xref: /freebsd/bin/sh/sh.1 (revision 4ec234c813eed05c166859bba82c882e40826eb9)
1.\"-
2.\" Copyright (c) 1991, 1993
3.\"	The Regents of the University of California.  All rights reserved.
4.\"
5.\" This code is derived from software contributed to Berkeley by
6.\" Kenneth Almquist.
7.\"
8.\" Redistribution and use in source and binary forms, with or without
9.\" modification, are permitted provided that the following conditions
10.\" are met:
11.\" 1. Redistributions of source code must retain the above copyright
12.\"    notice, this list of conditions and the following disclaimer.
13.\" 2. Redistributions in binary form must reproduce the above copyright
14.\"    notice, this list of conditions and the following disclaimer in the
15.\"    documentation and/or other materials provided with the distribution.
16.\" 4. Neither the name of the University nor the names of its contributors
17.\"    may be used to endorse or promote products derived from this software
18.\"    without specific prior written permission.
19.\"
20.\" THIS SOFTWARE IS PROVIDED BY THE REGENTS AND CONTRIBUTORS ``AS IS'' AND
21.\" ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
22.\" IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
23.\" ARE DISCLAIMED.  IN NO EVENT SHALL THE REGENTS OR CONTRIBUTORS BE LIABLE
24.\" FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
25.\" DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS
26.\" OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION)
27.\" HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT
28.\" LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY
29.\" OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
30.\" SUCH DAMAGE.
31.\"
32.\"	from: @(#)sh.1	8.6 (Berkeley) 5/4/95
33.\" $FreeBSD$
34.\"
35.Dd January 3, 2014
36.Dt SH 1
37.Os
38.Sh NAME
39.Nm sh
40.Nd command interpreter (shell)
41.Sh SYNOPSIS
42.Nm
43.Op Fl /+abCEefIimnPpTuVvx
44.Op Fl /+o Ar longname
45.Oo
46.Ar script
47.Op Ar arg ...
48.Oc
49.Nm
50.Op Fl /+abCEefIimnPpTuVvx
51.Op Fl /+o Ar longname
52.Fl c Ar string
53.Oo
54.Ar name
55.Op Ar arg ...
56.Oc
57.Nm
58.Op Fl /+abCEefIimnPpTuVvx
59.Op Fl /+o Ar longname
60.Fl s
61.Op Ar arg ...
62.Sh DESCRIPTION
63The
64.Nm
65utility is the standard command interpreter for the system.
66The current version of
67.Nm
68is close to the
69.St -p1003.1
70specification for the shell.
71It only supports features
72designated by
73.Tn POSIX ,
74plus a few Berkeley extensions.
75This man page is not intended to be a tutorial nor a complete
76specification of the shell.
77.Ss Overview
78The shell is a command that reads lines from
79either a file or the terminal, interprets them, and
80generally executes other commands.
81It is the program that is started when a user logs into the system,
82although a user can select a different shell with the
83.Xr chsh 1
84command.
85The shell
86implements a language that has flow control constructs,
87a macro facility that provides a variety of features in
88addition to data storage, along with built-in history and line
89editing capabilities.
90It incorporates many features to
91aid interactive use and has the advantage that the interpretative
92language is common to both interactive and non-interactive
93use (shell scripts).
94That is, commands can be typed directly
95to the running shell or can be put into a file,
96which can be executed directly by the shell.
97.Ss Invocation
98.\"
99.\" XXX This next sentence is incredibly confusing.
100.\"
101If no arguments are present and if the standard input of the shell
102is connected to a terminal
103(or if the
104.Fl i
105option is set),
106the shell is considered an interactive shell.
107An interactive shell
108generally prompts before each command and handles programming
109and command errors differently (as described below).
110When first starting, the shell inspects argument 0, and
111if it begins with a dash
112.Pq Ql - ,
113the shell is also considered a login shell.
114This is normally done automatically by the system
115when the user first logs in.
116A login shell first reads commands
117from the files
118.Pa /etc/profile
119and then
120.Pa .profile
121in a user's home directory,
122if they exist.
123If the environment variable
124.Ev ENV
125is set on entry to a shell, or is set in the
126.Pa .profile
127of a login shell, the shell then subjects its value to parameter expansion
128and arithmetic expansion and reads commands from the named file.
129Therefore, a user should place commands that are to be executed only
130at login time in the
131.Pa .profile
132file, and commands that are executed for every shell inside the
133.Ev ENV
134file.
135The user can set the
136.Ev ENV
137variable to some file by placing the following line in the file
138.Pa .profile
139in the home directory,
140substituting for
141.Pa .shrc
142the filename desired:
143.Pp
144.Dl "ENV=$HOME/.shrc; export ENV"
145.Pp
146The first non-option argument specified on the command line
147will be treated as the
148name of a file from which to read commands (a shell script), and
149the remaining arguments are set as the positional parameters
150of the shell
151.Li ( $1 , $2 ,
152etc.).
153Otherwise, the shell reads commands
154from its standard input.
155.Pp
156Unlike older versions of
157.Nm
158the
159.Ev ENV
160script is only sourced on invocation of interactive shells.
161This
162closes a well-known, and sometimes easily exploitable security
163hole related to poorly thought out
164.Ev ENV
165scripts.
166.Ss Argument List Processing
167All of the single letter options to
168.Nm
169have a corresponding long name,
170with the exception of
171.Fl c
172and
173.Fl /+o .
174These long names are provided next to the single letter options
175in the descriptions below.
176The long name for an option may be specified as an argument to the
177.Fl /+o
178option of
179.Nm .
180Once the shell is running,
181the long name for an option may be specified as an argument to the
182.Fl /+o
183option of the
184.Ic set
185built-in command
186(described later in the section called
187.Sx Built-in Commands ) .
188Introducing an option with a dash
189.Pq Ql -
190enables the option,
191while using a plus
192.Pq Ql +
193disables the option.
194A
195.Dq Li --
196or plain
197.Ql -
198will stop option processing and will force the remaining
199words on the command line to be treated as arguments.
200The
201.Fl /+o
202and
203.Fl c
204options do not have long names.
205They take arguments and are described after the single letter options.
206.Bl -tag -width indent
207.It Fl a Li allexport
208Flag variables for export when assignments are made to them.
209.It Fl b Li notify
210Enable asynchronous notification of background job
211completion.
212(UNIMPLEMENTED)
213.It Fl C Li noclobber
214Do not overwrite existing files with
215.Ql > .
216.It Fl E Li emacs
217Enable the built-in
218.Xr emacs 1
219command line editor (disables the
220.Fl V
221option if it has been set;
222set automatically when interactive on terminals).
223.It Fl e Li errexit
224Exit immediately if any untested command fails in non-interactive mode.
225The exit status of a command is considered to be
226explicitly tested if the command is part of the list used to control
227an
228.Ic if , elif , while ,
229or
230.Ic until ;
231if the command is the left
232hand operand of an
233.Dq Li &&
234or
235.Dq Li ||
236operator; or if the command is a pipeline preceded by the
237.Ic !\&
238keyword.
239If a shell function is executed and its exit status is explicitly
240tested, all commands of the function are considered to be tested as
241well.
242.Pp
243It is recommended to check for failures explicitly
244instead of relying on
245.Fl e
246because it tends to behave in unexpected ways,
247particularly in larger scripts.
248.It Fl f Li noglob
249Disable pathname expansion.
250.It Fl h Li trackall
251A do-nothing option for
252.Tn POSIX
253compliance.
254.It Fl I Li ignoreeof
255Ignore
256.Dv EOF Ap s
257from input when in interactive mode.
258.It Fl i Li interactive
259Force the shell to behave interactively.
260.It Fl m Li monitor
261Turn on job control (set automatically when interactive).
262.It Fl n Li noexec
263If not interactive, read commands but do not
264execute them.
265This is useful for checking the
266syntax of shell scripts.
267.It Fl P Li physical
268Change the default for the
269.Ic cd
270and
271.Ic pwd
272commands from
273.Fl L
274(logical directory layout)
275to
276.Fl P
277(physical directory layout).
278.It Fl p Li privileged
279Turn on privileged mode.
280This mode is enabled on startup
281if either the effective user or group ID is not equal to the
282real user or group ID.
283Turning this mode off sets the
284effective user and group IDs to the real user and group IDs.
285When this mode is enabled for interactive shells, the file
286.Pa /etc/suid_profile
287is sourced instead of
288.Pa ~/.profile
289after
290.Pa /etc/profile
291is sourced, and the contents of the
292.Ev ENV
293variable are ignored.
294.It Fl s Li stdin
295Read commands from standard input (set automatically
296if no file arguments are present).
297This option has
298no effect when set after the shell has already started
299running (i.e., when set with the
300.Ic set
301command).
302.It Fl T Li trapsasync
303When waiting for a child, execute traps immediately.
304If this option is not set,
305traps are executed after the child exits,
306as specified in
307.St -p1003.2 .
308This nonstandard option is useful for putting guarding shells around
309children that block signals.
310The surrounding shell may kill the child
311or it may just return control to the tty and leave the child alone,
312like this:
313.Bd -literal -offset indent
314sh -T -c "trap 'exit 1' 2 ; some-blocking-program"
315.Ed
316.It Fl u Li nounset
317Write a message to standard error when attempting
318to expand a variable, a positional parameter or
319the special parameter
320.Va \&!
321that is not set, and if the
322shell is not interactive, exit immediately.
323.It Fl V Li vi
324Enable the built-in
325.Xr vi 1
326command line editor (disables
327.Fl E
328if it has been set).
329.It Fl v Li verbose
330The shell writes its input to standard error
331as it is read.
332Useful for debugging.
333.It Fl x Li xtrace
334Write each command
335(preceded by the value of the
336.Va PS4
337variable subjected to parameter expansion and arithmetic expansion)
338to standard error before it is executed.
339Useful for debugging.
340.El
341.Pp
342The
343.Fl c
344option causes the commands to be read from the
345.Ar string
346operand instead of from the standard input.
347Keep in mind that this option only accepts a single string as its
348argument, hence multi-word strings must be quoted.
349.Pp
350The
351.Fl /+o
352option takes as its only argument the long name of an option
353to be enabled or disabled.
