add assignments name=value and unset

- name=value (one or more) without a command sets variables of the shell
- name=value before a command sets them only in its environment (for
  builtins only while they run)
- an assignment needs an unquoted name and =; the value is not split
  and not expanded as wildcard or brace pattern, ~ is expanded after =
  and :
- the status of an assignment is the one of its last $(...)
- new builtin unset

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

.goreleaser.yaml

@@ -22,7 +22,7 @@ builds:
     flags:
       - -trimpath
     ldflags:
-      - -s -w -X main.version={{ .Version }}
+      - -s -w -X main.version={{ .Version }} -X main.commit={{ .ShortCommit }} -X main.branch={{ .Branch }}
     goos:
       - linux
       - darwin

README.md

@@ -1,16 +1,28 @@
-`gosh` eine einfache Shell, geschrieben in golang.
+`gosh` eine Shell, in golang geschrieben.
 
 ```
 gosh - Go Shell
+Version: 0.13.0 (branch: main, commit: f79fb0b)
 
 Built-in commands:
   cd [dir]       - Change directory (cd with no args goes to home)
   pwd           - Print working directory
   echo [args]   - Echo arguments
-  exit [code]   - Exit shell with optional status code
+  exit [code]   - Exit shell with status code (default: $?)
-  quit [code]   - Quit shell with optional status code
+  quit [code]   - Quit shell with status code (default: $?)
   set VAR=val   - Set environment variable
   export VAR=val - Export environment variable
+  unset VAR     - Remove a variable
+  source file   - 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
+  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
   help          - Show this help
 
 Features:
@@ -22,15 +34,380 @@ Features:
     override with $GOSH_HISTFILE); lines starting with a space are not saved
   - Tab completion for commands and file paths
   - Tilde expansion (~, ~/path) at the start of unquoted words
-  - Colored prompt (user@host green, red for root; directory blue),
+  - Brace expansion: a{b,c}d -> abd acd, {1..5}, {01..10..2}, {a..e}
-    configurable with $GOSH_COLORS, e.g. GOSH_COLORS='user=1;33:path=36'
+  - Wildcards: * ? [abc] [a-z] [!abc] match file names (not hidden files
-    (keys user, root, path; values are ANSI SGR codes, empty = no color);
+    unless the pattern starts with a dot); quoted wildcards and values of
-    disabled with $NO_COLOR, TERM=dumb or when output is not a terminal
+    variables are not expanded, a pattern without match is kept as is
+  - Prompt user@host:dir $, with [N] before the $ if the last command
+    failed with exit status N
+  - Colored prompt (user@host green, red for root; directory blue; exit
+    status red), configurable with $GOSH_COLORS, e.g.
+    GOSH_COLORS='user=1;33:path=36' (keys user, root, path, error; values
+    are ANSI SGR codes, empty = no color); disabled with $NO_COLOR,
+    TERM=dumb or when output is not a terminal
+  - Variables: name=value sets a variable (like set), name=value command
+    sets it only for that command; the value is not split or expanded as
+    a pattern
   - Environment variable expansion ($VAR, ${VAR}, ${VAR:-default});
     using an unset variable is an error, use ${VAR:-} for an empty default
+  - Command substitution: $(command) is replaced by the output of command
+    (run in a subshell); unquoted it is split into words, "$(command)"
+    stays one word
+  - Command lists: a ; b (run both), a && b (b only if a succeeded),
+    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 "> ")
+  - Pipes (a | b) and redirections: < file, > file, >> file, 2> file,
+    2>> file, 2>&1, >&2, &> file (stdout and stderr), &>> file
+  - 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
+    (define them in ~/.goshrc); \name or 'name' skips the alias
+  - Non-interactive use: gosh -c 'command', gosh script, command | gosh;
+    the exit status is the one of the last command
+  - Startup files: login shells (-l or argv[0] starting with -) read
+    /etc/gosh/profile and ~/.gosh_profile, interactive shells read
+    /etc/gosh/goshrc and ~/.goshrc (skip with --noprofile, --norc)
 
 ```
 
+### Aufruf
+
+```
+gosh [-l] [-i] [--norc] [--noprofile] [script]
+gosh [-l] [--noprofile] -c command
+gosh -version
+```
+
+| Aufruf                 | Verhalten                                                        |
+|------------------------|------------------------------------------------------------------|
+| `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                             |
+| `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                                    |
+
+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.
+
+Damit funktionieren auch `ssh host befehl`, `scp` und `rsync`, wenn gosh als Login-Shell gesetzt ist. Befehle lassen sich mit `;`, `&&` und `||` verketten und mit Pipes verbinden, z. B. `ssh host 'cd /srv && git log | head'`.
+
+### Startdateien
+
+Beim Start liest gosh Startdateien und führt sie wie ein Skript in der laufenden Shell aus (Variablen, die dort gesetzt werden, bleiben also erhalten):
+
+| Shell                         | Dateien (in dieser Reihenfolge)              | abschalten mit  |
+|-------------------------------|----------------------------------------------|-----------------|
+| Login-Shell                   | `/etc/gosh/profile`, `~/.gosh_profile`       | `--noprofile`   |
+| interaktive Shell             | `/etc/gosh/goshrc`, `~/.goshrc`              | `--norc`        |
+
+- Eine Login-Shell ist gosh mit `-l` oder wenn `argv[0]` mit `-` beginnt (so starten `login`, `sshd` und `su -` die Shell). Eine interaktive Login-Shell liest erst die Profil-, dann die `goshrc`-Dateien.
+- `gosh -c '…'` und Skripte lesen keine Startdateien, außer als Login-Shell (`gosh -l -c '…'`).
+- Fehlende Dateien werden übersprungen. Fehler werden mit Datei und Zeile gemeldet (`gosh: ~/.goshrc:4: foo: command not found`), die übrigen Zeilen laufen trotzdem.
+- Bash-Dateien wie `/etc/profile` oder `~/.bashrc` liest gosh bewusst nicht, weil es deren Syntax (`if`, Funktionen, …) nicht versteht.
+- Mit `source datei` (oder `. datei`) lässt sich eine Datei auch später einlesen, z. B. nach einer Änderung: `source ~/.goshrc`.
+
+Beispiel für `~/.goshrc`:
+
+```bash
+# Eigene Programme zuerst
+export PATH=$HOME/bin:$HOME/go/bin:$PATH
+export EDITOR=vim
+
+# Aliase
+alias ll='ls -l'
+alias ..='cd ..'
+
+# Prompt-Farben (Anführungszeichen wegen des ;)
+export GOSH_COLORS='user=1;38;5;208:path=38;5;205'
+
+# Weitere Einstellungen nur, wenn die Datei existiert
+test -f ~/.goshrc.local && source ~/.goshrc.local
+```
+
+Beispiel für `~/.gosh_profile` (wird nur von Login-Shells gelesen, z. B. beim Anmelden an der Konsole oder per `ssh host` ohne Befehl):
+
+```bash
+export LANG=de_DE.UTF-8
+export PATH=$HOME/bin:$PATH
+```
+
+### Kontrollstrukturen
+
+gosh kennt `if`, `for`, `while` und `until` wie `sh`, auf einer Zeile oder über mehrere Zeilen:
+
+```bash
+if [ -f ~/.goshrc ]; then
+  echo "rc vorhanden"
+elif [ -d ~/.config ]; then
+  echo "nur .config"
+else
+  echo "nichts"
+fi
+
+for f in *.log; do
+  gzip "$f"
+done
+
+for i in {1..5}; do echo "Durchlauf $i"; done
+
+n=3
+while [ $n -gt 0 ]; do
+  echo $n
+  n=$(expr $n - 1)
+done
+
+until ping -c1 -W1 server >/dev/null; do sleep 1; done
+```
+
+| Konstrukt                                   | Bedeutung                                                         |
+|---------------------------------------------|-------------------------------------------------------------------|
+| `if befehl; then …; elif …; then …; else …; fi` | führt den Zweig aus, dessen Bedingung den Exit-Status 0 hat   |
+| `for x in wörter; do …; done`               | setzt `x` nacheinander auf jedes Wort                             |
+| `while befehl; do …; done`                  | wiederholt, solange `befehl` erfolgreich ist                      |
+| `until befehl; do …; done`                  | wiederholt, bis `befehl` erfolgreich ist                          |
+| `! befehl`                                  | kehrt den Exit-Status um                                          |
+| `break [n]`, `continue [n]`                 | verlässt die (n-te) Schleife bzw. springt zum nächsten Durchlauf  |
+| `:`                                         | tut nichts, Exit-Status 0 (z. B. `while :; do …; done`)           |
+
+- Bedingungen sind normale Befehle (auch Listen mit `&&`/`||`), meist `test` bzw. `[ … ]` (z. B. `[ -f datei ]`, `[ "$a" = b ]`, `[ $n -lt 3 ]`).
+- Die Wörter nach `for … in` werden wie Argumente expandiert: `*.go`, `{1..10}`, `$VAR`, `$(befehl)`. Ohne `in` läuft die Schleife nicht (Positionsparameter gibt es nicht).
+- Variablen, `$(...)` 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 $n + 1)`.
+
+### Variablen
+
+```bash
+name=wert                 # Variable setzen (wie set name=wert)
+a=1 b=2                   # mehrere auf einmal
+gruss="Hallo Welt"        # Leerzeichen im Wert brauchen Anführungszeichen
+heute=$(date +%F)         # Ausgabe eines Befehls
+PATH=~/bin:$PATH          # ~ wird auch nach = und : ersetzt
+LANG=C sort datei         # nur für diesen einen Befehl
+unset name                # Variable entfernen
+echo $name ${name:-standard}
+```
+
+- Eine Zuweisung ist ein Wort `name=wert` am Anfang eines Befehls, bei dem `name` und `=` ohne Anführungszeichen stehen und `name` aus Buchstaben, Ziffern und `_` besteht (nicht mit einer Ziffer beginnend). `"x=1"`, `x\=1` und `echo x=1` sind keine Zuweisungen.
+- Steht danach kein Befehl, wird die Variable in der Shell gesetzt. Wie bei `set` und `export` sind in gosh alle Variablen auch für gestartete Programme sichtbar (es gibt keine reinen Shell-Variablen).
+- Steht ein Befehl danach (`LANG=C sort datei`), gilt die Zuweisung nur für diesen Befehl, die Shell behält den alten Wert.
+- Der Wert wird nicht in Wörter geteilt und nicht als Wildcard oder `{a,b}` expandiert: `x=$(ls)` speichert die ganze Ausgabe, `x=*.go` speichert `*.go`. Variablen, `$(...)` und `~` (am Anfang, nach `=` und nach `:`) werden ersetzt.
+- `$?` ist nach einer Zuweisung der Status des letzten `$(...)` darin, sonst 0.
+- Variablen in den Argumenten werden ersetzt, bevor die Zuweisung davor gilt: `x=1 echo $x` gibt nicht `1` aus, sondern meldet `x: unbound variable` (wenn `x` vorher nicht gesetzt war).
+- In einer Pipeline (`x=1 | cat`) ändert eine Zuweisung die Shell nicht.
+
+### Befehlsersetzung
+
+`$(befehl)` wird durch die Ausgabe von `befehl` ersetzt:
+
+```
+$ echo "Heute ist $(date +%A)"
+Heute ist Montag
+$ kill $(pgrep -f mein-server)
+$ cd $(git rev-parse --show-toplevel)
+$ 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.
+- 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.
+
+### Befehlslisten und Exit-Status
+
+Mehrere Befehle in einer Zeile werden wie in `sh` verknüpft:
+
+| Liste      | Bedeutung                                         |
+|------------|---------------------------------------------------|
+| `a ; b`    | erst `a`, dann `b`                                |
+| `a && b`   | `b` nur, wenn `a` erfolgreich war (Exit-Status 0) |
+| `a \|\| b` | `b` nur, wenn `a` fehlgeschlagen ist              |
+
+`&&` und `||` werden von links nach rechts ausgewertet, `a && b || c` führt also `c` aus, wenn `a` oder `b` fehlschlägt. Variablen werden erst beim Ausführen des jeweiligen Befehls expandiert, `cd /tmp && echo $PWD` gibt also schon das neue Verzeichnis aus.
+
+`$?` (bzw. `${?}`) enthält den Exit-Status des letzten Befehls, `exit` ohne Argument beendet gosh mit diesem Status:
+
+```
+$ false; echo $?
+1
+$ gibtsnicht || echo "Status $?"
+gosh: gibtsnicht: command not found
+Status 127
+```
+
+Schlägt ein Programm fehl, gibt gosh selbst keine Meldung mehr aus (das Programm meldet den Fehler selbst), nur bei Fehlern von gosh, z. B. wenn ein Befehl nicht gefunden wird.
+
+### Klammer-Expansion
+
+Wie in bash erzeugt `{…}` aus einem Wort mehrere Wörter:
+
+| Ausdruck          | ergibt                          |
+|-------------------|---------------------------------|
+| `a{b,c}d`         | `abd acd`                       |
+| `file{,.bak}`     | `file file.bak`                 |
+| `{a,b}{1,2}`      | `a1 a2 b1 b2`                   |
+| `x{a,{b,c}}`      | `xa xb xc` (verschachtelt)      |
+| `{1..5}`          | `1 2 3 4 5`                     |
+| `{5..1}`          | `5 4 3 2 1`                     |
+| `{1..10..3}`      | `1 4 7 10` (Schrittweite)       |
+| `{01..10..4}`     | `01 05 09` (mit führenden Nullen) |
+| `{a..e}`          | `a b c d e`                     |
+
+```
+$ mkdir -p projekt/{src,doc,test}
+$ cp config.yaml{,.bak}          # Sicherungskopie
+$ ls *.{go,md}
+$ touch log-{01..12}.txt
+```
+
+- Die Klammer-Expansion kommt zuerst, die Ergebnisse durchlaufen danach `~`, Variablen und Wildcards: `*.{go,md}` wird zu `*.go *.md`, `{${A},b}` zu `$A b`.
+- Ohne Komma (und ohne gültige Folge) bleiben Klammern stehen: `{a}`, `{}`, `{a..1}`. Auch `${VAR}` wird nicht angefasst.
