xref: /freebsd/bin/sh/sh.1 (revision 98e0ffaefb0f241cda3a72395d3be04192ae0d47)
1.\"-
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5.\" This code is derived from software contributed to Berkeley by
6.\" Kenneth Almquist.
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31.\"
32.\"	from: @(#)sh.1	8.6 (Berkeley) 5/4/95
33.\" $FreeBSD$
34.\"
35.Dd April 18, 2015
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 /+abCEefhIimnPpTuVvx
44.Op Fl /+o Ar longname
45.Oo
46.Ar script
47.Op Ar arg ...
48.Oc
49.Nm
50.Op Fl /+abCEefhIimnPpTuVvx
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 /+abCEefhIimnPpTuVvx
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).
262A new process group is created for each pipeline (called a job).
263It is possible to suspend jobs or to have them run in the foreground or
264in the background.
265In a non-interactive shell,
266this option can be set even if no terminal is available
267and is useful to place processes in separate process groups.
268.It Fl n Li noexec
269If not interactive, read commands but do not
270execute them.
271This is useful for checking the
272syntax of shell scripts.
273.It Fl P Li physical
274Change the default for the
275.Ic cd
276and
277.Ic pwd
278commands from
279.Fl L
280(logical directory layout)
281to
282.Fl P
283(physical directory layout).
284.It Fl p Li privileged
285Turn on privileged mode.
286This mode is enabled on startup
287if either the effective user or group ID is not equal to the
288real user or group ID.
289Turning this mode off sets the
290effective user and group IDs to the real user and group IDs.
291When this mode is enabled for interactive shells, the file
292.Pa /etc/suid_profile
293is sourced instead of
294.Pa ~/.profile
295after
296.Pa /etc/profile
297is sourced, and the contents of the
298.Ev ENV
299variable are ignored.
300.It Fl s Li stdin
301Read commands from standard input (set automatically
302if no file arguments are present).
303This option has
304no effect when set after the shell has already started
305running (i.e., when set with the
306.Ic set
307command).
308.It Fl T Li trapsasync
309When waiting for a child, execute traps immediately.
310If this option is not set,
311traps are executed after the child exits,
312as specified in
313.St -p1003.2 .
314This nonstandard option is useful for putting guarding shells around
315children that block signals.
316The surrounding shell may kill the child
317or it may just return control to the tty and leave the child alone,
318like this:
319.Bd -literal -offset indent
320sh -T -c "trap 'exit 1' 2 ; some-blocking-program"
321.Ed
322.It Fl u Li nounset
323Write a message to standard error when attempting
324to expand a variable, a positional parameter or
325the special parameter
326.Va \&!
327that is not set, and if the
328shell is not interactive, exit immediately.
329.It Fl V Li vi
330Enable the built-in
331.Xr vi 1
332command line editor (disables
333.Fl E
334if it has been set).
335.It Fl v Li verbose
336The shell writes its input to standard error
337as it is read.
338Useful for debugging.
339.It Fl x Li xtrace
340Write each command
341(preceded by the value of the
342.Va PS4
343variable subjected to parameter expansion and arithmetic expansion)
344to standard error before it is executed.
345Useful for debugging.
346.El
347.Pp
348The
349.Fl c
350option causes the commands to be read from the
351.Ar string
352operand instead of from the standard input.
353Keep in mind that this option only accepts a single string as its
354argument, hence multi-word strings must be quoted.
355.Pp
356The
357.Fl /+o
358option takes as its only argument the long name of an option
359to be enabled or disabled.
360For example, the following two invocations of
361.Nm
362both enable the built-in
363.Xr emacs 1
364command line editor:
365.Bd -literal -offset indent
366set -E
367set -o emacs
368.Ed
369.Pp
370If used without an argument, the
371.Fl o
372option displays the current option settings in a human-readable format.
373If
374.Cm +o
375is used without an argument, the current option settings are output
376in a format suitable for re-input into the shell.
377.Ss Lexical Structure
378The shell reads input in terms of lines from a file and breaks
379it up into words at whitespace (blanks and tabs), and at
380certain sequences of
381characters called
382.Dq operators ,
383which are special to the shell.
384There are two types of operators: control operators and
385redirection operators (their meaning is discussed later).
386The following is a list of valid operators:
387.Bl -tag -width indent
388.It Control operators:
389.Bl -column "XXX" "XXX" "XXX" "XXX" "XXX" -offset center -compact
390.It Li & Ta Li && Ta Li \&( Ta Li \&) Ta Li \en
391.It Li ;; Ta Li ;& Ta Li \&; Ta Li \&| Ta Li ||
392.El
393.It Redirection operators:
394.Bl -column "XXX" "XXX" "XXX" "XXX" "XXX" -offset center -compact
395.It Li < Ta Li > Ta Li << Ta Li >> Ta Li <>
396.It Li <& Ta Li >& Ta Li <<- Ta Li >| Ta \&
397.El
398.El
399.Pp
400The character
401.Ql #
402introduces a comment if used at the beginning of a word.
403The word starting with
404.Ql #
405and the rest of the line are ignored.
406.Pp
407.Tn ASCII
408.Dv NUL
409characters (character code 0) are not allowed in shell input.
410.Ss Quoting
411Quoting is used to remove the special meaning of certain characters
412or words to the shell, such as operators, whitespace, keywords,
413or alias names.
414.Pp
415There are four types of quoting: matched single quotes,
416dollar-single quotes,
417matched double quotes, and backslash.
418.Bl -tag -width indent
419.It Single Quotes
420Enclosing characters in single quotes preserves the literal
421meaning of all the characters (except single quotes, making
422it impossible to put single-quotes in a single-quoted string).
423.It Dollar-Single Quotes
424Enclosing characters between
425.Li $'
426and
427.Li '
428preserves the literal meaning of all characters
429except backslashes and single quotes.
430A backslash introduces a C-style escape sequence:
431.Bl -tag -width xUnnnnnnnn
432.It \ea
433Alert (ring the terminal bell)
434.It \eb
435Backspace
436.It \ec Ns Ar c
437The control character denoted by
438.Li ^ Ns Ar c
439in
440.Xr stty 1 .
441If
442.Ar c
443is a backslash, it must be doubled.
444.It \ee
445The ESC character
446.Tn ( ASCII
4470x1b)
448.It \ef
449Formfeed
450.It \en
451Newline
452.It \er
453Carriage return
454.It \et
455Horizontal tab
456.It \ev
457Vertical tab
458.It \e\e
459Literal backslash
460.It \e\&'
461Literal single-quote
462.It \e\&"
463Literal double-quote
464.It \e Ns Ar nnn
465The byte whose octal value is
466.Ar nnn
467(one to three digits)
468.It \ex Ns Ar nn
469The byte whose hexadecimal value is
470.Ar nn
471(one or more digits only the last two of which are used)
472.It \eu Ns Ar nnnn
473The Unicode code point
474.Ar nnnn
475(four hexadecimal digits)
476.It \eU Ns Ar nnnnnnnn
477The Unicode code point
478.Ar nnnnnnnn
479(eight hexadecimal digits)
480.El
481.Pp
482The sequences for Unicode code points are currently only useful with
483UTF-8 locales.
484They reject code point 0 and UTF-16 surrogates.
485.Pp
486If an escape sequence would produce a byte with value 0,
487that byte and the rest of the string until the matching single-quote
488are ignored.
489.Pp
490Any other string starting with a backslash is an error.
491.It Double Quotes
492Enclosing characters within double quotes preserves the literal
493meaning of all characters except dollar sign
494.Pq Ql $ ,
495backquote
496.Pq Ql ` ,
497and backslash
498.Pq Ql \e .
499The backslash inside double quotes is historically weird.
500It remains literal unless it precedes the following characters,
501which it serves to quote:
502.Pp
503.Bl -column "XXX" "XXX" "XXX" "XXX" "XXX" -offset center -compact
504.It Li $ Ta Li ` Ta Li \&" Ta Li \e Ta Li \en
505.El
506.It Backslash
507A backslash preserves the literal meaning of the following
508character, with the exception of the newline character
509.Pq Ql \en .
510A backslash preceding a newline is treated as a line continuation.
511.El
512.Ss Keywords
513Keywords or reserved words are words that have special meaning to the
514shell and are recognized at the beginning of a line and
515after a control operator.
516The following are keywords:
517.Bl -column "doneXX" "elifXX" "elseXX" "untilXX" "whileX" -offset center
518.It Li \&! Ta { Ta } Ta Ic case Ta Ic do
519.It Ic done Ta Ic elif Ta Ic else Ta Ic esac Ta Ic fi
520.It Ic for Ta Ic if Ta Ic then Ta Ic until Ta Ic while
521.El
522.Ss Aliases
523An alias is a name and corresponding value set using the
524.Ic alias
525built-in command.
526Wherever the command word of a simple command may occur,
527and after checking for keywords if a keyword may occur, the shell
528checks the word to see if it matches an alias.
529If it does, it replaces it in the input stream with its value.
530For example, if there is an alias called
531.Dq Li lf
532with the value
533.Dq Li "ls -F" ,
534then the input
535.Pp
536.Dl "lf foobar"
537.Pp
538would become
539.Pp
540.Dl "ls -F foobar"
541.Pp
542Aliases are also recognized after an alias
543whose value ends with a space or tab.
544For example, if there is also an alias called
545.Dq Li nohup
546with the value
547.Dq Li "nohup " ,
548then the input
549.Pp
550.Dl "nohup lf foobar"
551.Pp
552would become
553.Pp
554.Dl "nohup ls -F foobar"
555.Pp
556Aliases provide a convenient way for naive users to
557create shorthands for commands without having to learn how
558to create functions with arguments.