354For example, the following two invocations of
355.Nm
356both enable the built-in
357.Xr emacs 1
358command line editor:
359.Bd -literal -offset indent
360set -E
361set -o emacs
362.Ed
363.Pp
364If used without an argument, the
365.Fl o
366option displays the current option settings in a human-readable format.
367If
368.Cm +o
369is used without an argument, the current option settings are output
370in a format suitable for re-input into the shell.
371.Ss Lexical Structure
372The shell reads input in terms of lines from a file and breaks
373it up into words at whitespace (blanks and tabs), and at
374certain sequences of
375characters called
376.Dq operators ,
377which are special to the shell.
378There are two types of operators: control operators and
379redirection operators (their meaning is discussed later).
380The following is a list of valid operators:
381.Bl -tag -width indent
382.It Control operators:
383.Bl -column "XXX" "XXX" "XXX" "XXX" "XXX" -offset center -compact
384.It Li & Ta Li && Ta Li \&( Ta Li \&) Ta Li \en
385.It Li ;; Ta Li ;& Ta Li \&; Ta Li \&| Ta Li ||
386.El
387.It Redirection operators:
388.Bl -column "XXX" "XXX" "XXX" "XXX" "XXX" -offset center -compact
389.It Li < Ta Li > Ta Li << Ta Li >> Ta Li <>
390.It Li <& Ta Li >& Ta Li <<- Ta Li >| Ta \&
391.El
392.El
393.Pp
394The character
395.Ql #
396introduces a comment if used at the beginning of a word.
397The word starting with
398.Ql #
399and the rest of the line are ignored.
400.Pp
401.Tn ASCII
402.Dv NUL
403characters (character code 0) are not allowed in shell input.
404.Ss Quoting
405Quoting is used to remove the special meaning of certain characters
406or words to the shell, such as operators, whitespace, keywords,
407or alias names.
408.Pp
409There are four types of quoting: matched single quotes,
410dollar-single quotes,
411matched double quotes, and backslash.
412.Bl -tag -width indent
413.It Single Quotes
414Enclosing characters in single quotes preserves the literal
415meaning of all the characters (except single quotes, making
416it impossible to put single-quotes in a single-quoted string).
417.It Dollar-Single Quotes
418Enclosing characters between
419.Li $'
420and
421.Li '
422preserves the literal meaning of all characters
423except backslashes and single quotes.
424A backslash introduces a C-style escape sequence:
425.Bl -tag -width xUnnnnnnnn
426.It \ea
427Alert (ring the terminal bell)
428.It \eb
429Backspace
430.It \ec Ns Ar c
431The control character denoted by
432.Li ^ Ns Ar c
433in
434.Xr stty 1 .
435If
436.Ar c
437is a backslash, it must be doubled.
438.It \ee
439The ESC character
440.Tn ( ASCII
4410x1b)
442.It \ef
443Formfeed
444.It \en
445Newline
446.It \er
447Carriage return
448.It \et
449Horizontal tab
450.It \ev
451Vertical tab
452.It \e\e
453Literal backslash
454.It \e\&'
455Literal single-quote
456.It \e\&"
457Literal double-quote
458.It \e Ns Ar nnn
459The byte whose octal value is
460.Ar nnn
461(one to three digits)
462.It \ex Ns Ar nn
463The byte whose hexadecimal value is
464.Ar nn
465(one or more digits only the last two of which are used)
466.It \eu Ns Ar nnnn
467The Unicode code point
468.Ar nnnn
469(four hexadecimal digits)
470.It \eU Ns Ar nnnnnnnn
471The Unicode code point
472.Ar nnnnnnnn
473(eight hexadecimal digits)
474.El
475.Pp
476The sequences for Unicode code points are currently only useful with
477UTF-8 locales.
478They reject code point 0 and UTF-16 surrogates.
479.Pp
480If an escape sequence would produce a byte with value 0,
481that byte and the rest of the string until the matching single-quote
482are ignored.
483.Pp
484Any other string starting with a backslash is an error.
485.It Double Quotes
486Enclosing characters within double quotes preserves the literal
487meaning of all characters except dollar sign
488.Pq Ql $ ,
489backquote
490.Pq Ql ` ,
491and backslash
492.Pq Ql \e .
493The backslash inside double quotes is historically weird.
494It remains literal unless it precedes the following characters,
495which it serves to quote:
496.Pp
497.Bl -column "XXX" "XXX" "XXX" "XXX" "XXX" -offset center -compact
498.It Li $ Ta Li ` Ta Li \&" Ta Li \e Ta Li \en
499.El
500.It Backslash
501A backslash preserves the literal meaning of the following
502character, with the exception of the newline character
503.Pq Ql \en .
504A backslash preceding a newline is treated as a line continuation.
505.El
506.Ss Keywords
507Keywords or reserved words are words that have special meaning to the
508shell and are recognized at the beginning of a line and
509after a control operator.
510The following are keywords:
511.Bl -column "doneXX" "elifXX" "elseXX" "untilXX" "whileX" -offset center
512.It Li \&! Ta { Ta } Ta Ic case Ta Ic do
513.It Ic done Ta Ic elif Ta Ic else Ta Ic esac Ta Ic fi
514.It Ic for Ta Ic if Ta Ic then Ta Ic until Ta Ic while
515.El
516.Ss Aliases
517An alias is a name and corresponding value set using the
518.Ic alias
519built-in command.
520Wherever the command word of a simple command may occur,
521and after checking for keywords if a keyword may occur, the shell
522checks the word to see if it matches an alias.
523If it does, it replaces it in the input stream with its value.
524For example, if there is an alias called
525.Dq Li lf
526with the value
527.Dq Li "ls -F" ,
528then the input
529.Pp
530.Dl "lf foobar"
531.Pp
532would become
533.Pp
534.Dl "ls -F foobar"
535.Pp
536Aliases provide a convenient way for naive users to
537create shorthands for commands without having to learn how
538to create functions with arguments.
539Using aliases in scripts is discouraged
540because the command that defines them must be executed
541before the code that uses them is parsed.
542This is fragile and not portable.
543.Pp
544An alias name may be escaped in a command line, so that it is not
545replaced by its alias value, by using quoting characters within or
546adjacent to the alias name.
547This is most often done by prefixing
548an alias name with a backslash to execute a function, built-in, or
549normal program with the same name.
550See the
551.Sx Quoting
552subsection.
553.Ss Commands
554The shell interprets the words it reads according to a
555language, the specification of which is outside the scope
556of this man page (refer to the BNF in the
557.St -p1003.2
558document).
559Essentially though, a line is read and if
560the first word of the line (or after a control operator)
561is not a keyword, then the shell has recognized a
562simple command.
563Otherwise, a complex command or some
564other special construct may have been recognized.
565.Ss Simple Commands
566If a simple command has been recognized, the shell performs
567the following actions:
568.Bl -enum
569.It
570Leading words of the form
571.Dq Li name=value
572are stripped off and assigned to the environment of
573the simple command.
574Redirection operators and
575their arguments (as described below) are stripped
576off and saved for processing.
577.It
578The remaining words are expanded as described in
579the section called
580.Sx Word Expansions ,
581and the first remaining word is considered the command
582name and the command is located.
583The remaining
584words are considered the arguments of the command.
585If no command name resulted, then the
586.Dq Li name=value
587variable assignments recognized in 1) affect the
588current shell.
589.It
590Redirections are performed as described in
591the next section.
592.El
593.Ss Redirections
594Redirections are used to change where a command reads its input
595or sends its output.
596In general, redirections open, close, or
597duplicate an existing reference to a file.
598The overall format
599used for redirection is:
600.Pp
601.D1 Oo Ar n Oc Ar redir-op file
602.Pp
603The
604.Ar redir-op
605is one of the redirection operators mentioned
606previously.
607The following gives some examples of how these
608operators can be used.
609Note that stdin and stdout are commonly used abbreviations
610for standard input and standard output respectively.
611.Bl -tag -width "1234567890XX" -offset indent
612.It Oo Ar n Oc Ns Li > Ar file
613redirect stdout (or file descriptor
614.Ar n )
615to
616.Ar file
617.It Oo Ar n Oc Ns Li >| Ar file
618same as above, but override the
619.Fl C
620option
621.It Oo Ar n Oc Ns Li >> Ar file
622append stdout (or file descriptor
623.Ar n )
624to
625.Ar file
626.It Oo Ar n Oc Ns Li < Ar file
627redirect stdin (or file descriptor
628.Ar n )
629from
630.Ar file
631.It Oo Ar n Oc Ns Li <> Ar file
632redirect stdin (or file descriptor
633.Ar n )
634to and from
635.Ar file
636.It Oo Ar n1 Oc Ns Li <& Ns Ar n2
637duplicate stdin (or file descriptor
638.Ar n1 )
639from file descriptor
640.Ar n2
641.It Oo Ar n Oc Ns Li <&-
642close stdin (or file descriptor
643.Ar n )
644.It Oo Ar n1 Oc Ns Li >& Ns Ar n2
645duplicate stdout (or file descriptor
646.Ar n1 )
647to file descriptor
648.Ar n2
649.It Oo Ar n Oc Ns Li >&-
650close stdout (or file descriptor
651.Ar n )
652.El
653.Pp
654The following redirection is often called a
655.Dq here-document .
656.Bd -unfilled -offset indent
657.Oo Ar n Oc Ns Li << Ar delimiter
658.Ar here-doc-text
659.Ar ...
660.Ar delimiter
661.Ed
662.Pp
663All the text on successive lines up to the delimiter is
664saved away and made available to the command on standard
665input, or file descriptor
666.Ar n
667if it is specified.
668If the
669.Ar delimiter
670as specified on the initial line is quoted, then the
671.Ar here-doc-text
672is treated literally, otherwise the text is subjected to
673parameter expansion, command substitution, and arithmetic
674expansion (as described in the section on
675.Sx Word Expansions ) .
676If the operator is
677.Dq Li <<-
678instead of
679.Dq Li << ,
680then leading tabs
681in the
682.Ar here-doc-text
683are stripped.
684.Ss Search and Execution
685There are three types of commands: shell functions,
686built-in commands, and normal programs.
687The command is searched for (by name) in that order.
688The three types of commands are all executed in a different way.
689.Pp
690When a shell function is executed, all of the shell positional
691parameters (except
692.Li $0 ,
693which remains unchanged) are
694set to the arguments of the shell function.