+- In Anführungszeichen oder mit `\` davor sind die Zeichen normale Zeichen: `"{a,b}"`, `\{a,b\}`. Ein Komma lässt sich mit `\,` schützen: `{a\,b,c}` ergibt `a,b c`.
+- Bei einer Umleitung muss genau ein Wort herauskommen, `> {a,b}` meldet `ambiguous redirect`.
+- Ein Wort darf höchstens 100 000 Wörter erzeugen.
+
+### Wildcards
+
+Wörter mit `*`, `?` oder `[...]` werden durch die passenden Dateinamen ersetzt, sortiert:
+
+| Muster    | passt auf                                           |
+|-----------|-----------------------------------------------------|
+| `*`       | beliebig viele Zeichen (auch keine)                 |
+| `?`       | genau ein Zeichen                                   |
+| `[abc]`   | eines der Zeichen `a`, `b`, `c`                     |
+| `[a-z]`   | ein Zeichen aus dem Bereich                         |
+| `[!abc]`  | ein Zeichen außer `a`, `b`, `c` (auch `[^abc]`)     |
+
+```
+$ ls *.go
+main.go  main_test.go
+$ cat logs/2026-*/error.log
+$ ls -d */            # nur Verzeichnisse
+```
+
+- Muster gelten pro Pfadteil, `*` passt nie auf `/`: `*/*.go` findet `.go`-Dateien eine Ebene tiefer.
+- Versteckte Dateien (mit `.` am Anfang) werden nur gefunden, wenn das Muster selbst mit `.` beginnt: `*` findet `.bashrc` nicht, `.*rc` schon.
+- Passt keine Datei, bleibt das Wort unverändert stehen (wie in `sh`), `ls *.xyz` meldet dann also `ls` den Fehler.
+- In Anführungszeichen oder mit `\` davor sind die Zeichen normale Zeichen: `echo "*"`, `echo '*.go'`, `echo \*`.
+- Werte von Variablen werden nicht als Muster behandelt (anders als in `sh`): Nach `P='*.go'` gibt `echo $P` wörtlich `*.go` aus. So kann ein Variablenwert nie unbemerkt auf viele Dateien passen. `echo $DIR/*.go` funktioniert dagegen, weil das `*` direkt in der Zeile steht.
+- Bei einer Umleitung muss das Muster genau eine Datei treffen (`> *.log`), sonst meldet gosh `ambiguous redirect`.
+
+### Pipes und Umleitungen
+
+```
+$ ls | sort -r | head -3
+$ make > build.log 2>&1
+$ grep -c error < build.log
+```
+
+| Syntax          | Bedeutung                                                  |
+|-----------------|------------------------------------------------------------|
+| `a \| b`        | stdout von `a` wird stdin von `b`                          |
+| `< datei`       | stdin aus `datei` lesen                                    |
+| `> datei`       | stdout in `datei` schreiben (wird überschrieben)           |
+| `>> datei`      | stdout an `datei` anhängen                                 |
+| `2> datei`      | stderr in `datei` schreiben (`2>>` hängt an)               |
+| `2>&1`          | stderr dorthin, wohin stdout gerade geht                   |
+| `>&2`           | stdout dorthin, wohin stderr gerade geht                   |
+| `&> datei`      | stdout und stderr in `datei` (`&>>` hängt an)              |
+| `> 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.
+
+### Aliase
+
+Ein Alias ist ein Kurzname für einen Befehl, am besten in `~/.goshrc` definiert:
+
+```bash
+alias ll='ls -l'
+alias la='ls -la'
+alias ..='cd ..'
+alias gs='git status'
+alias ls='ls --color=auto'      # ein Alias darf den eigenen Namen enthalten
+alias please='sudo '            # endet mit Leerzeichen: das nächste Wort wird auch ersetzt
+```
+
+| Befehl                  | Bedeutung                                         |
+|-------------------------|---------------------------------------------------|
+| `alias name='wert'`     | definiert einen Alias (mehrere in einem Aufruf möglich) |
+| `alias`                 | listet alle Aliase (in einer Form, die sich wieder einlesen lässt) |
+| `alias name`            | zeigt einen Alias                                 |
+| `unalias name`          | entfernt einen Alias, `unalias -a` alle           |
+
+- Ersetzt wird nur das erste Wort eines Befehls, also am Zeilenanfang und nach `;`, `&&`, `||`, `|` und `&`: `ll | less` funktioniert, `echo ll` gibt `ll` aus.
+- Der Wert darf selbst mehrere Befehle enthalten (`alias up='cd .. && ls'`) und wird wiederum auf Aliase geprüft. Ein Alias, der gerade ersetzt wird, wird darin nicht noch einmal ersetzt, deshalb funktioniert `alias ls='ls --color=auto'`.
+- Endet der Wert mit einem Leerzeichen, wird auch das nächste Wort als Alias geprüft: Mit den Aliasen oben wird `please ll` zu `sudo ls --color=auto -l`.
+- Mit `\ll` oder `'ll'` umgeht man den Alias und ruft das Programm direkt auf.
+- Aliase gelten nur in interaktiven Shells (wie in bash), also auch in `~/.goshrc`, aber nicht in Skripten und bei `gosh -c`. Ein Alias wirkt erst ab der nächsten Zeile, nicht in der Zeile, in der er definiert wird.
+- Erlaubt sind Namen aus Buchstaben, Ziffern und `_ - . + : , @ % ^`.
+- Aliase werden auch mit Tab vervollständigt.
+
+### Job-Control
+
+In einer interaktiven Shell läuft jede Befehlszeile (bzw. jede Pipeline) als eigener *Job* in einer eigenen Prozessgruppe:
+
+```
+$ sleep 100 &                 # im Hintergrund starten
+[1] 12345
+$ vim notizen.txt             # Ctrl+Z hält vim an
+^Z
+[2]+  Stopped                 vim notizen.txt
+$ jobs
+[1]-  Running                 sleep 100 &
+[2]+  Stopped                 vim notizen.txt
+$ fg                          # vim wieder im Vordergrund
+$ bg %2                       # oder: angehaltenen Job im Hintergrund weiterlaufen lassen
+```
+
+| Befehl / Taste | Bedeutung                                                                 |
+|----------------|---------------------------------------------------------------------------|
+| `befehl &`     | startet den Befehl im Hintergrund, gosh wartet nicht auf ihn (`$?` ist 0) |
+| Ctrl+Z         | hält den Vordergrund-Job an (`$?` wird 128+SIGTSTP, unter Linux 148)      |
+| Ctrl+C         | bricht nur den Vordergrund-Job ab, nicht die Shell                        |
+| `jobs`         | listet laufende und angehaltene Jobs                                      |
+| `fg [%n]`      | holt Job `n` in den Vordergrund (und setzt ihn fort, falls angehalten)    |
+| `bg [%n]`      | setzt einen angehaltenen Job im Hintergrund fort                          |
+| `wait [%n]`    | wartet auf Job `n` bzw. auf alle Hintergrund-Jobs                         |
+
+- Ohne Angabe gilt der *aktuelle* Job (in `jobs` mit `+` markiert, der zuletzt angehaltene oder in den Hintergrund geschickte), `%-` ist der vorherige (`-`). `%n` und `n` meinen Job Nummer `n`.
+- Beendete Hintergrund-Jobs meldet gosh vor dem nächsten Prompt (`[1]+  Done   sleep 100`, bei Fehlern `Exit N`).
+- Liest ein Hintergrund-Job vom Terminal, wird er angehalten (wie in bash), mit `fg` bekommt er die Eingabe.
+- Die Terminal-Einstellungen werden gesichert und wiederhergestellt: Nach dem Anhalten von `vim` oder `less` funktioniert der Prompt normal, nach `fg` bekommt das Programm seine Einstellungen zurück.
+- `exit` (oder Ctrl+D) mit angehaltenen Jobs warnt einmal (`there are stopped jobs`), ein zweites `exit` direkt danach beendet gosh.
+- `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.
+
+### Prompt
+
+Der Prompt zeigt Benutzer, Rechner und Verzeichnis. Ist der letzte Befehl fehlgeschlagen, steht sein Exit-Status in eckigen Klammern davor, bis wieder ein Befehl erfolgreich war:
+
+```
+flow@host:~/src $ false
+flow@host:~/src [1] $ gibtsnicht
+gosh: gibtsnicht: command not found
+flow@host:~/src [127] $ sleep 100     # mit Ctrl+C abgebrochen
+^C
+flow@host:~/src [130] $ true
+flow@host:~/src $
+```
+
+Typische Werte: `1` allgemeiner Fehler, `2` Syntaxfehler, `126` nicht ausführbar, `127` Befehl nicht gefunden, `128+n` durch Signal `n` beendet (`130` = Ctrl+C, `148` = mit Ctrl+Z angehalten unter Linux). Eine leere Eingabe ändert den Status nicht.
+
 ### Farben
 
 Der Prompt wird über die Umgebungsvariable `GOSH_COLORS` eingefärbt. Sie besteht aus durch `:` getrennten Einträgen `schlüssel=code`:
@@ -40,6 +417,7 @@ Der Prompt wird über die Umgebungsvariable `GOSH_COLORS` eingefärbt. Sie beste
 | `user`    | `user@host`                    | `1;32` (fett grün)  |
 | `root`    | `user@host`, wenn man root ist | `1;31` (fett rot)   |
 | `path`    | aktuelles Verzeichnis          | `1;34` (fett blau)  |
+| `error`   | Exit-Status `[N]` nach einem Fehler | `1;31` (fett rot) |
 
 Die Werte sind [ANSI-SGR-Codes](https://en.wikipedia.org/wiki/ANSI_escape_code#SGR_(Select_Graphic_Rendition)_parameters), mehrere werden mit `;` kombiniert:
 
@@ -77,6 +455,9 @@ GOSH_COLORS='user=1;38;2;136;192;208:path=38;2;216;222;233'
 # Ozean: türkis und kursiv blau
 GOSH_COLORS='user=1;96:path=3;94'
 
+# Fehler-Status gelb auf rotem Hintergrund
+GOSH_COLORS='error=1;33;41'
+
 # Root-Warnung: weiß auf rotem Hintergrund
 GOSH_COLORS='root=1;97;41'
 
@@ -102,6 +483,15 @@ _gosh is not meant for production use, it is just a proof of concept._
 go build ./
 ```
 
+Die Version lässt sich mit `gosh -version` (oder `--version`, `-V`) abfragen und steht auch in der Ausgabe von `help`:
+
+```
+$ gosh -version
+gosh 0.2.1 (branch: main, commit: 03e791c)
+```
+
+Version und Branch werden beim Bauen mit GoReleaser per `-ldflags` gesetzt. Bei einem einfachen `go build` steht dort `dev`, der Commit wird dann aus den von Go eingebetteten Git-Informationen gelesen (mit `-dirty`, falls es uncommittete Änderungen gab).
+
 ## Release
 
 Binaries sowie `.deb`- und `.rpm`-Pakete werden mit [GoReleaser](https://goreleaser.com) gebaut (Konfiguration: `.goreleaser.yaml`).

alias.go

@@ -0,0 +1,201 @@
+package main
+
+// Aliases: like in bash, an alias replaces the first word of a command and
+// is only expanded in interactive shells (including the startup files), not
+// in scripts or with gosh -c.
+
+import (
+	"fmt"
+	"io"
+	"sort"
+	"strings"
+	"sync"
+)
+
+var (
+	aliasMu sync.Mutex
+	aliases = map[string]string{}
+)
+
+// isAliasName reports whether s can be an alias name: letters, digits and a
+// few punctuation characters, but nothing that is special to the shell.
+func isAliasName(s string) bool {
+	if s == "" {
+		return false
+	}
+	for _, r := range s {
+		switch {
+		case r >= 'a' && r <= 'z', r >= 'A' && r <= 'Z', r >= '0' && r <= '9':
+		case strings.ContainsRune("_-.+:,@%^", r):
+		default:
+			return false
+		}
+	}
+	return true
+}
+
+// lookupAlias returns the value of an alias.
+func lookupAlias(name string) (string, bool) {
+	aliasMu.Lock()
+	defer aliasMu.Unlock()
+	value, ok := aliases[name]
+	return value, ok
+}
+
+// aliasNames returns the names of all aliases, sorted.
+func aliasNames() []string {
+	aliasMu.Lock()
+	defer aliasMu.Unlock()
+	names := make([]string, 0, len(aliases))
+	for name := range aliases {
+		names = append(names, name)
+	}
+	sort.Strings(names)
+	return names
+}
+
+// expandAliases replaces aliases at the start of every command in line (at
+// the start and after ;, &, &&, || and |). The value of an alias is expanded
+// again, except for aliases that are already being expanded, so that e.g.
+// alias ls='ls --color' works. If the value ends with a blank, the next word
+// is checked for an alias too. Quoted or escaped words (\ls, 'ls') are never
+// replaced.
+func expandAliases(line string) string {
+	return expandAliasesIn(line, map[string]bool{})
+}
+
+func expandAliasesIn(line string, active map[string]bool) string {
+	var (
+		out        strings.Builder
+		quote      byte
+		escaped    bool
+		commandPos = true // the next word is the name of a command
+	)
+
+	for i := 0; i < len(line); i++ {
+		ch := line[i]
+		if quote == 0 && !escaped && commandPos {
+			if ch == ' ' || ch == '\t' || ch == '\n' {
+				out.WriteByte(ch)
+				continue
+			}
+			commandPos = false
+			end := i
+			for end < len(line) && strings.IndexByte(" \t\n;&|<>", line[end]) < 0 {
+				end++
+			}
+			name := line[i:end]
+			if value, ok := lookupAlias(name); ok && isAliasName(name) && !active[name] {
+				active[name] = true
+				out.WriteString(expandAliasesIn(value, active))
+				delete(active, name)
+				// A trailing blank makes the next word a command name too
+				commandPos = strings.HasSuffix(value, " ") || strings.HasSuffix(value, "\t")
+				i = end - 1
+				continue
+			}
+		}
+
+		if quote != '\'' && !escaped && isSubstStart(line, i) {
+			// $(...) is copied as it is; the subshell does not expand
+			// aliases
+			if end := substEnd(line, i); end >= 0 {
+				out.WriteString(line[i : end+1])
+				i = end
+				continue
+			}
+		}
+
+		out.WriteByte(ch)
+		switch {
+		case escaped:
+			escaped = false
+		case quote == '\'':
+			if ch == '\'' {
+				quote = 0
+			}
+		case ch == '\\':
+			escaped = true
+		case quote == '"':
+			if ch == '"' {
+				quote = 0
+			}
+		case ch == '"' || ch == '\'':
+			quote = ch
+		case ch == '#' && (i == 0 || strings.IndexByte(" \t", line[i-1]) >= 0):
+			// Comment until the end of the line
+			out.WriteString(line[i+1:])
+			return out.String()
+		case ch == ';' || ch == '|':
+			commandPos = true
+		case ch == '&':
+			// & and && separate commands, &>, >& and <& do not
+			if !(i+1 < len(line) && line[i+1] == '>') && !(i > 0 && strings.IndexByte("<>", line[i-1]) >= 0) {
+				commandPos = true
+			}
+		}
+	}
+	return out.String()
+}
+
+// quoteAlias quotes a value for the output of alias, so that it can be read
+// back: 'value' with ' written as '\”.