559Using aliases in scripts is discouraged
560because the command that defines them must be executed
561before the code that uses them is parsed.
562This is fragile and not portable.
563.Pp
564An alias name may be escaped in a command line, so that it is not
565replaced by its alias value, by using quoting characters within or
566adjacent to the alias name.
567This is most often done by prefixing
568an alias name with a backslash to execute a function, built-in, or
569normal program with the same name.
570See the
571.Sx Quoting
572subsection.
573.Ss Commands
574The shell interprets the words it reads according to a
575language, the specification of which is outside the scope
576of this man page (refer to the BNF in the
577.St -p1003.2
578document).
579Essentially though, a line is read and if
580the first word of the line (or after a control operator)
581is not a keyword, then the shell has recognized a
582simple command.
583Otherwise, a complex command or some
584other special construct may have been recognized.
585.Ss Simple Commands
586If a simple command has been recognized, the shell performs
587the following actions:
588.Bl -enum
589.It
590Leading words of the form
591.Dq Li name=value
592are stripped off and assigned to the environment of
593the simple command
594(they do not affect expansions).
595Redirection operators and
596their arguments (as described below) are stripped
597off and saved for processing.
598.It
599The remaining words are expanded as described in
600the section called
601.Sx Word Expansions ,
602and the first remaining word is considered the command
603name and the command is located.
604The remaining
605words are considered the arguments of the command.
606If no command name resulted, then the
607.Dq Li name=value
608variable assignments recognized in 1) affect the
609current shell.
610.It
611Redirections are performed as described in
612the next section.
613.El
614.Ss Redirections
615Redirections are used to change where a command reads its input
616or sends its output.
617In general, redirections open, close, or
618duplicate an existing reference to a file.
619The overall format
620used for redirection is:
621.Pp
622.D1 Oo Ar n Oc Ar redir-op file
623.Pp
624The
625.Ar redir-op
626is one of the redirection operators mentioned
627previously.
628The following gives some examples of how these
629operators can be used.
630Note that stdin and stdout are commonly used abbreviations
631for standard input and standard output respectively.
632.Bl -tag -width "1234567890XX" -offset indent
633.It Oo Ar n Oc Ns Li > Ar file
634redirect stdout (or file descriptor
635.Ar n )
636to
637.Ar file
638.It Oo Ar n Oc Ns Li >| Ar file
639same as above, but override the
640.Fl C
641option
642.It Oo Ar n Oc Ns Li >> Ar file
643append stdout (or file descriptor
644.Ar n )
645to
646.Ar file
647.It Oo Ar n Oc Ns Li < Ar file
648redirect stdin (or file descriptor
649.Ar n )
650from
651.Ar file
652.It Oo Ar n Oc Ns Li <> Ar file
653redirect stdin (or file descriptor
654.Ar n )
655to and from
656.Ar file
657.It Oo Ar n1 Oc Ns Li <& Ns Ar n2
658duplicate stdin (or file descriptor
659.Ar n1 )
660from file descriptor
661.Ar n2
662.It Oo Ar n Oc Ns Li <&-
663close stdin (or file descriptor
664.Ar n )
665.It Oo Ar n1 Oc Ns Li >& Ns Ar n2
666duplicate stdout (or file descriptor
667.Ar n1 )
668to file descriptor
669.Ar n2
670.It Oo Ar n Oc Ns Li >&-
671close stdout (or file descriptor
672.Ar n )
673.El
674.Pp
675The following redirection is often called a
676.Dq here-document .
677.Bd -unfilled -offset indent
678.Oo Ar n Oc Ns Li << Ar delimiter
679.Ar here-doc-text
680.Ar ...
681.Ar delimiter
682.Ed
683.Pp
684All the text on successive lines up to the delimiter is
685saved away and made available to the command on standard
686input, or file descriptor
687.Ar n
688if it is specified.
689If the
690.Ar delimiter
691as specified on the initial line is quoted, then the
692.Ar here-doc-text
693is treated literally, otherwise the text is subjected to
694parameter expansion, command substitution, and arithmetic
695expansion (as described in the section on
696.Sx Word Expansions ) .
697If the operator is
698.Dq Li <<-
699instead of
700.Dq Li << ,
701then leading tabs
702in the
703.Ar here-doc-text
704are stripped.
705.Ss Search and Execution
706There are three types of commands: shell functions,
707built-in commands, and normal programs.
708The command is searched for (by name) in that order.
709The three types of commands are all executed in a different way.
710.Pp
711When a shell function is executed, all of the shell positional
712parameters (except
713.Li $0 ,
714which remains unchanged) are
715set to the arguments of the shell function.
716The variables which are explicitly placed in the environment of
717the command (by placing assignments to them before the
718function name) are made local to the function and are set
719to the values given.
720Then the command given in the function definition is executed.
721The positional parameters are restored to their original values
722when the command completes.
723This all occurs within the current shell.
724.Pp
725Shell built-in commands are executed internally to the shell, without
726spawning a new process.
727There are two kinds of built-in commands: regular and special.
728Assignments before special builtins persist after they finish
729executing and assignment errors, redirection errors and certain
730operand errors cause a script to be aborted.
731Special builtins cannot be overridden with a function.
732Both regular and special builtins can affect the shell in ways
733normal programs cannot.
734.Pp
735Otherwise, if the command name does not match a function
736or built-in command, the command is searched for as a normal
737program in the file system (as described in the next section).
738When a normal program is executed, the shell runs the program,
739passing the arguments and the environment to the program.
740If the program is not a normal executable file
741(i.e., if it does not begin with the
742.Dq "magic number"
743whose
744.Tn ASCII
745representation is
746.Dq Li #! ,
747resulting in an
748.Er ENOEXEC
749return value from
750.Xr execve 2 )
751but appears to be a text file,
752the shell will run a new instance of
753.Nm
754to interpret it.
755.Pp
756Note that previous versions of this document
757and the source code itself misleadingly and sporadically
758refer to a shell script without a magic number
759as a
760.Dq "shell procedure" .
761.Ss Path Search
762When locating a command, the shell first looks to see if
763it has a shell function by that name.
764Then it looks for a
765built-in command by that name.
766If a built-in command is not found,
767one of two things happen:
768.Bl -enum
769.It
770Command names containing a slash are simply executed without
771performing any searches.
772.It
773The shell searches each entry in the
774.Va PATH
775variable
776in turn for the command.
777The value of the
778.Va PATH
779variable should be a series of
780entries separated by colons.
781Each entry consists of a
782directory name.
783The current directory
784may be indicated implicitly by an empty directory name,
785or explicitly by a single period.
786.El
787.Ss Command Exit Status
788Each command has an exit status that can influence the behavior
789of other shell commands.
790The paradigm is that a command exits
791with zero for normal or success, and non-zero for failure,
792error, or a false indication.
793The man page for each command
794should indicate the various exit codes and what they mean.
795Additionally, the built-in commands return exit codes, as does
796an executed shell function.
797.Pp
798If a command is terminated by a signal, its exit status is greater than 128.
799The signal name can be found by passing the exit status to
800.Li kill -l .
801.Pp
802If there is no command word,
803the exit status is the exit status of the last command substitution executed,
804or zero if the command does not contain any command substitutions.
805.Ss Complex Commands
806Complex commands are combinations of simple commands
807with control operators or keywords, together creating a larger complex
808command.
809More generally, a command is one of the following:
810.Bl -item -offset indent
811.It
812simple command
813.It
814pipeline
815.It
816list or compound-list
817.It
818compound command
819.It
820function definition
821.El
822.Pp
823Unless otherwise stated, the exit status of a command is
824that of the last simple command executed by the command,
825or zero if no simple command was executed.
826.Ss Pipelines
827A pipeline is a sequence of one or more commands separated
828by the control operator
829.Ql \&| .
830The standard output of all but
831the last command is connected to the standard input
832of the next command.
833The standard output of the last
834command is inherited from the shell, as usual.
835.Pp
836The format for a pipeline is:
837.Pp
838.D1 Oo Li \&! Oc Ar command1 Op Li \&| Ar command2 ...
839.Pp
840The standard output of
841.Ar command1
842is connected to the standard input of
843.Ar command2 .
844The standard input, standard output, or
845both of a command is considered to be assigned by the
846pipeline before any redirection specified by redirection
847operators that are part of the command.
848.Pp
849Note that unlike some other shells,
850.Nm
851executes each process in a pipeline with more than one command
852in a subshell environment and as a child of the
853.Nm
854process.
855.Pp
856If the pipeline is not in the background (discussed later),
857the shell waits for all commands to complete.
858.Pp
859If the keyword
860.Ic !\&
861does not precede the pipeline, the
862exit status is the exit status of the last command specified
863in the pipeline.
864Otherwise, the exit status is the logical
865NOT of the exit status of the last command.
866That is, if
867the last command returns zero, the exit status is 1; if
868the last command returns greater than zero, the exit status
869is zero.
870.Pp
871Because pipeline assignment of standard input or standard
872output or both takes place before redirection, it can be
873modified by redirection.
874For example:
875.Pp
876.Dl "command1 2>&1 | command2"
877.Pp
878sends both the standard output and standard error of
879.Ar command1
880to the standard input of
881.Ar command2 .
882.Pp
883A
884.Ql \&;
885or newline terminator causes the preceding
886AND-OR-list
887(described below in the section called
888.Sx Short-Circuit List Operators )
889to be executed sequentially;
890an
891.Ql &
892causes asynchronous execution of the preceding AND-OR-list.
