gosh/packaging/man/gosh.1

.\" Man page for gosh. View with: man ./packaging/man/gosh.1
.\" @VERSION@ is replaced by the release version when building packages.
.TH GOSH 1 "October 2026" "gosh @VERSION@" "User Commands"
.SH NAME
gosh \- a simple shell written in Go
.SH SYNOPSIS
.B gosh
.RB [ \-l ]
.RB [ \-i ]
.RB [ \-\-norc ]
.RB [ \-\-noprofile ]
.RI [ script
.RI [ args " ...]]"
.br
.B gosh
.RB [ \-l ]
.RB [ \-\-noprofile ]
.B \-c
.I command
.RI [ name
.RI [ args " ...]]"
.br
.B gosh
.B \-version
.SH DESCRIPTION
.B gosh
is a small command interpreter with a syntax close to
.BR sh (1).
It supports command history, tab completion, variables, positional
parameters, command substitution, command lists, control structures,
functions, pipes, redirections, wildcards, brace expansion, aliases and job
control.
.PP
Without arguments and with a terminal on standard input,
.B gosh
starts an interactive shell. With a
.I script
argument it runs the commands of that file, with
.B \-c
the given command string, and otherwise it reads commands from standard
input. The
.I args
after the script, or after the
.I name
of
.BR \-c ,
become the positional parameters
.BR $1 ,
.BR $2 ", ..."
.PP
.B gosh
is a proof of concept and not meant for production use.
.SH OPTIONS
.TP
.B \-c \fIcommand\fP [\fIname\fP [\fIargs\fP ...]]
Run
.I command
and exit.
.I name
becomes
.BR $0 ,
the
.I args
become
.BR $1 ,
.BR $2 ", ..."
.TP
.B \-i
Force interactive mode, even if standard input is not a terminal.
.TP
.BR \-e ", " \-x ", " "\-o \fIoption\fP"
Set options like
.BR set ,
e.g.
.B gosh \-e script
or
.BR "gosh \-o pipefail \-c" " ...".
.TP
.BR \-l ", " \-\-login
Act as a login shell and read the profile files (see
.BR "STARTUP FILES" ).
A shell whose
.I argv[0]
starts with
.B \-
(as started by
.BR login (1),
.BR sshd (8)
or
.BR "su \-" )
is a login shell as well.
.TP
.B \-\-norc
Do not read the goshrc files.
.TP
.B \-\-noprofile
Do not read the profile files.
.TP
.BR \-version ", " \-\-version ", " \-V
Print the version, branch and commit and exit.
.TP
.BR \-h ", " \-\-help
Print a usage summary and exit.
.TP
.B \-
Read commands from standard input.
.SH NON-INTERACTIVE USE
Scripts, command strings and commands read from a pipe are executed line
by line. Empty lines and lines starting with
.B #
are skipped, so a script may start with
.BR "#!/usr/bin/gosh" .
A failing command does not abort the script; the exit status of
.B gosh
is the one of the last command.
.PP
Because
.B gosh
supports
.BR \-c ,
.BR ssh (1),
.BR scp (1)
and
.BR rsync (1)
work when it is used as login shell.
.SH STARTUP FILES
Startup files are executed in the running shell, so variables and
aliases defined there stay in effect.
.TP
Login shells
read
.I /etc/gosh/profile
and
.IR ~/.gosh_profile .
.TP
Interactive shells
read
.I /etc/gosh/goshrc
and
.IR ~/.goshrc .
.PP
An interactive login shell reads the profile files first, then the goshrc
files. Scripts and
.B \-c
read no startup files unless
.B gosh
is a login shell. Missing files are skipped; errors are reported with file
name and line number and the remaining lines still run. Files of other
shells such as
.I /etc/profile
or
.I ~/.bashrc
are not read.
.SH SYNTAX
.SS Quoting
.TP
.B \(aq...\(aq
Everything is literal.
.TP
.B \(dq...\(dq
Variables and command substitutions are expanded, the result stays one
word.
.TP
.B \e
Escapes the next character.
.SS Variables
.TP
.I name\fB=\fPvalue
Set a variable. All variables are exported to the environment of started
programs. The value is not split into words and not expanded as a pattern;
variables, command substitutions and
.B ~
(at the start, after
.B =
and after
.BR : )
are expanded.
.TP
.I name\fB=\fPvalue command
Set the variable only for
.IR command .
.TP
.BR $VAR ", " ${VAR}
The value of
.BR VAR .