+func quoteAlias(value string) string {
+	return "'" + strings.ReplaceAll(value, "'", `'\''`) + "'"
+}
+
+// builtinAlias defines aliases (alias name=value ...), prints them (alias
+// name ...) or lists all of them (alias).
+func builtinAlias(args []string, stdout io.Writer) error {
+	if len(args) == 1 {
+		for _, name := range aliasNames() {
+			value, _ := lookupAlias(name)
+			fmt.Fprintf(stdout, "alias %s=%s\n", name, sanitize(quoteAlias(value)))
+		}
+		return nil
+	}
+
+	var err error
+	for _, arg := range args[1:] {
+		name, value, define := strings.Cut(arg, "=")
+		if !isAliasName(name) {
+			err = fmt.Errorf("alias: `%s': invalid alias name", sanitize(name))
+			continue
+		}
+		if define {
+			aliasMu.Lock()
+			aliases[name] = value
+			aliasMu.Unlock()
+			continue
+		}
+		if value, ok := lookupAlias(name); ok {
+			fmt.Fprintf(stdout, "alias %s=%s\n", name, sanitize(quoteAlias(value)))
+		} else {
+			err = fmt.Errorf("alias: %s: not found", sanitize(name))
+		}
+	}
+	return err
+}
+
+// builtinUnalias removes aliases (unalias name ...) or all of them
+// (unalias -a).
+func builtinUnalias(args []string) error {
+	if len(args) < 2 {
+		return fmt.Errorf("usage: unalias [-a] name ...")
+	}
+	aliasMu.Lock()
+	defer aliasMu.Unlock()
+	if args[1] == "-a" {
+		aliases = map[string]string{}
+		return nil
+	}
+	var err error
+	for _, name := range args[1:] {
+		if _, ok := aliases[name]; !ok {
+			err = fmt.Errorf("unalias: %s: not found", sanitize(name))
+			continue
+		}
+		delete(aliases, name)
+	}
+	return err
+}

alias_test.go

@@ -0,0 +1,164 @@
+package main
+
+import (
+	"bytes"
+	"os"
+	"path/filepath"
+	"reflect"
+	"strings"
+	"testing"
+)
+
+// withAliases sets the aliases for a test and restores them afterwards.
+func withAliases(t *testing.T, defs map[string]string) {
+	t.Helper()
+	aliasMu.Lock()
+	saved := aliases
+	aliases = map[string]string{}
+	for name, value := range defs {
+		aliases[name] = value
+	}
+	aliasMu.Unlock()
+	t.Cleanup(func() {
+		aliasMu.Lock()
+		aliases = saved
+		aliasMu.Unlock()
+	})
+}
+
+func TestExpandAliases(t *testing.T) {
+	withAliases(t, map[string]string{
+		"ll":    "ls -l",
+		"ls":    "ls --color",
+		"..":    "cd ..",
+		"e":     "echo ",
+		"w":     "world",
+		"a":     "b",
+		"b":     "a",
+		"multi": "cd /tmp && ls",
+	})
+
+	tests := []struct {
+		input, want string
+	}{
+		{"ll", "ls --color -l"},
+		{"  ll -a", "  ls --color -l -a"},
+		{"ls", "ls --color"},
+		{"..", "cd .."},
+		// Only the command name is replaced
+		{"echo ll", "echo ll"},
+		{"ll ll", "ls --color -l ll"},
+		// ... also after ;, &&, ||, | and &
+		{"ll; ll && ll || ll | ll & ll", "ls --color -l; ls --color -l && ls --color -l || ls --color -l | ls --color -l & ls --color -l"},
+		// but not after redirections with &
+		{"ll 2>&1 ll", "ls --color -l 2>&1 ll"},
+		{"ll &> ll", "ls --color -l &> ll"},
+		// Quoted or escaped words are not replaced
+		{`\ll`, `\ll`},
+		{`'ll'`, `'ll'`},
+		{`"ll"`, `"ll"`},
+		{`echo "a; ll"`, `echo "a; ll"`},
+		{`echo 'a | ll'`, `echo 'a | ll'`},
+		// A trailing blank makes the next word a command name too
+		{"e w", "echo  world"},
+		{"e e w", "echo  echo  world"},
+		// Recursion stops at aliases that are already being expanded
+		{"a", "a"},
+		{"b", "b"},
+		// The value can contain several commands
+		{"multi", "cd /tmp && ls --color"},
+		// Comments are left alone
+		{"echo x # ll", "echo x # ll"},
+	}
+	for _, tc := range tests {
+		if got := expandAliases(tc.input); got != tc.want {
+			t.Errorf("expandAliases(%q) = %q, want %q", tc.input, got, tc.want)
+		}
+	}
+}
+
+func TestBuiltinAlias(t *testing.T) {
+	withAliases(t, nil)
+
+	run := func(args ...string) (string, error) {
+		var out bytes.Buffer
+		err := builtinAlias(append([]string{"alias"}, args...), &out)
+		return out.String(), err
+	}
+
+	if _, err := run("ll=ls -l", "q=echo it's", "..=cd .."); err != nil {
+		t.Fatal(err)
+	}
+	out, _ := run()
+	want := "alias ..='cd ..'\nalias ll='ls -l'\nalias q='echo it'\\''s'\n"
+	if out != want {
+		t.Errorf("alias = %q, want %q", out, want)
+	}
+	if out, _ := run("ll"); out != "alias ll='ls -l'\n" {
+		t.Errorf("alias ll = %q", out)
+	}
+	if _, err := run("nope"); err == nil || err.Error() != "alias: nope: not found" {
+		t.Errorf("alias nope: %v", err)
+	}
+	for _, name := range []string{"a/b", "a=b", "$x", "a b", ""} {
+		if isAliasName(name) {
+			t.Errorf("isAliasName(%q) = true", name)
+		}
+	}
+	if _, err := run("a/b=x"); err == nil || !strings.Contains(err.Error(), "invalid alias name") {
+		t.Errorf("alias a/b=x: %v", err)
+	}
+
+	if err := builtinUnalias([]string{"unalias", "ll", "nope"}); err == nil || err.Error() != "unalias: nope: not found" {
+		t.Errorf("unalias nope: %v", err)
+	}
+	if _, ok := lookupAlias("ll"); ok {
+		t.Error("ll still defined after unalias")
+	}
+	builtinUnalias([]string{"unalias", "-a"})
+	if names := aliasNames(); len(names) != 0 {
+		t.Errorf("aliases after unalias -a: %q", names)
+	}
+}
+
+func TestExecInput_Aliases(t *testing.T) {
+	withAliases(t, nil)
+	origDir, _ := os.Getwd()
+	defer os.Chdir(origDir)
+	dir := t.TempDir()
+	os.Chdir(dir)
+	defer func(saved bool) { interactiveShell = saved }(interactiveShell)
+
+	// Aliases are expanded in interactive shells only
+	interactiveShell = true
+	execInput(`alias say='echo hello' to=out`)
+	execInput("say world > out")
+	if got, _ := os.ReadFile("out"); string(got) != "hello world\n" {
+		t.Errorf("alias in interactive shell: out = %q", got)
+	}
+
+	interactiveShell = false
+	os.Remove("out")
+	if err := execInput("say world > out"); err == nil {
+		t.Error("alias was expanded in a non-interactive shell")
+	}
+
+	// alias works in pipelines (listing), unalias does not
+	interactiveShell = true
+	execInput("alias | grep say > out")
+	if got, _ := os.ReadFile(filepath.Join(dir, "out")); string(got) != "alias say='echo hello'\n" {
+		t.Errorf("alias | grep = %q", got)
+	}
+	if err := execInput("echo | unalias say"); err == nil {
+		t.Error("unalias in a pipeline must fail")
+	}
+}
+
+func TestShellCompleter_Aliases(t *testing.T) {
+	withAliases(t, map[string]string{"gst": "git status"})
+	t.Setenv("PATH", t.TempDir())
+	got, length := completeLine("gs")
+	if !reflect.DeepEqual(got, []string{"t "}) || length != 2 {
+		t.Errorf("completion of gs = %q, %d", got, length)
+	}
+}

assign_test.go

@@ -0,0 +1,109 @@
+package main
+
+import (
+	"os"
+	"testing"
+)
+
+func TestTokenize_Assignments(t *testing.T) {
+	t.Setenv("HOME", "/home/u")
+	tests := []struct {
+		input  string
+		word   string
+		assign bool
+	}{
+		{"x=1", "x=1", true},
+		{"_a1=", "_a1=", true},
+		{`x="a b"`, "x=a b", true},
+		{"x=a=b", "x=a=b", true},
+		{"P=~/bin:~/go/bin", "P=/home/u/bin:/home/u/go/bin", true},
+		{"x=a~b", "x=a~b", true},
+		{"x=~", "x=/home/u", true},
+		// Not an assignment: quoted or escaped name or =, invalid name
+		{`"x=1"`, "x=1", false},
+		{`x"=1"`, "x=1", false},
+		{`x\=1`, "x=1", false},
+		{"1x=2", "1x=2", false},
+		{"=x", "=x", false},
+		{"a-b=1", "a-b=1", false},
+	}
+	for _, tc := range tests {
+		tokens, err := tokenize(tc.input)
+		if err != nil || len(tokens) != 1 {
+			t.Errorf("tokenize(%q) = %+v, %v", tc.input, tokens, err)
+			continue
+		}
+		if tokens[0].word != tc.word || tokens[0].assign != tc.assign {
+			t.Errorf("tokenize(%q) = %q (assign %v), want %q (assign %v)",
+				tc.input, tokens[0].word, tokens[0].assign, tc.word, tc.assign)
+		}
+	}
+
+	// The output of $(...) is not split in an assignment
+	tokens, _ := tokenize("x=$(echo a b) y")
+	if len(tokens) != 2 || tokens[0].word != "x=a b" || !tokens[0].assign {
+		t.Errorf("x=$(echo a b): %+v", tokens)
+	}
+}
+
+func TestExec_Assignments(t *testing.T) {
+	for _, name := range []string{"GOSH_A", "GOSH_B", "GOSH_C"} {
+		os.Unsetenv(name)
+		defer os.Unsetenv(name)
+	}
+	tests := []struct {
+		input string
+		want  string
+	}{
+		{"GOSH_A=1; echo $GOSH_A > out", "1\n"},
+		{"GOSH_A=1 GOSH_B=2; echo $GOSH_A$GOSH_B > out", "12\n"},
+		{`GOSH_A="a  b"; echo "$GOSH_A" > out`, "a  b\n"},
+		{"GOSH_A=$(printf 'a b\\nc'); echo \"$GOSH_A\" > out", "a b\nc\n"},
+		// No wildcard or brace expansion in the value
+		{"touch x.go; GOSH_A=*.go; echo \"$GOSH_A\" > out", "*.go\n"},
+		{"GOSH_A={a,b}; echo $GOSH_A > out", "{a,b}\n"},
+		// ... but as an argument, assignment-like words are normal words
+		{"echo GOSH_A={a,b} > out", "GOSH_A=a GOSH_A=b\n"},
+		// Before a command, only in its environment
+		{"GOSH_C=temp sh -c 'echo $GOSH_C' > out; echo ${GOSH_C:-unset} >> out", "temp\nunset\n"},
+		{"GOSH_A=old; GOSH_A=new sh -c 'echo $GOSH_A' > out; echo $GOSH_A >> out", "new\nold\n"},
+		// ... and before a builtin only while it runs
+		{"GOSH_C=temp pwd > /dev/null; echo ${GOSH_C:-unset} > out", "unset\n"},
+		// In a pipeline or with a command they do not change the shell
+		{"GOSH_C=x | cat; echo ${GOSH_C:-unset} > out", "unset\n"},
+		// Redirections are applied
+		{"GOSH_A=r > out", ""},
+		// In loops
+		{"for i in 1 2 3; do GOSH_A=$i; done; echo $GOSH_A > out", "3\n"},
+		{"GOSH_B=0; while [ $GOSH_B -lt 3 ]; do echo $GOSH_B >> out; GOSH_B=$(expr $GOSH_B + 1); done", "0\n1\n2\n"},
+		// Not assignments
+		{`echo "GOSH_A=1" GOSH_B=2 > out`, "GOSH_A=1 GOSH_B=2\n"},
+		// unset
+		{"GOSH_A=1; unset GOSH_A; echo ${GOSH_A:-gone} > out", "gone\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 status of an assignment is the one of its last $(...)
+	for input, want := range map[string]int{
+		"GOSH_A=1":                       0,
+		"GOSH_A=$(false)":                1,
+		"GOSH_A=$(sh -c 'exit 3')":       3,
+		"GOSH_A=$(false) GOSH_B=$(true)": 0,
+	} {
+		runIn(t, input)
+		if lastStatus != want {
+			t.Errorf("%q: $? = %d, want %d", input, lastStatus, want)
+		}
+	}
+
+	if err := execInput("unset 1x"); err == nil || err.Error() != "unset: `1x': not a valid identifier" {
+		t.Errorf("unset 1x: %v", err)
+	}
+	if err := execInput(`"GOSH_A=1"`); err == nil || exitStatus(err) != 127 {
+		t.Errorf(`"GOSH_A=1" must be a command: %v`, err)
+	}
+}

brace.go

@@ -0,0 +1,298 @@
+package main
+
+// Brace expansion like in bash: a{b,c}d becomes abd acd, {1..5} becomes
+// 1 2 3 4 5. It happens first, on the text of the command line, so that the
+// resulting words go through the other expansions (~, variables, wildcards).