893.Ss Background Commands (&)
894If a command is terminated by the control operator ampersand
895.Pq Ql & ,
896the shell executes the command in a subshell environment (see
897.Sx Grouping Commands Together
898below) and asynchronously;
899the shell does not wait for the command to finish
900before executing the next command.
901.Pp
902The format for running a command in background is:
903.Pp
904.D1 Ar command1 Li & Op Ar command2 Li & Ar ...
905.Pp
906If the shell is not interactive, the standard input of an
907asynchronous command is set to
908.Pa /dev/null .
909.Pp
910The exit status is zero.
911.Ss Lists (Generally Speaking)
912A list is a sequence of zero or more commands separated by
913newlines, semicolons, or ampersands,
914and optionally terminated by one of these three characters.
915The commands in a
916list are executed in the order they are written.
917If command is followed by an ampersand, the shell starts the
918command and immediately proceeds onto the next command;
919otherwise it waits for the command to terminate before
920proceeding to the next one.
921.Ss Short-Circuit List Operators
922.Dq Li &&
923and
924.Dq Li ||
925are AND-OR list operators.
926.Dq Li &&
927executes the first command, and then executes the second command
928if the exit status of the first command is zero.
929.Dq Li ||
930is similar, but executes the second command if the exit
931status of the first command is nonzero.
932.Dq Li &&
933and
934.Dq Li ||
935both have the same priority.
936.Ss Flow-Control Constructs (if, while, for, case)
937The syntax of the
938.Ic if
939command is:
940.Bd -unfilled -offset indent -compact
941.Ic if Ar list
942.Ic then Ar list
943.Oo Ic elif Ar list
944.Ic then Ar list Oc Ar ...
945.Op Ic else Ar list
946.Ic fi
947.Ed
948.Pp
949The exit status is that of selected
950.Ic then
951or
952.Ic else
953list,
954or zero if no list was selected.
955.Pp
956The syntax of the
957.Ic while
958command is:
959.Bd -unfilled -offset indent -compact
960.Ic while Ar list
961.Ic do Ar list
962.Ic done
963.Ed
964.Pp
965The two lists are executed repeatedly while the exit status of the
966first list is zero.
967The
968.Ic until
969command is similar, but has the word
970.Ic until
971in place of
972.Ic while ,
973which causes it to
974repeat until the exit status of the first list is zero.
975.Pp
976The exit status is that of the last execution of the second list,
977or zero if it was never executed.
978.Pp
979The syntax of the
980.Ic for
981command is:
982.Bd -unfilled -offset indent -compact
983.Ic for Ar variable Op Ic in Ar word ...
984.Ic do Ar list
985.Ic done
986.Ed
987.Pp
988If
989.Ic in
990and the following words are omitted,
991.Ic in Li \&"$@\&"
992is used instead.
993The words are expanded, and then the list is executed
994repeatedly with the variable set to each word in turn.
995The
996.Ic do
997and
998.Ic done
999commands may be replaced with
1000.Ql {
1001and
1002.Ql } .
1003.Pp
1004The syntax of the
1005.Ic break
1006and
1007.Ic continue
1008commands is:
1009.D1 Ic break Op Ar num
1010.D1 Ic continue Op Ar num
1011.Pp
1012The
1013.Ic break
1014command terminates the
1015.Ar num
1016innermost
1017.Ic for
1018or
1019.Ic while
1020loops.
1021The
1022.Ic continue
1023command continues with the next iteration of the innermost loop.
1024These are implemented as special built-in commands.
1025.Pp
1026The syntax of the
1027.Ic case
1028command is:
1029.Bd -unfilled -offset indent -compact
1030.Ic case Ar word Ic in
1031.Ar pattern Ns Li ) Ar list Li ;;
1032.Ar ...
1033.Ic esac
1034.Ed
1035.Pp
1036The pattern can actually be one or more patterns
1037(see
1038.Sx Shell Patterns
1039described later),
1040separated by
1041.Ql \&|
1042characters.
1043Tilde expansion, parameter expansion, command substitution,
1044arithmetic expansion and quote removal are applied to the word.
1045Then, each pattern is expanded in turn using tilde expansion,
1046parameter expansion, command substitution and arithmetic expansion and
1047the expanded form of the word is checked against it.
1048If a match is found, the corresponding list is executed.
1049If the selected list is terminated by the control operator
1050.Ql ;&
1051instead of
1052.Ql ;; ,
1053execution continues with the next list,
1054continuing until a list terminated with
1055.Ql ;;
1056or the end of the
1057.Ic case
1058command.
1059.Ss Grouping Commands Together
1060Commands may be grouped by writing either
1061.Pp
1062.D1 Li \&( Ns Ar list Ns Li \%)
1063.Pp
1064or
1065.Pp
1066.D1 Li { Ar list Ns Li \&; }
1067.Pp
1068The first form executes the commands in a subshell environment.
1069A subshell environment has its own copy of:
1070.Bl -enum
1071.It
1072The current working directory as set by
1073.Ic cd .
1074.It
1075The file creation mask as set by
1076.Ic umask .
1077.It
1078Resource limits as set by
1079.Ic ulimit .
1080.It
1081References to open files.
1082.It
1083Traps as set by
1084.Ic trap .
1085.It
1086Known jobs.
1087.It
1088Positional parameters and variables.
1089.It
1090Shell options.
1091.It
1092Shell functions.
1093.It
1094Shell aliases.
1095.El
1096.Pp
1097These are copied from the parent shell environment,
1098except that trapped (but not ignored) signals are reset to the default action
1099and known jobs are cleared.
1100Any changes do not affect the parent shell environment.
1101.Pp
1102A subshell environment may be implemented as a child process or differently.
1103If job control is enabled in an interactive shell,
1104commands grouped in parentheses can be suspended and continued as a unit.
1105.Pp
1106For compatibility with other shells,
1107two open parentheses in sequence should be separated by whitespace.
1108.Pp
1109The second form never forks another shell,
1110so it is slightly more efficient.
1111Grouping commands together this way allows the user to
1112redirect their output as though they were one program:
1113.Bd -literal -offset indent
1114{ echo -n "hello"; echo " world"; } > greeting
1115.Ed
1116.Ss Functions
1117The syntax of a function definition is
1118.Pp
1119.D1 Ar name Li \&( \&) Ar command
1120.Pp
1121A function definition is an executable statement; when
1122executed it installs a function named
1123.Ar name
1124and returns an
1125exit status of zero.
1126The
1127.Ar command
1128is normally a list
1129enclosed between
1130.Ql {
1131and
1132.Ql } .
1133.Pp
1134Variables may be declared to be local to a function by
1135using the
1136.Ic local
1137command.
1138This should appear as the first statement of a function,
1139and the syntax is:
1140.Pp
1141.D1 Ic local Oo Ar variable ... Oc Op Fl
1142.Pp
1143The
1144.Ic local
1145command is implemented as a built-in command.
1146The exit status is zero
1147unless the command is not in a function or a variable name is invalid.
1148.Pp
1149When a variable is made local, it inherits the initial
1150value and exported and readonly flags from the variable
1151with the same name in the surrounding scope, if there is
1152one.
1153Otherwise, the variable is initially unset.
1154The shell
1155uses dynamic scoping, so that if the variable
1156.Va x
1157is made local to function
1158.Em f ,
1159which then calls function
1160.Em g ,
1161references to the variable
1162.Va x
1163made inside
1164.Em g
1165will refer to the variable
1166.Va x
1167declared inside
1168.Em f ,
1169not to the global variable named
1170.Va x .
1171.Pp
1172The only special parameter that can be made local is
1173.Ql - .
1174Making
1175.Ql -
1176local causes any shell options that are
1177changed via the
1178.Ic set
1179command inside the function to be
1180restored to their original values when the function
1181returns.
1182.Pp
1183The syntax of the
1184.Ic return
1185command is
1186.Pp
1187.D1 Ic return Op Ar exitstatus
1188.Pp
1189It terminates the current executional scope, returning from the closest
1190nested function or sourced script;
1191if no function or sourced script is being executed,
1192it exits the shell instance.
1193The
1194.Ic return
1195command is implemented as a special built-in command.
1196.Ss Variables and Parameters
1197The shell maintains a set of parameters.
1198A parameter
1199denoted by a name
1200(consisting solely
1201of alphabetics, numerics, and underscores,
1202and starting with an alphabetic or an underscore)
1203is called a variable.
1204When starting up,
1205the shell turns all environment variables with valid names into shell
1206variables.
1207New variables can be set using the form
1208.Pp
1209.D1 Ar name Ns = Ns Ar value
1210.Pp
1211A parameter can also be denoted by a number
1212or a special character as explained below.
1213.Pp
1214Assignments are expanded differently from other words:
1215tilde expansion is also performed after the equals sign and after any colon
1216and usernames are also terminated by colons,
1217and field splitting and pathname expansion are not performed.
1218.Pp
1219This special expansion applies not only to assignments that form a simple
1220command by themselves or precede a command word,
1221but also to words passed to the
1222.Ic export ,
1223.Ic local
1224or
1225.Ic readonly
1226built-in commands that have this form.
1227For this, the builtin's name must be literal
1228(not the result of an expansion)
1229and may optionally be preceded by one or more literal instances of
1230.Ic command
1231without options.
1232.Ss Positional Parameters
1233A positional parameter is a parameter denoted by a number greater than zero.
1234The shell sets these initially to the values of its command line
1235arguments that follow the name of the shell script.
1236The
1237.Ic set
1238built-in command can also be used to set or reset them.