695The variables which are explicitly placed in the environment of
696the command (by placing assignments to them before the
697function name) are made local to the function and are set
698to the values given.
699Then the command given in the function definition is executed.
700The positional parameters are restored to their original values
701when the command completes.
702This all occurs within the current shell.
703.Pp
704Shell built-in commands are executed internally to the shell, without
705spawning a new process.
706There are two kinds of built-in commands: regular and special.
707Assignments before special builtins persist after they finish
708executing and assignment errors, redirection errors and certain
709operand errors cause a script to be aborted.
710Special builtins cannot be overridden with a function.
711Both regular and special builtins can affect the shell in ways
712normal programs cannot.
713.Pp
714Otherwise, if the command name does not match a function
715or built-in command, the command is searched for as a normal
716program in the file system (as described in the next section).
717When a normal program is executed, the shell runs the program,
718passing the arguments and the environment to the program.
719If the program is not a normal executable file
720(i.e., if it does not begin with the
721.Dq "magic number"
722whose
723.Tn ASCII
724representation is
725.Dq Li #! ,
726resulting in an
727.Er ENOEXEC
728return value from
729.Xr execve 2 )
730but appears to be a text file,
731the shell will run a new instance of
732.Nm
733to interpret it.
734.Pp
735Note that previous versions of this document
736and the source code itself misleadingly and sporadically
737refer to a shell script without a magic number
738as a
739.Dq "shell procedure" .
740.Ss Path Search
741When locating a command, the shell first looks to see if
742it has a shell function by that name.
743Then it looks for a
744built-in command by that name.
745If a built-in command is not found,
746one of two things happen:
747.Bl -enum
748.It
749Command names containing a slash are simply executed without
750performing any searches.
751.It
752The shell searches each entry in the
753.Va PATH
754variable
755in turn for the command.
756The value of the
757.Va PATH
758variable should be a series of
759entries separated by colons.
760Each entry consists of a
761directory name.
762The current directory
763may be indicated implicitly by an empty directory name,
764or explicitly by a single period.
765.El
766.Ss Command Exit Status
767Each command has an exit status that can influence the behavior
768of other shell commands.
769The paradigm is that a command exits
770with zero for normal or success, and non-zero for failure,
771error, or a false indication.
772The man page for each command
773should indicate the various exit codes and what they mean.
774Additionally, the built-in commands return exit codes, as does
775an executed shell function.
776.Pp
777If a command is terminated by a signal, its exit status is 128 plus
778the signal number.
779Signal numbers are defined in the header file
780.In sys/signal.h .
781.Ss Complex Commands
782Complex commands are combinations of simple commands
783with control operators or keywords, together creating a larger complex
784command.
785More generally, a command is one of the following:
786.Bl -item -offset indent
787.It
788simple command
789.It
790pipeline
791.It
792list or compound-list
793.It
794compound command
795.It
796function definition
797.El
798.Pp
799Unless otherwise stated, the exit status of a command is
800that of the last simple command executed by the command.
801.Ss Pipelines
802A pipeline is a sequence of one or more commands separated
803by the control operator
804.Ql \&| .
805The standard output of all but
806the last command is connected to the standard input
807of the next command.
808The standard output of the last
809command is inherited from the shell, as usual.
810.Pp
811The format for a pipeline is:
812.Pp
813.D1 Oo Li \&! Oc Ar command1 Op Li \&| Ar command2 ...
814.Pp
815The standard output of
816.Ar command1
817is connected to the standard input of
818.Ar command2 .
819The standard input, standard output, or
820both of a command is considered to be assigned by the
821pipeline before any redirection specified by redirection
822operators that are part of the command.
823.Pp
824Note that unlike some other shells,
825.Nm
826executes each process in a pipeline with more than one command
827in a subshell environment and as a child of the
828.Nm
829process.
830.Pp
831If the pipeline is not in the background (discussed later),
832the shell waits for all commands to complete.
833.Pp
834If the keyword
835.Ic !\&
836does not precede the pipeline, the
837exit status is the exit status of the last command specified
838in the pipeline.
839Otherwise, the exit status is the logical
840NOT of the exit status of the last command.
841That is, if
842the last command returns zero, the exit status is 1; if
843the last command returns greater than zero, the exit status
844is zero.
845.Pp
846Because pipeline assignment of standard input or standard
847output or both takes place before redirection, it can be
848modified by redirection.
849For example:
850.Pp
851.Dl "command1 2>&1 | command2"
852.Pp
853sends both the standard output and standard error of
854.Ar command1
855to the standard input of
856.Ar command2 .
857.Pp
858A
859.Ql \&;
860or newline terminator causes the preceding
861AND-OR-list
862(described below in the section called
863.Sx Short-Circuit List Operators )
864to be executed sequentially;
865an
866.Ql &
867causes asynchronous execution of the preceding AND-OR-list.
868.Ss Background Commands (&)
869If a command is terminated by the control operator ampersand
870.Pq Ql & ,
871the shell executes the command in a subshell environment (see
872.Sx Grouping Commands Together
873below) and asynchronously;
874the shell does not wait for the command to finish
875before executing the next command.
876.Pp
877The format for running a command in background is:
878.Pp
879.D1 Ar command1 Li & Op Ar command2 Li & Ar ...
880.Pp
881If the shell is not interactive, the standard input of an
882asynchronous command is set to
883.Pa /dev/null .
884.Ss Lists (Generally Speaking)
885A list is a sequence of zero or more commands separated by
886newlines, semicolons, or ampersands,
887and optionally terminated by one of these three characters.
888The commands in a
889list are executed in the order they are written.
890If command is followed by an ampersand, the shell starts the
891command and immediately proceeds onto the next command;
892otherwise it waits for the command to terminate before
893proceeding to the next one.
894.Ss Short-Circuit List Operators
895.Dq Li &&
896and
897.Dq Li ||
898are AND-OR list operators.
899.Dq Li &&
900executes the first command, and then executes the second command
901if the exit status of the first command is zero.
902.Dq Li ||
903is similar, but executes the second command if the exit
904status of the first command is nonzero.
905.Dq Li &&
906and
907.Dq Li ||
908both have the same priority.
909.Ss Flow-Control Constructs (if, while, for, case)
910The syntax of the
911.Ic if
912command is:
913.Bd -unfilled -offset indent -compact
914.Ic if Ar list
915.Ic then Ar list
916.Oo Ic elif Ar list
917.Ic then Ar list Oc Ar ...
918.Op Ic else Ar list
919.Ic fi
920.Ed
921.Pp
922The syntax of the
923.Ic while
924command is:
925.Bd -unfilled -offset indent -compact
926.Ic while Ar list
927.Ic do Ar list
928.Ic done
929.Ed
930.Pp
931The two lists are executed repeatedly while the exit status of the
932first list is zero.
933The
934.Ic until
935command is similar, but has the word
936.Ic until
937in place of
938.Ic while ,
939which causes it to
940repeat until the exit status of the first list is zero.
941.Pp
942The syntax of the
943.Ic for
944command is:
945.Bd -unfilled -offset indent -compact
946.Ic for Ar variable Op Ic in Ar word ...
947.Ic do Ar list
948.Ic done
949.Ed
950.Pp
951If
952.Ic in
953and the following words are omitted,
954.Ic in Li \&"$@\&"
955is used instead.
956The words are expanded, and then the list is executed
957repeatedly with the variable set to each word in turn.
958The
959.Ic do
960and
961.Ic done
962commands may be replaced with
963.Ql {
964and
965.Ql } .
966.Pp
967The syntax of the
968.Ic break
969and
970.Ic continue
971commands is:
972.D1 Ic break Op Ar num
973.D1 Ic continue Op Ar num
974.Pp
975The
976.Ic break
977command terminates the
978.Ar num
979innermost
980.Ic for
981or
982.Ic while
983loops.
984The
985.Ic continue
986command continues with the next iteration of the innermost loop.
987These are implemented as special built-in commands.
988.Pp
989The syntax of the
990.Ic case
991command is:
992.Bd -unfilled -offset indent -compact
993.Ic case Ar word Ic in
994.Ar pattern Ns Li ) Ar list Li ;;
995.Ar ...
996.Ic esac
997.Ed
998.Pp
999The pattern can actually be one or more patterns
1000(see
1001.Sx Shell Patterns
1002described later),
1003separated by
1004.Ql \&|
1005characters.
1006Tilde expansion, parameter expansion, command substitution,
1007arithmetic expansion and quote removal are applied to the word.
1008Then, each pattern is expanded in turn using tilde expansion,
1009parameter expansion, command substitution and arithmetic expansion and
1010the expanded form of the word is checked against it.
1011If a match is found, the corresponding list is executed.
1012If the selected list is terminated by the control operator
1013.Ql ;&
1014instead of
1015.Ql ;; ,
1016execution continues with the next list,
1017continuing until a list terminated with
1018.Ql ;;
1019or the end of the
1020.Ic case
1021command.
1022The exit code of the
1023.Ic case
1024command is the exit code of the last command executed in the list or
1025zero if no patterns were matched.
1026.Ss Grouping Commands Together
1027Commands may be grouped by writing either
1028.Pp
1029.D1 Li \&( Ns Ar list Ns Li \%)
1030.Pp
1031or
1032.Pp
1033.D1 Li { Ar list Ns Li \&; }
1034.Pp
1035The first form executes the commands in a subshell environment.
1036A subshell environment has its own copy of:
1037.Bl -enum
1038.It
1039The current working directory as set by
1040.Ic cd .
1041.It
1042The file creation mask as set by
1043.Ic umask .
1044.It
1045Resource limits as set by
1046.Ic ulimit .
1047.It
1048References to open files.
1049.It
1050Traps as set by
1051.Ic trap .
1052.It
1053Known jobs.
1054.It
1055Positional parameters and variables.
1056.It
1057Shell options.
1058.It
1059Shell functions.
1060.It
1061Shell aliases.
1062.El
1063.Pp
1064These are copied from the parent shell environment,
1065except that trapped (but not ignored) signals are reset to the default action
1066and known jobs are cleared.
1067Any changes do not affect the parent shell environment.
1068.Pp
1069A subshell environment may be implemented as a child process or differently.
1070If job control is enabled in an interactive shell,
1071commands grouped in parentheses can be suspended and continued as a unit.
