add parameter expansion, arithmetic, set -e/-x/pipefail, trap, eval, exec
- ${#v}, ${v#p} ${v##p} ${v%p} ${v%%p}, ${v/p/r} ${v//p/r} ${v/#p/r}
${v/%p/r}, ${v:off:len}, ${v-w} ${v:=w} ${v:+w} ${v:?msg}; nested ${}
- arithmetic expansion $((...)) with the C operators, ** and assignments
- set -e, set -x, set -o pipefail (also as gosh options, passed on to
subshells); set shows variables, set -o the options
- trap for EXIT and signals; scripts with an EXIT trap run it on
SIGINT/SIGTERM/SIGHUP too
- eval, exec (also exec > file without a command), $!, wait pid
Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>
This commit is contained in:
Florian WaltherandClaude Opus 5.5 committed
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@@ -68,6 +68,14 @@ become
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.B \-i
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Force interactive mode, even if standard input is not a terminal.
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.TP
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.BR \-e ", " \-x ", " "\-o \fIoption\fP"
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Set options like
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.BR set ,
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e.g.
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.B gosh \-e script
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or
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.BR "gosh \-o pipefail \-c" " ...".
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.TP
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.BR \-l ", " \-\-login
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Act as a login shell and read the profile files (see
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.BR "STARTUP FILES" ).
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@@ -188,6 +196,85 @@ for an empty default.
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.TP
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.B $?
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The exit status of the last command.
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.SS Parameter expansion
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.TP
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.B ${#VAR}
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The length of the value in characters.
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.TP
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.BR ${VAR#\fIpattern\fP} ", " ${VAR##\fIpattern\fP}
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The value without the shortest (longest) prefix matching
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.IR pattern .
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.TP
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.BR ${VAR%\fIpattern\fP} ", " ${VAR%%\fIpattern\fP}
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The value without the shortest (longest) suffix matching
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.IR pattern .
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.TP
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.BR ${VAR/\fIpattern\fP/\fIstring\fP} ", " ${VAR//\fIpattern\fP/\fIstring\fP}
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The value with the first (every) longest match of
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.I pattern
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replaced by
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.IR string ;
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.B /#
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and
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.B /%
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only match at the start and at the end.
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.TP
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.BR ${VAR:\fIoffset\fP} ", " ${VAR:\fIoffset\fP:\fIlength\fP}
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A substring; offset and length are arithmetic expressions, negative values
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count from the end.
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.TP
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.BR ${VAR:\-\fIword\fP} ", " ${VAR:=\fIword\fP} ", " ${VAR:+\fIword\fP} ", " ${VAR:?\fIword\fP}
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.I word
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if
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.B VAR
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is unset or empty (and assign it with
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.BR := ),
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.I word
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if it is set and not empty, or an error with the message
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.IR word .
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Without the colon, only an unset variable counts.
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.PP
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The word is expanded but not split. In patterns,
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.BR * ,
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.B ?
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and
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.B [...]
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are wildcards that also match
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.BR / ;
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quoted characters and values of variables match literally.
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.SS Arithmetic expansion
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.B $((\fIexpression\fP))
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is replaced by the value of
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.IR expression ,
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computed with 64-bit integers. The operators of C are supported,
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in order of precedence:
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.BR "++ \-\-" ,
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unary
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.BR "+ \- ! ~" ,
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.B **
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(power),
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.BR "* / %" ,
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.BR "+ \-" ,
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.BR "<< >>" ,
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.BR "< <= > >=" ,
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.BR "== !=" ,
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.BR & ,
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.BR ^ ,
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.BR | ,
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.BR && ,
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.BR || ,
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.BR "? :" ,
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the assignments
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.B = += \-= *= /= %= <<= >>= &= ^= |=
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and
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.BR , .
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Variables can be used with or without
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.BR $ ;
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an unset variable is an error, an empty one is 0. Numbers can be
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hexadecimal
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.RB ( 0x1F )
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or octal
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.RB ( 017 ).
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.SS Positional parameters
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.TP
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.B $0
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@@ -219,6 +306,9 @@ All positional parameters as one word, separated by blanks.
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.TP
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.B $$
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The process ID of the shell.