1239.Ss Special Parameters
1240Special parameters are parameters denoted by a single special character
1241or the digit zero.
1242They are shown in the following list, exactly as they would appear in input
1243typed by the user or in the source of a shell script.
1244.Bl -hang
1245.It Li $*
1246Expands to the positional parameters, starting from one.
1247When
1248the expansion occurs within a double-quoted string
1249it expands to a single field with the value of each parameter
1250separated by the first character of the
1251.Va IFS
1252variable,
1253or by a space if
1254.Va IFS
1255is unset.
1256.It Li $@
1257Expands to the positional parameters, starting from one.
1258When
1259the expansion occurs within double-quotes, each positional
1260parameter expands as a separate argument.
1261If there are no positional parameters, the
1262expansion of
1263.Li @
1264generates zero arguments, even when
1265.Li @
1266is double-quoted.
1267What this basically means, for example, is
1268if
1269.Li $1
1270is
1271.Dq Li abc
1272and
1273.Li $2
1274is
1275.Dq Li "def ghi" ,
1276then
1277.Li \&"$@\&"
1278expands to
1279the two arguments:
1280.Bd -literal -offset indent
1281"abc"   "def ghi"
1282.Ed
1283.It Li $#
1284Expands to the number of positional parameters.
1285.It Li $?
1286Expands to the exit status of the most recent pipeline.
1287.It Li $-
1288(hyphen) Expands to the current option flags (the single-letter
1289option names concatenated into a string) as specified on
1290invocation, by the
1291.Ic set
1292built-in command, or implicitly
1293by the shell.
1294.It Li $$
1295Expands to the process ID of the invoked shell.
1296A subshell
1297retains the same value of
1298.Va $
1299as its parent.
1300.It Li $!
1301Expands to the process ID of the most recent background
1302command executed from the current shell.
1303For a
1304pipeline, the process ID is that of the last command in the
1305pipeline.
1306If this parameter is referenced, the shell will remember
1307the process ID and its exit status until the
1308.Ic wait
1309built-in command reports completion of the process.
1310.It Li $0
1311(zero) Expands to the name of the shell script if passed on the command line,
1312the
1313.Ar name
1314operand if given (with
1315.Fl c )
1316or otherwise argument 0 passed to the shell.
1317.El
1318.Ss Special Variables
1319The following variables are set by the shell or
1320have special meaning to it:
1321.Bl -tag -width ".Va HISTSIZE"
1322.It Va CDPATH
1323The search path used with the
1324.Ic cd
1325built-in.
1326.It Va EDITOR
1327The fallback editor used with the
1328.Ic fc
1329built-in.
1330If not set, the default editor is
1331.Xr ed 1 .
1332.It Va FCEDIT
1333The default editor used with the
1334.Ic fc
1335built-in.
1336.It Va HISTSIZE
1337The number of previous commands that are accessible.
1338.It Va HOME
1339The user's home directory,
1340used in tilde expansion and as a default directory for the
1341.Ic cd
1342built-in.
1343.It Va IFS
1344Input Field Separators.
1345The default value is
1346.Aq space ,
1347.Aq tab ,
1348and
1349.Aq newline
1350in that order.
1351This default also applies if
1352.Va IFS
1353is unset, but not if it is set to the empty string.
1354See the
1355.Sx White Space Splitting
1356section for more details.
1357.It Va LINENO
1358The current line number in the script or function.
1359.It Va MAIL
1360The name of a mail file, that will be checked for the arrival of new
1361mail.
1362Overridden by
1363.Va MAILPATH .
1364.It Va MAILPATH
1365A colon
1366.Pq Ql \&:
1367separated list of file names, for the shell to check for incoming
1368mail.
1369This variable overrides the
1370.Va MAIL
1371setting.
1372There is a maximum of 10 mailboxes that can be monitored at once.
1373.It Va OPTIND
1374The index of the next argument to be processed by
1375.Ic getopts .
1376This is initialized to 1 at startup.
1377.It Va PATH
1378The default search path for executables.
1379See the
1380.Sx Path Search
1381section for details.
1382.It Va PPID
1383The parent process ID of the invoked shell.
1384This is set at startup
1385unless this variable is in the environment.
1386A later change of parent process ID is not reflected.
1387A subshell retains the same value of
1388.Va PPID .
1389.It Va PS1
1390The primary prompt string, which defaults to
1391.Dq Li "$ " ,
1392unless you are the superuser, in which case it defaults to
1393.Dq Li "# " .
1394.Va PS1
1395may include any of the following formatting sequences,
1396which are replaced by the given information:
1397.Bl -tag -width indent
1398.It Li \eH
1399The local hostname.
1400.It Li \eh
1401The fully-qualified hostname.
1402.It Li \eW
1403The final component of the current working directory.
1404.It Li \ew
1405The entire path of the current working directory.
1406.It Li \e$
1407Superuser status.
1408.Dq Li "$ "
1409for normal users and
1410.Dq Li "# "
1411for superusers.
1412.It Li \e\e
1413A literal backslash.
1414.El
1415.It Va PS2
1416The secondary prompt string, which defaults to
1417.Dq Li "> " .
1418.Va PS2
1419may include any of the formatting sequences from
1420.Va PS1 .
1421.It Va PS4
1422The prefix for the trace output (if
1423.Fl x
1424is active).
1425The default is
1426.Dq Li "+ " .
1427.El
1428.Ss Word Expansions
1429This clause describes the various expansions that are
1430performed on words.
1431Not all expansions are performed on
1432every word, as explained later.
1433.Pp
1434Tilde expansions, parameter expansions, command substitutions,
1435arithmetic expansions, and quote removals that occur within
1436a single word expand to a single field.
1437It is only field
1438splitting or pathname expansion that can create multiple
1439fields from a single word.
1440The single exception to this rule is
1441the expansion of the special parameter
1442.Va @
1443within double-quotes,
1444as was described above.
1445.Pp
1446The order of word expansion is:
1447.Bl -enum
1448.It
1449Tilde Expansion, Parameter Expansion, Command Substitution,
1450Arithmetic Expansion (these all occur at the same time).
1451.It
1452Field Splitting is performed on fields generated by step (1)
1453unless the
1454.Va IFS
1455variable is null.
1456.It
1457Pathname Expansion (unless the
1458.Fl f
1459option is in effect).
1460.It
1461Quote Removal.
1462.El
1463.Pp
1464The
1465.Ql $
1466character is used to introduce parameter expansion, command
1467substitution, or arithmetic expansion.
1468.Ss Tilde Expansion (substituting a user's home directory)
1469A word beginning with an unquoted tilde character
1470.Pq Ql ~
1471is
1472subjected to tilde expansion.
1473All the characters up to a slash
1474.Pq Ql /
1475or the end of the word are treated as a username
1476and are replaced with the user's home directory.
1477If the
1478username is missing (as in
1479.Pa ~/foobar ) ,
1480the tilde is replaced with the value of the
1481.Va HOME
1482variable (the current user's home directory).
1483.Ss Parameter Expansion
1484The format for parameter expansion is as follows:
1485.Pp
1486.D1 Li ${ Ns Ar expression Ns Li }
1487.Pp
1488where
1489.Ar expression
1490consists of all characters until the matching
1491.Ql } .
1492Any
1493.Ql }
1494escaped by a backslash or within a single-quoted or double-quoted
1495string, and characters in
1496embedded arithmetic expansions, command substitutions, and variable
1497expansions, are not examined in determining the matching
1498.Ql } .
1499If the variants with
1500.Ql + ,
1501.Ql - ,
1502.Ql =
1503or
1504.Ql ?\&
1505occur within a double-quoted string,
1506as an extension there may be unquoted parts
1507(via double-quotes inside the expansion);
1508.Ql }
1509within such parts are also not examined in determining the matching
1510.Ql } .
1511.Pp
1512The simplest form for parameter expansion is:
1513.Pp
1514.D1 Li ${ Ns Ar parameter Ns Li }
1515.Pp
1516The value, if any, of
1517.Ar parameter
1518is substituted.
1519.Pp
1520The parameter name or symbol can be enclosed in braces, which are
1521optional except for positional parameters with more than one digit or
1522when parameter is followed by a character that could be interpreted as
1523part of the name.
1524If a parameter expansion occurs inside double-quotes:
1525.Bl -enum
1526.It
1527Field splitting is not performed on the results of the
1528expansion, with the exception of the special parameter
1529.Va @ .
1530.It
1531Pathname expansion is not performed on the results of the
1532expansion.
1533.El
1534.Pp
1535In addition, a parameter expansion can be modified by using one of the
1536following formats.
1537.Bl -tag -width indent
1538.It Li ${ Ns Ar parameter Ns Li :- Ns Ar word Ns Li }
1539Use Default Values.
1540If
1541.Ar parameter
1542is unset or null, the expansion of
1543.Ar word
1544is substituted; otherwise, the value of
1545.Ar parameter
1546is substituted.
1547.It Li ${ Ns Ar parameter Ns Li := Ns Ar word Ns Li }
1548Assign Default Values.
1549If
1550.Ar parameter
1551is unset or null, the expansion of
1552.Ar word
1553is assigned to
1554.Ar parameter .
1555In all cases, the
1556final value of
1557.Ar parameter
1558is substituted.
1559Quoting inside
1560.Ar word
1561does not prevent field splitting or pathname expansion.
1562Only variables, not positional
1563parameters or special parameters, can be
1564assigned in this way.
1565.It Li ${ Ns Ar parameter Ns Li :? Ns Oo Ar word Oc Ns Li }
1566Indicate Error if Null or Unset.