1072.Pp
1073For compatibility with other shells,
1074two open parentheses in sequence should be separated by whitespace.
1075.Pp
1076The second form never forks another shell,
1077so it is slightly more efficient.
1078Grouping commands together this way allows the user to
1079redirect their output as though they were one program:
1080.Bd -literal -offset indent
1081{ echo -n "hello"; echo " world"; } > greeting
1082.Ed
1083.Ss Functions
1084The syntax of a function definition is
1085.Pp
1086.D1 Ar name Li \&( \&) Ar command
1087.Pp
1088A function definition is an executable statement; when
1089executed it installs a function named
1090.Ar name
1091and returns an
1092exit status of zero.
1093The
1094.Ar command
1095is normally a list
1096enclosed between
1097.Ql {
1098and
1099.Ql } .
1100.Pp
1101Variables may be declared to be local to a function by
1102using the
1103.Ic local
1104command.
1105This should appear as the first statement of a function,
1106and the syntax is:
1107.Pp
1108.D1 Ic local Oo Ar variable ... Oc Op Fl
1109.Pp
1110The
1111.Ic local
1112command is implemented as a built-in command.
1113.Pp
1114When a variable is made local, it inherits the initial
1115value and exported and readonly flags from the variable
1116with the same name in the surrounding scope, if there is
1117one.
1118Otherwise, the variable is initially unset.
1119The shell
1120uses dynamic scoping, so that if the variable
1121.Va x
1122is made local to function
1123.Em f ,
1124which then calls function
1125.Em g ,
1126references to the variable
1127.Va x
1128made inside
1129.Em g
1130will refer to the variable
1131.Va x
1132declared inside
1133.Em f ,
1134not to the global variable named
1135.Va x .
1136.Pp
1137The only special parameter that can be made local is
1138.Ql - .
1139Making
1140.Ql -
1141local causes any shell options that are
1142changed via the
1143.Ic set
1144command inside the function to be
1145restored to their original values when the function
1146returns.
1147.Pp
1148The syntax of the
1149.Ic return
1150command is
1151.Pp
1152.D1 Ic return Op Ar exitstatus
1153.Pp
1154It terminates the current executional scope, returning from the closest
1155nested function or sourced script;
1156if no function or sourced script is being executed,
1157it exits the shell instance.
1158The
1159.Ic return
1160command is implemented as a special built-in command.
1161.Ss Variables and Parameters
1162The shell maintains a set of parameters.
1163A parameter
1164denoted by a name is called a variable.
1165When starting up,
1166the shell turns all the environment variables into shell
1167variables.
1168New variables can be set using the form
1169.Pp
1170.D1 Ar name Ns = Ns Ar value
1171.Pp
1172Variables set by the user must have a name consisting solely
1173of alphabetics, numerics, and underscores.
1174The first letter of a variable name must not be numeric.
1175A parameter can also be denoted by a number
1176or a special character as explained below.
1177.Pp
1178Assignments are expanded differently from other words:
1179tilde expansion is also performed after the equals sign and after any colon
1180and usernames are also terminated by colons,
1181and field splitting and pathname expansion are not performed.
1182.Pp
1183This special expansion applies not only to assignments that form a simple
1184command by themselves or precede a command word,
1185but also to words passed to the
1186.Ic export ,
1187.Ic local
1188or
1189.Ic readonly
1190built-in commands that have this form.
1191For this, the builtin's name must be literal
1192(not the result of an expansion)
1193and may optionally be preceded by one or more literal instances of
1194.Ic command
1195without options.
1196.Ss Positional Parameters
1197A positional parameter is a parameter denoted by a number greater than zero.
1198The shell sets these initially to the values of its command line
1199arguments that follow the name of the shell script.
1200The
1201.Ic set
1202built-in command can also be used to set or reset them.
1203.Ss Special Parameters
1204Special parameters are parameters denoted by a single special character
1205or the digit zero.
1206They are shown in the following list, exactly as they would appear in input
1207typed by the user or in the source of a shell script.
1208.Bl -hang
1209.It Li $*
1210Expands to the positional parameters, starting from one.
1211When
1212the expansion occurs within a double-quoted string
1213it expands to a single field with the value of each parameter
1214separated by the first character of the
1215.Va IFS
1216variable,
1217or by a space if
1218.Va IFS
1219is unset.
1220.It Li $@
1221Expands to the positional parameters, starting from one.
1222When
1223the expansion occurs within double-quotes, each positional
1224parameter expands as a separate argument.
1225If there are no positional parameters, the
1226expansion of
1227.Li @
1228generates zero arguments, even when
1229.Li @
1230is double-quoted.
1231What this basically means, for example, is
1232if
1233.Li $1
1234is
1235.Dq Li abc
1236and
1237.Li $2
1238is
1239.Dq Li "def ghi" ,
1240then
1241.Li \&"$@\&"
1242expands to
1243the two arguments:
1244.Bd -literal -offset indent
1245"abc"   "def ghi"
1246.Ed
1247.It Li $#
1248Expands to the number of positional parameters.
1249.It Li $?
1250Expands to the exit status of the most recent pipeline.
1251.It Li $-
1252(hyphen) Expands to the current option flags (the single-letter
1253option names concatenated into a string) as specified on
1254invocation, by the
1255.Ic set
1256built-in command, or implicitly
1257by the shell.
1258.It Li $$
1259Expands to the process ID of the invoked shell.
1260A subshell
1261retains the same value of
1262.Va $
1263as its parent.
1264.It Li $!
1265Expands to the process ID of the most recent background
1266command executed from the current shell.
1267For a
1268pipeline, the process ID is that of the last command in the
1269pipeline.
1270If this parameter is referenced, the shell will remember
1271the process ID and its exit status until the
1272.Ic wait
1273built-in command reports completion of the process.
1274.It Li $0
1275(zero) Expands to the name of the shell script if passed on the command line,
1276the
1277.Ar name
1278operand if given (with
1279.Fl c )
1280or otherwise argument 0 passed to the shell.
1281.El
1282.Ss Special Variables
1283The following variables are set by the shell or
1284have special meaning to it:
1285.Bl -tag -width ".Va HISTSIZE"
1286.It Va CDPATH
1287The search path used with the
1288.Ic cd
1289built-in.
1290.It Va EDITOR
1291The fallback editor used with the
1292.Ic fc
1293built-in.
1294If not set, the default editor is
1295.Xr ed 1 .
1296.It Va FCEDIT
1297The default editor used with the
1298.Ic fc
1299built-in.
1300.It Va HISTSIZE
1301The number of previous commands that are accessible.
1302.It Va HOME
1303The user's home directory,
1304used in tilde expansion and as a default directory for the
1305.Ic cd
1306built-in.
1307.It Va IFS
1308Input Field Separators.
1309The default value is
1310.Aq space ,
1311.Aq tab ,
1312and
1313.Aq newline
1314in that order.
1315This default also applies if
1316.Va IFS
1317is unset, but not if it is set to the empty string.
1318See the
1319.Sx White Space Splitting
1320section for more details.
1321.It Va LINENO
1322The current line number in the script or function.
1323.It Va MAIL
1324The name of a mail file, that will be checked for the arrival of new
1325mail.
1326Overridden by
1327.Va MAILPATH .
1328.It Va MAILPATH
1329A colon
1330.Pq Ql \&:
1331separated list of file names, for the shell to check for incoming
1332mail.
1333This variable overrides the
1334.Va MAIL
1335setting.
1336There is a maximum of 10 mailboxes that can be monitored at once.
1337.It Va PATH
1338The default search path for executables.
1339See the
1340.Sx Path Search
1341section for details.
1342.It Va PPID
1343The parent process ID of the invoked shell.
1344This is set at startup
1345unless this variable is in the environment.
1346A later change of parent process ID is not reflected.
1347A subshell retains the same value of
1348.Va PPID .
1349.It Va PS1
1350The primary prompt string, which defaults to
1351.Dq Li "$ " ,
1352unless you are the superuser, in which case it defaults to
1353.Dq Li "# " .
1354.Va PS1
1355may include any of the following formatting sequences,
1356which are replaced by the given information:
1357.Bl -tag -width indent
1358.It Li \eH
1359The local hostname.
1360.It Li \eh
1361The fully-qualified hostname.
1362.It Li \eW
1363The final component of the current working directory.
1364.It Li \ew
1365The entire path of the current working directory.
1366.It Li \e$
1367Superuser status.
1368.Dq Li "$ "
1369for normal users and
1370.Dq Li "# "
1371for superusers.
1372.It Li \e\e
1373A literal backslash.
1374.El
1375.It Va PS2
1376The secondary prompt string, which defaults to
1377.Dq Li "> " .
1378.Va PS2
1379may include any of the formatting sequences from
1380.Va PS1 .
1381.It Va PS4
1382The prefix for the trace output (if
1383.Fl x
1384is active).
1385The default is
1386.Dq Li "+ " .
1387.El
1388.Ss Word Expansions
1389This clause describes the various expansions that are
1390performed on words.
1391Not all expansions are performed on
1392every word, as explained later.
1393.Pp
1394Tilde expansions, parameter expansions, command substitutions,
1395arithmetic expansions, and quote removals that occur within
1396a single word expand to a single field.
1397It is only field
1398splitting or pathname expansion that can create multiple
1399fields from a single word.
1400The single exception to this rule is
1401the expansion of the special parameter
1402.Va @
1403within double-quotes,
1404as was described above.
1405.Pp
1406The order of word expansion is:
1407.Bl -enum
1408.It
1409Tilde Expansion, Parameter Expansion, Command Substitution,
1410Arithmetic Expansion (these all occur at the same time).
1411.It
1412Field Splitting is performed on fields generated by step (1)
1413unless the
1414.Va IFS
1415variable is null.
1416.It
1417Pathname Expansion (unless the
1418.Fl f
1419option is in effect).
1420.It
1421Quote Removal.
1422.El
1423.Pp
1424The
1425.Ql $
1426character is used to introduce parameter expansion, command
1427substitution, or arithmetic expansion.
1428.Ss Tilde Expansion (substituting a user's home directory)
1429A word beginning with an unquoted tilde character
1430.Pq Ql ~
1431is
1432subjected to tilde expansion.
