func readInputLine(f *os.File, raw, interruptible bool) (line string, literal []bool, eof bool, err error) {
+	readByte := plainByteReader(f)
+	if interruptible {
+		intr := make(chan os.Signal, 1)
+		signal.Notify(intr, os.Interrupt)
+		defer signal.Stop(intr)
+		readByte = interruptibleByteReader(f, intr)
+	}
+
+	var b []byte
+	for {
+		c, err := readByte()
+		if err == io.EOF {
+			return string(b), literal, true, nil
+		}
+		if err != nil {
+			return "", nil, false, err
+		}
+		if c == '\n' {
+			return string(b), literal, false, nil
+		}
+		if c == '\\' && !raw {
+			c, err = readByte()
+			if err == io.EOF {
+				return string(b), literal, true, nil
+			}
+			if err != nil {
+				return "", nil, false, err
+			}
+			if c == '\n' {
+				continue // the line goes on
+			}
+			b = append(b, c)
+			literal = append(literal, true)
+			continue
+		}
+		b = append(b, c)
+		literal = append(literal, false)
+	}
+}
+
+func plainByteReader(f *os.File) func() (byte, error) {
+	buf := make([]byte, 1)
+	return func() (byte, error) {
+		for {
+			n, err := f.Read(buf)
+			if n == 1 {
+				return buf[0], nil
+			}
+			if err != nil {
+				return 0, err
+			}
+		}
+	}
+}
+
+// interruptibleByteReader reads from the terminal f only when input is
+// available, so that a SIGINT on intr can end the read in between.
+func interruptibleByteReader(f *os.File, intr chan os.Signal) func() (byte, error) {
+	next := plainByteReader(f)
+	fds := []unix.PollFd{{Fd: int32(f.Fd()), Events: unix.POLLIN}}
+	return func() (byte, error) {
+		for {
+			select {
+			case <-intr:
+				fmt.Fprintln(stdio(2))
+				return 0, statusError(128 + int(syscall.SIGINT))
+			default:
+			}
+			if hasPendingSignal() {
+				return 0, statusError(128 + int(syscall.SIGINT))
+			}
+			n, err := unix.Poll(fds, 100)
+			if err != nil && !errors.Is(err, unix.EINTR) {
+				return 0, err
+			}
+			if n > 0 {
+				return next()
+			}
+		}
+	}
+}
+
+// splitFields splits line into at most n fields like read does: IFS
+// whitespace (blank, tab, newline in ifs) around fields is removed, other IFS
+// characters separate fields (also empty ones). The last field is the rest of
+// the line. Characters marked in literal are never separators.
+func splitFields(line string, literal []bool, ifs string, n int) []string {
+	isSep := func(i int) bool { return !literal[i] && strings.IndexByte(ifs, line[i]) >= 0 }
+	isSpace := func(i int) bool { return isSep(i) && strings.IndexByte(" \t\n", line[i]) >= 0 }
+
+	start, end := 0, len(line)
+	for start < end && isSpace(start) {
+		start++
+	}
+	for end > start && isSpace(end-1) {
+		end--
+	}
+
+	var fields []string
+	i := start
+	for i < end && len(fields) < n-1 {
+		j := i
+		for j < end && !isSep(j) {
+			j++
+		}
+		fields = append(fields, line[i:j])
+		// The separator: whitespace, at most one other IFS character,
+		// whitespace
+		for j < end && isSpace(j) {
+			j++
+		}
+		if j < end && isSep(j) && !isSpace(j) {
+			j++
+			for j < end && isSpace(j) {
+				j++
+			}
+		}
+		i = j
+	}
+	if i < end {
+		fields = append(fields, line[i:end])
+	}
+	return fields
+}

subst.go

@@ -2,7 +2,8 @@ package main
 
 // Command substitution: $(command) is replaced by the output of command,
 // which runs in a subshell (a new gosh process), so that cd, set etc. in it
-// do not change the shell.
+// do not change the shell. Functions also run in a subshell in pipelines and
+// in the background.
 
 import (
 	"bytes"
@@ -67,24 +68,32 @@ func substEnd(s string, i int) int {
 	return -1
 }
 
-// commandSubst runs command in a subshell and returns its output without
+// subshellCommand returns a command that runs script in a new gosh process
-// trailing newlines. stdin and stderr are those of the shell.
+// with the same $0, the given positional parameters and the functions of the
-func commandSubst(command string) (string, error) {
+// shell. (Variables need not be passed: they are all in the environment.)
-	if strings.HasPrefix(command, "(") {
+func subshellCommand(script string, params []string) (*exec.Cmd, error) {
-		return "", errors.New("arithmetic expansion $((...)) is not supported")
-	}
 	path := subshellPath
 	if path == "" {
 		var err error
 		if path, err = os.Executable(); err != nil {
-			return "", err
+			return nil, err
 		}
 	}
+	args := append(optionFlags(), "-c", functionDefs()+script, scriptName)
+	args = append(args, params...)
+	return exec.Command(path, args...), nil
+}
 