1567If
1568.Ar parameter
1569is unset or null, the expansion of
1570.Ar word
1571(or a message indicating it is unset if
1572.Ar word
1573is omitted) is written to standard
1574error and the shell exits with a nonzero
1575exit status.
1576Otherwise, the value of
1577.Ar parameter
1578is substituted.
1579An
1580interactive shell need not exit.
1581.It Li ${ Ns Ar parameter Ns Li :+ Ns Ar word Ns Li }
1582Use Alternate Value.
1583If
1584.Ar parameter
1585is unset or null, null is substituted;
1586otherwise, the expansion of
1587.Ar word
1588is substituted.
1589.El
1590.Pp
1591In the parameter expansions shown previously, use of the colon in the
1592format results in a test for a parameter that is unset or null; omission
1593of the colon results in a test for a parameter that is only unset.
1594.Pp
1595The
1596.Ar word
1597inherits the type of quoting
1598(unquoted, double-quoted or here-document)
1599from the surroundings,
1600with the exception that a backslash that quotes a closing brace is removed
1601during quote removal.
1602.Bl -tag -width indent
1603.It Li ${# Ns Ar parameter Ns Li }
1604String Length.
1605The length in characters of
1606the value of
1607.Ar parameter .
1608.El
1609.Pp
1610The following four varieties of parameter expansion provide for substring
1611processing.
1612In each case, pattern matching notation
1613(see
1614.Sx Shell Patterns ) ,
1615rather than regular expression notation,
1616is used to evaluate the patterns.
1617If parameter is one of the special parameters
1618.Va *
1619or
1620.Va @ ,
1621the result of the expansion is unspecified.
1622Enclosing the full parameter expansion string in double-quotes does not
1623cause the following four varieties of pattern characters to be quoted,
1624whereas quoting characters within the braces has this effect.
1625.Bl -tag -width indent
1626.It Li ${ Ns Ar parameter Ns Li % Ns Ar word Ns Li }
1627Remove Smallest Suffix Pattern.
1628The
1629.Ar word
1630is expanded to produce a pattern.
1631The
1632parameter expansion then results in
1633.Ar parameter ,
1634with the smallest portion of the
1635suffix matched by the pattern deleted.
1636.It Li ${ Ns Ar parameter Ns Li %% Ns Ar word Ns Li }
1637Remove Largest Suffix Pattern.
1638The
1639.Ar word
1640is expanded to produce a pattern.
1641The
1642parameter expansion then results in
1643.Ar parameter ,
1644with the largest portion of the
1645suffix matched by the pattern deleted.
1646.It Li ${ Ns Ar parameter Ns Li # Ns Ar word Ns Li }
1647Remove Smallest Prefix Pattern.
1648The
1649.Ar word
1650is expanded to produce a pattern.
1651The
1652parameter expansion then results in
1653.Ar parameter ,
1654with the smallest portion of the
1655prefix matched by the pattern deleted.
1656.It Li ${ Ns Ar parameter Ns Li ## Ns Ar word Ns Li }
1657Remove Largest Prefix Pattern.
1658The
1659.Ar word
1660is expanded to produce a pattern.
1661The
1662parameter expansion then results in
1663.Ar parameter ,
1664with the largest portion of the
1665prefix matched by the pattern deleted.
1666.El
1667.Ss Command Substitution
1668Command substitution allows the output of a command to be substituted in
1669place of the command name itself.
1670Command substitution occurs when
1671the command is enclosed as follows:
1672.Pp
1673.D1 Li $( Ns Ar command Ns Li )\&
1674.Pp
1675or the backquoted version:
1676.Pp
1677.D1 Li ` Ns Ar command Ns Li `
1678.Pp
1679The shell expands the command substitution by executing command
1680and replacing the command substitution
1681with the standard output of the command,
1682removing sequences of one or more newlines at the end of the substitution.
1683Embedded newlines before the end of the output are not removed;
1684however, during field splitting, they may be translated into spaces
1685depending on the value of
1686.Va IFS
1687and the quoting that is in effect.
1688The command is executed in a subshell environment,
1689except that the built-in commands
1690.Ic jobid ,
1691.Ic jobs ,
1692and
1693.Ic trap
1694return information about the parent shell environment
1695and
1696.Ic times
1697returns information about the same process
1698if they are the only command in a command substitution.
1699.Pp
1700If a command substitution of the
1701.Li $(
1702form begins with a subshell,
1703the
1704.Li $(
1705and
1706.Li (\&
1707must be separated by whitespace
1708to avoid ambiguity with arithmetic expansion.
1709.Ss Arithmetic Expansion
1710Arithmetic expansion provides a mechanism for evaluating an arithmetic
1711expression and substituting its value.
1712The format for arithmetic expansion is as follows:
1713.Pp
1714.D1 Li $(( Ns Ar expression Ns Li ))
1715.Pp
1716The
1717.Ar expression
1718is treated as if it were in double-quotes, except
1719that a double-quote inside the expression is not treated specially.
1720The
1721shell expands all tokens in the
1722.Ar expression
1723for parameter expansion,
1724command substitution,
1725arithmetic expansion
1726and quote removal.
1727.Pp
1728The allowed expressions are a subset of C expressions,
1729summarized below.
1730.Bl -tag -width "Variables" -offset indent
1731.It Values
1732All values are of type
1733.Ft intmax_t .
1734.It Constants
1735Decimal, octal (starting with
1736.Li 0 )
1737and hexadecimal (starting with
1738.Li 0x )
1739integer constants.
1740.It Variables
1741Shell variables can be read and written
1742and contain integer constants.
1743.It Unary operators
1744.Li "! ~ + -"
1745.It Binary operators
1746.Li "* / % + - << >> < <= > >= == != & ^ | && ||"
1747.It Assignment operators
1748.Li "= += -= *= /= %= <<= >>= &= ^= |="
1749.It Conditional operator
1750.Li "? :"
1751.El
1752.Pp
1753The result of the expression is substituted in decimal.
1754.Ss White Space Splitting (Field Splitting)
1755In certain contexts,
1756after parameter expansion, command substitution, and
1757arithmetic expansion the shell scans the results of
1758expansions and substitutions that did not occur in double-quotes for
1759field splitting and multiple fields can result.
1760.Pp
1761Characters in
1762.Va IFS
1763that are whitespace
1764.Po
1765.Aq space ,
1766.Aq tab ,
1767and
1768.Aq newline
1769.Pc
1770are treated differently from other characters in
1771.Va IFS .
1772.Pp
1773Whitespace in
1774.Va IFS
1775at the beginning or end of a word is discarded.
1776.Pp
1777Subsequently, a field is delimited by either
1778.Bl -enum
1779.It
1780a non-whitespace character in
1781.Va IFS
1782with any whitespace in
1783.Va IFS
1784surrounding it, or
1785.It
1786one or more whitespace characters in
1787.Va IFS .
1788.El
1789.Pp
1790If a word ends with a non-whitespace character in
1791.Va IFS ,
1792there is no empty field after this character.
1793.Pp
1794If no field is delimited, the word is discarded.
1795In particular, if a word consists solely of an unquoted substitution
1796and the result of the substitution is null,
1797it is removed by field splitting even if
1798.Va IFS
1799is null.
1800.Ss Pathname Expansion (File Name Generation)
1801Unless the
1802.Fl f
1803option is set,
1804file name generation is performed
1805after word splitting is complete.
1806Each word is
1807viewed as a series of patterns, separated by slashes.
1808The
1809process of expansion replaces the word with the names of
1810all existing files whose names can be formed by replacing
1811each pattern with a string that matches the specified pattern.
1812There are two restrictions on this: first, a pattern cannot match
1813a string containing a slash, and second,
1814a pattern cannot match a string starting with a period
1815unless the first character of the pattern is a period.
1816The next section describes the patterns used for
1817Pathname Expansion,
1818the four varieties of parameter expansion for substring processing and the
1819.Ic case
1820command.
1821.Ss Shell Patterns
1822A pattern consists of normal characters, which match themselves,
1823and meta-characters.
1824The meta-characters are
1825.Ql * ,
1826.Ql \&? ,
1827and
1828.Ql \&[ .
1829These characters lose their special meanings if they are quoted.
1830When command or variable substitution is performed and the dollar sign
1831or back quotes are not double-quoted, the value of the
1832variable or the output of the command is scanned for these
1833characters and they are turned into meta-characters.
1834.Pp
1835An asterisk
1836.Pq Ql *
1837matches any string of characters.
1838A question mark
1839.Pq Ql \&?
1840matches any single character.
1841A left bracket
1842.Pq Ql \&[
1843introduces a character class.
1844The end of the character class is indicated by a
1845.Ql \&] ;
1846if the
1847.Ql \&]
1848is missing then the
1849.Ql \&[
1850matches a
1851.Ql \&[
1852rather than introducing a character class.
1853A character class matches any of the characters between the square brackets.
1854A locale-dependent range of characters may be specified using a minus sign.
1855A named class of characters (see
1856.Xr wctype 3 )
1857may be specified by surrounding the name with
1858.Ql \&[:
1859and
1860.Ql :\&] .
1861For example,
1862.Ql \&[\&[:alpha:\&]\&]
1863is a shell pattern that matches a single letter.
1864The character class may be complemented by making an exclamation point
1865.Pq Ql !\&
1866the first character of the character class.
1867A caret
1868.Pq Ql ^
1869has the same effect but is non-standard.
1870.Pp
1871To include a
1872.Ql \&]
1873in a character class, make it the first character listed
1874(after the
1875.Ql \&!
1876or
1877.Ql ^ ,
1878if any).