+
+import (
+	"errors"
+	"fmt"
+	"strconv"
+	"strings"
+)
+
+// maxBraceWords limits the number of words a single word may expand to.
+const maxBraceWords = 100000
+
+// expandBraceWords applies brace expansion to every word of a command (the
+// text of a pipeline). Quoted or escaped braces, ${...} and $(...) are left
+// alone.
+// A redirection target must expand to a single word.
+func expandBraceWords(input string) (string, error) {
+	var (
+		out           strings.Builder
+		afterRedirect bool // the next word is the target of a redirection
+		commandStart  = true
+	)
+
+	for i := 0; i < len(input); {
+		ch := input[i]
+		switch {
+		case ch == ' ' || ch == '\t' || ch == '\n':
+			out.WriteByte(ch)
+			i++
+		case strings.IndexByte(";&|<>", ch) >= 0:
+			if ch == '<' || ch == '>' {
+				afterRedirect = true
+			} else {
+				commandStart = true
+			}
+			out.WriteByte(ch)
+			i++
+		case ch == '#':
+			// A comment, until the end of the line
+			out.WriteString(input[i:])
+			return out.String(), nil
+		default:
+			end := wordEnd(input, i)
+			if commandStart && !afterRedirect && isAssignment(input[i:end]) {
+				// name=value before the command: no brace expansion, like
+				// in bash
+				out.WriteString(input[i:end])
+				i = end
+				continue
+			}
+			if !afterRedirect {
+				commandStart = false
+			}
+			words, err := expandBraces(input[i:end])
+			if err != nil {
+				return "", err
+			}
+			if afterRedirect && len(words) > 1 {
+				return "", fmt.Errorf("%s: ambiguous redirect", sanitize(input[i:end]))
+			}
+			afterRedirect = false
+			out.WriteString(strings.Join(words, " "))
+			i = end
+		}
+	}
+	return out.String(), nil
+}
+
+// isAssignment reports whether a word starts with name= (unquoted).
+func isAssignment(word string) bool {
+	name, _, ok := strings.Cut(word, "=")
+	return ok && isVarName(name)
+}
+
+// wordEnd returns the end of the word starting at i: the next unquoted blank
+// or operator character.
+func wordEnd(s string, i int) int {
+	var quote byte
+	for ; i < len(s); i++ {
+		ch := s[i]
+		switch {
+		case quote == '\'':
+			if ch == '\'' {
+				quote = 0
+			}
+		case ch == '\\':
+			i++
+		case isSubstStart(s, i):
+			if j := substEnd(s, i); j >= 0 {
+				i = j
+			}
+		case ch == '$' && i+1 < len(s) && s[i+1] == '{':
+			if j := strings.IndexByte(s[i:], '}'); j >= 0 {
+				i += j
+			}
+		case quote == '"':
+			if ch == '"' {
+				quote = 0
+			}
+		case ch == '"' || ch == '\'':
+			quote = ch
+		case strings.IndexByte(" \t\n;&|<>", ch) >= 0:
+			return i
+		}
+	}
+	return len(s)
+}
+
+// braceScan calls fn for every unquoted, unescaped character of s that is
+// not part of a ${...} reference, with its index and the brace depth.
+// Scanning stops when fn returns false.
+func braceScan(s string, fn func(i, depth int) bool) {
+	var quote byte
+	depth := 0
+	for i := 0; i < len(s); i++ {
+		ch := s[i]
+		switch {
+		case quote == '\'':
+			if ch == '\'' {
+				quote = 0
+			}
+			continue
+		case ch == '\\':
+			i++
+			continue
+		case isSubstStart(s, i):
+			// The subshell does its own brace expansion
+			if j := substEnd(s, i); j >= 0 {
+				i = j
+			}
+			continue
+		case ch == '$' && i+1 < len(s) && s[i+1] == '{':
+			if j := strings.IndexByte(s[i:], '}'); j >= 0 {
+				i += j
+			}
+			continue
+		case quote == '"':
+			if ch == '"' {
+				quote = 0
+			}
+			continue
+		case ch == '"' || ch == '\'':
+			quote = ch
+			continue
+		}
+		if ch == '}' {
+			depth--
+		}
+		if !fn(i, depth) {
+			return
+		}
+		if ch == '{' {
+			depth++
+		}
+	}
+}
+
+// expandBraces expands the first valid brace expression of a word and then
+// recursively the results: a{b,c}d -> abd acd, x{1..3} -> x1 x2 x3. A brace
+// expression is valid if it contains an unquoted comma at its top level or
+// is a sequence; other braces ({}, {a}, ${x}) are kept as they are.
+func expandBraces(word string) ([]string, error) {
+	// Find the candidates: unquoted { with their matching }
+	var opens []int
+	pairs := map[int]int{}
+	braceScan(word, func(i, depth int) bool {
+		switch word[i] {
+		case '{':
+			opens = append(opens, i)
+		case '}':
+			if len(opens) > 0 {
+				pairs[opens[len(opens)-1]] = i
+				opens = opens[:len(opens)-1]
+			}
+		}
+		return true
+	})
+
+	for start := 0; start < len(word); start++ {
+		end, ok := pairs[start]
+		if !ok {
+			continue
+		}
+		inner := word[start+1 : end]
+		alternatives := splitTopLevelCommas(inner)
+		if len(alternatives) < 2 {
+			seq, ok, err := braceSequence(inner)
+			if err != nil {
+				return nil, err
+			}
+			if !ok {
+				continue
+			}
+			alternatives = seq
+		}
+
+		prefix, suffix := word[:start], word[end+1:]
+		var words []string
+		for _, alt := range alternatives {
+			expanded, err := expandBraces(prefix + alt + suffix)
+			if err != nil {
+				return nil, err
+			}
+			words = append(words, expanded...)
+			if len(words) > maxBraceWords {
+				return nil, errors.New("brace expansion: too many words")
+			}
+		}
+		return words, nil
+	}
+	return []string{word}, nil
+}
+
+// splitTopLevelCommas splits s at its unquoted commas that are not inside
+// nested braces.
+func splitTopLevelCommas(s string) []string {
+	var parts []string
+	last := 0
+	braceScan(s, func(i, depth int) bool {
+		if s[i] == ',' && depth == 0 {
+			parts = append(parts, s[last:i])
+			last = i + 1
+		}
+		return true
+	})
+	return append(parts, s[last:])
+}
+
+// braceSequence expands a sequence expression: x..y or x..y..step with
+// integers (zero-padded to the same width if one of them has a leading zero)
+// or single letters. ok is false if s is no sequence.
+func braceSequence(s string) (words []string, ok bool, err error) {
+	parts := strings.Split(s, "..")
+	if len(parts) != 2 && len(parts) != 3 {
+		return nil, false, nil
+	}
+	step := 1
+	if len(parts) == 3 {
+		step, err = strconv.Atoi(parts[2])
+		if err != nil {
+			return nil, false, nil
+		}
+		if step < 0 {
+			step = -step
+		}
+		if step == 0 {
+			step = 1
+		}
+	}
+
+	from, errFrom := strconv.Atoi(parts[0])
+	to, errTo := strconv.Atoi(parts[1])
+	isLetter := func(p string) bool {
+		return len(p) == 1 && (p[0] >= 'a' && p[0] <= 'z' || p[0] >= 'A' && p[0] <= 'Z')
+	}
+	format := func(n int) string { return strconv.Itoa(n) }
+	switch {
+	case errFrom == nil && errTo == nil:
+		// {01..10}: pad to the width of the longer number
+		if hasLeadingZero(parts[0]) || hasLeadingZero(parts[1]) {
+			width := max(len(parts[0]), len(parts[1]))
+			format = func(n int) string {
+				if n < 0 {
+					return fmt.Sprintf("-%0*d", width-1, -n)
+				}
+				return fmt.Sprintf("%0*d", width, n)
+			}
+		}
+	case isLetter(parts[0]) && isLetter(parts[1]):
+		from, to = int(parts[0][0]), int(parts[1][0])
+		format = func(n int) string { return string(rune(n)) }
+	default:
+		return nil, false, nil
+	}
+
+	count := (max(from, to)-min(from, to))/step + 1
+	if count > maxBraceWords {
+		return nil, false, errors.New("brace expansion: too many words")
+	}
+	if to < from {
+		step = -step
+	}
+	for n := from; (step > 0 && n <= to) || (step < 0 && n >= to); n += step {
+		words = append(words, format(n))
+	}
+	return words, true, nil
+}
+
+// hasLeadingZero reports whether a number is written with a leading zero
+// (01, -05), which makes a sequence zero-padded.
+func hasLeadingZero(s string) bool {
+	s = strings.TrimPrefix(s, "-")
+	return len(s) > 1 && s[0] == '0'
+}

brace_test.go

@@ -0,0 +1,118 @@
+package main
+
+import (
+	"os"
+	"reflect"
+	"strings"
+	"testing"
+)
+
+func TestExpandBraces(t *testing.T) {
+	tests := []struct {
+		word string
+		want []string
+	}{
+		{"a{b,c}d", []string{"abd", "acd"}},
+		{"{a,b}{1,2}", []string{"a1", "a2", "b1", "b2"}},
+		{"x{a,{b,c}}y", []string{"xay", "xby", "xcy"}},
+		{"file{,.bak}", []string{"file", "file.bak"}},
+		{"{1..5}", []string{"1", "2", "3", "4", "5"}},
+		{"{3..1}", []string{"3", "2", "1"}},
+		{"{1..10..3}", []string{"1", "4", "7", "10"}},
+		{"{10..1..-4}", []string{"10", "6", "2"}},
+		{"{01..10..4}", []string{"01", "05", "09"}},
+		{"{8..010..1}", []string{"008", "009", "010"}},
+		{"{-2..2}", []string{"-2", "-1", "0", "1", "2"}},
+		{"{-01..1}", []string{"-01", "000", "001"}},
+		{"{a..e}", []string{"a", "b", "c", "d", "e"}},
+		{"{C..A}", []string{"C", "B", "A"}},
+		{"*.{go,md}", []string{"*.go", "*.md"}},
+		{`{"a b",c}`, []string{`"a b"`, "c"}},
+		{`{a\,b,c}`, []string{`a\,b`, "c"}},
+		{"{$HOME,~}/x", []string{"$HOME/x", "~/x"}},
+		// Not expanded: quoted, escaped, no comma, ${...}, invalid sequences
+		{`"{a,b}"`, []string{`"{a,b}"`}},
+		{`'{a,b}'`, []string{`'{a,b}'`}},
+		{`\{a,b\}`, []string{`\{a,b\}`}},
+		{"{a}", []string{"{a}"}},
+		{"{}", []string{"{}"}},
+		{"{a,b", []string{"{a,b"}},
+		{"a,b}", []string{"a,b}"}},
+		{"${HOME}", []string{"${HOME}"}},
+		{"${X:-a,b}", []string{"${X:-a,b}"}},
+		{"{a..1}", []string{"{a..1}"}},
+		{"{1..2..x}", []string{"{1..2..x}"}},
+		{"{ab..cd}", []string{"{ab..cd}"}},
+		// An invalid brace before a valid one
+		{"{a}{b,c}", []string{"{a}b", "{a}c"}},
+	}
+	for _, tc := range tests {
+		got, err := expandBraces(tc.word)
+		if err != nil {
+			t.Errorf("expandBraces(%q) returned error: %v", tc.word, err)
+			continue
+		}
+		if !reflect.DeepEqual(got, tc.want) {
+			t.Errorf("expandBraces(%q) = %q, want %q", tc.word, got, tc.want)
+		}
+	}
+
+	if _, err := expandBraces("{1..1000000}"); err == nil {
+		t.Error("expected an error for a too large sequence")
+	}
+	if _, err := expandBraces("{1..11}{1..100}{1..100}"); err == nil {
+		t.Error("expected an error for too many words")
+	}
+}
+
+func TestExpandBraceWords(t *testing.T) {
+	tests := []struct {
+		input, want string
+	}{
+		{"echo a{b,c} d", "echo ab ac d"},
+		{"echo {1..3}|wc -w", "echo 1 2 3|wc -w"},
+		{"echo a > {f}", "echo a > {f}"},
+		{"echo {a,b} 2>&1", "echo a b 2>&1"},
+		{"echo x # {a,b}", "echo x # {a,b}"},
+		{`echo "{a,b} c" {d,e}`, `echo "{a,b} c" d e`},
+	}
+	for _, tc := range tests {
+		got, err := expandBraceWords(tc.input)
+		if err != nil || got != tc.want {
+			t.Errorf("expandBraceWords(%q) = %q, %v; want %q", tc.input, got, err, tc.want)
+		}
+	}
+
+	for _, input := range []string{"echo a > {f,g}", "cat < x{1..2}", "echo a 2>> {a,b}"} {
+		if _, err := expandBraceWords(input); err == nil || !strings.Contains(err.Error(), "ambiguous redirect") {
+			t.Errorf("expandBraceWords(%q): %v, want ambiguous redirect", input, err)
+		}
+	}
+}
+
+func TestExecInput_BraceExpansion(t *testing.T) {
+	origDir, _ := os.Getwd()
+	defer os.Chdir(origDir)
+	dir := t.TempDir()
+	os.Chdir(dir)
+
+	if err := execInput("mkdir -p d/{x,y}/{1..2} && touch d/x/1/f{a,b}.txt"); err != nil {
+		t.Fatal(err)
+	}
+	for _, path := range []string{"d/x/1", "d/x/2", "d/y/1", "d/y/2", "d/x/1/fa.txt", "d/x/1/fb.txt"} {
+		if _, err := os.Stat(path); err != nil {
+			t.Errorf("%s was not created", path)
+		}
+	}
+
+	// Brace expansion comes before wildcards and variables
+	t.Setenv("GOSH_BRACE", "v")
+	execInput("echo d/x/1/*.{txt,go} {${GOSH_BRACE},w}1 > out")
+	if got, _ := os.ReadFile("out"); string(got) != "d/x/1/fa.txt d/x/1/fb.txt d/x/1/*.go v1 w1\n" {
+		t.Errorf("out = %q", got)
+	}
+
+	if err := execInput("echo a > {f,g}"); err == nil || lastStatus != 1 {
+		t.Errorf("ambiguous redirect: %v, $? = %d", err, lastStatus)
+	}
+}

go.mod

@@ -7,4 +7,4 @@ require (
 	github.com/google/shlex v0.0.0-20191202100458-e7afc7fbc510
 )
 
-require golang.org/x/sys v0.48.0 // indirect
+require golang.org/x/sys v0.48.0

jobs.go

@@ -0,0 +1,536 @@
+package main
+
+// Job control: in an interactive shell every pipeline runs in its own process
+// group, which gets the terminal while it runs in the foreground. Ctrl+Z stops
+// the foreground job, "&" starts a job in the background, and the builtins
+// jobs, fg, bg and wait manage the jobs. Without a terminal (scripts, gosh -c)
+// there is no job control, but "&" and wait still work.