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.TP
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.B $!
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The process ID of the last background job.
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.SS Command substitution
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.B $(\fIcommand\fP)
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is replaced by the output of
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@@ -226,7 +316,7 @@ is replaced by the output of
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which runs in a subshell. Trailing newlines are removed. Unquoted, the
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output is split into words at blanks and newlines; inside double quotes it
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stays one word. Wildcards and operators in the output are not interpreted.
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Backticks and arithmetic expansion are not supported.
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Backticks are not supported.
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.SS Tilde and brace expansion
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.B ~
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and
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@@ -444,8 +534,39 @@ Exit the shell with status
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.BI set " VAR" = value
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Set a variable.
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.TP
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.BR "set \-\-" " [\fIargs\fP ...]"
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Set the positional parameters.
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.BR set " [\fB\-+ex\fP] [\fB\-+o\fP \fIoption\fP] [\fB\-\-\fP] [\fIargs\fP ...]"
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Set
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.RB ( \- )
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or unset
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.RB ( + )
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options and set the positional parameters to
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.IR args .
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.B \-e
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.RB ( errexit )
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exits the shell when a command fails, except in conditions of
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.BR if ,
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.B while
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and
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.BR until ,
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negated commands and all but the last command of
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.B &&
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and
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.B ||
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lists.
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.B \-x
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.RB ( xtrace )
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prints every simple command after expansion.
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.B \-o pipefail
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makes the status of a pipeline the one of the last command that failed.
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.B \-u
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.RB ( nounset )
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is always on.
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.B set \-o
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and
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.B set +o
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show the options,
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.B set
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without arguments shows the variables.
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.TP
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.BI export " VAR" = value
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Export a variable.
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@@ -473,9 +594,13 @@ Continue stopped job
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.I n
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in the background.
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.TP
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.BR wait " [\fB%\fP\fIn\fP]"
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.BR wait " [\fB%\fP\fIn\fP | \fIpid\fP]"
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Wait for job
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.I n
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.IR n ,
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the job with process
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.I pid
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(e.g.
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.BR $! ),
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or for all background jobs.
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.TP
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.BR alias " [\fIname\fP[\fB=\fP\fIvalue\fP] ...]"
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@@ -525,6 +650,48 @@ prints
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.I prompt
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if the input is a terminal. The exit status is 1 at the end of the input.
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.TP
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.BR eval " [\fIargs\fP ...]"
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Join the arguments with blanks and run the result as a command in the
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current shell.
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.TP
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.BR exec " [\fIcommand\fP [\fIargs\fP ...]]"
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Replace the shell with
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.IR command .
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Without a command, the redirections of
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.B exec
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apply to the shell itself
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.RB ( "exec > log 2>&1" ).
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.TP
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.BR trap " [\fB\-lp\fP] [[\fIaction\fP] \fIsignal\fP ...]"
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Run
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.I action
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in the shell when
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.I signal
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arrives (after the running command) or, for
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.B EXIT
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.RB ( 0 ),
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when the shell exits; a script with an EXIT trap also runs it when it is
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ended by SIGINT, SIGTERM or SIGHUP. Signals:
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.BR HUP ,
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.BR INT ,
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.BR QUIT ,
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.BR TERM ,
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.BR USR1 ,
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.BR USR2 ,
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.BR ALRM ,
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.BR WINCH .
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An empty
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.I action
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ignores the signal (also in started programs),
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.B \-
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restores the default.
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.B trap
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and
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.B trap \-p
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show the traps,
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.B trap \-l
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the signals.
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.TP
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.B help
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Show a summary of builtins and features.
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.SH JOB CONTROL
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@@ -662,6 +829,8 @@ make > build.log 2>&1 || echo "failed: $?"
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LANG=C sort file
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alias ll=\(aqls \-l\(aq
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greet() { echo "Hello ${1:\-World}"; }
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set \-euo pipefail; trap \(aqrm \-rf "$tmp"\(aq EXIT
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echo ${file##*/} $((n + 1))
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git ls\-files | while read \-r f; do wc \-l "$f"; done
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while read \-r user rest; do echo "$user"; done < /etc/passwd
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(cd build && make) > build.log 2>&1
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