2 .\" Copyright (c) 1991, 1993
3 .\" The Regents of the University of California. All rights reserved.
5 .\" This code is derived from software contributed to Berkeley by
8 .\" Redistribution and use in source and binary forms, with or without
9 .\" modification, are permitted provided that the following conditions
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.
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
32 .\" from: @(#)sh.1 8.6 (Berkeley) 5/4/95
40 .Nd command interpreter (shell)
43 .Op Fl /+abCEefhIimnPpTuVvx
44 .Op Fl /+o Ar longname
50 .Op Fl /+abCEefhIimnPpTuVvx
51 .Op Fl /+o Ar longname
58 .Op Fl /+abCEefhIimnPpTuVvx
59 .Op Fl /+o Ar longname
65 utility is the standard command interpreter for the system.
66 The current version of
70 specification for the shell.
71 It only supports features
74 plus a few Berkeley extensions.
75 This man page is not intended to be a tutorial nor a complete
76 specification of the shell.
78 The shell is a command that reads lines from
79 either a file or the terminal, interprets them, and
80 generally executes other commands.
81 It is the program that is started when a user logs into the system,
82 although a user can select a different shell with the
86 implements a language that has flow control constructs,
87 a macro facility that provides a variety of features in
88 addition to data storage, along with built-in history and line
90 It incorporates many features to
91 aid interactive use and has the advantage that the interpretative
92 language is common to both interactive and non-interactive
94 That is, commands can be typed directly
95 to the running shell or can be put into a file,
96 which can be executed directly by the shell.
99 .\" XXX This next sentence is incredibly confusing.
101 If no arguments are present and if the standard input of the shell
102 is connected to a terminal
106 the shell is considered an interactive shell.
108 generally prompts before each command and handles programming
109 and command errors differently (as described below).
110 When first starting, the shell inspects argument 0, and
111 if it begins with a dash
113 the shell is also considered a login shell.
114 This is normally done automatically by the system
115 when the user first logs in.
116 A login shell first reads commands
121 in a user's home directory,
123 If the environment variable
125 is set on entry to a shell, or is set in the
127 of a login shell, the shell then subjects its value to parameter expansion
128 and arithmetic expansion and reads commands from the named file.
129 Therefore, a user should place commands that are to be executed only
132 file, and commands that are executed for every shell inside the
137 variable to some file by placing the following line in the file
139 in the home directory,
142 the filename desired:
144 .Dl "ENV=$HOME/.shrc; export ENV"
146 The first non-option argument specified on the command line
147 will be treated as the
148 name of a file from which to read commands (a shell script), and
149 the remaining arguments are set as the positional parameters
153 Otherwise, the shell reads commands
154 from its standard input.
156 Unlike older versions of
160 script is only sourced on invocation of interactive shells.
162 closes a well-known, and sometimes easily exploitable security
163 hole related to poorly thought out
166 .Ss Argument List Processing
167 All of the single letter options to
169 have a corresponding long name,
170 with the exception of
174 These long names are provided next to the single letter options
175 in the descriptions below.
176 The long name for an option may be specified as an argument to the
180 Once the shell is running,
181 the long name for an option may be specified as an argument to the
186 (described later in the section called
187 .Sx Built-in Commands ) .
188 Introducing an option with a dash
198 will stop option processing and will force the remaining
199 words on the command line to be treated as arguments.
204 options do not have long names.
205 They take arguments and are described after the single letter options.
206 .Bl -tag -width indent
207 .It Fl a Li allexport
208 Flag variables for export when assignments are made to them.
210 Enable asynchronous notification of background job
213 .It Fl C Li noclobber
214 Do not overwrite existing files with
219 command line editor (disables the
221 option if it has been set;
222 set automatically when interactive on terminals).
224 Exit immediately if any untested command fails in non-interactive mode.
225 The exit status of a command is considered to be
226 explicitly tested if the command is part of the list used to control
228 .Ic if , elif , while ,
231 if the command is the left
236 operator; or if the command is a pipeline preceded by the
239 If a shell function is executed and its exit status is explicitly
240 tested, all commands of the function are considered to be tested as
243 It is recommended to check for failures explicitly
244 instead of relying on
246 because it tends to behave in unexpected ways,
247 particularly in larger scripts.
249 Disable pathname expansion.
251 A do-nothing option for
254 .It Fl I Li ignoreeof
257 from input when in interactive mode.
258 .It Fl i Li interactive
259 Force the shell to behave interactively.
261 Turn on job control (set automatically when interactive).
262 A new process group is created for each pipeline (called a job).
263 It is possible to suspend jobs or to have them run in the foreground or
265 In a non-interactive shell,
266 this option can be set even if no terminal is available
267 and is useful to place processes in separate process groups.
269 If not interactive, read commands but do not
271 This is useful for checking the
272 syntax of shell scripts.
274 Change the default for the
280 (logical directory layout)
283 (physical directory layout).
284 .It Fl p Li privileged
285 Turn on privileged mode.
286 This mode is enabled on startup
287 if either the effective user or group ID is not equal to the
288 real user or group ID.
289 Turning this mode off sets the
290 effective user and group IDs to the real user and group IDs.
291 When this mode is enabled for interactive shells, the file
292 .Pa /etc/suid_profile
293 is sourced instead of
297 is sourced, and the contents of the
299 variable are ignored.
301 Read commands from standard input (set automatically
302 if no file arguments are present).
304 no effect when set after the shell has already started
305 running (i.e., when set with the
308 .It Fl T Li trapsasync
309 When waiting for a child, execute traps immediately.
310 If this option is not set,
311 traps are executed after the child exits,
314 This nonstandard option is useful for putting guarding shells around
315 children that block signals.