+
+import (
+	"errors"
+	"fmt"
+	"io"
+	"os"
+	"os/exec"
+	"os/signal"
+	"strconv"
+	"strings"
+	"syscall"
+
+	"github.com/chzyer/readline"
+	"golang.org/x/sys/unix"
+)
+
+// proc is a stage of a job: a process, or a builtin or a stage that failed to
+// start (both without process).
+type proc struct {
+	cmd      *exec.Cmd  // nil if the stage is no process
+	done     chan error // the result of a stage without process
+	finished bool
+	stopped  bool
+	err      error
+}
+
+// job is a pipeline that was started by the shell.
+type job struct {
+	id    int    // number in the job table, 0 if not in the table
+	pgid  int    // process group, 0 without job control or processes
+	text  string // the command line
+	procs []*proc
+	tty   *readline.State // terminal modes of the job when it was stopped
+}
+
+var (
+	jobControl       bool            // job control is enabled
+	interactiveShell bool            // the shell reads commands from a user
+	ttyFd            int             // the terminal of the shell
+	shellPgid        int             // the process group of the shell
+	origPgid         int             // the foreground process group at start
+	shellTTY         *readline.State // terminal modes of the shell
+	jobTable         []*job          // background and stopped jobs
+	exitWarned       bool            // "there are stopped jobs" was shown
+)
+
+// initJobControl enables job control if stdin is a terminal: the shell moves
+// into its own process group and takes the terminal.
+func initJobControl() {
+	fd := int(os.Stdin.Fd())
+	if !readline.IsTerminal(fd) {
+		return
+	}
+	pgrp, err := unix.IoctlGetInt(fd, unix.TIOCGPGRP)
+	if err != nil {
+		return
+	}
+	pid := os.Getpid()
+	if syscall.Getpgrp() != pid {
+		if err := syscall.Setpgid(0, 0); err != nil {
+			return
+		}
+	}
+	origPgid, ttyFd, shellPgid = pgrp, fd, pid
+	if err := setForeground(pid); err != nil {
+		return
+	}
+	// Ctrl+Z must not stop the shell itself. (signal.Ignore would be
+	// inherited by the child processes.)
+	signal.Notify(make(chan os.Signal, 1), syscall.SIGTSTP)
+	jobControl = true
+}
+
+// releaseTerminal gives the terminal back to the process group that had it
+// when the shell started.
+func releaseTerminal() {
+	if jobControl && origPgid > 0 && origPgid != shellPgid {
+		setForeground(origPgid)
+	}
+}
+
+// setForeground makes pgid the foreground process group of the terminal.
+func setForeground(pgid int) error {
+	// The shell gets SIGTTOU if it does this while it is in the background
+	// (when it takes the terminal back from a job), unless the signal is
+	// ignored. It is only ignored for this call, since ignored signals are
+	// inherited by child processes.
+	signal.Ignore(syscall.SIGTTOU)
+	defer signal.Reset(syscall.SIGTTOU)
+	return unix.IoctlSetPointerInt(ttyFd, unix.TIOCSPGRP, pgid)
+}
+
+// ttyIndex returns the index of the file in fds that is the terminal of the
+// shell, or -1.
+func ttyIndex(fds [3]*os.File) int {
+	tty, err := os.Stdin.Stat()
+	if err != nil {
+		return -1
+	}
+	for i, f := range fds {
+		if info, err := f.Stat(); err == nil && os.SameFile(info, tty) {
+			return i
+		}
+	}
+	return -1
+}
+
+// finishedProc returns a proc without process that already has its result.
+func finishedProc(err error) *proc {
+	p := &proc{done: make(chan error, 1)}
+	p.done <- err
+	return p
+}
+
+// running reports whether a process of the job is running.
+func (j *job) running() bool {
+	for _, p := range j.procs {
+		if p.cmd != nil && !p.finished && !p.stopped {
+			return true
+		}
+	}
+	return false
+}
+
+// stopped reports whether the job is stopped: no process is running, but
+// one is stopped.
+func (j *job) stopped() bool {
+	if j.running() {
+		return false
+	}
+	for _, p := range j.procs {
+		if p.stopped {
+			return true
+		}
+	}
+	return false
+}
+
+// finished reports whether all stages of the job have finished.
+func (j *job) finished() bool {
+	for _, p := range j.procs {
+		if !p.finished {
+			return false
+		}
+	}
+	return true
+}
+
+// update records a status change of process pid.
+func (j *job) update(pid int, ws syscall.WaitStatus) {
+	for _, p := range j.procs {
+		if p.cmd == nil || p.cmd.Process.Pid != pid {
+			continue
+		}
+		switch {
+		case ws.Stopped():
+			p.stopped = true
+		case ws.Exited() || ws.Signaled():
+			p.finished, p.stopped = true, false
+			p.err = waitStatusError(ws)
+			p.cmd.Process.Release()
+		}
+	}
+}
+
+// waitStatusError converts the status of a finished process into an error:
+// nil for exit code 0, otherwise a statusError with the exit code, or 128+n
+// if the process was killed by signal n.
+func waitStatusError(ws syscall.WaitStatus) error {
+	switch {
+	case ws.Signaled():
+		return statusError(128 + int(ws.Signal()))
+	case ws.ExitStatus() != 0:
+		return statusError(ws.ExitStatus())
+	}
+	return nil
+}
+
+// waitFlags returns the options for wait4: WUNTRACED to see stopped
+// processes (with job control) and WNOHANG to not block.
+//
+// WCONTINUED is not used: Go's syscall.WaitStatus decodes the "continued"
+// status wrongly on FreeBSD (as killed by SIGCONT) and macOS (as stopped).
+// The shell marks jobs as running itself when it continues them (fg, bg); a
+// job continued from outside (kill -CONT) stays "Stopped" in the job table
+// until it stops again or exits.
+func waitFlags(j *job, nohang bool) int {
+	flags := 0
+	if jobControl && j.pgid != 0 {
+		flags |= syscall.WUNTRACED
+	}
+	if nohang {
+		flags |= syscall.WNOHANG
+	}
+	return flags
+}
+
+// wait waits until no process of the job is running any more (all finished
+// or, with job control, stopped). With nohang it only collects the status
+// changes that are already available and does not block.
+func (j *job) wait(nohang bool) {
+	flags := waitFlags(j, nohang)
+
+	for {
+		// With job control all processes of the job are in its process
+		// group, otherwise they are waited for one by one.
+		target := 0
+		if jobControl && j.pgid != 0 {
+			if !j.running() && !(nohang && j.stopped()) {
+				break
+			}
+			target = -j.pgid
+		} else {
+			if nohang {
+				// Check every process once
+				for _, p := range j.procs {
+					if p.cmd == nil || p.finished {
+						continue
+					}
+					var ws syscall.WaitStatus
+					if pid, err := syscall.Wait4(p.cmd.Process.Pid, &ws, flags, nil); err == nil && pid > 0 {
+						j.update(pid, ws)
+					}
+				}
+				break
+			}
+			for _, p := range j.procs {
+				if p.cmd != nil && !p.finished {
+					target = p.cmd.Process.Pid
+					break
+				}
+			}
+			if target == 0 {
+				break
+			}
+		}
+
+		var ws syscall.WaitStatus
+		pid, err := syscall.Wait4(target, &ws, flags, nil)
+		if errors.Is(err, syscall.EINTR) {
+			continue
+		}
+		if err != nil {
+			// Should not happen; do not wait forever
+			for _, p := range j.procs {
+				if p.cmd != nil && !p.finished {
+					p.finished, p.stopped = true, false
+				}
+			}
+			break
+		}
+		if pid == 0 {
+			break // nohang and nothing changed
+		}
+		j.update(pid, ws)
+	}
+
+	// Stages without process (builtins in pipelines)
+	for _, p := range j.procs {
+		if p.cmd != nil || p.finished {
+			continue
+		}
+		if nohang || j.stopped() {
+			select {
+			case p.err = <-p.done:
+				p.finished = true
+			default:
+			}
+		} else {
+			p.err = <-p.done
+			p.finished = true
+		}
+	}
+}
+
+// result returns the error of the last stage of a finished job (so $? is its
+// exit status, like in sh) and prints the errors of the other stages.
+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
+}
+
+// waitForeground waits for a job in the foreground. If it is stopped, it is
+// added to the job table.
+func waitForeground(j *job) error {
+	j.wait(false)
+	if jobControl && j.pgid != 0 {
+		setForeground(shellPgid)
+		if j.stopped() {
+			j.tty, _ = readline.GetState(ttyFd)
+		}
+		if shellTTY != nil {
+			readline.Restore(ttyFd, shellTTY)
+		}
+	}
+
+	if j.stopped() {
+		addJob(j)
+		fmt.Fprintln(os.Stderr)
+		fmt.Fprintln(os.Stderr, j.describe("Stopped"))
+		return statusError(128 + int(syscall.SIGTSTP))
+	}
+	removeJob(j)
+	j.wait(false) // wait for the builtins, if any
+	return j.result()
+}
+
+// addJob adds j to the job table (if it is not there yet) and makes it the
+// current job.
+func addJob(j *job) {
+	removeJob(j)
+	if j.id == 0 {
+		for _, other := range jobTable {
+			j.id = max(j.id, other.id)
+		}
+		j.id++
+	}
+	jobTable = append(jobTable, j)
+}
+
+// removeJob removes j from the job table.
+func removeJob(j *job) {
+	for i, other := range jobTable {
+		if other == j {
+			jobTable = append(jobTable[:i], jobTable[i+1:]...)
+			return
+		}
+	}
+}
+
+// describe formats a job for jobs and the notifications, like bash:
+// "[1]+  Stopped                 sleep 30". The current job (the last one in
+// the table, i.e. the one stopped or put into the background most recently) is
+// marked with +, the previous one with -.
+func (j *job) describe(state string) string {
+	mark := ' '
+	if n := len(jobTable); n > 0 && jobTable[n-1] == j {
+		mark = '+'
+	} else if n > 1 && jobTable[n-2] == j {
+		mark = '-'
+	}
+	text := j.text
+	if state == "Running" {
+		text += " &"
+	}
+	return fmt.Sprintf("[%d]%c  %-24s%s", j.id, mark, state, sanitize(text))
+}
+
+// state returns the state of a job for jobs and the notifications.
+func (j *job) state() string {
+	switch {
+	case j.stopped():
+		return "Stopped"
+	case !j.finished():
+		return "Running"
+	}
+	if status := exitStatus(j.procs[len(j.procs)-1].err); status != 0 {
+		return "Exit " + strconv.Itoa(status)
+	}
+	return "Done"
+}
+
+// hasStoppedJobs reports whether a job in the table is stopped.
+func hasStoppedJobs() bool {
+	for _, j := range jobTable {
+		if j.stopped() {
+			return true
+		}
+	}
+	return false
+}
+
+// reapJobs collects the status changes of the background jobs, reports
+// finished and newly stopped jobs (if notify is set) and removes finished
+// jobs from the table.
+func reapJobs(notify bool) {
+	for _, j := range append([]*job(nil), jobTable...) {
+		wasStopped := j.stopped()
+		j.wait(true)
+		switch {
+		case j.finished():
+			if notify {
+				for _, p := range j.procs {
+					printError(p.err)
+				}
+				fmt.Fprintln(os.Stderr, j.describe(j.state()))
+			}
+			removeJob(j)
+		case j.stopped() && !wasStopped:
+			addJob(j) // the current job now
+			if notify {
+				fmt.Fprintln(os.Stderr, j.describe("Stopped"))
+			}
+		}
+	}
+}
+
+// findJob returns the job for a job spec: %N or N for job N, %+, %% or nothing
+// for the current job, %- for the previous one.
+func findJob(cmd string, args []string) (*job, error) {
+	spec := "%+"
+	if len(args) > 1 {
+		spec = args[1]
+	}
+	n := len(jobTable)
+	switch spec {
+	case "%+", "%%", "%":
+		if n > 0 {
+			return jobTable[n-1], nil
+		}
+		return nil, fmt.Errorf("%s: current: no such job", cmd)
+	case "%-":
+		if n > 1 {
+			return jobTable[n-2], nil
+		}
+		return nil, fmt.Errorf("%s: previous: no such job", cmd)
+	}
+	id, err := strconv.Atoi(strings.TrimPrefix(spec, "%"))
+	if err == nil {
+		for _, j := range jobTable {
+			if j.id == id {
+				return j, nil
+			}
+		}
+	}
+	return nil, fmt.Errorf("%s: %s: no such job", cmd, sanitize(spec))
+}
+
+// continueJob sends SIGCONT to a stopped job.
+func continueJob(j *job) {
+	for _, p := range j.procs {
+		p.stopped = false
+	}
+	if j.pgid != 0 {
+		syscall.Kill(-j.pgid, syscall.SIGCONT)
+	}
+}
+
+// builtinJobs lists the jobs.
+func builtinJobs(stdout io.Writer) error {
+	for _, j := range jobTable {
+		j.wait(true)
+	}
+	for _, j := range append([]*job(nil), jobTable...) {
+		fmt.Fprintln(stdout, j.describe(j.state()))
+		if j.finished() {
+			removeJob(j)
+		}
+	}
+	return nil
+}
+
+// builtinFg continues a job in the foreground and waits for it.