Using an unset variable is an error and aborts the command.
.TP
.B ${VAR:\-default}
The value of
.BR VAR ,
or
.I default
if it is unset or empty. Use
.B ${VAR:\-}
for an empty default.
.TP
.B $?
The exit status of the last command.
.SS Parameter expansion
.TP
.B ${#VAR}
The length of the value in characters.
.TP
.BR ${VAR#\fIpattern\fP} ", " ${VAR##\fIpattern\fP}
The value without the shortest (longest) prefix matching
.IR pattern .
.TP
.BR ${VAR%\fIpattern\fP} ", " ${VAR%%\fIpattern\fP}
The value without the shortest (longest) suffix matching
.IR pattern .
.TP
.BR ${VAR/\fIpattern\fP/\fIstring\fP} ", " ${VAR//\fIpattern\fP/\fIstring\fP}
The value with the first (every) longest match of
.I pattern
replaced by
.IR string ;
.B /#
and
.B /%
only match at the start and at the end.
.TP
.BR ${VAR:\fIoffset\fP} ", " ${VAR:\fIoffset\fP:\fIlength\fP}
A substring; offset and length are arithmetic expressions, negative values
count from the end.
.TP
.BR ${VAR:\-\fIword\fP} ", " ${VAR:=\fIword\fP} ", " ${VAR:+\fIword\fP} ", " ${VAR:?\fIword\fP}
.I word
if
.B VAR
is unset or empty (and assign it with
.BR := ),
.I word
if it is set and not empty, or an error with the message
.IR word .
Without the colon, only an unset variable counts.
.PP
The word is expanded but not split. In patterns,
.BR * ,
.B ?
and
.B [...]
are wildcards that also match
.BR / ;
quoted characters and values of variables match literally.
.SS Arithmetic expansion
.B $((\fIexpression\fP))
is replaced by the value of
.IR expression ,
computed with 64-bit integers. The operators of C are supported,
in order of precedence:
.BR "++ \-\-" ,
unary
.BR "+ \- ! ~" ,
.B **
(power),
.BR "* / %" ,
.BR "+ \-" ,
.BR "<< >>" ,
.BR "< <= > >=" ,
.BR "== !=" ,
.BR & ,
.BR ^ ,
.BR | ,
.BR && ,
.BR || ,
.BR "? :" ,
the assignments
.B = += \-= *= /= %= <<= >>= &= ^= |=
and
.BR , .
Variables can be used with or without
.BR $ ;
an unset variable is an error, an empty one is 0. Numbers can be
hexadecimal
.RB ( 0x1F )
or octal
.RB ( 017 ).
.SS Positional parameters
.TP
.B $0
The name of the script, or the
.I name
given after
.BR "gosh \-c" .
.TP
.BR $1 " ... " $9 ", " ${10}
The arguments of the script, of
.BR "gosh \-c" ,
of a function call or of
.BR source ,
or the words set with
.BR "set \-\-" .
An unset parameter is an error like an unset variable; use
.B ${1:\-}
for an optional argument.
.TP
.B $#
The number of positional parameters.
.TP
.B \(dq$@\(dq
All positional parameters, each as a separate word. Without parameters it
expands to no word at all.
.TP
.B \(dq$*\(dq
All positional parameters as one word, separated by blanks.
.TP
.B $$
The process ID of the shell.
.TP
.B $!
The process ID of the last background job.
.SS Command substitution
.B $(\fIcommand\fP)
is replaced by the output of
.IR command ,
which runs in a subshell. Trailing newlines are removed. Unquoted, the
output is split into words at blanks and newlines; inside double quotes it
stays one word. Wildcards and operators in the output are not interpreted.
Backticks are not supported.
.SS Tilde and brace expansion
.B ~
and
.B ~/path
at the start of an unquoted word are replaced by the home directory.
.PP
Brace expansion generates several words from one:
.B a{b,c}d
becomes
.BR "abd acd" ,
.B {1..5}
becomes
.BR "1 2 3 4 5" ,
.B {01..10..4}
becomes
.B 01 05 09
and
.B {a..e}
becomes
.BR "a b c d e" .
Brace expansion happens before all other expansions.
.SS Wildcards
.B *
matches any string,
.B ?
any single character,
.B [abc]
and
.B [a\-z]
one of the given characters and
.B [!abc]
(or
.BR [^abc] )
any character except those. Matches are sorted. Hidden files are only
matched if the pattern starts with a dot. A pattern without match is kept
unchanged. Quoted wildcards and values of variables are never expanded.