316 The surrounding shell may kill the child
317 or it may just return control to the tty and leave the child alone,
319 .Bd -literal -offset indent
320 sh -T -c "trap 'exit 1' 2 ; some-blocking-program"
323 Write a message to standard error when attempting
324 to expand a variable, a positional parameter or
325 the special parameter
327 that is not set, and if the
328 shell is not interactive, exit immediately.
332 command line editor (disables
336 The shell writes its input to standard error
338 Useful for debugging.
341 (preceded by the value of the
343 variable subjected to parameter expansion and arithmetic expansion)
344 to standard error before it is executed.
345 Useful for debugging.
347 Another do-nothing option for
350 It only has a long name.
355 option causes the commands to be read from the
357 operand instead of from the standard input.
358 Keep in mind that this option only accepts a single string as its
359 argument, hence multi-word strings must be quoted.
363 option takes as its only argument the long name of an option
364 to be enabled or disabled.
365 For example, the following two invocations of
367 both enable the built-in
370 .Bd -literal -offset indent
375 If used without an argument, the
377 option displays the current option settings in a human-readable format.
380 is used without an argument, the current option settings are output
381 in a format suitable for re-input into the shell.
382 .Ss Lexical Structure
383 The shell reads input in terms of lines from a file and breaks
384 it up into words at whitespace (blanks and tabs), and at
388 which are special to the shell.
389 There are two types of operators: control operators and
390 redirection operators (their meaning is discussed later).
391 The following is a list of valid operators:
392 .Bl -tag -width indent
393 .It Control operators:
394 .Bl -column "XXX" "XXX" "XXX" "XXX" "XXX" -offset center -compact
395 .It Li & Ta Li && Ta Li \&( Ta Li \&) Ta Li \en
396 .It Li ;; Ta Li ;& Ta Li \&; Ta Li \&| Ta Li ||
398 .It Redirection operators:
399 .Bl -column "XXX" "XXX" "XXX" "XXX" "XXX" -offset center -compact
400 .It Li < Ta Li > Ta Li << Ta Li >> Ta Li <>
401 .It Li <& Ta Li >& Ta Li <<- Ta Li >| Ta \&
407 introduces a comment if used at the beginning of a word.
408 The word starting with
410 and the rest of the line are ignored.
414 characters (character code 0) are not allowed in shell input.
416 Quoting is used to remove the special meaning of certain characters
417 or words to the shell, such as operators, whitespace, keywords,
420 There are four types of quoting: matched single quotes,
421 dollar-single quotes,
422 matched double quotes, and backslash.
423 .Bl -tag -width indent
425 Enclosing characters in single quotes preserves the literal
426 meaning of all the characters (except single quotes, making
427 it impossible to put single-quotes in a single-quoted string).
428 .It Dollar-Single Quotes
429 Enclosing characters between
433 preserves the literal meaning of all characters
434 except backslashes and single quotes.
435 A backslash introduces a C-style escape sequence:
436 .Bl -tag -width xUnnnnnnnn
438 Alert (ring the terminal bell)
442 The control character denoted by
448 is a backslash, it must be doubled.
470 The byte whose octal value is
472 (one to three digits)
474 The byte whose hexadecimal value is
476 (one or more digits only the last two of which are used)
478 The Unicode code point
480 (four hexadecimal digits)
481 .It \eU Ns Ar nnnnnnnn
482 The Unicode code point
484 (eight hexadecimal digits)
487 The sequences for Unicode code points are currently only useful with
489 They reject code point 0 and UTF-16 surrogates.
491 If an escape sequence would produce a byte with value 0,
492 that byte and the rest of the string until the matching single-quote
495 Any other string starting with a backslash is an error.
497 Enclosing characters within double quotes preserves the literal
498 meaning of all characters except dollar sign
504 The backslash inside double quotes is historically weird.
505 It remains literal unless it precedes the following characters,
506 which it serves to quote:
508 .Bl -column "XXX" "XXX" "XXX" "XXX" "XXX" -offset center -compact
509 .It Li $ Ta Li ` Ta Li \&" Ta Li \e Ta Li \en
512 A backslash preserves the literal meaning of the following
513 character, with the exception of the newline character
515 A backslash preceding a newline is treated as a line continuation.
518 Keywords or reserved words are words that have special meaning to the
519 shell and are recognized at the beginning of a line and
520 after a control operator.
521 The following are keywords:
522 .Bl -column "doneXX" "elifXX" "elseXX" "untilXX" "whileX" -offset center
523 .It Li \&! Ta { Ta } Ta Ic case Ta Ic do
524 .It Ic done Ta Ic elif Ta Ic else Ta Ic esac Ta Ic fi
525 .It Ic for Ta Ic if Ta Ic then Ta Ic until Ta Ic while
528 An alias is a name and corresponding value set using the
531 Wherever the command word of a simple command may occur,
532 and after checking for keywords if a keyword may occur, the shell
533 checks the word to see if it matches an alias.
534 If it does, it replaces it in the input stream with its value.
535 For example, if there is an alias called
547 Aliases are also recognized after an alias
548 whose value ends with a space or tab.
549 For example, if there is also an alias called
555 .Dl "nohup lf foobar"
559 .Dl "nohup ls -F foobar"
561 Aliases provide a convenient way for naive users to
562 create shorthands for commands without having to learn how
563 to create functions with arguments.
564 Using aliases in scripts is discouraged
565 because the command that defines them must be executed
566 before the code that uses them is parsed.
567 This is fragile and not portable.
569 An alias name may be escaped in a command line, so that it is not
570 replaced by its alias value, by using quoting characters within or
571 adjacent to the alias name.
572 This is most often done by prefixing
573 an alias name with a backslash to execute a function, built-in, or
574 normal program with the same name.
579 The shell interprets the words it reads according to a
580 language, the specification of which is outside the scope
581 of this man page (refer to the BNF in the
584 Essentially though, a line is read and if
585 the first word of the line (or after a control operator)
586 is not a keyword, then the shell has recognized a
588 Otherwise, a complex command or some
589 other special construct may have been recognized.