+func builtinFg(args []string, stdout io.Writer) error {
+	if !jobControl {
+		return errors.New("fg: no job control")
+	}
+	j, err := findJob("fg", args)
+	if err != nil {
+		return err
+	}
+	fmt.Fprintln(stdout, sanitize(j.text))
+
+	if j.pgid != 0 {
+		shellTTY, _ = readline.GetState(ttyFd)
+		if j.stopped() && j.tty != nil {
+			readline.Restore(ttyFd, j.tty)
+		}
+		setForeground(j.pgid)
+	}
+	continueJob(j)
+	return waitForeground(j)
+}
+
+// builtinBg continues a stopped job in the background.
+func builtinBg(args []string, stdout io.Writer) error {
+	if !jobControl {
+		return errors.New("bg: no job control")
+	}
+	j, err := findJob("bg", args)
+	if err != nil {
+		return err
+	}
+	if !j.stopped() {
+		return fmt.Errorf("bg: job %d already in background", j.id)
+	}
+	continueJob(j)
+	addJob(j) // the current job now
+	fmt.Fprintln(stdout, j.describe("Running"))
+	return nil
+}
+
+// builtinWait waits for a job, or for all background jobs. Stopped jobs are
+// not waited for.
+func builtinWait(args []string) error {
+	jobs := append([]*job(nil), jobTable...)
+	if len(args) > 1 {
+		j, err := findJob("wait", args)
+		if err != nil {
+			return err
+		}
+		jobs = []*job{j}
+	}
+
+	var err error
+	for _, j := range jobs {
+		j.wait(false)
+		err = nil
+		if j.finished() {
+			removeJob(j)
+			err = j.result()
+		}
+	}
+	return err
+}
+
+// exitShell exits the shell, unless there are stopped jobs and the user was
+// not warned yet (like bash).
+func exitShell(code int) error {
+	if interactiveShell && hasStoppedJobs() && !exitWarned {
+		exitWarned = true
+		return errors.New("there are stopped jobs")
+	}
+	releaseTerminal()
+	os.Exit(code)
+	return nil
+}

jobs_linux_test.go

@@ -0,0 +1,204 @@
+package main
+
+import (
+	"bytes"
+	"os"
+	"os/exec"
+	"strconv"
+	"strings"
+	"sync"
+	"syscall"
+	"testing"
+	"time"
+
+	"golang.org/x/sys/unix"
+)
+
+// openPty opens a new pseudo terminal and returns the master and slave side.
+func openPty(t *testing.T) (*os.File, *os.File) {
+	t.Helper()
+	master, err := os.OpenFile("/dev/ptmx", os.O_RDWR, 0)
+	if err != nil {
+		t.Skipf("no pty available: %v", err)
+	}
+	if err := unix.IoctlSetPointerInt(int(master.Fd()), unix.TIOCSPTLCK, 0); err != nil {
+		t.Fatal(err)
+	}
+	n, err := unix.IoctlGetInt(int(master.Fd()), unix.TIOCGPTN)
+	if err != nil {
+		t.Fatal(err)
+	}
+	slave, err := os.OpenFile("/dev/pts/"+strconv.Itoa(n), os.O_RDWR|syscall.O_NOCTTY, 0)
+	if err != nil {
+		t.Fatal(err)
+	}
+	return master, slave
+}
+
+// ptyShell is the shell running on a pseudo terminal.
+type ptyShell struct {
+	t      *testing.T
+	master *os.File
+	mu     sync.Mutex
+	out    bytes.Buffer
+	cmd    *exec.Cmd
+}
+
+func startPtyShell(t *testing.T) *ptyShell {
+	bin := buildShell(t)
+	master, slave := openPty(t)
+	cmd := exec.Command(bin, "--norc")
+	cmd.Stdin, cmd.Stdout, cmd.Stderr = slave, slave, slave
+	cmd.Env = append(os.Environ(), "NO_COLOR=1")
+	// New session with the pty as controlling terminal, like a terminal
+	// emulator does
+	cmd.SysProcAttr = &syscall.SysProcAttr{Setsid: true, Setctty: true, Ctty: 0}
+	if err := cmd.Start(); err != nil {
+		t.Fatal(err)
+	}
+	slave.Close()
+
+	s := &ptyShell{t: t, master: master, cmd: cmd}
+	go func() {
+		buf := make([]byte, 4096)
+		for {
+			n, err := master.Read(buf)
+			s.mu.Lock()
+			s.out.Write(buf[:n])
+			s.mu.Unlock()
+			if err != nil {
+				return
+			}
+		}
+	}()
+	t.Cleanup(func() {
+		cmd.Process.Kill()
+		cmd.Wait()
+		master.Close()
+	})
+	s.expect("$ ")
+	return s
+}
+
+func (s *ptyShell) send(text string) {
+	s.master.WriteString(text)
+}
+
+// expect waits until want appears in the output after the position of the
+// last match and consumes the output up to it.
+func (s *ptyShell) expect(want string) {
+	s.t.Helper()
+	deadline := time.Now().Add(5 * time.Second)
+	for time.Now().Before(deadline) {
+		s.mu.Lock()
+		out := s.out.String()
+		if i := strings.Index(out, want); i >= 0 {
+			s.out.Next(i + len(want))
+			s.mu.Unlock()
+			return
+		}
+		s.mu.Unlock()
+		time.Sleep(20 * time.Millisecond)
+	}
+	s.mu.Lock()
+	defer s.mu.Unlock()
+	s.t.Fatalf("timeout waiting for %q, output:\n%s", want, s.out.String())
+}
+
+func TestWaitFlags_NoWCONTINUED(t *testing.T) {
+	defer func(saved bool) { jobControl = saved }(jobControl)
+	jobControl = true
+	j := &job{pgid: 1}
+	for _, nohang := range []bool{false, true} {
+		flags := waitFlags(j, nohang)
+		if flags&syscall.WCONTINUED != 0 {
+			t.Errorf("waitFlags(nohang=%v) contains WCONTINUED, which Go decodes wrongly on BSD", nohang)
+		}
+		if flags&syscall.WUNTRACED == 0 {
+			t.Errorf("waitFlags(nohang=%v) misses WUNTRACED", nohang)
+		}
+	}
+}
+
+func TestJobControl(t *testing.T) {
+	s := startPtyShell(t)
+
+	// Ctrl+Z stops the foreground job, the shell gets the terminal back
+	s.send("sleep 30\n")
+	time.Sleep(300 * time.Millisecond)
+	s.send("\x1a")
+	s.expect("[1]+  Stopped                 sleep 30")
+	s.send("jobs\n")
+	s.expect("[1]+  Stopped                 sleep 30")
+
+	// bg continues it in the background
+	s.send("bg\n")
+	s.expect("[1]+  Running                 sleep 30 &")
+
+	// After bg the job keeps running and is not reported as finished
+	// (regression: on FreeBSD the "continued" status was read as killed by
+	// SIGCONT, "Exit 147")
+	time.Sleep(300 * time.Millisecond)
+	s.send("jobs\n")
+	s.expect("[1]+  Running                 sleep 30 &")
+
+	// fg brings it back, Ctrl+C reaches only the job
+	s.send("fg %1\n")
+	s.expect("sleep 30")
+	time.Sleep(300 * time.Millisecond)
+	s.send("\x03")
+	s.send("echo status=$?\n")
+	s.expect("status=130")
+
+	// A pipeline is stopped and continued as a whole
+	s.send("sleep 30 | cat\n")
+	time.Sleep(300 * time.Millisecond)
+	s.send("\x1a")
+	s.expect("Stopped                 sleep 30 | cat")
+	s.send("fg\n")
+	time.Sleep(300 * time.Millisecond)
+	s.send("\x03")
+	s.send("echo pipeline=$?\n")
+	s.expect("pipeline=130")
+
+	// A background job that reads from the terminal is stopped (SIGTTIN),
+	// in the foreground it gets the input
+	s.send("cat &\n")
+	s.expect("[1] ")
+	time.Sleep(300 * time.Millisecond)
+	s.send("echo next\n")
+	s.expect("[1]+  Stopped                 cat")
+	s.send("fg\n")
+	time.Sleep(300 * time.Millisecond)
+	s.send("hello cat\n")
+	s.expect("hello cat\r\nhello cat")
+	s.send("\x04")
+	s.send("echo cat=$?\n")
+	s.expect("cat=0")
+
+	// Finished background jobs are reported before the next prompt
+	s.send("sleep 0.2 &\n")
+	time.Sleep(500 * time.Millisecond)
+	s.send("echo tick\n")
+	s.expect("Done                    sleep 0.2")
+
+	// exit warns about stopped jobs once
+	s.send("sleep 30\n")
+	time.Sleep(300 * time.Millisecond)
+	s.send("\x1a")
+	s.expect("Stopped")
+	s.send("exit\n")
+	s.expect("there are stopped jobs")
+	s.send("exit 0\n")
+
+	done := make(chan error, 1)
+	go func() { done <- s.cmd.Wait() }()
+	select {
+	case err := <-done:
+		if err != nil {
+			t.Errorf("shell exited with %v", err)
+		}
+	case <-time.After(5 * time.Second):
+		t.Fatal("shell did not exit")
+	}
+}

parser.go

@@ -0,0 +1,841 @@
+package main
+
+// Parser and executor for command lines and scripts: lists (; & && || and
+// newlines), pipelines, ! and the control structures if, for, while and
+// until. 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.
+
+import (
+	"errors"
+	"fmt"
+	"os"
+	"strconv"
+	"strings"
+	"syscall"
+)
+
+// incompleteError is returned by parse if the input ends inside a
+// construct (if without fi, an open quote, a trailing && ...): an
+// interactive shell then reads another line.
+type incompleteError struct{}
+
+func (incompleteError) Error() string { return "syntax error: unexpected end of input" }
+
+var errIncomplete error = incompleteError{}
+
+// loopControl is returned by break and continue and ends the given number of
+// enclosing loops (break) or iterations (continue).
+type loopControl struct {
+	isBreak bool
+	n       int
+}
+
+func (c loopControl) Error() string {
+	if c.isBreak {
+		return "break"
+	}
+	return "continue"
+}
+
+// loopDepth is the number of loops that are currently running.
+var loopDepth int
+
+// aliasExpansion is false while the result of an alias expansion runs, so
+// that it is not expanded again.
+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}
+
+// ---------------------------------------------------------------------------
+// Lexer
+
+type tokenKind int
+
+const (
+	tWord tokenKind = iota
+	tOp             // ; & && || | or newline
+)
+
+type rawToken struct {
+	kind       tokenKind
+	text       string
+	start, end int
+}
+
+// joinContinuationLines removes backslash-newline (outside single quotes),
+// which continues a line. continued reports whether src ends with such a
+// continuation (so that the command goes on in the next line).
+func joinContinuationLines(src string) (joined string, continued bool) {
+	if !strings.Contains(src, "\\\n") {
+		return src, false
+	}
+	var b strings.Builder
+	var quote byte
+	for i := 0; i < len(src); i++ {
+		ch := src[i]
+		switch {
+		case quote == '\'':
+			if ch == '\'' {
+				quote = 0
+			}
+		case ch == '\\' && i+1 < len(src):
+			if src[i+1] == '\n' {
+				i++
+				continued = i == len(src)-1
+				continue
+			}
+			continued = false
+			b.WriteByte(ch)
+			i++
+			ch = src[i]
+		case ch == '"':
+			if quote == '"' {
+				quote = 0
+			} else {
+				quote = '"'
+			}
+		case ch == '\'' && quote == 0:
+			quote = '\''
+		}
+		if ch != '\n' && ch != ' ' && ch != '\t' {
+			continued = false
+		}
+		b.WriteByte(ch)
+	}
+	return b.String(), continued
+}
+
+// lex splits src into words and list operators. Words keep their quotes,
+// escapes, $(...) and redirections; they are only split at blanks and list
+// operators.
+func lex(src string) ([]rawToken, error) {
+	var toks []rawToken
+	op := func(text string, i int) {
+		toks = append(toks, rawToken{tOp, text, i, i + len(text)})
+	}
+	for i := 0; i < len(src); {
+		ch := src[i]
+		next := byte(0)
+		if i+1 < len(src) {
+			next = src[i+1]
+		}
+		switch {
+		case ch == ' ' || ch == '\t':
+			i++
+		case ch == '\n' || ch == ';':
+			op(string(ch), i)
+			i++
+		case ch == '#':
+			// Comment until the end of the line
+			for i < len(src) && src[i] != '\n' {
+				i++
+			}
+		case ch == '|' && next == '|', ch == '&' && next == '&':
+			op(src[i:i+2], i)
+			i += 2
+		case ch == '|', ch == '&' && next != '>':
+			op(string(ch), i)
+			i++
+		default:
+			end, err := lexWord(src, i)
+			if err != nil {
+				return nil, err
+			}
+			toks = append(toks, rawToken{tWord, src[i:end], i, end})
+			i = end
+		}
+	}
+	return toks, nil
+}
+
+// lexWord returns the end of the word that starts at src[i].
+func lexWord(src string, i int) (int, error) {
+	var quote byte
+	for j := i; j < len(src); j++ {
+		ch := src[j]
+		switch {
+		case quote == '\'':
+			if ch == '\'' {
+				quote = 0
+			}
+		case ch == '\\':
+			if j+1 == len(src) {
+				return 0, errIncomplete
+			}
+			j++
+		case isSubstStart(src, j):
+			end := substEnd(src, j)
+			if end < 0 {
+				return 0, errIncomplete
+			}
+			j = end
+		case ch == '$' && j+1 < len(src) && src[j+1] == '{':
+			if k := strings.IndexByte(src[j:], '}'); k >= 0 {
+				j += k
+			}
+		case quote == '"':
+			if ch == '"' {
+				quote = 0
+			}
+		case ch == '"' || ch == '\'':
+			quote = ch
+		case ch == ' ' || ch == '\t' || ch == '\n' || ch == ';' || ch == '|':
+			return j, nil
+		case ch == '&':
+			// &>, >& and <& are redirections, not the & operator
+			if !(j+1 < len(src) && src[j+1] == '>') && !(j > i && (src[j-1] == '>' || src[j-1] == '<')) {
+				return j, nil
+			}
+		}
+	}
+	if quote != 0 {
+		return 0, errIncomplete
+	}
+	return len(src), nil
+}
+
+// ---------------------------------------------------------------------------
+// Syntax tree
+
+// node is a command that can be executed: it returns the error of the last
+// command it ran (so that exitStatus gives its status).