1879To include a
1880.Ql - ,
1881make it the first or last character listed.
1882.Ss Built-in Commands
1883This section lists the built-in commands.
1884.Bl -tag -width indent
1885.It Ic \&:
1886A null command that returns a 0 (true) exit value.
1887.It Ic \&. Ar file
1888The commands in the specified file are read and executed by the shell.
1889The
1890.Ic return
1891command may be used to return to the
1892.Ic \&.
1893command's caller.
1894If
1895.Ar file
1896contains any
1897.Ql /
1898characters, it is used as is.
1899Otherwise, the shell searches the
1900.Va PATH
1901for the file.
1902If it is not found in the
1903.Va PATH ,
1904it is sought in the current working directory.
1905.It Ic \&[
1906A built-in equivalent of
1907.Xr test 1 .
1908.It Ic alias Oo Ar name Ns Oo = Ns Ar string Oc ... Oc
1909If
1910.Ar name Ns = Ns Ar string
1911is specified, the shell defines the alias
1912.Ar name
1913with value
1914.Ar string .
1915If just
1916.Ar name
1917is specified, the value of the alias
1918.Ar name
1919is printed.
1920With no arguments, the
1921.Ic alias
1922built-in command prints the names and values of all defined aliases
1923(see
1924.Ic unalias ) .
1925Alias values are written with appropriate quoting so that they are
1926suitable for re-input to the shell.
1927Also see the
1928.Sx Aliases
1929subsection.
1930.It Ic bg Op Ar job ...
1931Continue the specified jobs
1932(or the current job if no jobs are given)
1933in the background.
1934.It Ic bind Oo Fl aeklrsv Oc Oo Ar key Oo Ar command Oc Oc
1935List or alter key bindings for the line editor.
1936This command is documented in
1937.Xr editrc 5 .
1938.It Ic break Op Ar num
1939See the
1940.Sx Flow-Control Constructs
1941subsection.
1942.It Ic builtin Ar cmd Op Ar arg ...
1943Execute the specified built-in command,
1944.Ar cmd .
1945This is useful when the user wishes to override a shell function
1946with the same name as a built-in command.
1947.It Ic cd Oo Fl L | P Oc Oo Fl e Oc Op Ar directory
1948Switch to the specified
1949.Ar directory ,
1950or to the directory specified in the
1951.Va HOME
1952environment variable if no
1953.Ar directory
1954is specified.
1955If
1956.Ar directory
1957does not begin with
1958.Pa / , \&. ,
1959or
1960.Pa .. ,
1961then the directories listed in the
1962.Va CDPATH
1963variable will be
1964searched for the specified
1965.Ar directory .
1966If
1967.Va CDPATH
1968is unset, the current directory is searched.
1969The format of
1970.Va CDPATH
1971is the same as that of
1972.Va PATH .
1973In an interactive shell,
1974the
1975.Ic cd
1976command will print out the name of the directory
1977that it actually switched to
1978if this is different from the name that the user gave.
1979These may be different either because the
1980.Va CDPATH
1981mechanism was used or because a symbolic link was crossed.
1982.Pp
1983If the
1984.Fl P
1985option is specified,
1986.Pa ..
1987is handled physically and symbolic links are resolved before
1988.Pa ..
1989components are processed.
1990If the
1991.Fl L
1992option is specified,
1993.Pa ..
1994is handled logically.
1995This is the default.
1996.Pp
1997The
1998.Fl e
1999option causes
2000.Ic cd
2001to return exit status 1 if the full pathname of the new directory
2002cannot be determined reliably or at all.
2003Normally this is not considered an error,
2004although a warning is printed.
2005.It Ic chdir
2006A synonym for the
2007.Ic cd
2008built-in command.
2009.It Ic command Oo Fl p Oc Op Ar utility Op Ar argument ...
2010.It Ic command Oo Fl p Oc Fl v Ar utility
2011.It Ic command Oo Fl p Oc Fl V Ar utility
2012The first form of invocation executes the specified
2013.Ar utility ,
2014ignoring shell functions in the search.
2015If
2016.Ar utility
2017is a special builtin,
2018it is executed as if it were a regular builtin.
2019.Pp
2020If the
2021.Fl p
2022option is specified, the command search is performed using a
2023default value of
2024.Va PATH
2025that is guaranteed to find all of the standard utilities.
2026.Pp
2027If the
2028.Fl v
2029option is specified,
2030.Ar utility
2031is not executed but a description of its interpretation by the shell is
2032printed.
2033For ordinary commands the output is the path name; for shell built-in
2034commands, shell functions and keywords only the name is written.
2035Aliases are printed as
2036.Dq Ic alias Ar name Ns = Ns Ar value .
2037.Pp
2038The
2039.Fl V
2040option is identical to
2041.Fl v
2042except for the output.
2043It prints
2044.Dq Ar utility Ic is Ar description
2045where
2046.Ar description
2047is either
2048the path name to
2049.Ar utility ,
2050a special shell builtin,
2051a shell builtin,
2052a shell function,
2053a shell keyword
2054or
2055an alias for
2056.Ar value .
2057.It Ic continue Op Ar num
2058See the
2059.Sx Flow-Control Constructs
2060subsection.
2061.It Ic echo Oo Fl e | n Oc Op Ar string ...
2062Print a space-separated list of the arguments to the standard output
2063and append a newline character.
2064.Bl -tag -width indent
2065.It Fl n
2066Suppress the output of the trailing newline.
2067.It Fl e
2068Process C-style backslash escape sequences.
2069The
2070.Ic echo
2071command understands the following character escapes:
2072.Bl -tag -width indent
2073.It \ea
2074Alert (ring the terminal bell)
2075.It \eb
2076Backspace
2077.It \ec
2078Suppress the trailing newline (this has the side-effect of truncating the
2079line if it is not the last character)
2080.It \ee
2081The ESC character
2082.Tn ( ASCII
20830x1b)
2084.It \ef
2085Formfeed
2086.It \en
2087Newline
2088.It \er
2089Carriage return
2090.It \et
2091Horizontal tab
2092.It \ev
2093Vertical tab
2094.It \e\e
2095Literal backslash
2096.It \e0nnn
2097(Zero) The character whose octal value is
2098.Ar nnn
2099.El
2100.Pp
2101If
2102.Ar string
2103is not enclosed in quotes then the backslash itself must be escaped
2104with a backslash to protect it from the shell.
2105For example
2106.Bd -literal -offset indent
2107$ echo -e "a\evb"
2108a
2109 b
2110$ echo -e a\e\evb
2111a
2112 b
2113$ echo -e "a\e\eb"
2114a\eb
2115$ echo -e a\e\e\e\eb
2116a\eb
2117.Ed
2118.El
2119.Pp
2120Only one of the
2121.Fl e
2122and
2123.Fl n
2124options may be specified.
2125.It Ic eval Ar string ...
2126Concatenate all the arguments with spaces.
2127Then re-parse and execute the command.
2128.It Ic exec Op Ar command Op arg ...
2129Unless
2130.Ar command
2131is omitted,
2132the shell process is replaced with the specified program
2133(which must be a real program, not a shell built-in command or function).
2134Any redirections on the
2135.Ic exec
2136command are marked as permanent,
2137so that they are not undone when the
2138.Ic exec
2139command finishes.
2140.It Ic exit Op Ar exitstatus
2141Terminate the shell process.
2142If
2143.Ar exitstatus
2144is given
2145it is used as the exit status of the shell.
2146Otherwise, if the shell is executing an
2147.Cm EXIT
2148trap, the exit status of the last command before the trap is used;
2149if the shell is executing a trap for a signal,
2150the shell exits by resending the signal to itself.
2151Otherwise, the exit status of the preceding command is used.
2152The exit status should be an integer between 0 and 255.
2153.It Ic export Ar name ...
2154.It Ic export Op Fl p
2155The specified names are exported so that they will
2156appear in the environment of subsequent commands.
2157The only way to un-export a variable is to
2158.Ic unset
2159it.
2160The shell allows the value of a variable to be set
2161at the same time as it is exported by writing
2162.Pp
2163.D1 Ic export Ar name Ns = Ns Ar value
2164.Pp
2165With no arguments the
2166.Ic export
2167command lists the names
2168of all exported variables.
2169If the
2170.Fl p
2171option is specified, the exported variables are printed as
2172.Dq Ic export Ar name Ns = Ns Ar value
2173lines, suitable for re-input to the shell.
2174.It Ic false
2175A null command that returns a non-zero (false) exit value.
2176.It Ic fc Oo Fl e Ar editor Oc Op Ar first Op Ar last
2177.It Ic fc Fl l Oo Fl nr Oc Op Ar first Op Ar last
2178.It Ic fc Fl s Oo Ar old Ns = Ns Ar new Oc Op Ar first
2179The
2180.Ic fc
2181built-in command lists, or edits and re-executes,
2182commands previously entered to an interactive shell.
2183.Bl -tag -width indent
2184.It Fl e Ar editor
2185Use the editor named by
2186.Ar editor
2187to edit the commands.
2188The
2189.Ar editor
2190string is a command name,
2191subject to search via the
2192.Va PATH
2193variable.
2194The value in the
2195.Va FCEDIT
2196variable is used as a default when
2197.Fl e
2198is not specified.
2199If
2200.Va FCEDIT
2201is null or unset, the value of the
2202.Va EDITOR
2203variable is used.
2204If
2205.Va EDITOR
2206is null or unset,
2207.Xr ed 1
2208is used as the editor.
2209.It Fl l No (ell)
2210List the commands rather than invoking
2211an editor on them.