1433All the characters up to a slash
1434.Pq Ql /
1435or the end of the word are treated as a username
1436and are replaced with the user's home directory.
1437If the
1438username is missing (as in
1439.Pa ~/foobar ) ,
1440the tilde is replaced with the value of the
1441.Va HOME
1442variable (the current user's home directory).
1443.Ss Parameter Expansion
1444The format for parameter expansion is as follows:
1445.Pp
1446.D1 Li ${ Ns Ar expression Ns Li }
1447.Pp
1448where
1449.Ar expression
1450consists of all characters until the matching
1451.Ql } .
1452Any
1453.Ql }
1454escaped by a backslash or within a single-quoted or double-quoted
1455string, and characters in
1456embedded arithmetic expansions, command substitutions, and variable
1457expansions, are not examined in determining the matching
1458.Ql } .
1459If the variants with
1460.Ql + ,
1461.Ql - ,
1462.Ql =
1463or
1464.Ql ?\&
1465occur within a double-quoted string,
1466as an extension there may be unquoted parts
1467(via double-quotes inside the expansion);
1468.Ql }
1469within such parts are also not examined in determining the matching
1470.Ql } .
1471.Pp
1472The simplest form for parameter expansion is:
1473.Pp
1474.D1 Li ${ Ns Ar parameter Ns Li }
1475.Pp
1476The value, if any, of
1477.Ar parameter
1478is substituted.
1479.Pp
1480The parameter name or symbol can be enclosed in braces, which are
1481optional except for positional parameters with more than one digit or
1482when parameter is followed by a character that could be interpreted as
1483part of the name.
1484If a parameter expansion occurs inside double-quotes:
1485.Bl -enum
1486.It
1487Field splitting is not performed on the results of the
1488expansion, with the exception of the special parameter
1489.Va @ .
1490.It
1491Pathname expansion is not performed on the results of the
1492expansion.
1493.El
1494.Pp
1495In addition, a parameter expansion can be modified by using one of the
1496following formats.
1497.Bl -tag -width indent
1498.It Li ${ Ns Ar parameter Ns Li :- Ns Ar word Ns Li }
1499Use Default Values.
1500If
1501.Ar parameter
1502is unset or null, the expansion of
1503.Ar word
1504is substituted; otherwise, the value of
1505.Ar parameter
1506is substituted.
1507.It Li ${ Ns Ar parameter Ns Li := Ns Ar word Ns Li }
1508Assign Default Values.
1509If
1510.Ar parameter
1511is unset or null, the expansion of
1512.Ar word
1513is assigned to
1514.Ar parameter .
1515In all cases, the
1516final value of
1517.Ar parameter
1518is substituted.
1519Quoting inside
1520.Ar word
1521does not prevent field splitting or pathname expansion.
1522Only variables, not positional
1523parameters or special parameters, can be
1524assigned in this way.
1525.It Li ${ Ns Ar parameter Ns Li :? Ns Oo Ar word Oc Ns Li }
1526Indicate Error if Null or Unset.
1527If
1528.Ar parameter
1529is unset or null, the expansion of
1530.Ar word
1531(or a message indicating it is unset if
1532.Ar word
1533is omitted) is written to standard
1534error and the shell exits with a nonzero
1535exit status.
1536Otherwise, the value of
1537.Ar parameter
1538is substituted.
1539An
1540interactive shell need not exit.
1541.It Li ${ Ns Ar parameter Ns Li :+ Ns Ar word Ns Li }
1542Use Alternate Value.
1543If
1544.Ar parameter
1545is unset or null, null is substituted;
1546otherwise, the expansion of
1547.Ar word
1548is substituted.
1549.El
1550.Pp
1551In the parameter expansions shown previously, use of the colon in the
1552format results in a test for a parameter that is unset or null; omission
1553of the colon results in a test for a parameter that is only unset.
1554.Pp
1555The
1556.Ar word
1557inherits the type of quoting
1558(unquoted, double-quoted or here-document)
1559from the surroundings,
1560with the exception that a backslash that quotes a closing brace is removed
1561during quote removal.
1562.Bl -tag -width indent
1563.It Li ${# Ns Ar parameter Ns Li }
1564String Length.
1565The length in characters of
1566the value of
1567.Ar parameter .
1568.El
1569.Pp
1570The following four varieties of parameter expansion provide for substring
1571processing.
1572In each case, pattern matching notation
1573(see
1574.Sx Shell Patterns ) ,
1575rather than regular expression notation,
1576is used to evaluate the patterns.
1577If parameter is one of the special parameters
1578.Va *
1579or
1580.Va @ ,
1581the result of the expansion is unspecified.
1582Enclosing the full parameter expansion string in double-quotes does not
1583cause the following four varieties of pattern characters to be quoted,
1584whereas quoting characters within the braces has this effect.
1585.Bl -tag -width indent
1586.It Li ${ Ns Ar parameter Ns Li % Ns Ar word Ns Li }
1587Remove Smallest Suffix Pattern.
1588The
1589.Ar word
1590is expanded to produce a pattern.
1591The
1592parameter expansion then results in
1593.Ar parameter ,
1594with the smallest portion of the
1595suffix matched by the pattern deleted.
1596.It Li ${ Ns Ar parameter Ns Li %% Ns Ar word Ns Li }
1597Remove Largest Suffix Pattern.
1598The
1599.Ar word
1600is expanded to produce a pattern.
1601The
1602parameter expansion then results in
1603.Ar parameter ,
1604with the largest portion of the
1605suffix matched by the pattern deleted.
1606.It Li ${ Ns Ar parameter Ns Li # Ns Ar word Ns Li }
1607Remove Smallest Prefix Pattern.
1608The
1609.Ar word
1610is expanded to produce a pattern.
1611The
1612parameter expansion then results in
1613.Ar parameter ,
1614with the smallest portion of the
1615prefix matched by the pattern deleted.
1616.It Li ${ Ns Ar parameter Ns Li ## Ns Ar word Ns Li }
1617Remove Largest Prefix Pattern.
1618The
1619.Ar word
1620is expanded to produce a pattern.
1621The
1622parameter expansion then results in
1623.Ar parameter ,
1624with the largest portion of the
1625prefix matched by the pattern deleted.
1626.El
1627.Ss Command Substitution
1628Command substitution allows the output of a command to be substituted in
1629place of the command name itself.
1630Command substitution occurs when
1631the command is enclosed as follows:
1632.Pp
1633.D1 Li $( Ns Ar command Ns Li )\&
1634.Pp
1635or the backquoted version:
1636.Pp
1637.D1 Li ` Ns Ar command Ns Li `
1638.Pp
1639The shell expands the command substitution by executing command
1640and replacing the command substitution
1641with the standard output of the command,
1642removing sequences of one or more newlines at the end of the substitution.
1643Embedded newlines before the end of the output are not removed;
1644however, during field splitting, they may be translated into spaces
1645depending on the value of
1646.Va IFS
1647and the quoting that is in effect.
1648The command is executed in a subshell environment,
1649except that the built-in commands
1650.Ic jobid ,
1651.Ic jobs ,
1652and
1653.Ic trap
1654return information about the parent shell environment
1655and
1656.Ic times
1657returns information about the same process
1658if they are the only command in a command substitution.
1659.Pp
1660If a command substitution of the
1661.Li $(
1662form begins with a subshell,
1663the
1664.Li $(
1665and
1666.Li (\&
1667must be separated by whitespace
1668to avoid ambiguity with arithmetic expansion.
1669.Ss Arithmetic Expansion
1670Arithmetic expansion provides a mechanism for evaluating an arithmetic
1671expression and substituting its value.
1672The format for arithmetic expansion is as follows:
1673.Pp
1674.D1 Li $(( Ns Ar expression Ns Li ))
1675.Pp
1676The
1677.Ar expression
1678is treated as if it were in double-quotes, except
1679that a double-quote inside the expression is not treated specially.
1680The
1681shell expands all tokens in the
1682.Ar expression
1683for parameter expansion,
1684command substitution,
1685arithmetic expansion
1686and quote removal.
1687.Pp
1688The allowed expressions are a subset of C expressions,
1689summarized below.
1690.Bl -tag -width "Variables" -offset indent
1691.It Values
1692All values are of type
1693.Ft intmax_t .
1694.It Constants
1695Decimal, octal (starting with
1696.Li 0 )
1697and hexadecimal (starting with
1698.Li 0x )
1699integer constants.
1700.It Variables
1701Shell variables can be read and written
1702and contain integer constants.
1703.It Unary operators
1704.Li "! ~ + -"
1705.It Binary operators
1706.Li "* / % + - << >> < <= > >= == != & ^ | && ||"
1707.It Assignment operators
1708.Li "= += -= *= /= %= <<= >>= &= ^= |="
1709.It Conditional operator
1710.Li "? :"
1711.El
1712.Pp
1713The result of the expression is substituted in decimal.
1714.Ss White Space Splitting (Field Splitting)
1715In certain contexts,
1716after parameter expansion, command substitution, and
1717arithmetic expansion the shell scans the results of
1718expansions and substitutions that did not occur in double-quotes for
1719field splitting and multiple fields can result.
1720.Pp
1721Characters in
1722.Va IFS
1723that are whitespace
1724.Po
1725.Aq space ,
1726.Aq tab ,
1727and
1728.Aq newline
1729.Pc
1730are treated differently from other characters in
1731.Va IFS .
1732.Pp
1733Whitespace in
1734.Va IFS
1735at the beginning or end of a word is discarded.
1736.Pp
1737Subsequently, a field is delimited by either
1738.Bl -enum
1739.It
1740a non-whitespace character in
1741.Va IFS
1742with any whitespace in
1743.Va IFS
1744surrounding it, or
1745.It
1746one or more whitespace characters in
1747.Va IFS .
1748.El
1749.Pp
1750If a word ends with a non-whitespace character in
1751.Va IFS ,
1752there is no empty field after this character.
1753.Pp
1754If no field is delimited, the word is discarded.
1755In particular, if a word consists solely of an unquoted substitution
1756and the result of the substitution is null,
1757it is removed by field splitting even if
1758.Va IFS
1759is null.
1760.Ss Pathname Expansion (File Name Generation)
1761Unless the
1762.Fl f
1763option is set,
1764file name generation is performed
1765after word splitting is complete.