+type node interface {
+	exec() error
+}
+
+// listNode is a list of and-or lists separated by ;, & or newlines.
+type listNode struct {
+	items []listEntry
+}
+
+type listEntry struct {
+	andOr      *andOrNode
+	background bool
+}
+
+// andOrNode is a pipeline followed by && and || pipelines.
+type andOrNode struct {
+	first *pipelineNode
+	rest  []andOrPart
+}
+
+type andOrPart struct {
+	op       string // && or ||
+	pipeline *pipelineNode
+}
+
+// pipelineNode is a simple command (whose text may contain a pipeline) or a
+// control structure, optionally negated with !.
+type pipelineNode struct {
+	negate bool
+	cmd    node
+}
+
+// simpleNode is the text of a pipeline of simple commands.
+type simpleNode struct {
+	text string
+}
+
+type ifNode struct {
+	conds    []*listNode
+	bodies   []*listNode
+	elseBody *listNode
+}
+
+type forNode struct {
+	name  string
+	words string // the words after "in", expanded when the loop starts
+	hasIn bool
+	body  *listNode
+}
+
+type whileNode struct {
+	until bool
+	cond  *listNode
+	body  *listNode
+}
+
+// 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 {
+		return nil
+	}
+	ao := l.items[0].andOr
+	if len(ao.rest) > 0 || ao.first.negate {
+		return nil
+	}
+	s, _ := ao.first.cmd.(*simpleNode)
+	return s
+}
+
+// ---------------------------------------------------------------------------
+// Parser
+
+type parser struct {
+	src  string
+	toks []rawToken
+	pos  int
+}
+
+// parse parses a command line or script. It returns errIncomplete if the
+// input ends inside a construct.
+func parse(src string) (*listNode, error) {
+	src, continued := joinContinuationLines(src)
+	if continued {
+		return nil, errIncomplete
+	}
+	toks, err := lex(src)
+	if err != nil {
+		return nil, err
+	}
+	p := &parser{src: src, toks: toks}
+	list, err := p.parseList(nil)
+	if err != nil {
+		return nil, err
+	}
+	if t := p.peek(); t != nil {
+		return nil, p.unexpected(t)
+	}
+	return list, nil
+}
+
+func (p *parser) peek() *rawToken {
+	if p.pos < len(p.toks) {
+		return &p.toks[p.pos]
+	}
+	return nil
+}
+
+func (p *parser) peekWord(words ...string) bool {
+	t := p.peek()
+	if t == nil || t.kind != tWord {
+		return false
+	}
+	for _, w := range words {
+		if t.text == w {
+			return true
+		}
+	}
+	return false
+}
+
+func (p *parser) skipNewlines() {
+	for t := p.peek(); t != nil && t.kind == tOp && t.text == "\n"; t = p.peek() {
+		p.pos++
+	}
+}
+
+func (p *parser) unexpected(t *rawToken) error {
+	if t.text == "\n" {
+		return syntaxError("newline")
+	}
+	return syntaxError(t.text)
+}
+
+// expect consumes the reserved word w.
+func (p *parser) expect(w string) error {
+	t := p.peek()
+	if t == nil {
+		return errIncomplete
+	}
+	if t.kind != tWord || t.text != w {
+		return p.unexpected(t)
+	}
+	p.pos++
+	return nil
+}
+
+// parseList parses and-or lists until the end of the input or one of the
+// reserved words in terms at the start of a command.
+func (p *parser) parseList(terms map[string]bool) (*listNode, error) {
+	list := &listNode{}
+	for {
+		p.skipNewlines()
+		t := p.peek()
+		if t == nil || t.kind == tWord && terms[t.text] {
+			return list, nil
+		}
+		ao, err := p.parseAndOr()
+		if err != nil {
+			return nil, err
+		}
+		entry := listEntry{andOr: ao}
+
+		t = p.peek()
+		switch {
+		case t == nil:
+		case t.kind == tOp && (t.text == ";" || t.text == "&" || t.text == "\n"):
+			p.pos++
+			entry.background = t.text == "&"
+		case t.kind == tWord && terms[t.text]:
+			// e.g. "fi" right after the end of a nested control structure
+		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)
+	}
+}
+
+// nonEmpty returns an error if a list that must contain commands is empty.
+func (p *parser) nonEmpty(list *listNode) error {
+	if len(list.items) > 0 {
+		return nil
+	}
+	if t := p.peek(); t != nil {
+		return p.unexpected(t)
+	}
+	return errIncomplete
+}
+
+func (p *parser) parseAndOr() (*andOrNode, error) {
+	first, err := p.parsePipeline()
+	if err != nil {
+		return nil, err
+	}
+	ao := &andOrNode{first: first}
+	for {
+		t := p.peek()
+		if t == nil || t.kind != tOp || (t.text != "&&" && t.text != "||") {
+			return ao, nil
+		}
+		p.pos++
+		p.skipNewlines()
+		if p.peek() == nil {
+			return nil, errIncomplete
+		}
+		next, err := p.parsePipeline()
+		if err != nil {
+			return nil, err
+		}
+		ao.rest = append(ao.rest, andOrPart{op: t.text, pipeline: next})
+	}
+}
+
+func (p *parser) parsePipeline() (*pipelineNode, error) {
+	pl := &pipelineNode{}
+	if p.peekWord("!") {
+		pl.negate = true
+		p.pos++
+	}
+	t := p.peek()
+	if t == nil {
+		return nil, errIncomplete
+	}
+	if t.kind == tOp || terminators[t.text] {
+		return nil, p.unexpected(t)
+	}
+
+	var err error
+	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)
+			}
+		}
+	}
+	return pl, nil
+}
+
+// parseSimple parses a pipeline of simple commands 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() {
+		if t.kind == tWord {
+			end = t.end
+			p.pos++
+			continue
+		}
+		if t.text != "|" {
+			break
+		}
+		p.pos++
+		end = t.end
+		p.skipNewlines()
+		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
+}
+
+func (p *parser) parseIf() (*ifNode, error) {
+	p.pos++ // if
+	n := &ifNode{}
+	for {
+		cond, err := p.parseList(map[string]bool{"then": true})
+		if err == nil {
+			err = p.nonEmpty(cond)
+		}
+		if err == nil {
+			err = p.expect("then")
+		}
+		if err != nil {
+			return nil, err
+		}
+		body, err := p.parseList(map[string]bool{"elif": true, "else": true, "fi": true})
+		if err == nil {
+			err = p.nonEmpty(body)
+		}
+		if err != nil {
+			return nil, err
+		}
+		n.conds = append(n.conds, cond)
+		n.bodies = append(n.bodies, body)
+
+		t := p.peek()
+		if t == nil {
+			return nil, errIncomplete
+		}
+		p.pos++
+		switch t.text {
+		case "elif":
+			continue
+		case "else":
+			body, err := p.parseList(map[string]bool{"fi": true})
+			if err == nil {
+				err = p.nonEmpty(body)
+			}
+			if err == nil {
+				err = p.expect("fi")
+			}
+			if err != nil {
+				return nil, err
+			}
+			n.elseBody = body
+		}
+		return n, nil // fi
+	}
+}
+
+func (p *parser) parseFor() (*forNode, error) {
+	p.pos++ // for
+	t := p.peek()
+	if t == nil {
+		return nil, errIncomplete
+	}
+	if t.kind != tWord || !isVarName(t.text) {
+		return nil, fmt.Errorf("for: `%s': not a valid identifier", sanitize(t.text))
+	}
+	n := &forNode{name: t.text}
+	p.pos++
+
+	p.skipNewlines()
+	if p.peekWord("in") {
+		p.pos++
+		n.hasIn = true
+		var words []string
+		for t := p.peek(); t != nil && t.kind == tWord; t = p.peek() {
+			words = append(words, t.text)
+			p.pos++
+		}
+		n.words = strings.Join(words, " ")
+	}
+	t = p.peek()
+	switch {
+	case t == nil:
+		return nil, errIncomplete
+	case t.kind == tOp && (t.text == ";" || t.text == "\n"):
+		p.pos++
+	case !n.hasIn && t.kind == tWord && t.text == "do":
+	default:
+		return nil, p.unexpected(t)
+	}
+
+	p.skipNewlines()
+	body, err := p.parseLoopBody()
+	if err != nil {
+		return nil, err
+	}
+	n.body = body
+	return n, nil
+}
+
+func (p *parser) parseWhile() (*whileNode, error) {
+	n := &whileNode{until: p.peek().text == "until"}
+	p.pos++
+	cond, err := p.parseList(map[string]bool{"do": true})
+	if err == nil {
+		err = p.nonEmpty(cond)
+	}
+	if err != nil {
+		return nil, err
+	}
+	n.cond = cond
+	body, err := p.parseLoopBody()
+	if err != nil {
+		return nil, err
+	}
+	n.body = body
+	return n, nil
+}
+
+// parseLoopBody parses "do list done".
+func (p *parser) parseLoopBody() (*listNode, error) {
+	if err := p.expect("do"); err != nil {
+		return nil, err
+	}
+	body, err := p.parseList(map[string]bool{"done": true})
+	if err == nil {
+		err = p.nonEmpty(body)
+	}
+	if err == nil {
+		err = p.expect("done")
+	}
+	return body, err
+}
+
+// ---------------------------------------------------------------------------
+// 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
+// bash, Ctrl+C aborts the whole command line, e.g. a loop).
+func isAbort(err error) bool {
+	var lc loopControl
+	return errors.As(err, &lc) || exitStatus(err) == 128+int(syscall.SIGINT)
+}
+
+// silent returns an error with only the exit status of err, for errors that
+// were already reported.
+func silent(err error) error {
+	if err == nil {
+		return nil
+	}
+	return statusError(exitStatus(err))
+}
+
+func (l *listNode) exec() error {
+	var err error
+	for _, entry := range l.items {
+		printError(err)
+		if entry.background {
+			err = entry.andOr.first.cmd.(*simpleNode).run(true)
+		} else {
+			err = entry.andOr.exec()
+		}
+		lastStatus = exitStatus(err)
+		if isAbort(err) {
+			return err
+		}
+	}
+	return err
+}
+
+func (a *andOrNode) exec() error {
+	err := a.first.exec()
+	for _, part := range a.rest {
+		lastStatus = exitStatus(err)
+		if isAbort(err) {
+			return err
+		}
+		if (part.op == "&&") != (lastStatus == 0) {
+			continue
+		}
+		printError(err)
+		err = part.pipeline.exec()
+	}
+	return err
+}
+
+func (pl *pipelineNode) exec() error {
+	err := pl.cmd.exec()
+	if !pl.negate || isAbort(err) {
+		return err
+	}
+	printError(err)
+	if exitStatus(err) == 0 {
+		return statusError(1)
+	}
+	return nil
+}
+
+func (s *simpleNode) exec() error {
+	return s.run(false)
+}
+
+// run executes the simple command, in the background if background is set.
+// Aliases are expanded here (in interactive shells), so that they work at
+// the start of every command, also inside control structures.
+func (s *simpleNode) run(background bool) error {
+	text := s.text
+	if interactiveShell && aliasExpansion {
+		if expanded := expandAliases(text); expanded != text {
+			tree, err := parse(expanded)
+			if err != nil {
+				return err
+			}
+			if simple := tree.singleSimple(); simple != nil {
+				text = simple.text
+			} else {
+				if background {
+					return errors.New("an alias with a command list cannot run in the background")
+				}
+				aliasExpansion = false
+				defer func() { aliasExpansion = true }()
+				return tree.exec()
+			}
+		}
+	}
+	return execCommand(text, background)
+}
+
+func (n *ifNode) exec() error {
+	for i, cond := range n.conds {
+		err := cond.exec()
+		if isAbort(err) {
+			return err
+		}
+		printError(err)
+		if exitStatus(err) == 0 {
+			return n.bodies[i].exec()
+		}
+	}
+	if n.elseBody != nil {
+		return n.elseBody.exec()
+	}
+	lastStatus = 0
+	return nil
+}
+
+// runLoopBody runs one iteration of a loop. It returns whether the loop
+// must stop, and the error to return from the loop.
+func runLoopBody(body *listNode, result *error) (stop bool, err error) {
+	err = body.exec()
+	var lc loopControl
+	if errors.As(err, &lc) {
+		*result = nil
+		if lc.n > 1 {
+			lc.n--
+			return true, lc // ends an outer loop too
+		}
+		return lc.isBreak, nil
+	}
+	if isAbort(err) {
+		return true, err
+	}
+	printError(err)
+	*result = silent(err)
+	return false, nil
+}
+
+func (n *whileNode) exec() error {
+	loopDepth++
+	defer func() { loopDepth-- }()
+
+	var result error
+	for {
+		err := n.cond.exec()
+		if isAbort(err) {
+			return err
+		}
+		printError(err)
+		if (exitStatus(err) == 0) == n.until {
+			break
+		}
+		if stop, err := runLoopBody(n.body, &result); stop {
+			if err != nil {
+				return err
+			}
+			break
+		}
+	}
+	lastStatus = exitStatus(result)
+	return result
+}
+
+func (n *forNode) exec() error {
+	var words []string
+	if n.hasIn {
+		var err error
+		if words, err = expandWordList(n.words); err != nil {
+			return err
+		}
+	}
+
+	loopDepth++
+	defer func() { loopDepth-- }()
+
+	var result error
+	for _, word := range words {
+		os.Setenv(n.name, word)
+		if stop, err := runLoopBody(n.body, &result); stop {
+			if err != nil {
+				return err
+			}
+			break
+		}
+	}
+	lastStatus = exitStatus(result)
+	return result
+}
+
+// expandWordList expands the words of a for loop like the arguments of a
+// command (braces, ~, variables, $(...), wildcards).
+func expandWordList(text string) ([]string, error) {
+	text, err := expandBraceWords(text)
+	if err != nil {
+		return nil, err
+	}
+	tokens, err := tokenize(text)
+	if err != nil {
+		return nil, fmt.Errorf("invalid input: %w", err)
+	}
+	var words []string
+	for _, t := range tokens {
+		if t.op != "" {
+			return nil, syntaxError(t.op)
+		}
+		words = append(words, expandWord(t)...)
+	}
+	return words, nil
+}
+
+// builtinLoopControl implements break [n] and continue [n].