.SS Command lists
.TP
.IB a " ; " b
Run
.IR a ,
then
.IR b .
.TP
.IB a " && " b
Run
.I b
only if
.I a
succeeded.
.TP
.IB a " || " b
Run
.I b
only if
.I a
failed.
.TP
.IB command " &"
Run
.I command
in the background.
.SS Pipes and redirections
.TP
.IB a " | " b
Connect standard output of
.I a
to standard input of
.IR b .
The exit status is the one of
.IR b .
.TP
.BI < " file"
Read standard input from
.IR file .
.TP
.BR > " \fIfile\fP, " >> " \fIfile\fP"
Write (or append) standard output to
.IR file .
.TP
.BR 2> " \fIfile\fP, " 2>> " \fIfile\fP"
Write (or append) standard error to
.IR file .
.TP
.B 2>&1
Redirect standard error to where standard output goes.
.TP
.B >&2
Redirect standard output to where standard error goes.
.TP
.BR &> " \fIfile\fP, " &>> " \fIfile\fP"
Write (or append) standard output and standard error to
.IR file .
.TP
.BI << word
Here-document: the lines after the command, up to a line that is exactly
.IR word ,
are standard input. If no part of
.I word
is quoted, variables, command substitutions and backslashes before
.BR $ ,
.BR \(ga ,
.B \e
and newline are expanded in the lines.
.BI <<\- word
also removes leading tabs from the lines and the delimiter line.
.TP
.BI <<< " word"
Here-string:
.I word
and a newline are standard input.
.PP
Redirections are evaluated from left to right. Only file descriptors 0, 1
and 2 are supported.
.SS Control structures
.nf
\fBif\fP \fIlist\fP; \fBthen\fP \fIlist\fP; [\fBelif\fP \fIlist\fP; \fBthen\fP \fIlist\fP;] [\fBelse\fP \fIlist\fP;] \fBfi\fP
\fBfor\fP \fIname\fP \fBin\fP \fIwords\fP; \fBdo\fP \fIlist\fP; \fBdone\fP
\fBwhile\fP \fIlist\fP; \fBdo\fP \fIlist\fP; \fBdone\fP
\fBuntil\fP \fIlist\fP; \fBdo\fP \fIlist\fP; \fBdone\fP
\fBcase\fP \fIword\fP \fBin\fP [\fB(\fP]\fIpattern\fP[\fB|\fP\fIpattern\fP]...\fB)\fP \fIlist\fP \fB;;\fP ... \fBesac\fP
\fB{\fP \fIlist\fP; \fB}\fP
\fB(\fP \fIlist\fP \fB)\fP
\fB!\fP \fIcommand\fP
.fi
.PP
Control structures may span several lines; an incomplete command shows
the continuation prompt
.BR "> " .
.B !
negates the exit status of a command.
.B for
without
.B in
loops over the positional parameters.
.PP
.B case
runs the list of the first clause with a pattern that matches
.IR word .
Patterns are wildcards as for file names, but
.B *
and
.B ?
also match a
.BR / ;
quoted characters match literally, and values of variables are not
patterns. The
.B ;;
of the last clause may be omitted.
.PP
.B {
.IR list ;
.B }
groups commands; they run in the current shell.
.B (
.I list
.B )
runs the commands in a subshell, a new
.B gosh
process, so that changes of the directory, variables and functions only
apply there.
.PP
Redirections after a control structure
.RB ( "done < file" ,
.BR "fi > log 2>&1" )
apply to all commands in it, which still run in the current shell. In a
pipe and in the background
.RB ( & ),
a control structure runs in a subshell, like in
.BR sh (1).
The subshell knows the functions and positional parameters of the shell.
.SS Functions
.nf
\fIname\fP\fB() {\fP \fIlist\fP; \fB}\fP
\fBfunction\fP \fIname\fP \fB{\fP \fIlist\fP; \fB}\fP
.fi
.PP
defines a function; the body can be any compound command. When the
function is called, its arguments are the positional parameters, which get
their old values back afterwards. Functions run in the current shell, so
variables they set stay set; use
.B local
for variables that belong to the function. Redirections of a call apply to
all commands of the function. In pipes, in the background and in
.B $(...)
a function runs in a subshell that knows all functions. Functions take
precedence over builtins and programs of the same name. Calls can be nested
up to a depth of 1000.