1766Each word is
1767viewed as a series of patterns, separated by slashes.
1768The
1769process of expansion replaces the word with the names of
1770all existing files whose names can be formed by replacing
1771each pattern with a string that matches the specified pattern.
1772There are two restrictions on this: first, a pattern cannot match
1773a string containing a slash, and second,
1774a pattern cannot match a string starting with a period
1775unless the first character of the pattern is a period.
1776The next section describes the patterns used for
1777Pathname Expansion,
1778the four varieties of parameter expansion for substring processing and the
1779.Ic case
1780command.
1781.Ss Shell Patterns
1782A pattern consists of normal characters, which match themselves,
1783and meta-characters.
1784The meta-characters are
1785.Ql * ,
1786.Ql \&? ,
1787and
1788.Ql \&[ .
1789These characters lose their special meanings if they are quoted.
1790When command or variable substitution is performed and the dollar sign
1791or back quotes are not double-quoted, the value of the
1792variable or the output of the command is scanned for these
1793characters and they are turned into meta-characters.
1794.Pp
1795An asterisk
1796.Pq Ql *
1797matches any string of characters.
1798A question mark
1799.Pq Ql \&?
1800matches any single character.
1801A left bracket
1802.Pq Ql \&[
1803introduces a character class.
1804The end of the character class is indicated by a
1805.Ql \&] ;
1806if the
1807.Ql \&]
1808is missing then the
1809.Ql \&[
1810matches a
1811.Ql \&[
1812rather than introducing a character class.
1813A character class matches any of the characters between the square brackets.
1814A locale-dependent range of characters may be specified using a minus sign.
1815A named class of characters (see
1816.Xr wctype 3 )
1817may be specified by surrounding the name with
1818.Ql \&[:
1819and
1820.Ql :\&] .
1821For example,
1822.Ql \&[\&[:alpha:\&]\&]
1823is a shell pattern that matches a single letter.
1824The character class may be complemented by making an exclamation point
1825.Pq Ql !\&
1826the first character of the character class.
1827A caret
1828.Pq Ql ^
1829has the same effect but is non-standard.
1830.Pp
1831To include a
1832.Ql \&]
1833in a character class, make it the first character listed
1834(after the
1835.Ql \&!
1836or
1837.Ql ^ ,
1838if any).
1839To include a
1840.Ql - ,
1841make it the first or last character listed.
1842.Ss Built-in Commands
1843This section lists the built-in commands.
1844.Bl -tag -width indent
1845.It Ic \&:
1846A null command that returns a 0 (true) exit value.
1847.It Ic \&. Ar file
1848The commands in the specified file are read and executed by the shell.
1849The
1850.Ic return
1851command may be used to return to the
1852.Ic \&.
1853command's caller.
1854If
1855.Ar file
1856contains any
1857.Ql /
1858characters, it is used as is.
1859Otherwise, the shell searches the
1860.Va PATH
1861for the file.
1862If it is not found in the
1863.Va PATH ,
1864it is sought in the current working directory.
1865.It Ic \&[
1866A built-in equivalent of
1867.Xr test 1 .
1868.It Ic alias Oo Ar name Ns Oo = Ns Ar string Oc ... Oc
1869If
1870.Ar name Ns = Ns Ar string
1871is specified, the shell defines the alias
1872.Ar name
1873with value
1874.Ar string .
1875If just
1876.Ar name
1877is specified, the value of the alias
1878.Ar name
1879is printed.
1880With no arguments, the
1881.Ic alias
1882built-in command prints the names and values of all defined aliases
1883(see
1884.Ic unalias ) .
1885Alias values are written with appropriate quoting so that they are
1886suitable for re-input to the shell.
1887Also see the
1888.Sx Aliases
1889subsection.
1890.It Ic bg Op Ar job ...
1891Continue the specified jobs
1892(or the current job if no jobs are given)
1893in the background.
1894.It Ic bind Oo Fl aeklrsv Oc Oo Ar key Oo Ar command Oc Oc
1895List or alter key bindings for the line editor.
1896This command is documented in
1897.Xr editrc 5 .
1898.It Ic break Op Ar num
1899See the
1900.Sx Flow-Control Constructs
1901subsection.
1902.It Ic builtin Ar cmd Op Ar arg ...
1903Execute the specified built-in command,
1904.Ar cmd .
1905This is useful when the user wishes to override a shell function
1906with the same name as a built-in command.
1907.It Ic cd Oo Fl L | P Oc Oo Fl e Oc Op Ar directory
1908Switch to the specified
1909.Ar directory ,
1910or to the directory specified in the
1911.Va HOME
1912environment variable if no
1913.Ar directory
1914is specified.
1915If
1916.Ar directory
1917does not begin with
1918.Pa / , \&. ,
1919or
1920.Pa .. ,
1921then the directories listed in the
1922.Va CDPATH
1923variable will be
1924searched for the specified
1925.Ar directory .
1926If
1927.Va CDPATH
1928is unset, the current directory is searched.
1929The format of
1930.Va CDPATH
1931is the same as that of
1932.Va PATH .
1933In an interactive shell,
1934the
1935.Ic cd
1936command will print out the name of the directory
1937that it actually switched to
1938if this is different from the name that the user gave.
1939These may be different either because the
1940.Va CDPATH
1941mechanism was used or because a symbolic link was crossed.
1942.Pp
1943If the
1944.Fl P
1945option is specified,
1946.Pa ..
1947is handled physically and symbolic links are resolved before
1948.Pa ..
1949components are processed.
1950If the
1951.Fl L
1952option is specified,
1953.Pa ..
1954is handled logically.
1955This is the default.
1956.Pp
1957The
1958.Fl e
1959option causes
1960.Ic cd
1961to return exit status 1 if the full pathname of the new directory
1962cannot be determined reliably or at all.
1963Normally this is not considered an error,
1964although a warning is printed.
1965.It Ic chdir
1966A synonym for the
1967.Ic cd
1968built-in command.
1969.It Ic command Oo Fl p Oc Op Ar utility Op Ar argument ...
1970.It Ic command Oo Fl p Oc Fl v Ar utility
1971.It Ic command Oo Fl p Oc Fl V Ar utility
1972The first form of invocation executes the specified
1973.Ar utility ,
1974ignoring shell functions in the search.
1975If
1976.Ar utility
1977is a special builtin,
1978it is executed as if it were a regular builtin.
1979.Pp
1980If the
1981.Fl p
1982option is specified, the command search is performed using a
1983default value of
1984.Va PATH
1985that is guaranteed to find all of the standard utilities.
1986.Pp
1987If the
1988.Fl v
1989option is specified,
1990.Ar utility
1991is not executed but a description of its interpretation by the shell is
1992printed.
1993For ordinary commands the output is the path name; for shell built-in
1994commands, shell functions and keywords only the name is written.
1995Aliases are printed as
1996.Dq Ic alias Ar name Ns = Ns Ar value .
1997.Pp
1998The
1999.Fl V
2000option is identical to
2001.Fl v
2002except for the output.
2003It prints
2004.Dq Ar utility Ic is Ar description
2005where
2006.Ar description
2007is either
2008the path name to
2009.Ar utility ,
2010a special shell builtin,
2011a shell builtin,
2012a shell function,
2013a shell keyword
2014or
2015an alias for
2016.Ar value .
2017.It Ic continue Op Ar num
2018See the
2019.Sx Flow-Control Constructs
2020subsection.
2021.It Ic echo Oo Fl e | n Oc Op Ar string ...
2022Print a space-separated list of the arguments to the standard output
2023and append a newline character.
2024.Bl -tag -width indent
2025.It Fl n
2026Suppress the output of the trailing newline.
2027.It Fl e
2028Process C-style backslash escape sequences.
2029The
2030.Ic echo
2031command understands the following character escapes:
2032.Bl -tag -width indent
2033.It \ea
2034Alert (ring the terminal bell)
2035.It \eb
2036Backspace
2037.It \ec
2038Suppress the trailing newline (this has the side-effect of truncating the
2039line if it is not the last character)
2040.It \ee
2041The ESC character
2042.Tn ( ASCII
20430x1b)
2044.It \ef
2045Formfeed
2046.It \en
2047Newline
2048.It \er
2049Carriage return
2050.It \et
2051Horizontal tab
2052.It \ev
2053Vertical tab
2054.It \e\e
2055Literal backslash
2056.It \e0nnn
2057(Zero) The character whose octal value is
2058.Ar nnn
2059.El
2060.Pp
2061If
2062.Ar string
2063is not enclosed in quotes then the backslash itself must be escaped
2064with a backslash to protect it from the shell.
2065For example
2066.Bd -literal -offset indent
2067$ echo -e "a\evb"
2068a
2069 b
2070$ echo -e a\e\evb
2071a
2072 b
2073$ echo -e "a\e\eb"
2074a\eb
2075$ echo -e a\e\e\e\eb
2076a\eb
2077.Ed
2078.El
2079.Pp
2080Only one of the
2081.Fl e
2082and
2083.Fl n
2084options may be specified.
2085.It Ic eval Ar string ...
2086Concatenate all the arguments with spaces.
2087Then re-parse and execute the command.
2088.It Ic exec Op Ar command Op arg ...
2089Unless
2090.Ar command
2091is omitted,
2092the shell process is replaced with the specified program
2093(which must be a real program, not a shell built-in command or function).
2094Any redirections on the
2095.Ic exec
2096command are marked as permanent,
2097so that they are not undone when the
2098.Ic exec
2099command finishes.
2100.It Ic exit Op Ar exitstatus
2101Terminate the shell process.
2102If
2103.Ar exitstatus
2104is given
2105it is used as the exit status of the shell.
2106Otherwise, if the shell is executing an
2107.Cm EXIT
2108trap, the exit status of the last command before the trap is used;
2109if the shell is executing a trap for a signal,
2110the shell exits by resending the signal to itself.
2111Otherwise, the exit status of the preceding command is used.
2112The exit status should be an integer between 0 and 255.
2113.It Ic export Ar name ...
2114.It Ic export Op Fl p
2115The specified names are exported so that they will
2116appear in the environment of subsequent commands.
2117The only way to un-export a variable is to
2118.Ic unset
2119it.