591 If a simple command has been recognized, the shell performs
592 the following actions:
595 Leading words of the form
597 are stripped off and assigned to the environment of
599 (they do not affect expansions).
600 Redirection operators and
601 their arguments (as described below) are stripped
602 off and saved for processing.
604 The remaining words are expanded as described in
606 .Sx Word Expansions ,
607 and the first remaining word is considered the command
608 name and the command is located.
610 words are considered the arguments of the command.
611 If no command name resulted, then the
613 variable assignments recognized in 1) affect the
616 Redirections are performed as described in
620 Redirections are used to change where a command reads its input
622 In general, redirections open, close, or
623 duplicate an existing reference to a file.
625 used for redirection is:
627 .D1 Oo Ar n Oc Ar redir-op file
631 is one of the redirection operators mentioned
633 The following gives some examples of how these
634 operators can be used.
635 Note that stdin and stdout are commonly used abbreviations
636 for standard input and standard output respectively.
637 .Bl -tag -width "1234567890XX" -offset indent
638 .It Oo Ar n Oc Ns Li > Ar file
639 redirect stdout (or file descriptor
643 .It Oo Ar n Oc Ns Li >| Ar file
644 same as above, but override the
647 .It Oo Ar n Oc Ns Li >> Ar file
648 append stdout (or file descriptor
652 .It Oo Ar n Oc Ns Li < Ar file
653 redirect stdin (or file descriptor
657 .It Oo Ar n Oc Ns Li <> Ar file
658 redirect stdin (or file descriptor
662 .It Oo Ar n1 Oc Ns Li <& Ns Ar n2
663 duplicate stdin (or file descriptor
667 .It Oo Ar n Oc Ns Li <&-
668 close stdin (or file descriptor
670 .It Oo Ar n1 Oc Ns Li >& Ns Ar n2
671 duplicate stdout (or file descriptor
675 .It Oo Ar n Oc Ns Li >&-
676 close stdout (or file descriptor
680 The following redirection is often called a
682 .Bd -unfilled -offset indent
683 .Oo Ar n Oc Ns Li << Ar delimiter
689 All the text on successive lines up to the delimiter is
690 saved away and made available to the command on standard
691 input, or file descriptor
696 as specified on the initial line is quoted, then the
698 is treated literally, otherwise the text is subjected to
699 parameter expansion, command substitution, and arithmetic
700 expansion (as described in the section on
701 .Sx Word Expansions ) .
710 .Ss Search and Execution
711 There are three types of commands: shell functions,
712 built-in commands, and normal programs.
713 The command is searched for (by name) in that order.
714 The three types of commands are all executed in a different way.
716 When a shell function is executed, all of the shell positional
719 which remains unchanged) are
720 set to the arguments of the shell function.
721 The variables which are explicitly placed in the environment of
722 the command (by placing assignments to them before the
723 function name) are made local to the function and are set
725 Then the command given in the function definition is executed.
726 The positional parameters are restored to their original values
727 when the command completes.
728 This all occurs within the current shell.
730 Shell built-in commands are executed internally to the shell, without
731 spawning a new process.
732 There are two kinds of built-in commands: regular and special.
733 Assignments before special builtins persist after they finish
734 executing and assignment errors, redirection errors and certain
735 operand errors cause a script to be aborted.
736 Special builtins cannot be overridden with a function.
737 Both regular and special builtins can affect the shell in ways
738 normal programs cannot.
740 Otherwise, if the command name does not match a function
741 or built-in command, the command is searched for as a normal
742 program in the file system (as described in the next section).
743 When a normal program is executed, the shell runs the program,
744 passing the arguments and the environment to the program.
745 If the program is not a normal executable file
746 (i.e., if it does not begin with the
756 but appears to be a text file,
757 the shell will run a new instance of
761 Note that previous versions of this document
762 and the source code itself misleadingly and sporadically
763 refer to a shell script without a magic number
765 .Dq "shell procedure" .
767 When locating a command, the shell first looks to see if
768 it has a shell function by that name.
770 built-in command by that name.
771 If a built-in command is not found,
772 one of two things happen:
775 Command names containing a slash are simply executed without
776 performing any searches.
778 The shell searches each entry in the
781 in turn for the command.
784 variable should be a series of
785 entries separated by colons.
786 Each entry consists of a
788 The current directory
789 may be indicated implicitly by an empty directory name,
790 or explicitly by a single period.
792 .Ss Command Exit Status
793 Each command has an exit status that can influence the behavior
794 of other shell commands.
795 The paradigm is that a command exits
796 with zero for normal or success, and non-zero for failure,
797 error, or a false indication.
798 The man page for each command
799 should indicate the various exit codes and what they mean.
800 Additionally, the built-in commands return exit codes, as does
801 an executed shell function.
803 If a command is terminated by a signal, its exit status is greater than 128.
804 The signal name can be found by passing the exit status to
807 If there is no command word,
808 the exit status is the exit status of the last command substitution executed,
809 or zero if the command does not contain any command substitutions.
811 Complex commands are combinations of simple commands
812 with control operators or keywords, together creating a larger complex
814 More generally, a command is one of the following:
815 .Bl -item -offset indent
821 list or compound-list
828 Unless otherwise stated, the exit status of a command is
829 that of the last simple command executed by the command,
830 or zero if no simple command was executed.
832 A pipeline is a sequence of one or more commands separated
833 by the control operator
835 The standard output of all but
836 the last command is connected to the standard input
838 The standard output of the last
839 command is inherited from the shell, as usual.
841 The format for a pipeline is:
843 .D1 Oo Li \&! Oc Ar command1 Op Li \&| Ar command2 ...
845 The standard output of
847 is connected to the standard input of
849 The standard input, standard output, or
850 both of a command is considered to be assigned by the
851 pipeline before any redirection specified by redirection
852 operators that are part of the command.