+// commandSubst runs command in a subshell and returns its output without
+// trailing newlines. stdin and stderr are those of the shell.
+func commandSubst(command string) (string, error) {
 	var out bytes.Buffer
-	cmd := exec.Command(path, "-c", command)
+	cmd, err := subshellCommand(command, positional)
-	cmd.Stdin, cmd.Stdout, cmd.Stderr = os.Stdin, &out, os.Stderr
+	if err != nil {
-	err := cmd.Run()
+		return "", err
+	}
+	cmd.Stdin, cmd.Stdout, cmd.Stderr = stdio(0), &out, stdio(2)
+	err = cmd.Run()
 	substStatus = exitStatus(err)
 	if substStatus == 128+int(syscall.SIGINT) {
 		// Ctrl+C aborts the whole command, like in bash

subst_test.go

@@ -94,8 +94,7 @@ func TestExecInput_CommandSubstitution(t *testing.T) {
 	}
 
 	for input, wantErr := range map[string]string{
-		"echo $(echo a":   "syntax error: unexpected end of input",
+		"echo $(echo a": "syntax error: unexpected end of input",
-		"echo $((1 + 2))": "invalid input: arithmetic expansion $((...)) is not supported",
 	} {
 		if err := execInput(input); err == nil || err.Error() != wantErr {
 			t.Errorf("%q: error %v, want %q", input, err, wantErr)