.SS Aliases
In interactive shells, the first word of a command is replaced by its
alias. If the alias value ends with a blank, the next word is checked for
an alias as well.
.B \e\fIname\fP
or
.B \(aq\fIname\fP\(aq
skips the alias. Aliases are not used in scripts and with
.BR \-c .
.SH BUILTIN COMMANDS
.TP
.BR cd " [\fIdir\fP]"
Change the directory; without argument to the home directory.
.TP
.B pwd
Print the working directory.
.TP
.BR echo " [\fIargs\fP]"
Print the arguments.
.TP
.BR exit " [\fIcode\fP], " quit " [\fIcode\fP]"
Exit the shell with status
.I code
(default:
.BR $? ).
.TP
.BI set " VAR" = value
Set a variable.
.TP
.BR set " [\fB\-+ex\fP] [\fB\-+o\fP \fIoption\fP] [\fB\-\-\fP] [\fIargs\fP ...]"
Set
.RB ( \- )
or unset
.RB ( + )
options and set the positional parameters to
.IR args .
.B \-e
.RB ( errexit )
exits the shell when a command fails, except in conditions of
.BR if ,
.B while
and
.BR until ,
negated commands and all but the last command of
.B &&
and
.B ||
lists.
.B \-x
.RB ( xtrace )
prints every simple command after expansion.
.B \-o pipefail
makes the status of a pipeline the one of the last command that failed.
.B \-u
.RB ( nounset )
is always on.
.B set \-o
and
.B set +o
show the options,
.B set
without arguments shows the variables.
.TP
.BI export " VAR" = value
Export a variable.
.TP
.BR unset " [\fB\-v\fP] \fIVAR\fP ..., " "unset \-f" " \fIname\fP ..."
Remove variables, or functions.
.TP
.BR source " \fIfile\fP [\fIargs\fP ...], " . " \fIfile\fP [\fIargs\fP ...]"
Run the commands of
.I file
in the current shell, with
.I args
as positional parameters if given.
.TP
.B jobs
List background and stopped jobs.
.TP
.BR fg " [\fB%\fP\fIn\fP]"
Continue job
.I n
(default: the current job) in the foreground.
.TP
.BR bg " [\fB%\fP\fIn\fP]"
Continue stopped job
.I n
in the background.
.TP
.BR wait " [\fB%\fP\fIn\fP | \fIpid\fP]"
Wait for job
.IR n ,
the job with process
.I pid
(e.g.
.BR $! ),
or for all background jobs.
.TP
.BR alias " [\fIname\fP[\fB=\fP\fIvalue\fP] ...]"
Define or show aliases.
.TP
.BR unalias " \fIname\fP, " "unalias \-a"
Remove an alias, or all aliases.
.TP
.B :
Do nothing, exit status 0.
.TP
.BR break " [\fIn\fP], " continue " [\fIn\fP]"
Leave the innermost (or
.IR n -th)
loop, or continue with its next iteration.
.TP
.BR return " [\fIn\fP]"
Leave a function or sourced file with status
.I n
(default:
.BR $? ).
.TP
.BR local " \fIVAR\fP[\fB=\fP\fIvalue\fP] ..."
In a function: the variable gets its previous value back when the function
returns. Without a value it is unset.
.TP
.BR shift " [\fIn\fP]"
Remove the first
.I n
(default 1) positional parameters.
.TP
.BR read " [\fB\-r\fP] [\fB\-p\fP \fIprompt\fP] [\fIVAR\fP ...]"
Read a line from standard input and split it into fields at the
characters of
.B IFS
(default blank, tab and newline). Each
.I VAR
gets one field, the last one the rest of the line; without
.I VAR
the whole line is stored in
.BR REPLY .
Without
.BR \-r ,
a backslash escapes the next character and continues the line at its end.
.B \-p
prints
.I prompt
if the input is a terminal. The exit status is 1 at the end of the input.
.TP
.BR eval " [\fIargs\fP ...]"
Join the arguments with blanks and run the result as a command in the
current shell.
.TP
.BR exec " [\fIcommand\fP [\fIargs\fP ...]]"
Replace the shell with
.IR command .
Without a command, the redirections of
.B exec
apply to the shell itself
.RB ( "exec > log 2>&1" ).
.TP
.BR trap " [\fB\-lp\fP] [[\fIaction\fP] \fIsignal\fP ...]"