854 Note that unlike some other shells,
856 executes each process in a pipeline with more than one command
857 in a subshell environment and as a child of the
861 If the pipeline is not in the background (discussed later),
862 the shell waits for all commands to complete.
866 does not precede the pipeline, the
867 exit status is the exit status of the last command specified
869 Otherwise, the exit status is the logical
870 NOT of the exit status of the last command.
872 the last command returns zero, the exit status is 1; if
873 the last command returns greater than zero, the exit status
876 Because pipeline assignment of standard input or standard
877 output or both takes place before redirection, it can be
878 modified by redirection.
881 .Dl "command1 2>&1 | command2"
883 sends both the standard output and standard error of
885 to the standard input of
890 or newline terminator causes the preceding
892 (described below in the section called
893 .Sx Short-Circuit List Operators )
894 to be executed sequentially;
897 causes asynchronous execution of the preceding AND-OR-list.
898 .Ss Background Commands (&)
899 If a command is terminated by the control operator ampersand
901 the shell executes the command in a subshell environment (see
902 .Sx Grouping Commands Together
903 below) and asynchronously;
904 the shell does not wait for the command to finish
905 before executing the next command.
907 The format for running a command in background is:
909 .D1 Ar command1 Li & Op Ar command2 Li & Ar ...
911 If the shell is not interactive, the standard input of an
912 asynchronous command is set to
915 The exit status is zero.
916 .Ss Lists (Generally Speaking)
917 A list is a sequence of zero or more commands separated by
918 newlines, semicolons, or ampersands,
919 and optionally terminated by one of these three characters.
921 list are executed in the order they are written.
922 If command is followed by an ampersand, the shell starts the
923 command and immediately proceeds onto the next command;
924 otherwise it waits for the command to terminate before
925 proceeding to the next one.
926 .Ss Short-Circuit List Operators
930 are AND-OR list operators.
932 executes the first command, and then executes the second command
933 if the exit status of the first command is zero.
935 is similar, but executes the second command if the exit
936 status of the first command is nonzero.
940 both have the same priority.
941 .Ss Flow-Control Constructs (if, while, for, case)
945 .Bd -unfilled -offset indent -compact
949 .Ic then Ar list Oc Ar ...
954 The exit status is that of selected
959 or zero if no list was selected.
964 .Bd -unfilled -offset indent -compact
970 The two lists are executed repeatedly while the exit status of the
974 command is similar, but has the word
979 repeat until the exit status of the first list is zero.
981 The exit status is that of the last execution of the second list,
982 or zero if it was never executed.
987 .Bd -unfilled -offset indent -compact
988 .Ic for Ar variable Op Ic in Ar word ...
995 and the following words are omitted,
998 The words are expanded, and then the list is executed
999 repeatedly with the variable set to each word in turn.
1004 commands may be replaced with
1014 .D1 Ic break Op Ar num
1015 .D1 Ic continue Op Ar num
1019 command terminates the
1028 command continues with the next iteration of the innermost loop.
1029 These are implemented as special built-in commands.
1034 .Bd -unfilled -offset indent -compact
1035 .Ic case Ar word Ic in
1036 .Ar pattern Ns Li ) Ar list Li ;;
1041 The pattern can actually be one or more patterns
1048 Tilde expansion, parameter expansion, command substitution,
1049 arithmetic expansion and quote removal are applied to the word.
1050 Then, each pattern is expanded in turn using tilde expansion,
1051 parameter expansion, command substitution and arithmetic expansion and
1052 the expanded form of the word is checked against it.
1053 If a match is found, the corresponding list is executed.
1054 If the selected list is terminated by the control operator
1058 execution continues with the next list,
1059 continuing until a list terminated with
1064 .Ss Grouping Commands Together
1065 Commands may be grouped by writing either
1067 .D1 Li \&( Ns Ar list Ns Li \%)
1071 .D1 Li { Ar list Ns Li \&; }
1073 The first form executes the commands in a subshell environment.
1074 A subshell environment has its own copy of:
1077 The current working directory as set by
1080 The file creation mask as set by
1083 Resource limits as set by
1086 References to open files.
1093 Positional parameters and variables.
1102 These are copied from the parent shell environment,
1103 except that trapped (but not ignored) signals are reset to the default action
1104 and known jobs are cleared.
1105 Any changes do not affect the parent shell environment.
1107 A subshell environment may be implemented as a child process or differently.
1108 If job control is enabled in an interactive shell,
1109 commands grouped in parentheses can be suspended and continued as a unit.
1111 For compatibility with other shells,
1112 two open parentheses in sequence should be separated by whitespace.
1114 The second form never forks another shell,
1115 so it is slightly more efficient.
1116 Grouping commands together this way allows the user to
1117 redirect their output as though they were one program:
1118 .Bd -literal -offset indent
1119 { echo -n "hello"; echo " world"; } > greeting
1122 The syntax of a function definition is
1124 .D1 Ar name Li \&( \&) Ar command
1126 A function definition is an executable statement; when
1127 executed it installs a function named
1130 exit status of zero.
1139 Variables may be declared to be local to a function by
1143 This should appear as the first statement of a function,
1146 .D1 Ic local Oo Ar variable ... Oc Op Fl
1150 command is implemented as a built-in command.
1151 The exit status is zero
1152 unless the command is not in a function or a variable name is invalid.
1154 When a variable is made local, it inherits the initial
1155 value and exported and readonly flags from the variable
1156 with the same name in the surrounding scope, if there is
1158 Otherwise, the variable is initially unset.
1160 uses dynamic scoping, so that if the variable
1162 is made local to function
1164 which then calls function
1166 references to the variable
1170 will refer to the variable
1174 not to the global variable named
1177 The only special parameter that can be made local is
1181 local causes any shell options
1182 (including those that only have long names)
1186 command inside the function to be
1187 restored to their original values when the function
1194 .D1 Ic return Op Ar exitstatus
1196 It terminates the current executional scope, returning from the closest
1197 nested function or sourced script;
1198 if no function or sourced script is being executed,
1199 it exits the shell instance.