trap.go

@@ -0,0 +1,286 @@
+package main
+
+// The trap builtin. A trapped signal is only noted when it arrives; its
+// command runs in the shell at the next safe point: after the running
+// command has finished (like in sh, a shell waiting for a foreground command
+// handles the signal afterwards).
+
+import (
+	"fmt"
+	"io"
+	"os"
+	"os/signal"
+	"sort"
+	"strconv"
+	"strings"
+	"sync"
+	"syscall"
+)
+
+// trapSignals are the signals that can be trapped, besides EXIT.
+var trapSignals = map[string]syscall.Signal{
+	"HUP":   syscall.SIGHUP,
+	"INT":   syscall.SIGINT,
+	"QUIT":  syscall.SIGQUIT,
+	"TERM":  syscall.SIGTERM,
+	"USR1":  syscall.SIGUSR1,
+	"USR2":  syscall.SIGUSR2,
+	"ALRM":  syscall.SIGALRM,
+	"WINCH": syscall.SIGWINCH,
+}
+
+// fatalSignals end a non-interactive shell; with an EXIT trap the shell
+// catches them to run it first.
+var fatalSignals = []string{"HUP", "INT", "TERM"}
+
+var (
+	// traps maps EXIT and signal names to their commands ("" = ignore).
+	traps = map[string]string{}
+	// trapChans are the channels of the signals the shell catches.
+	trapChans = map[string]chan os.Signal{}
+
+	pendingMu      sync.Mutex
+	pendingSignals []string
+
+	inTrap bool
+
+	// interruptChan swallows SIGINT in an interactive shell, so that Ctrl+C
+	// only stops the running command.
+	interruptChan = make(chan os.Signal, 1)
+)
+
+// signalName returns the canonical name (EXIT, INT, ...) of a signal given
+// by name (with or without SIG) or number, or "".
+func signalName(spec string) string {
+	s := strings.ToUpper(strings.TrimPrefix(strings.ToUpper(spec), "SIG"))
+	if s == "EXIT" || s == "0" {
+		return "EXIT"
+	}
+	if _, ok := trapSignals[s]; ok {
+		return s
+	}
+	if n, err := strconv.Atoi(spec); err == nil {
+		for name, sig := range trapSignals {
+			if int(sig) == n {
+				return name
+			}
+		}
+	}
+	return ""
+}
+
+// builtinTrap implements trap [-lp] [[action] signal ...].
+func builtinTrap(args []string, stdout io.Writer) error {
+	args = args[1:]
+	switch {
+	case len(args) == 0 || args[0] == "-p":
+		names := args
+		if len(names) > 0 {
+			names = names[1:]
+		}
+		return printTraps(stdout, names)
+	case args[0] == "-l":
+		names := []string{"EXIT"}
+		for name := range trapSignals {
+			names = append(names, name)
+		}
+		sort.Slice(names, func(i, j int) bool { return signalNumber(names[i]) < signalNumber(names[j]) })
+		for _, name := range names {
+			fmt.Fprintf(stdout, "%2d) %s\n", signalNumber(name), name)
+		}
+		return nil
+	case args[0] == "--":
+		args = args[1:]
+	}
+
+	action := "-"
+	if len(args) > 1 || len(args) == 1 && signalName(args[0]) == "" {
+		action, args = args[0], args[1:]
+	}
+	if len(args) == 0 {
+		return fmt.Errorf("trap: usage: trap [-lp] [[action] signal ...]")
+	}
+	var err error
+	for _, spec := range args {
+		name := signalName(spec)
+		if name == "" {
+			err = fmt.Errorf("trap: %s: invalid signal specification", sanitize(spec))
+			continue
+		}
+		setTrap(name, action)
+	}
+	return err
+}
+
+func signalNumber(name string) int {
+	if name == "EXIT" {
+		return 0
+	}
+	return int(trapSignals[name])
+}
+
+func printTraps(w io.Writer, only []string) error {
+	var names []string
+	for name := range traps {
+		names = append(names, name)
+	}
+	if len(only) > 0 {
+		names = nil
+		for _, spec := range only {
+			name := signalName(spec)
+			if name == "" {
+				return fmt.Errorf("trap: %s: invalid signal specification", sanitize(spec))
+			}
+			if _, ok := traps[name]; ok {
+				names = append(names, name)
+			}
+		}
+	}
+	sort.Slice(names, func(i, j int) bool { return signalNumber(names[i]) < signalNumber(names[j]) })
+	for _, name := range names {
+		fmt.Fprintf(w, "trap -- %s %s\n", quoteAlias(traps[name]), name)
+	}
+	return nil
+}
+
+// setTrap sets the action of a trap: "-" restores the default, "" ignores
+// the signal, anything else is a command.
+func setTrap(name, action string) {
+	if action == "-" {
+		delete(traps, name)
+	} else {
+		traps[name] = action
+	}
+	if name == "EXIT" {
+		updateFatalCatch()
+		return
+	}
+	sig := trapSignals[name]
+	stopCatching(name)
+	switch action {
+	case "-":
+		signal.Reset(sig)
+		restoreShellSignal(sig)
+		if _, exit := traps["EXIT"]; exit {
+			updateFatalCatch()
+		}
+	case "":
+		// Ignored signals stay ignored in the programs the shell starts
+		signal.Ignore(sig)
+	default:
+		catch(name)
+	}
+}
+
+// catch makes the shell note the signal, to run its trap later.
+func catch(name string) {
+	if _, ok := trapChans[name]; ok {
+		return
+	}
+	ch := make(chan os.Signal, 4)
+	trapChans[name] = ch
+	signal.Notify(ch, trapSignals[name])
+	go func() {
+		for range ch {
+			pendingMu.Lock()
+			pendingSignals = append(pendingSignals, name)
+			pendingMu.Unlock()
+		}
+	}()
+}
+
+func stopCatching(name string) {
+	if ch, ok := trapChans[name]; ok {
+		signal.Stop(ch)
+		close(ch)
+		delete(trapChans, name)
+	}
+}
+
+// restoreShellSignal installs the handling the shell itself needs for sig
+// again after signal.Reset.
+func restoreShellSignal(sig syscall.Signal) {
+	if sig == syscall.SIGINT && interactiveShell {
+		signal.Notify(interruptChan, os.Interrupt)
+	}
+}
+
+// updateFatalCatch catches the fatal signals in a non-interactive shell with
+// an EXIT trap (unless they have traps of their own), so that the EXIT trap
+// runs before the shell ends.
+func updateFatalCatch() {
+	if interactiveShell {
+		return
+	}
+	_, exitTrap := traps["EXIT"]
+	for _, name := range fatalSignals {
+		if _, own := traps[name]; own {
+			continue
+		}
+		if exitTrap {
+			catch(name)
+		} else {
+			stopCatching(name)
+		}
+	}
+}
+
+// hasPendingSignal reports whether a caught signal waits for its trap.
+func hasPendingSignal() bool {
+	pendingMu.Lock()
+	defer pendingMu.Unlock()
+	return len(pendingSignals) > 0
+}
+
+// runPendingTraps runs the traps of the signals that arrived. A fatal signal
+// without a trap of its own (caught for the EXIT trap) ends the shell.
+func runPendingTraps() {
+	if inTrap {
+		return
+	}
+	pendingMu.Lock()
+	names := pendingSignals
+	pendingSignals = nil
+	pendingMu.Unlock()
+
+	for _, name := range names {
+		if action, ok := traps[name]; ok {
+			if action != "" {
+				runTrap(action)
+			}
+			continue
+		}
+		// Caught only for the EXIT trap: run it and die from the signal
+		runExitTrap()
+		sig := trapSignals[name]
+		signal.Reset(sig)
+		releaseTerminal()
+		syscall.Kill(os.Getpid(), sig)
+		os.Exit(128 + int(sig))
+	}
+}
+
+// runTrap runs the command of a trap; $? is kept.
+func runTrap(action string) {
+	saved := lastStatus
+	inTrap = true
+	defer func() { inTrap = false }()
+	tree, err := parse(action)
+	if err == nil {
+		err = tree.exec()
+	}
+	printError(err)
+	lastStatus = saved
+}
+
+// runExitTrap runs the EXIT trap (once) before the shell exits.
+func runExitTrap() {
+	action, ok := traps["EXIT"]
+	if !ok {
+		return
+	}
+	delete(traps, "EXIT")
+	if action != "" {
+		runTrap(action)
+	}
+}