2120The shell allows the value of a variable to be set
2121at the same time as it is exported by writing
2122.Pp
2123.D1 Ic export Ar name Ns = Ns Ar value
2124.Pp
2125With no arguments the
2126.Ic export
2127command lists the names
2128of all exported variables.
2129If the
2130.Fl p
2131option is specified, the exported variables are printed as
2132.Dq Ic export Ar name Ns = Ns Ar value
2133lines, suitable for re-input to the shell.
2134.It Ic false
2135A null command that returns a non-zero (false) exit value.
2136.It Ic fc Oo Fl e Ar editor Oc Op Ar first Op Ar last
2137.It Ic fc Fl l Oo Fl nr Oc Op Ar first Op Ar last
2138.It Ic fc Fl s Oo Ar old Ns = Ns Ar new Oc Op Ar first
2139The
2140.Ic fc
2141built-in command lists, or edits and re-executes,
2142commands previously entered to an interactive shell.
2143.Bl -tag -width indent
2144.It Fl e Ar editor
2145Use the editor named by
2146.Ar editor
2147to edit the commands.
2148The
2149.Ar editor
2150string is a command name,
2151subject to search via the
2152.Va PATH
2153variable.
2154The value in the
2155.Va FCEDIT
2156variable is used as a default when
2157.Fl e
2158is not specified.
2159If
2160.Va FCEDIT
2161is null or unset, the value of the
2162.Va EDITOR
2163variable is used.
2164If
2165.Va EDITOR
2166is null or unset,
2167.Xr ed 1
2168is used as the editor.
2169.It Fl l No (ell)
2170List the commands rather than invoking
2171an editor on them.
2172The commands are written in the
2173sequence indicated by the
2174.Ar first
2175and
2176.Ar last
2177operands, as affected by
2178.Fl r ,
2179with each command preceded by the command number.
2180.It Fl n
2181Suppress command numbers when listing with
2182.Fl l .
2183.It Fl r
2184Reverse the order of the commands listed
2185(with
2186.Fl l )
2187or edited
2188(with neither
2189.Fl l
2190nor
2191.Fl s ) .
2192.It Fl s
2193Re-execute the command without invoking an editor.
2194.It Ar first
2195.It Ar last
2196Select the commands to list or edit.
2197The number of previous commands that can be accessed
2198are determined by the value of the
2199.Va HISTSIZE
2200variable.
2201The value of
2202.Ar first
2203or
2204.Ar last
2205or both are one of the following:
2206.Bl -tag -width indent
2207.It Oo Cm + Oc Ns Ar num
2208A positive number representing a command number;
2209command numbers can be displayed with the
2210.Fl l
2211option.
2212.It Fl Ar num
2213A negative decimal number representing the
2214command that was executed
2215.Ar num
2216of
2217commands previously.
2218For example, \-1 is the immediately previous command.
2219.It Ar string
2220A string indicating the most recently entered command
2221that begins with that string.
2222If the
2223.Ar old Ns = Ns Ar new
2224operand is not also specified with
2225.Fl s ,
2226the string form of the first operand cannot contain an embedded equal sign.
2227.El
2228.El
2229.Pp
2230The following variables affect the execution of
2231.Ic fc :
2232.Bl -tag -width ".Va HISTSIZE"
2233.It Va FCEDIT
2234Name of the editor to use for history editing.
2235.It Va HISTSIZE
2236The number of previous commands that are accessible.
2237.El
2238.It Ic fg Op Ar job
2239Move the specified
2240.Ar job
2241or the current job to the foreground.
2242.It Ic getopts Ar optstring var
2243The
2244.Tn POSIX
2245.Ic getopts
2246command.
2247The
2248.Ic getopts
2249command deprecates the older
2250.Xr getopt 1
2251command.
2252The first argument should be a series of letters, each possibly
2253followed by a colon which indicates that the option takes an argument.
2254The specified variable is set to the parsed option.
2255The index of
2256the next argument is placed into the shell variable
2257.Va OPTIND .
2258If an option takes an argument, it is placed into the shell variable
2259.Va OPTARG .
2260If an invalid option is encountered,
2261.Ar var
2262is set to
2263.Ql \&? .
2264It returns a false value (1) when it encounters the end of the options.
2265.It Ic hash Oo Fl rv Oc Op Ar command ...
2266The shell maintains a hash table which remembers the locations of commands.
2267With no arguments whatsoever, the
2268.Ic hash
2269command prints out the contents of this table.
2270.Pp
2271With arguments, the
2272.Ic hash
2273command removes each specified
2274.Ar command
2275from the hash table (unless they are functions) and then locates it.
2276With the
2277.Fl v
2278option,
2279.Ic hash
2280prints the locations of the commands as it finds them.
2281The
2282.Fl r
2283option causes the
2284.Ic hash
2285command to delete all the entries in the hash table except for functions.
2286.It Ic jobid Op Ar job
2287Print the process IDs of the processes in the specified
2288.Ar job .
2289If the
2290.Ar job
2291argument is omitted, use the current job.
2292.It Ic jobs Oo Fl lps Oc Op Ar job ...
2293Print information about the specified jobs, or all jobs if no
2294.Ar job
2295argument is given.
2296The information printed includes job ID, status and command name.
2297.Pp
2298If the
2299.Fl l
2300option is specified, the PID of each job is also printed.
2301If the
2302.Fl p
2303option is specified, only the process IDs for the process group leaders
2304are printed, one per line.
2305If the
2306.Fl s
2307option is specified, only the PIDs of the job commands are printed, one per
2308line.
2309.It Ic kill
2310A built-in equivalent of
2311.Xr kill 1
2312that additionally supports sending signals to jobs.
2313.It Ic local Oo Ar variable ... Oc Op Fl
2314See the
2315.Sx Functions
2316subsection.
2317.It Ic printf
2318A built-in equivalent of
2319.Xr printf 1 .
2320.It Ic pwd Op Fl L | P
2321Print the path of the current directory.
2322The built-in command may
2323differ from the program of the same name because the
2324built-in command remembers what the current directory
2325is rather than recomputing it each time.
2326This makes
2327it faster.
2328However, if the current directory is
2329renamed,
2330the built-in version of
2331.Xr pwd 1
2332will continue to print the old name for the directory.
2333.Pp
2334If the
2335.Fl P
2336option is specified, symbolic links are resolved.
2337If the
2338.Fl L
2339option is specified, the shell's notion of the current directory
2340is printed (symbolic links are not resolved).
2341This is the default.
2342.It Ic read Oo Fl p Ar prompt Oc Oo
2343.Fl t Ar timeout Oc Oo Fl er Oc Ar variable ...
2344The
2345.Ar prompt
2346is printed if the
2347.Fl p
2348option is specified
2349and the standard input is a terminal.
2350Then a line is
2351read from the standard input.
2352The trailing newline
2353is deleted from the line and the line is split as
2354described in the section on
2355.Sx White Space Splitting (Field Splitting)
2356above, and
2357the pieces are assigned to the variables in order.
2358If there are more pieces than variables, the remaining
2359pieces (along with the characters in
2360.Va IFS
2361that separated them)
2362are assigned to the last variable.
2363If there are more variables than pieces, the remaining
2364variables are assigned the null string.
2365.Pp
2366Backslashes are treated specially, unless the
2367.Fl r
2368option is
2369specified.
2370If a backslash is followed by
2371a newline, the backslash and the newline will be
2372deleted.
2373If a backslash is followed by any other
2374character, the backslash will be deleted and the following
2375character will be treated as though it were not in
2376.Va IFS ,
2377even if it is.
2378.Pp
2379If the
2380.Fl t
2381option is specified and the
2382.Ar timeout
2383elapses before a complete line of input is supplied,
2384the
2385.Ic read
2386command will return an exit status as if terminated by
2387.Dv SIGALRM
2388without assigning any values.
2389The
2390.Ar timeout
2391value may optionally be followed by one of
2392.Ql s ,
2393.Ql m
2394or
2395.Ql h
2396to explicitly specify seconds, minutes or hours.
2397If none is supplied,
2398.Ql s
2399is assumed.
2400.Pp
2401The
2402.Fl e
2403option exists only for backward compatibility with older scripts.
2404.Pp
2405The exit status is 0 on success, 1 on end of file,
2406between 2 and 128 if an error occurs
2407and greater than 128 if a trapped signal interrupts
2408.Ic read .
2409.It Ic readonly Oo Fl p Oc Op Ar name ...
2410Each specified
2411.Ar name
2412is marked as read only,
2413so that it cannot be subsequently modified or unset.
2414The shell allows the value of a variable to be set
2415at the same time as it is marked read only
2416by using the following form:
2417.Pp
2418.D1 Ic readonly Ar name Ns = Ns Ar value
2419.Pp
2420With no arguments the
2421.Ic readonly
2422command lists the names of all read only variables.
2423If the
2424.Fl p
2425option is specified, the read-only variables are printed as
2426.Dq Ic readonly Ar name Ns = Ns Ar value
2427lines, suitable for re-input to the shell.
2428.It Ic return Op Ar exitstatus
2429See the
2430.Sx Functions
2431subsection.
2432.It Ic set Oo Fl /+abCEefIimnpTuVvx Oc Oo Fl /+o Ar longname Oc Oo
2433.Fl c Ar string Oc Op Fl - Ar arg ...
2434The
2435.Ic set
2436command performs three different functions:
2437.Bl -item
2438.It
2439With no arguments, it lists the values of all shell variables.
2440.It
2441If options are given,
2442either in short form or using the long
2443.Dq Fl /+o Ar longname
2444form,
2445it sets or clears the specified options as described in the section called
2446.Sx Argument List Processing .
2447.It
2448If the
2449.Dq Fl -
2450option is specified,
2451.Ic set
2452will replace the shell's positional parameters with the subsequent
2453arguments.
2454If no arguments follow the
2455.Dq Fl -
2456option,
2457all the positional parameters will be cleared,
2458which is equivalent to executing the command
2459.Dq Li "shift $#" .
2460The
2461.Dq Fl -
2462flag may be omitted when specifying arguments to be used
2463as positional replacement parameters.
2464This is not recommended,
2465because the first argument may begin with a dash
2466.Pq Ql -
2467or a plus
2468.Pq Ql + ,
2469which the
2470.Ic set
2471command will interpret as a request to enable or disable options.
2472.El
2473.It Ic setvar Ar variable value
2474Assigns the specified
2475.Ar value
2476to the specified
2477.Ar variable .