1202 command is implemented as a special built-in command.
1203 .Ss Variables and Parameters
1204 The shell maintains a set of parameters.
1208 of alphabetics, numerics, and underscores,
1209 and starting with an alphabetic or an underscore)
1210 is called a variable.
1212 the shell turns all environment variables with valid names into shell
1214 New variables can be set using the form
1216 .D1 Ar name Ns = Ns Ar value
1218 A parameter can also be denoted by a number
1219 or a special character as explained below.
1221 Assignments are expanded differently from other words:
1222 tilde expansion is also performed after the equals sign and after any colon
1223 and usernames are also terminated by colons,
1224 and field splitting and pathname expansion are not performed.
1226 This special expansion applies not only to assignments that form a simple
1227 command by themselves or precede a command word,
1228 but also to words passed to the
1233 built-in commands that have this form.
1234 For this, the builtin's name must be literal
1235 (not the result of an expansion)
1236 and may optionally be preceded by one or more literal instances of
1239 .Ss Positional Parameters
1240 A positional parameter is a parameter denoted by a number greater than zero.
1241 The shell sets these initially to the values of its command line
1242 arguments that follow the name of the shell script.
1245 built-in command can also be used to set or reset them.
1246 .Ss Special Parameters
1247 Special parameters are parameters denoted by a single special character
1249 They are shown in the following list, exactly as they would appear in input
1250 typed by the user or in the source of a shell script.
1253 Expands to the positional parameters, starting from one.
1255 the expansion occurs within a double-quoted string
1256 it expands to a single field with the value of each parameter
1257 separated by the first character of the
1264 Expands to the positional parameters, starting from one.
1266 the expansion occurs within double-quotes, each positional
1267 parameter expands as a separate argument.
1268 If there are no positional parameters, the
1271 generates zero arguments, even when
1274 What this basically means, for example, is
1287 .Bd -literal -offset indent
1291 Expands to the number of positional parameters.
1293 Expands to the exit status of the most recent pipeline.
1295 (hyphen) Expands to the current option flags (the single-letter
1296 option names concatenated into a string) as specified on
1299 built-in command, or implicitly
1302 Expands to the process ID of the invoked shell.
1304 retains the same value of
1308 Expands to the process ID of the most recent background
1309 command executed from the current shell.
1311 pipeline, the process ID is that of the last command in the
1313 If this parameter is referenced, the shell will remember
1314 the process ID and its exit status until the
1316 built-in command reports completion of the process.
1318 (zero) Expands to the name of the shell script if passed on the command line,
1321 operand if given (with
1323 or otherwise argument 0 passed to the shell.
1325 .Ss Special Variables
1326 The following variables are set by the shell or
1327 have special meaning to it:
1328 .Bl -tag -width ".Va HISTSIZE"
1330 The search path used with the
1334 The fallback editor used with the
1337 If not set, the default editor is
1340 The default editor used with the
1344 The number of previous commands that are accessible.
1346 The user's home directory,
1347 used in tilde expansion and as a default directory for the
1351 Input Field Separators.
1352 The default value is
1358 This default also applies if
1360 is unset, but not if it is set to the empty string.
1362 .Sx White Space Splitting
1363 section for more details.
1365 The current line number in the script or function.
1367 The name of a mail file, that will be checked for the arrival of new
1374 separated list of file names, for the shell to check for incoming
1376 This variable overrides the
1379 There is a maximum of 10 mailboxes that can be monitored at once.
1381 The index of the next argument to be processed by
1383 This is initialized to 1 at startup.
1385 The default search path for executables.
1388 section for details.
1390 The parent process ID of the invoked shell.
1391 This is set at startup
1392 unless this variable is in the environment.
1393 A later change of parent process ID is not reflected.
1394 A subshell retains the same value of
1397 The primary prompt string, which defaults to
1399 unless you are the superuser, in which case it defaults to
1402 may include any of the following formatting sequences,
1403 which are replaced by the given information:
1404 .Bl -tag -width indent
1408 The fully-qualified hostname.
1410 The final component of the current working directory.
1412 The entire path of the current working directory.
1416 for normal users and
1420 A literal backslash.
1423 The secondary prompt string, which defaults to
1426 may include any of the formatting sequences from
1429 The prefix for the trace output (if
1436 This clause describes the various expansions that are
1438 Not all expansions are performed on
1439 every word, as explained later.
1441 Tilde expansions, parameter expansions, command substitutions,
1442 arithmetic expansions, and quote removals that occur within
1443 a single word expand to a single field.
1445 splitting or pathname expansion that can create multiple
1446 fields from a single word.
1447 The single exception to this rule is
1448 the expansion of the special parameter
1450 within double-quotes,
1451 as was described above.
1453 The order of word expansion is:
1456 Tilde Expansion, Parameter Expansion, Command Substitution,
1457 Arithmetic Expansion (these all occur at the same time).
1459 Field Splitting is performed on fields generated by step (1)
1464 Pathname Expansion (unless the
1466 option is in effect).
1473 character is used to introduce parameter expansion, command
1474 substitution, or arithmetic expansion.
1475 .Ss Tilde Expansion (substituting a user's home directory)
1476 A word beginning with an unquoted tilde character
1479 subjected to tilde expansion.
1480 All the characters up to a slash
1482 or the end of the word are treated as a username
1483 and are replaced with the user's home directory.
1485 username is missing (as in
1487 the tilde is replaced with the value of the
1489 variable (the current user's home directory).