2212The commands are written in the
2213sequence indicated by the
2214.Ar first
2215and
2216.Ar last
2217operands, as affected by
2218.Fl r ,
2219with each command preceded by the command number.
2220.It Fl n
2221Suppress command numbers when listing with
2222.Fl l .
2223.It Fl r
2224Reverse the order of the commands listed
2225(with
2226.Fl l )
2227or edited
2228(with neither
2229.Fl l
2230nor
2231.Fl s ) .
2232.It Fl s
2233Re-execute the command without invoking an editor.
2234.It Ar first
2235.It Ar last
2236Select the commands to list or edit.
2237The number of previous commands that can be accessed
2238are determined by the value of the
2239.Va HISTSIZE
2240variable.
2241The value of
2242.Ar first
2243or
2244.Ar last
2245or both are one of the following:
2246.Bl -tag -width indent
2247.It Oo Cm + Oc Ns Ar num
2248A positive number representing a command number;
2249command numbers can be displayed with the
2250.Fl l
2251option.
2252.It Fl Ar num
2253A negative decimal number representing the
2254command that was executed
2255.Ar num
2256of
2257commands previously.
2258For example, \-1 is the immediately previous command.
2259.It Ar string
2260A string indicating the most recently entered command
2261that begins with that string.
2262If the
2263.Ar old Ns = Ns Ar new
2264operand is not also specified with
2265.Fl s ,
2266the string form of the first operand cannot contain an embedded equal sign.
2267.El
2268.El
2269.Pp
2270The following variables affect the execution of
2271.Ic fc :
2272.Bl -tag -width ".Va HISTSIZE"
2273.It Va FCEDIT
2274Name of the editor to use for history editing.
2275.It Va HISTSIZE
2276The number of previous commands that are accessible.
2277.El
2278.It Ic fg Op Ar job
2279Move the specified
2280.Ar job
2281or the current job to the foreground.
2282.It Ic getopts Ar optstring var
2283The
2284.Tn POSIX
2285.Ic getopts
2286command.
2287The
2288.Ic getopts
2289command deprecates the older
2290.Xr getopt 1
2291command.
2292The first argument should be a series of letters, each possibly
2293followed by a colon which indicates that the option takes an argument.
2294The specified variable is set to the parsed option.
2295The index of
2296the next argument is placed into the shell variable
2297.Va OPTIND .
2298If an option takes an argument, it is placed into the shell variable
2299.Va OPTARG .
2300If an invalid option is encountered,
2301.Ar var
2302is set to
2303.Ql \&? .
2304It returns a false value (1) when it encounters the end of the options.
2305A new set of arguments may be parsed by assigning
2306.Li OPTIND=1 .
2307.It Ic hash Oo Fl rv Oc Op Ar command ...
2308The shell maintains a hash table which remembers the locations of commands.
2309With no arguments whatsoever, the
2310.Ic hash
2311command prints out the contents of this table.
2312.Pp
2313With arguments, the
2314.Ic hash
2315command removes each specified
2316.Ar command
2317from the hash table (unless they are functions) and then locates it.
2318With the
2319.Fl v
2320option,
2321.Ic hash
2322prints the locations of the commands as it finds them.
2323The
2324.Fl r
2325option causes the
2326.Ic hash
2327command to delete all the entries in the hash table except for functions.
2328.It Ic jobid Op Ar job
2329Print the process IDs of the processes in the specified
2330.Ar job .
2331If the
2332.Ar job
2333argument is omitted, use the current job.
2334.It Ic jobs Oo Fl lps Oc Op Ar job ...
2335Print information about the specified jobs, or all jobs if no
2336.Ar job
2337argument is given.
2338The information printed includes job ID, status and command name.
2339.Pp
2340If the
2341.Fl l
2342option is specified, the PID of each job is also printed.
2343If the
2344.Fl p
2345option is specified, only the process IDs for the process group leaders
2346are printed, one per line.
2347If the
2348.Fl s
2349option is specified, only the PIDs of the job commands are printed, one per
2350line.
2351.It Ic kill
2352A built-in equivalent of
2353.Xr kill 1
2354that additionally supports sending signals to jobs.
2355.It Ic local Oo Ar variable ... Oc Op Fl
2356See the
2357.Sx Functions
2358subsection.
2359.It Ic printf
2360A built-in equivalent of
2361.Xr printf 1 .
2362.It Ic pwd Op Fl L | P
2363Print the path of the current directory.
2364The built-in command may
2365differ from the program of the same name because the
2366built-in command remembers what the current directory
2367is rather than recomputing it each time.
2368This makes
2369it faster.
2370However, if the current directory is
2371renamed,
2372the built-in version of
2373.Xr pwd 1
2374will continue to print the old name for the directory.
2375.Pp
2376If the
2377.Fl P
2378option is specified, symbolic links are resolved.
2379If the
2380.Fl L
2381option is specified, the shell's notion of the current directory
2382is printed (symbolic links are not resolved).
2383This is the default.
2384.It Ic read Oo Fl p Ar prompt Oc Oo
2385.Fl t Ar timeout Oc Oo Fl er Oc Ar variable ...
2386The
2387.Ar prompt
2388is printed if the
2389.Fl p
2390option is specified
2391and the standard input is a terminal.
2392Then a line is
2393read from the standard input.
2394The trailing newline
2395is deleted from the line and the line is split as
2396described in the section on
2397.Sx White Space Splitting (Field Splitting)
2398above, and
2399the pieces are assigned to the variables in order.
2400If there are more pieces than variables, the remaining
2401pieces (along with the characters in
2402.Va IFS
2403that separated them)
2404are assigned to the last variable.
2405If there are more variables than pieces, the remaining
2406variables are assigned the null string.
2407.Pp
2408Backslashes are treated specially, unless the
2409.Fl r
2410option is
2411specified.
2412If a backslash is followed by
2413a newline, the backslash and the newline will be
2414deleted.
2415If a backslash is followed by any other
2416character, the backslash will be deleted and the following
2417character will be treated as though it were not in
2418.Va IFS ,
2419even if it is.
2420.Pp
2421If the
2422.Fl t
2423option is specified and the
2424.Ar timeout
2425elapses before a complete line of input is supplied,
2426the
2427.Ic read
2428command will return an exit status as if terminated by
2429.Dv SIGALRM
2430without assigning any values.
2431The
2432.Ar timeout
2433value may optionally be followed by one of
2434.Ql s ,
2435.Ql m
2436or
2437.Ql h
2438to explicitly specify seconds, minutes or hours.
2439If none is supplied,
2440.Ql s
2441is assumed.
2442.Pp
2443The
2444.Fl e
2445option exists only for backward compatibility with older scripts.
2446.Pp
2447The exit status is 0 on success, 1 on end of file,
2448between 2 and 128 if an error occurs
2449and greater than 128 if a trapped signal interrupts
2450.Ic read .
2451.It Ic readonly Oo Fl p Oc Op Ar name ...
2452Each specified
2453.Ar name
2454is marked as read only,
2455so that it cannot be subsequently modified or unset.
2456The shell allows the value of a variable to be set
2457at the same time as it is marked read only
2458by using the following form:
2459.Pp
2460.D1 Ic readonly Ar name Ns = Ns Ar value
2461.Pp
2462With no arguments the
2463.Ic readonly
2464command lists the names of all read only variables.
2465If the
2466.Fl p
2467option is specified, the read-only variables are printed as
2468.Dq Ic readonly Ar name Ns = Ns Ar value
2469lines, suitable for re-input to the shell.
2470.It Ic return Op Ar exitstatus
2471See the
2472.Sx Functions
2473subsection.
2474.It Ic set Oo Fl /+abCEefIimnpTuVvx Oc Oo Fl /+o Ar longname Oc Oo
2475.Fl c Ar string Oc Op Fl - Ar arg ...
2476The
2477.Ic set
2478command performs three different functions:
2479.Bl -item
2480.It
2481With no arguments, it lists the values of all shell variables.
2482.It
2483If options are given,
2484either in short form or using the long
2485.Dq Fl /+o Ar longname
2486form,
2487it sets or clears the specified options as described in the section called
2488.Sx Argument List Processing .
2489.It
2490If the
2491.Dq Fl -
2492option is specified,
2493.Ic set
2494will replace the shell's positional parameters with the subsequent
2495arguments.
2496If no arguments follow the
2497.Dq Fl -
2498option,
2499all the positional parameters will be cleared,
2500which is equivalent to executing the command
2501.Dq Li "shift $#" .
2502The
2503.Dq Fl -
2504flag may be omitted when specifying arguments to be used
2505as positional replacement parameters.
2506This is not recommended,
2507because the first argument may begin with a dash
2508.Pq Ql -
2509or a plus
2510.Pq Ql + ,
2511which the
2512.Ic set
2513command will interpret as a request to enable or disable options.
2514.El
2515.It Ic setvar Ar variable value
2516Assigns the specified
2517.Ar value
2518to the specified
2519.Ar variable .
2520The
2521.Ic setvar
2522command is intended to be used in functions that
2523assign values to variables whose names are passed as parameters.
2524In general it is better to write
2525.Dq Ar variable Ns = Ns Ar value
2526rather than using
2527.Ic setvar .
2528.It Ic shift Op Ar n
2529Shift the positional parameters
2530.Ar n
2531times, or once if
2532.Ar n
2533is not specified.
2534A shift sets the value of
2535.Li $1
2536to the value of
2537.Li $2 ,
2538the value of
2539.Li $2
2540to the value of
2541.Li $3 ,
2542and so on,
2543decreasing the value of
2544.Li $#
2545by one.