2478The
2479.Ic setvar
2480command is intended to be used in functions that
2481assign values to variables whose names are passed as parameters.
2482In general it is better to write
2483.Dq Ar variable Ns = Ns Ar value
2484rather than using
2485.Ic setvar .
2486.It Ic shift Op Ar n
2487Shift the positional parameters
2488.Ar n
2489times, or once if
2490.Ar n
2491is not specified.
2492A shift sets the value of
2493.Li $1
2494to the value of
2495.Li $2 ,
2496the value of
2497.Li $2
2498to the value of
2499.Li $3 ,
2500and so on,
2501decreasing the value of
2502.Li $#
2503by one.
2504If there are zero positional parameters, shifting does not do anything.
2505.It Ic test
2506A built-in equivalent of
2507.Xr test 1 .
2508.It Ic times
2509Print the amount of time spent executing the shell process and its children.
2510The first output line shows the user and system times for the shell process
2511itself, the second one contains the user and system times for the
2512children.
2513.It Ic trap Oo Ar action Oc Ar signal ...
2514.It Ic trap Fl l
2515Cause the shell to parse and execute
2516.Ar action
2517when any specified
2518.Ar signal
2519is received.
2520The signals are specified by name or number.
2521In addition, the pseudo-signal
2522.Cm EXIT
2523may be used to specify an
2524.Ar action
2525that is performed when the shell terminates.
2526The
2527.Ar action
2528may be an empty string or a dash
2529.Pq Ql - ;
2530the former causes the specified signal to be ignored
2531and the latter causes the default action to be taken.
2532Omitting the
2533.Ar action
2534is another way to request the default action, for compatibility reasons this
2535usage is not recommended though.
2536In a subshell or utility environment,
2537the shell resets trapped (but not ignored) signals to the default action.
2538The
2539.Ic trap
2540command has no effect on signals that were ignored on entry to the shell.
2541.Pp
2542Option
2543.Fl l
2544causes the
2545.Ic trap
2546command to display a list of valid signal names.
2547.It Ic true
2548A null command that returns a 0 (true) exit value.
2549.It Ic type Op Ar name ...
2550Interpret each
2551.Ar name
2552as a command and print the resolution of the command search.
2553Possible resolutions are:
2554shell keyword, alias, special shell builtin, shell builtin, command,
2555tracked alias
2556and not found.
2557For aliases the alias expansion is printed;
2558for commands and tracked aliases
2559the complete pathname of the command is printed.
2560.It Ic ulimit Oo Fl HSabcdfklmnpstuvw Oc Op Ar limit
2561Set or display resource limits (see
2562.Xr getrlimit 2 ) .
2563If
2564.Ar limit
2565is specified, the named resource will be set;
2566otherwise the current resource value will be displayed.
2567.Pp
2568If
2569.Fl H
2570is specified, the hard limits will be set or displayed.
2571While everybody is allowed to reduce a hard limit,
2572only the superuser can increase it.
2573The
2574.Fl S
2575option
2576specifies the soft limits instead.
2577When displaying limits,
2578only one of
2579.Fl S
2580or
2581.Fl H
2582can be given.
2583The default is to display the soft limits,
2584and to set both the hard and the soft limits.
2585.Pp
2586Option
2587.Fl a
2588causes the
2589.Ic ulimit
2590command to display all resources.
2591The parameter
2592.Ar limit
2593is not acceptable in this mode.
2594.Pp
2595The remaining options specify which resource value is to be
2596displayed or modified.
2597They are mutually exclusive.
2598.Bl -tag -width indent
2599.It Fl b Ar sbsize
2600The maximum size of socket buffer usage, in bytes.
2601.It Fl c Ar coredumpsize
2602The maximal size of core dump files, in 512-byte blocks.
2603.It Fl d Ar datasize
2604The maximal size of the data segment of a process, in kilobytes.
2605.It Fl f Ar filesize
2606The maximal size of a file, in 512-byte blocks.
2607.It Fl k Ar kqueues
2608The maximal number of kqueues
2609(see
2610.Xr kqueue 2 )
2611for this user ID.
2612.It Fl l Ar lockedmem
2613The maximal size of memory that can be locked by a process, in
2614kilobytes.
2615.It Fl m Ar memoryuse
2616The maximal resident set size of a process, in kilobytes.
2617.It Fl n Ar nofiles
2618The maximal number of descriptors that could be opened by a process.
2619.It Fl p Ar pseudoterminals
2620The maximal number of pseudo-terminals for this user ID.
2621.It Fl s Ar stacksize
2622The maximal size of the stack segment, in kilobytes.
2623.It Fl t Ar time
2624The maximal amount of CPU time to be used by each process, in seconds.
2625.It Fl u Ar userproc
2626The maximal number of simultaneous processes for this user ID.
2627.It Fl v Ar virtualmem
2628The maximal virtual size of a process, in kilobytes.
2629.It Fl w Ar swapuse
2630The maximum amount of swap space reserved or used for this user ID,
2631in kilobytes.
2632.El
2633.It Ic umask Oo Fl S Oc Op Ar mask
2634Set the file creation mask (see
2635.Xr umask 2 )
2636to the octal or symbolic (see
2637.Xr chmod 1 )
2638value specified by
2639.Ar mask .
2640If the argument is omitted, the current mask value is printed.
2641If the
2642.Fl S
2643option is specified, the output is symbolic, otherwise the output is octal.
2644.It Ic unalias Oo Fl a Oc Op Ar name ...
2645The specified alias names are removed.
2646If
2647.Fl a
2648is specified, all aliases are removed.
2649.It Ic unset Oo Fl fv Oc Ar name ...
2650The specified variables or functions are unset and unexported.
2651If the
2652.Fl v
2653option is specified or no options are given, the
2654.Ar name
2655arguments are treated as variable names.
2656If the
2657.Fl f
2658option is specified, the
2659.Ar name
2660arguments are treated as function names.
2661.It Ic wait Op Ar job ...
2662Wait for each specified
2663.Ar job
2664to complete and return the exit status of the last process in the
2665last specified
2666.Ar job .
2667If any
2668.Ar job
2669specified is unknown to the shell, it is treated as if it
2670were a known job that exited with exit status 127.
2671If no operands are given, wait for all jobs to complete
2672and return an exit status of zero.
2673.El
2674.Ss Commandline Editing
2675When
2676.Nm
2677is being used interactively from a terminal, the current command
2678and the command history
2679(see
2680.Ic fc
2681in
2682.Sx Built-in Commands )
2683can be edited using
2684.Nm vi Ns -mode
2685command line editing.
2686This mode uses commands similar
2687to a subset of those described in the
2688.Xr vi 1
2689man page.
2690The command
2691.Dq Li "set -o vi"
2692(or
2693.Dq Li "set -V" )
2694enables
2695.Nm vi Ns -mode
2696editing and places
2697.Nm
2698into
2699.Nm vi
2700insert mode.
2701With
2702.Nm vi Ns -mode
2703enabled,
2704.Nm
2705can be switched between insert mode and command mode by typing
2706.Aq ESC .
2707Hitting
2708.Aq return
2709while in command mode will pass the line to the shell.
2710.Pp
2711Similarly, the
2712.Dq Li "set -o emacs"
2713(or
2714.Dq Li "set -E" )
2715command can be used to enable a subset of
2716.Nm emacs Ns -style
2717command line editing features.
2718.Sh ENVIRONMENT
2719The following environment variables affect the execution of
2720.Nm :
2721.Bl -tag -width ".Ev LANGXXXXXX"
2722.It Ev ENV
2723Initialization file for interactive shells.
2724.It Ev LANG , Ev LC_*
2725Locale settings.
2726These are inherited by children of the shell,
2727and is used in a limited manner by the shell itself.
2728.It Ev PWD
2729An absolute pathname for the current directory,
2730possibly containing symbolic links.
2731This is used and updated by the shell.
2732.It Ev TERM
2733The default terminal setting for the shell.
2734This is inherited by children of the shell, and is used in the history
2735editing modes.
2736.El
2737.Pp
2738Additionally, all environment variables are turned into shell variables
2739at startup,
2740which may affect the shell as described under
2741.Sx Special Variables .
2742.Sh FILES
2743.Bl -tag -width "/etc/suid_profileXX" -compact
2744.It Pa ~/.profile
2745User's login profile.
2746.It Pa /etc/profile
2747System login profile.
2748.It Pa /etc/shells
2749Shell database.
2750.It Pa /etc/suid_profile
2751Privileged shell profile.
2752.El
2753.Sh EXIT STATUS
2754Errors that are detected by the shell, such as a syntax error, will
2755cause the shell to exit with a non-zero exit status.
2756If the shell is not an interactive shell, the execution of the shell
2757file will be aborted.
2758Otherwise the shell will return the exit status of the last command
2759executed, or if the
2760.Ic exit
2761builtin is used with a numeric argument, it
2762will return the argument.
2763.Sh SEE ALSO
2764.Xr builtin 1 ,
2765.Xr chsh 1 ,
2766.Xr echo 1 ,
2767.Xr ed 1 ,
2768.Xr emacs 1 ,
2769.Xr kill 1 ,
2770.Xr printf 1 ,
2771.Xr pwd 1 ,
2772.Xr test 1 ,
2773.Xr vi 1 ,
2774.Xr execve 2 ,
2775.Xr getrlimit 2 ,
2776.Xr umask 2 ,
2777.Xr wctype 3 ,
2778.Xr editrc 5 ,
2779.Xr shells 5
2780.Sh HISTORY
2781A
2782.Nm
2783command, the Thompson shell, appeared in
2784.At v1 .
2785It was superseded in
2786.At v7
2787by the Bourne shell, which inherited the name
2788.Nm .
2789.Pp
2790This version of
2791.Nm
2792was rewritten in 1989 under the
2793.Bx
2794license after the Bourne shell from
2795.At V.4 .
2796.Sh AUTHORS
2797This version of
2798.Nm
2799was originally written by
2800.An Kenneth Almquist .
2801.Sh BUGS
2802The
2803.Nm
2804utility does not recognize multibyte characters other than UTF-8.
2805Splitting using
2806.Va IFS
2807and the line editing library
2808.Xr editline 3
2809do not recognize multibyte characters.
2810