1490 .Ss Parameter Expansion
1491 The format for parameter expansion is as follows:
1493 .D1 Li ${ Ns Ar expression Ns Li }
1497 consists of all characters until the matching
1501 escaped by a backslash or within a single-quoted or double-quoted
1502 string, and characters in
1503 embedded arithmetic expansions, command substitutions, and variable
1504 expansions, are not examined in determining the matching
1506 If the variants with
1512 occur within a double-quoted string,
1513 as an extension there may be unquoted parts
1514 (via double-quotes inside the expansion);
1516 within such parts are also not examined in determining the matching
1519 The simplest form for parameter expansion is:
1521 .D1 Li ${ Ns Ar parameter Ns Li }
1523 The value, if any, of
1527 The parameter name or symbol can be enclosed in braces, which are
1528 optional except for positional parameters with more than one digit or
1529 when parameter is followed by a character that could be interpreted as
1531 If a parameter expansion occurs inside double-quotes:
1534 Field splitting is not performed on the results of the
1535 expansion, with the exception of the special parameter
1538 Pathname expansion is not performed on the results of the
1542 In addition, a parameter expansion can be modified by using one of the
1544 .Bl -tag -width indent
1545 .It Li ${ Ns Ar parameter Ns Li :- Ns Ar word Ns Li }
1549 is unset or null, the expansion of
1551 is substituted; otherwise, the value of
1554 .It Li ${ Ns Ar parameter Ns Li := Ns Ar word Ns Li }
1555 Assign Default Values.
1558 is unset or null, the expansion of
1568 does not prevent field splitting or pathname expansion.
1569 Only variables, not positional
1570 parameters or special parameters, can be
1571 assigned in this way.
1572 .It Li ${ Ns Ar parameter Ns Li :? Ns Oo Ar word Oc Ns Li }
1573 Indicate Error if Null or Unset.
1576 is unset or null, the expansion of
1578 (or a message indicating it is unset if
1580 is omitted) is written to standard
1581 error and the shell exits with a nonzero
1583 Otherwise, the value of
1587 interactive shell need not exit.
1588 .It Li ${ Ns Ar parameter Ns Li :+ Ns Ar word Ns Li }
1589 Use Alternate Value.
1592 is unset or null, null is substituted;
1593 otherwise, the expansion of
1598 In the parameter expansions shown previously, use of the colon in the
1599 format results in a test for a parameter that is unset or null; omission
1600 of the colon results in a test for a parameter that is only unset.
1604 inherits the type of quoting
1605 (unquoted, double-quoted or here-document)
1606 from the surroundings,
1607 with the exception that a backslash that quotes a closing brace is removed
1608 during quote removal.
1609 .Bl -tag -width indent
1610 .It Li ${# Ns Ar parameter Ns Li }
1612 The length in characters of
1617 The following four varieties of parameter expansion provide for substring
1619 In each case, pattern matching notation
1621 .Sx Shell Patterns ) ,
1622 rather than regular expression notation,
1623 is used to evaluate the patterns.
1624 If parameter is one of the special parameters
1628 the result of the expansion is unspecified.
1629 Enclosing the full parameter expansion string in double-quotes does not
1630 cause the following four varieties of pattern characters to be quoted,
1631 whereas quoting characters within the braces has this effect.
1632 .Bl -tag -width indent
1633 .It Li ${ Ns Ar parameter Ns Li % Ns Ar word Ns Li }
1634 Remove Smallest Suffix Pattern.
1637 is expanded to produce a pattern.
1639 parameter expansion then results in
1641 with the smallest portion of the
1642 suffix matched by the pattern deleted.
1643 .It Li ${ Ns Ar parameter Ns Li %% Ns Ar word Ns Li }
1644 Remove Largest Suffix Pattern.
1647 is expanded to produce a pattern.
1649 parameter expansion then results in
1651 with the largest portion of the
1652 suffix matched by the pattern deleted.
1653 .It Li ${ Ns Ar parameter Ns Li # Ns Ar word Ns Li }
1654 Remove Smallest Prefix Pattern.
1657 is expanded to produce a pattern.
1659 parameter expansion then results in
1661 with the smallest portion of the
1662 prefix matched by the pattern deleted.
1663 .It Li ${ Ns Ar parameter Ns Li ## Ns Ar word Ns Li }
1664 Remove Largest Prefix Pattern.
1667 is expanded to produce a pattern.
1669 parameter expansion then results in
1671 with the largest portion of the
1672 prefix matched by the pattern deleted.
1674 .Ss Command Substitution
1675 Command substitution allows the output of a command to be substituted in
1676 place of the command name itself.
1677 Command substitution occurs when
1678 the command is enclosed as follows:
1680 .D1 Li $( Ns Ar command Ns Li )\&
1682 or the backquoted version:
1684 .D1 Li ` Ns Ar command Ns Li `
1686 The shell expands the command substitution by executing command
1687 and replacing the command substitution
1688 with the standard output of the command,
1689 removing sequences of one or more newlines at the end of the substitution.
1690 Embedded newlines before the end of the output are not removed;
1691 however, during field splitting, they may be translated into spaces
1692 depending on the value of
1694 and the quoting that is in effect.
1695 The command is executed in a subshell environment,
1696 except that the built-in commands
1701 return information about the parent shell environment
1704 returns information about the same process
1705 if they are the only command in a command substitution.
1707 If a command substitution of the
1709 form begins with a subshell,
1714 must be separated by whitespace
1715 to avoid ambiguity with arithmetic expansion.
1716 .Ss Arithmetic Expansion
1717 Arithmetic expansion provides a mechanism for evaluating an arithmetic
1718 expression and substituting its value.
1719 The format for arithmetic expansion is as follows:
1721 .D1 Li $(( Ns Ar expression Ns Li ))
1725 is treated as if it were in double-quotes, except
1726 that a double-quote inside the expression is not treated specially.