Run
.I action
in the shell when
.I signal
arrives (after the running command) or, for
.B EXIT
.RB ( 0 ),
when the shell exits; a script with an EXIT trap also runs it when it is
ended by SIGINT, SIGTERM or SIGHUP. Signals:
.BR HUP ,
.BR INT ,
.BR QUIT ,
.BR TERM ,
.BR USR1 ,
.BR USR2 ,
.BR ALRM ,
.BR WINCH .
An empty
.I action
ignores the signal (also in started programs),
.B \-
restores the default.
.B trap
and
.B trap \-p
show the traps,
.B trap \-l
the signals.
.TP
.B help
Show a summary of builtins and features.
.SH JOB CONTROL
In interactive shells, each command line runs as a job in its own process
group.
.B Ctrl+Z
stops the foreground job,
.B Ctrl+C
interrupts it.
.BR jobs ,
.BR fg ,
.B bg
and
.B wait
manage the jobs;
.B %n
or
.I n
refers to job
.IR n ,
.B %\-
to the previous job. Finished background jobs are reported before the
next prompt. Exiting with stopped jobs warns once.
.SH INTERACTIVE USE
.TP
.B Up/Down
Browse the command history.
.TP
.B Tab
Complete commands, aliases and file names.
.TP
.B Ctrl+C
Cancel the current line or command.
.TP
.B Ctrl+D
Exit the shell.
.PP
Lines starting with a space are not saved in the history.
.PP
The prompt shows
.IR user @ host : dir
followed by
.BR $ .
If the last command failed, its exit status is shown as
.BI [ N ]
before the
.BR $ .
.SH ENVIRONMENT
.TP
.B GOSH_HISTFILE
Path of the history file. If set to an empty value, no history is saved.
.TP
.B XDG_STATE_HOME
Base directory of the default history file
.IR $XDG_STATE_HOME/gosh/history .
.TP
.B GOSH_COLORS
Prompt colors as colon-separated
.IB key = code
entries. Keys are
.B user
(default
.BR 1;32 ),
.B root
.RB ( 1;31 ),
.B path
.RB ( 1;34 )
and
.B error
.RB ( 1;31 );
values are ANSI SGR codes, an empty value disables the color. Example:
.B GOSH_COLORS=\(aquser=1;33:path=36\(aq
.TP
.B NO_COLOR
If set, the prompt is not colored. Colors are also disabled with
.B TERM=dumb
or when the output is not a terminal.
.TP
.B HOME
Used for
.B ~
and
.B cd
without argument.
.TP
.B PATH
Directories searched for commands.
.TP
.B IFS
Field separators for
.BR read .
.SH FILES
.TP
.I /etc/gosh/profile
System-wide profile for login shells.
.TP
.I ~/.gosh_profile
Personal profile for login shells.
.TP
.I /etc/gosh/goshrc
System-wide startup file for interactive shells.
.TP
.I ~/.goshrc
Personal startup file for interactive shells.
.TP
.I ~/.local/state/gosh/history
Default history file (mode 0600).
.SH EXIT STATUS
The exit status of the last command, or the argument of
.BR exit .
Typical values:
.TP
.B 1
General error.
.TP
.B 2
Syntax error or invalid option.
.TP
.B 126
Command not executable.
.TP
.B 127
Command not found.
.TP
.BI 128+ n
Command terminated by signal
.I n
(130 for Ctrl+C).
.SH EXAMPLES
.nf
gosh \-c \(aqcd /srv && git log | head\(aq
for f in *.log; do gzip "$f"; done
cp config.yaml{,.bak}
make > build.log 2>&1 || echo "failed: $?"
LANG=C sort file
alias ll=\(aqls \-l\(aq
greet() { echo "Hello ${1:\-World}"; }
set \-euo pipefail; trap \(aqrm \-rf "$tmp"\(aq EXIT
echo ${file##*/} $((n + 1))
git ls\-files | while read \-r f; do wc \-l "$f"; done
while read \-r user rest; do echo "$user"; done < /etc/passwd
(cd build && make) > build.log 2>&1
case "$1" in start|stop) echo "$1ing" ;; *) echo "usage: $0 start|stop" ;; esac
read \-r \-p \(aqName? \(aq name
chsh \-s /usr/bin/gosh
.fi
.SH SEE ALSO
.BR sh (1),
.BR bash (1),
.BR chsh (1),
.BR shells (5)
.SH AUTHOR
Florian Walther <florian.walther@certainity.com>