2546For portability, shifting if there are zero positional parameters
2547should be avoided, since the shell may abort.
2548.It Ic test
2549A built-in equivalent of
2550.Xr test 1 .
2551.It Ic times
2552Print the amount of time spent executing the shell process and its children.
2553The first output line shows the user and system times for the shell process
2554itself, the second one contains the user and system times for the
2555children.
2556.It Ic trap Oo Ar action Oc Ar signal ...
2557.It Ic trap Fl l
2558Cause the shell to parse and execute
2559.Ar action
2560when any specified
2561.Ar signal
2562is received.
2563The signals are specified by name or number.
2564In addition, the pseudo-signal
2565.Cm EXIT
2566may be used to specify an
2567.Ar action
2568that is performed when the shell terminates.
2569The
2570.Ar action
2571may be an empty string or a dash
2572.Pq Ql - ;
2573the former causes the specified signal to be ignored
2574and the latter causes the default action to be taken.
2575Omitting the
2576.Ar action
2577and using only signal numbers is another way to request the default action.
2578In a subshell or utility environment,
2579the shell resets trapped (but not ignored) signals to the default action.
2580The
2581.Ic trap
2582command has no effect on signals that were ignored on entry to the shell.
2583.Pp
2584Option
2585.Fl l
2586causes the
2587.Ic trap
2588command to display a list of valid signal names.
2589.It Ic true
2590A null command that returns a 0 (true) exit value.
2591.It Ic type Op Ar name ...
2592Interpret each
2593.Ar name
2594as a command and print the resolution of the command search.
2595Possible resolutions are:
2596shell keyword, alias, special shell builtin, shell builtin, command,
2597tracked alias
2598and not found.
2599For aliases the alias expansion is printed;
2600for commands and tracked aliases
2601the complete pathname of the command is printed.
2602.It Ic ulimit Oo Fl HSabcdfklmnpstuvw Oc Op Ar limit
2603Set or display resource limits (see
2604.Xr getrlimit 2 ) .
2605If
2606.Ar limit
2607is specified, the named resource will be set;
2608otherwise the current resource value will be displayed.
2609.Pp
2610If
2611.Fl H
2612is specified, the hard limits will be set or displayed.
2613While everybody is allowed to reduce a hard limit,
2614only the superuser can increase it.
2615The
2616.Fl S
2617option
2618specifies the soft limits instead.
2619When displaying limits,
2620only one of
2621.Fl S
2622or
2623.Fl H
2624can be given.
2625The default is to display the soft limits,
2626and to set both the hard and the soft limits.
2627.Pp
2628Option
2629.Fl a
2630causes the
2631.Ic ulimit
2632command to display all resources.
2633The parameter
2634.Ar limit
2635is not acceptable in this mode.
2636.Pp
2637The remaining options specify which resource value is to be
2638displayed or modified.
2639They are mutually exclusive.
2640.Bl -tag -width indent
2641.It Fl b Ar sbsize
2642The maximum size of socket buffer usage, in bytes.
2643.It Fl c Ar coredumpsize
2644The maximal size of core dump files, in 512-byte blocks.
2645.It Fl d Ar datasize
2646The maximal size of the data segment of a process, in kilobytes.
2647.It Fl f Ar filesize
2648The maximal size of a file, in 512-byte blocks.
2649.It Fl k Ar kqueues
2650The maximal number of kqueues
2651(see
2652.Xr kqueue 2 )
2653for this user ID.
2654.It Fl l Ar lockedmem
2655The maximal size of memory that can be locked by a process, in
2656kilobytes.
2657.It Fl m Ar memoryuse
2658The maximal resident set size of a process, in kilobytes.
2659.It Fl n Ar nofiles
2660The maximal number of descriptors that could be opened by a process.
2661.It Fl p Ar pseudoterminals
2662The maximal number of pseudo-terminals for this user ID.
2663.It Fl s Ar stacksize
2664The maximal size of the stack segment, in kilobytes.
2665.It Fl t Ar time
2666The maximal amount of CPU time to be used by each process, in seconds.
2667.It Fl u Ar userproc
2668The maximal number of simultaneous processes for this user ID.
2669.It Fl v Ar virtualmem
2670The maximal virtual size of a process, in kilobytes.
2671.It Fl w Ar swapuse
2672The maximum amount of swap space reserved or used for this user ID,
2673in kilobytes.
2674.El
2675.It Ic umask Oo Fl S Oc Op Ar mask
2676Set the file creation mask (see
2677.Xr umask 2 )
2678to the octal or symbolic (see
2679.Xr chmod 1 )
2680value specified by
2681.Ar mask .
2682If the argument is omitted, the current mask value is printed.
2683If the
2684.Fl S
2685option is specified, the output is symbolic, otherwise the output is octal.
2686.It Ic unalias Oo Fl a Oc Op Ar name ...
2687The specified alias names are removed.
2688If
2689.Fl a
2690is specified, all aliases are removed.
2691.It Ic unset Oo Fl fv Oc Ar name ...
2692The specified variables or functions are unset and unexported.
2693If the
2694.Fl v
2695option is specified or no options are given, the
2696.Ar name
2697arguments are treated as variable names.
2698If the
2699.Fl f
2700option is specified, the
2701.Ar name
2702arguments are treated as function names.
2703.It Ic wait Op Ar job ...
2704Wait for each specified
2705.Ar job
2706to complete and return the exit status of the last process in the
2707last specified
2708.Ar job .
2709If any
2710.Ar job
2711specified is unknown to the shell, it is treated as if it
2712were a known job that exited with exit status 127.
2713If no operands are given, wait for all jobs to complete
2714and return an exit status of zero.
2715.El
2716.Ss Commandline Editing
2717When
2718.Nm
2719is being used interactively from a terminal, the current command
2720and the command history
2721(see
2722.Ic fc
2723in
2724.Sx Built-in Commands )
2725can be edited using
2726.Nm vi Ns -mode
2727command line editing.
2728This mode uses commands similar
2729to a subset of those described in the
2730.Xr vi 1
2731man page.
2732The command
2733.Dq Li "set -o vi"
2734(or
2735.Dq Li "set -V" )
2736enables
2737.Nm vi Ns -mode
2738editing and places
2739.Nm
2740into
2741.Nm vi
2742insert mode.
2743With
2744.Nm vi Ns -mode
2745enabled,
2746.Nm
2747can be switched between insert mode and command mode by typing
2748.Aq ESC .
2749Hitting
2750.Aq return
2751while in command mode will pass the line to the shell.
2752.Pp
2753Similarly, the
2754.Dq Li "set -o emacs"
2755(or
2756.Dq Li "set -E" )
2757command can be used to enable a subset of
2758.Nm emacs Ns -style
2759command line editing features.
2760.Sh ENVIRONMENT
2761The following environment variables affect the execution of
2762.Nm :
2763.Bl -tag -width ".Ev LANGXXXXXX"
2764.It Ev ENV
2765Initialization file for interactive shells.
2766.It Ev LANG , Ev LC_*
2767Locale settings.
2768These are inherited by children of the shell,
2769and is used in a limited manner by the shell itself.
2770.It Ev PWD
2771An absolute pathname for the current directory,
2772possibly containing symbolic links.
2773This is used and updated by the shell.
2774.It Ev TERM
2775The default terminal setting for the shell.
2776This is inherited by children of the shell, and is used in the history
2777editing modes.
2778.El
2779.Pp
2780Additionally, environment variables are turned into shell variables
2781at startup,
2782which may affect the shell as described under
2783.Sx Special Variables .
2784.Sh FILES
2785.Bl -tag -width "/etc/suid_profileXX" -compact
2786.It Pa ~/.profile
2787User's login profile.
2788.It Pa /etc/profile
2789System login profile.
2790.It Pa /etc/shells
2791Shell database.
2792.It Pa /etc/suid_profile
2793Privileged shell profile.
2794.El
2795.Sh EXIT STATUS
2796Errors that are detected by the shell, such as a syntax error, will
2797cause the shell to exit with a non-zero exit status.
2798If the shell is not an interactive shell, the execution of the shell
2799file will be aborted.
2800Otherwise the shell will return the exit status of the last command
2801executed, or if the
2802.Ic exit
2803builtin is used with a numeric argument, it
2804will return the argument.
2805.Sh SEE ALSO
2806.Xr builtin 1 ,
2807.Xr chsh 1 ,
2808.Xr echo 1 ,
2809.Xr ed 1 ,
2810.Xr emacs 1 ,
2811.Xr kill 1 ,
2812.Xr printf 1 ,
2813.Xr pwd 1 ,
2814.Xr test 1 ,
2815.Xr vi 1 ,
2816.Xr execve 2 ,
2817.Xr getrlimit 2 ,
2818.Xr umask 2 ,
2819.Xr wctype 3 ,
2820.Xr editrc 5 ,
2821.Xr shells 5
2822.Sh HISTORY
2823A
2824.Nm
2825command, the Thompson shell, appeared in
2826.At v1 .
2827It was superseded in
2828.At v7
2829by the Bourne shell, which inherited the name
2830.Nm .
2831.Pp
2832This version of
2833.Nm
2834was rewritten in 1989 under the
2835.Bx
2836license after the Bourne shell from
2837.At V.4 .
2838.Sh AUTHORS
2839This version of
2840.Nm
2841was originally written by
2842.An Kenneth Almquist .
2843.Sh BUGS
2844The
2845.Nm
2846utility does not recognize multibyte characters other than UTF-8.
2847Splitting using
2848.Va IFS
2849and the line editing library
2850.Xr editline 3
2851do not recognize multibyte characters.
2852