1728 shell expands all tokens in the
1730 for parameter expansion,
1731 command substitution,
1732 arithmetic expansion
1735 The allowed expressions are a subset of C expressions,
1737 .Bl -tag -width "Variables" -offset indent
1739 All values are of type
1742 Decimal, octal (starting with
1744 and hexadecimal (starting with
1748 Shell variables can be read and written
1749 and contain integer constants.
1752 .It Binary operators
1753 .Li "* / % + - << >> < <= > >= == != & ^ | && ||"
1754 .It Assignment operators
1755 .Li "= += -= *= /= %= <<= >>= &= ^= |="
1756 .It Conditional operator
1760 The result of the expression is substituted in decimal.
1761 .Ss White Space Splitting (Field Splitting)
1762 In certain contexts,
1763 after parameter expansion, command substitution, and
1764 arithmetic expansion the shell scans the results of
1765 expansions and substitutions that did not occur in double-quotes for
1766 field splitting and multiple fields can result.
1777 are treated differently from other characters in
1782 at the beginning or end of a word is discarded.
1784 Subsequently, a field is delimited by either
1787 a non-whitespace character in
1789 with any whitespace in
1793 one or more whitespace characters in
1797 If a word ends with a non-whitespace character in
1799 there is no empty field after this character.
1801 If no field is delimited, the word is discarded.
1802 In particular, if a word consists solely of an unquoted substitution
1803 and the result of the substitution is null,
1804 it is removed by field splitting even if
1807 .Ss Pathname Expansion (File Name Generation)
1811 file name generation is performed
1812 after word splitting is complete.
1814 viewed as a series of patterns, separated by slashes.
1816 process of expansion replaces the word with the names of
1817 all existing files whose names can be formed by replacing
1818 each pattern with a string that matches the specified pattern.
1819 There are two restrictions on this: first, a pattern cannot match
1820 a string containing a slash, and second,
1821 a pattern cannot match a string starting with a period
1822 unless the first character of the pattern is a period.
1823 The next section describes the patterns used for
1825 the four varieties of parameter expansion for substring processing and the
1829 A pattern consists of normal characters, which match themselves,
1830 and meta-characters.
1831 The meta-characters are
1836 These characters lose their special meanings if they are quoted.
1837 When command or variable substitution is performed and the dollar sign
1838 or back quotes are not double-quoted, the value of the
1839 variable or the output of the command is scanned for these
1840 characters and they are turned into meta-characters.
1844 matches any string of characters.
1847 matches any single character.
1850 introduces a character class.
1851 The end of the character class is indicated by a
1859 rather than introducing a character class.
1860 A character class matches any of the characters between the square brackets.
1861 A locale-dependent range of characters may be specified using a minus sign.
1862 A named class of characters (see
1864 may be specified by surrounding the name with
1869 .Ql \&[\&[:alpha:\&]\&]
1870 is a shell pattern that matches a single letter.
1871 The character class may be complemented by making an exclamation point
1873 the first character of the character class.
1876 has the same effect but is non-standard.
1880 in a character class, make it the first character listed
1888 make it the first or last character listed.
1889 .Ss Built-in Commands
1890 This section lists the built-in commands.
1891 .Bl -tag -width indent
1893 A null command that returns a 0 (true) exit value.
1895 The commands in the specified file are read and executed by the shell.
1898 command may be used to return to the
1905 characters, it is used as is.
1906 Otherwise, the shell searches the
1909 If it is not found in the
1911 it is sought in the current working directory.
1913 A built-in equivalent of
1915 .It Ic alias Oo Ar name Ns Oo = Ns Ar string Oc ... Oc
1917 .Ar name Ns = Ns Ar string
1918 is specified, the shell defines the alias
1924 is specified, the value of the alias
1927 With no arguments, the
1929 built-in command prints the names and values of all defined aliases
1932 Alias values are written with appropriate quoting so that they are
1933 suitable for re-input to the shell.
1937 .It Ic bg Op Ar job ...
1938 Continue the specified jobs
1939 (or the current job if no jobs are given)
1941 .It Ic bind Oo Fl aeklrsv Oc Oo Ar key Oo Ar command Oc Oc
1942 List or alter key bindings for the line editor.
1943 This command is documented in
1945 .It Ic break Op Ar num
1947 .Sx Flow-Control Constructs
1949 .It Ic builtin Ar cmd Op Ar arg ...
1950 Execute the specified built-in command,
1952 This is useful when the user wishes to override a shell function
1953 with the same name as a built-in command.
1954 .It Ic cd Oo Fl L | P Oc Oo Fl e Oc Op Ar directory
1956 Switch to the specified
1958 to the directory specified in the
1960 environment variable if no
1963 to the directory specified in the
1965 environment variable if
1975 then the directories listed in the
1978 searched for the specified
1982 is unset, the current directory is searched.
1985 is the same as that of
1987 In an interactive shell,
1990 command will print out the name of the directory
1991 that it actually switched to
1994 mechanism was used or if
2001 option is specified,
2003 is handled physically and symbolic links are resolved before
2005 components are processed.
2008 option is specified,
2010 is handled logically.
2011 This is the default.
2017 to return exit status 1 if the full pathname of the new directory
2018 cannot be determined reliably or at all.
2019 Normally this is not considered an error,
2020 although a warning is printed.
2025 .It Ic command Oo Fl p Oc Op Ar utility Op Ar argument ...
2026 .It Ic command Oo Fl p Oc Fl v Ar utility
2027 .It Ic command Oo Fl p Oc Fl V Ar utility
2028 The first form of invocation executes the specified
2030 ignoring shell functions in the search.
2033 is a special builtin,
2034 it is executed as if it were a regular builtin.
2038 option is specified, the command search is performed using a
2041 that is guaranteed to find all of the standard utilities.
2045 option is specified,
2047 is not executed but a description of its interpretation by the shell is
2049 For ordinary commands the output is the path name; for shell built-in
2050 commands, shell functions and keywords only the name is written.