+func builtinLoopControl(args []string) error {
+	n := 1
+	if len(args) > 1 {
+		var err error
+		if n, err = strconv.Atoi(args[1]); err != nil || n < 1 {
+			return fmt.Errorf("%s: %s: loop count out of range", args[0], sanitize(args[1]))
+		}
+	}
+	if loopDepth == 0 {
+		return fmt.Errorf("%s: only meaningful in a loop", args[0])
+	}
+	return loopControl{isBreak: args[0] == "break", n: min(n, loopDepth)}
+}

parser_test.go

@@ -0,0 +1,164 @@
+package main
+
+import (
+	"os"
+	"strings"
+	"testing"
+)
+
+// runIn runs input in a temporary directory and returns the content of the
+// file "out" there.
+func runIn(t *testing.T, input string) string {
+	t.Helper()
+	origDir, _ := os.Getwd()
+	defer os.Chdir(origDir)
+	os.Chdir(t.TempDir())
+	execInput(input)
+	data, _ := os.ReadFile("out")
+	return string(data)
+}
+
+func TestExec_If(t *testing.T) {
+	tests := []struct {
+		input string
+		want  string
+	}{
+		{"if true; then echo yes >> out; fi", "yes\n"},
+		{"if false; then echo yes >> out; fi", ""},
+		{"if false; then echo a >> out; else echo b >> out; fi", "b\n"},
+		{"if false; then echo a >> out; elif true; then echo b >> out; else echo c >> out; fi", "b\n"},
+		{"if false; then echo a >> out; elif false; then echo b >> out; else echo c >> out; fi", "c\n"},
+		{"if ! false; then echo negated >> out; fi", "negated\n"},
+		{"if true && false; then echo a >> out; else echo b >> out; fi", "b\n"},
+		{"if false || true; then echo a >> out; fi", "a\n"},
+		{"if echo cond >> out; then echo body >> out; fi", "cond\nbody\n"},
+		{"if true\nthen\n  echo multi >> out\n  echo line >> out\nfi", "multi\nline\n"},
+		{"if true; then if false; then echo a >> out; else echo nested >> out; fi; fi", "nested\n"},
+		{"if [ -d / ]; then echo dir >> out; fi", "dir\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_Loops(t *testing.T) {
+	defer os.Unsetenv("GOSH_I")
+	tests := []struct {
+		input string
+		want  string
+	}{
+		{"for x in a b c; do echo $x >> out; done", "a\nb\nc\n"},
+		{"for x in {1..3}; do echo $x >> out; done", "1\n2\n3\n"},
+		{"for x in $(echo a b); do echo $x >> out; done", "a\nb\n"},
+		{"for x in \"a b\" c; do echo $x >> out; done", "a b\nc\n"},
+		{"touch f1 f2; for f in f*; do echo $f >> out; done", "f1\nf2\n"},
+		{"for x in; do echo never >> out; done", ""},
+		{"for x; do echo never >> out; done", ""},
+		{"set GOSH_I=0; while [ $GOSH_I -lt 3 ]; do echo $GOSH_I >> out; set GOSH_I=$(expr $GOSH_I + 1); done", "0\n1\n2\n"},
+		{"set GOSH_I=3; until [ $GOSH_I -eq 0 ]; do echo $GOSH_I >> out; set GOSH_I=$(expr $GOSH_I - 1); done", "3\n2\n1\n"},
+		{"while false; do echo never >> out; done", ""},
+		// The loop variable keeps the last value
+		{"for GOSH_I in a b; do :; done; echo $GOSH_I > out", "b\n"},
+		// break and continue
+		{"for x in 1 2 3 4; do if [ $x = 3 ]; then break; fi; echo $x >> out; done", "1\n2\n"},
+		{"for x in 1 2 3; do if [ $x = 2 ]; then continue; fi; echo $x >> out; done", "1\n3\n"},
+		{"for a in 1 2; do for b in x y; do if [ $b = y ]; then continue 2; fi; echo $a$b >> out; done; done", "1x\n2x\n"},
+		{"for a in 1 2; do for b in x y; do echo $a$b >> out; break 2; done; done", "1x\n"},
+		{"for a in 1 2; do for b in x y; do echo $a$b >> out; break 5; done; done", "1x\n"},
+		{"while true; do echo once >> out; break; done", "once\n"},
+		{"for x in 1 2; do echo $x >> out; break; echo never >> out; done; echo after >> out", "1\nafter\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 loopDepth != 0 {
+		t.Errorf("loopDepth = %d after the loops", loopDepth)
+	}
+}
+
+func TestExec_Status(t *testing.T) {
+	tests := []struct {
+		input  string
+		status int
+	}{
+		{"if false; then :; fi", 0},
+		{"if true; then false; fi", 1},
+		{"if false; then :; else sh -c 'exit 3'; fi", 3},
+		{"for x in a; do false; done", 1},
+		{"for x in a; do false; done; true", 0},
+		{"for x in; do false; done", 0},
+		{"while false; do :; done", 0},
+		{"for x in a b; do sh -c 'exit 4'; break; done", 0},
+		{"! true", 1},
+		{"! false", 0},
+		{"! gosh-no-such-command", 0},
+		{":", 0},
+		{"break", 1},
+		{"continue", 1},
+		{"for x in a; do break x; done", 1},
+		{"if a; then", 2},
+		{"fi", 2},
+	}
+	for _, tc := range tests {
+		runIn(t, tc.input)
+		if lastStatus != tc.status {
+			t.Errorf("%q: $? = %d, want %d", tc.input, lastStatus, tc.status)
+		}
+	}
+	if err := execInput("break"); err == nil || err.Error() != "break: only meaningful in a loop" {
+		t.Errorf("break outside a loop: %v", err)
+	}
+}
+
+func TestRunScript_MultiLine(t *testing.T) {
+	origDir, _ := os.Getwd()
+	defer os.Chdir(origDir)
+	os.Chdir(t.TempDir())
+
+	script := `# a script with control structures
+for x in a b
+do
+  if [ $x = a ]; then
+    echo first >> out
+  else
+    echo second >> out
+  fi
+done
+echo continued \
+  line >> out
+`
+	if status := runScript(strings.NewReader(script), ""); status != 0 {
+		t.Errorf("status = %d", status)
+	}
+	if got, _ := os.ReadFile("out"); string(got) != "first\nsecond\ncontinued line\n" {
+		t.Errorf("out = %q", got)
+	}
+
+	// A script that ends inside a control structure is a syntax error
+	if status := runScript(strings.NewReader("echo ok >> out2\nif true; then\n  echo never >> out2\n"), ""); status != 2 {
+		t.Errorf("status = %d for an unterminated if, want 2", status)
+	}
+	if got, _ := os.ReadFile("out2"); string(got) != "ok\n" {
+		t.Errorf("out2 = %q", got)
+	}
+}
+
+func TestExec_AliasesInControlStructures(t *testing.T) {
+	withAliases(t, map[string]string{"say": "echo said", "both": "echo one >> out; echo two"})
+	defer func(saved bool) { interactiveShell = saved }(interactiveShell)
+	interactiveShell = true
+
+	if got := runIn(t, "for x in a b; do say $x >> out; done"); got != "said a\nsaid b\n" {
+		t.Errorf("alias in for: out = %q", got)
+	}
+	if got := runIn(t, "if true; then both >> out; fi"); got != "one\ntwo\n" {
+		t.Errorf("alias with a list in if: out = %q", got)
+	}
+	if got := runIn(t, "if say x > out; then :; fi"); got != "said x\n" {
+		t.Errorf("alias in condition: out = %q", got)
+	}
+}

subst.go

@@ -0,0 +1,98 @@
+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.
+
+import (
+	"bytes"
+	"errors"
+	"os"
+	"os/exec"
+	"strings"
+	"syscall"
+)
+
+// subshellPath is the gosh binary used for command substitution; empty means
+// the running executable. Tests set it, since there the running executable is
+// the test binary.
+var subshellPath string
+
+// substStatus is the exit status of the last command substitution of the
+// current command (a command that consists only of a substitution has this
+// status, like in sh).
+var substStatus int
+
+// isSubstStart reports whether a command substitution $( starts at s[i].
+func isSubstStart(s string, i int) bool {
+	return s[i] == '$' && i+1 < len(s) && s[i+1] == '('
+}
+
+// substEnd returns the index of the ) that ends the command substitution
+// starting with $( at s[i], or -1 if it is not terminated. Quotes, escapes
+// and nested substitutions inside are taken into account.
+func substEnd(s string, i int) int {
+	depth := 0
+	var quote byte
+	for j := i + 1; j < len(s); j++ {
+		ch := s[j]
+		switch {
+		case quote == '\'':
+			if ch == '\'' {
+				quote = 0
+			}
+		case ch == '\\':
+			j++
+		case quote == '"':
+			if ch == '"' {
+				quote = 0
+			} else if isSubstStart(s, j) {
+				end := substEnd(s, j)
+				if end < 0 {
+					return -1
+				}
+				j = end
+			}
+		case ch == '"' || ch == '\'':
+			quote = ch
+		case ch == '(':
+			depth++
+		case ch == ')':
+			depth--
+			if depth == 0 {
+				return j
+			}
+		}
+	}
+	return -1
+}
+
+// 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) {
+	if strings.HasPrefix(command, "(") {
+		return "", errors.New("arithmetic expansion $((...)) is not supported")
+	}
+	path := subshellPath
+	if path == "" {
+		var err error
+		if path, err = os.Executable(); err != nil {
+			return "", err
+		}
+	}
+
+	var out bytes.Buffer
+	cmd := exec.Command(path, "-c", command)
+	cmd.Stdin, cmd.Stdout, cmd.Stderr = os.Stdin, &out, os.Stderr
+	err := cmd.Run()
+	substStatus = exitStatus(err)
+	if substStatus == 128+int(syscall.SIGINT) {
+		// Ctrl+C aborts the whole command, like in bash
+		return "", statusError(substStatus)
+	}
+	var exitErr *exec.ExitError
+	if err != nil && !errors.As(err, &exitErr) {
+		return "", err
+	}
+	return strings.TrimRight(out.String(), "\n"), nil
+}

subst_test.go

@@ -0,0 +1,104 @@
+package main
+
+import (
+	"os"
+	"testing"
+)
+
+func TestSubstEnd(t *testing.T) {
+	tests := []struct {
+		s    string
+		want int
+	}{
+		{"$(echo a)", 8},
+		{"$(echo a) b", 8},
+		{"$(echo $(date))x", 14},
+		{`$(echo ")")`, 10},
+		{`$(echo ')')`, 10},
+		{`$(echo \))`, 9},
+		{`$(echo "$(echo ")")")`, 20},
+		{"$(echo (a))", 10},
+		{"$(echo a", -1},
+		{`$(echo ")`, -1},
+	}
+	for _, tc := range tests {
+		if got := substEnd(tc.s, 0); got != tc.want {
+			t.Errorf("substEnd(%q) = %d, want %d", tc.s, got, tc.want)
+		}
+	}
+}
+
+func TestExpandAliasesAndBraces_SkipSubstitution(t *testing.T) {
+	withAliases(t, map[string]string{"ll": "ls -l"})
+	if got := expandAliases("echo $(ll; ll) && ll"); got != "echo $(ll; ll) && ls -l" {
+		t.Errorf("expandAliases = %q", got)
+	}
+	got, err := expandBraceWords("echo $(echo {a,b}) {c,d}")
+	if err != nil || got != "echo $(echo {a,b}) c d" {
+		t.Errorf("expandBraceWords = %q, %v", got, err)
+	}
+}
+
+func TestExecInput_CommandSubstitution(t *testing.T) {
+	origDir, _ := os.Getwd()
+	defer os.Chdir(origDir)
+	dir := t.TempDir()
+	os.Chdir(dir)
+	os.WriteFile("a.go", nil, 0644)
+	os.WriteFile("b.go", nil, 0644)
+
+	tests := []struct {
+		input string
+		want  string
+	}{
+		{"echo $(echo hello) > out", "hello\n"},
+		// Unquoted, the output is split into words
+		{"printf '[%s]' $(printf 'a b\\nc\\n\\n') > out", "[a][b][c]"},
+		{"printf '[%s]' x$(echo a b)y > out", "[xa][by]"},
+		// Quoted, it is a single word, only trailing newlines are removed
+		{`printf '[%s]' "$(printf 'a  b\nc\n\n')" > out`, "[a  b\nc]"},
+		{`printf '[%s]' "$(true)" > out`, "[]"},
+		{"printf '[%s]' $(true) x > out", "[x]"},
+		// Nested, with quotes and operators inside
+		{"echo $(echo $(echo nested)) > out", "nested\n"},
+		{`echo "$(echo "a;b|c")" > out`, "a;b|c\n"},
+		{"echo $(echo a | tr a-z A-Z) > out", "A\n"},
+		// Wildcards in the output are not expanded, in the command they are
+		{`echo $(echo "*") > out`, "*\n"},
+		{"echo $(echo *.go) > out", "a.go b.go\n"},
+		// Quoted or escaped, $( is literal
+		{`echo '$(echo a)' \$(echo b) > out`, "$(echo a) $(echo b)\n"},
+		// The subshell does not change the shell
+		{"echo $(cd /; pwd) > out; pwd >> out", "/\n" + dir + "\n"},
+		{"set GOSH_SUBST=$(echo value); echo $GOSH_SUBST > out", "value\n"},
+	}
+	for _, tc := range tests {
+		if err := execInput(tc.input); err != nil {
+			t.Errorf("%q: %v", tc.input, err)
+		}
+		if got, _ := os.ReadFile("out"); string(got) != tc.want {
+			t.Errorf("%q: out = %q, want %q", tc.input, got, tc.want)
+		}
+	}
+	os.Unsetenv("GOSH_SUBST")
+
+	// A command that consists only of a substitution has its status
+	execInput("$(sh -c 'exit 3')")
+	if lastStatus != 3 {
+		t.Errorf("$? = %d after $(exit 3), want 3", lastStatus)
+	}
+	// Otherwise the status of the command counts
+	execInput("echo $(false) > out")
+	if lastStatus != 0 {
+		t.Errorf("$? = %d after echo $(false), want 0", lastStatus)
+	}
+
+	for input, wantErr := range map[string]string{
+		"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)
+		}
+	}
+}