2051 Aliases are printed as
2052 .Dq Ic alias Ar name Ns = Ns Ar value .
2056 option is identical to
2058 except for the output.
2060 .Dq Ar utility Ic is Ar description
2066 a special shell builtin,
2073 .It Ic continue Op Ar num
2075 .Sx Flow-Control Constructs
2077 .It Ic echo Oo Fl e | n Oc Op Ar string ...
2078 Print a space-separated list of the arguments to the standard output
2079 and append a newline character.
2080 .Bl -tag -width indent
2082 Suppress the output of the trailing newline.
2084 Process C-style backslash escape sequences.
2087 command understands the following character escapes:
2088 .Bl -tag -width indent
2090 Alert (ring the terminal bell)
2094 Suppress the trailing newline (this has the side-effect of truncating the
2095 line if it is not the last character)
2113 (Zero) The character whose octal value is
2119 is not enclosed in quotes then the backslash itself must be escaped
2120 with a backslash to protect it from the shell.
2122 .Bd -literal -offset indent
2131 $ echo -e a\e\e\e\eb
2140 options may be specified.
2141 .It Ic eval Ar string ...
2142 Concatenate all the arguments with spaces.
2143 Then re-parse and execute the command.
2144 .It Ic exec Op Ar command Op arg ...
2148 the shell process is replaced with the specified program
2149 (which must be a real program, not a shell built-in command or function).
2150 Any redirections on the
2152 command are marked as permanent,
2153 so that they are not undone when the
2156 .It Ic exit Op Ar exitstatus
2157 Terminate the shell process.
2161 it is used as the exit status of the shell.
2162 Otherwise, if the shell is executing an
2164 trap, the exit status of the last command before the trap is used;
2165 if the shell is executing a trap for a signal,
2166 the shell exits by resending the signal to itself.
2167 Otherwise, the exit status of the preceding command is used.
2168 The exit status should be an integer between 0 and 255.
2169 .It Ic export Ar name ...
2170 .It Ic export Op Fl p
2171 The specified names are exported so that they will
2172 appear in the environment of subsequent commands.
2173 The only way to un-export a variable is to
2176 The shell allows the value of a variable to be set
2177 at the same time as it is exported by writing
2179 .D1 Ic export Ar name Ns = Ns Ar value
2181 With no arguments the
2183 command lists the names
2184 of all exported variables.
2187 option is specified, the exported variables are printed as
2188 .Dq Ic export Ar name Ns = Ns Ar value
2189 lines, suitable for re-input to the shell.
2191 A null command that returns a non-zero (false) exit value.
2192 .It Ic fc Oo Fl e Ar editor Oc Op Ar first Op Ar last
2193 .It Ic fc Fl l Oo Fl nr Oc Op Ar first Op Ar last
2194 .It Ic fc Fl s Oo Ar old Ns = Ns Ar new Oc Op Ar first
2197 built-in command lists, or edits and re-executes,
2198 commands previously entered to an interactive shell.
2199 .Bl -tag -width indent
2201 Use the editor named by
2203 to edit the commands.
2206 string is a command name,
2207 subject to search via the
2212 variable is used as a default when
2217 is null or unset, the value of the
2224 is used as the editor.
2226 List the commands rather than invoking
2228 The commands are written in the
2229 sequence indicated by the
2233 operands, as affected by
2235 with each command preceded by the command number.
2237 Suppress command numbers when listing with
2240 Reverse the order of the commands listed
2249 Re-execute the command without invoking an editor.
2252 Select the commands to list or edit.
2253 The number of previous commands that can be accessed
2254 are determined by the value of the
2261 or both are one of the following:
2262 .Bl -tag -width indent
2263 .It Oo Cm + Oc Ns Ar num
2264 A positive number representing a command number;
2265 command numbers can be displayed with the
2269 A negative decimal number representing the
2270 command that was executed
2273 commands previously.
2274 For example, \-1 is the immediately previous command.
2276 A string indicating the most recently entered command
2277 that begins with that string.
2279 .Ar old Ns = Ns Ar new
2280 operand is not also specified with
2282 the string form of the first operand cannot contain an embedded equal sign.
2286 The following variables affect the execution of
2288 .Bl -tag -width ".Va HISTSIZE"
2290 Name of the editor to use for history editing.
2292 The number of previous commands that are accessible.
2297 or the current job to the foreground.
2298 .It Ic getopts Ar optstring var
2305 command deprecates the older
2308 The first argument should be a series of letters, each possibly
2309 followed by a colon which indicates that the option takes an argument.
2310 The specified variable is set to the parsed option.
2312 the next argument is placed into the shell variable
2314 If an option takes an argument, it is placed into the shell variable
2316 If an invalid option is encountered,
2320 It returns a false value (1) when it encounters the end of the options.
2321 A new set of arguments may be parsed by assigning
2323 .It Ic hash Oo Fl rv Oc Op Ar command ...
2324 The shell maintains a hash table which remembers the locations of commands.
2325 With no arguments whatsoever, the
2327 command prints out the contents of this table.
2331 command removes each specified
2333 from the hash table (unless they are functions) and then locates it.
2338 prints the locations of the commands as it finds them.
2343 command to delete all the entries in the hash table except for functions.
2344 .It Ic jobid Op Ar job
2345 Print the process IDs of the processes in the specified
2349 argument is omitted, use the current job.
2350 .It Ic jobs Oo Fl lps Oc Op Ar job ...
2351 Print information about the specified jobs, or all jobs if no
2354 The information printed includes job ID, status and command name.
2358 option is specified, the PID of each job is also printed.
2361 option is specified, only the process IDs for the process group leaders
2362 are printed, one per line.
2365 option is specified, only the PIDs of the job commands are printed, one per
2368 A built-in equivalent of
2370 that additionally supports sending signals to jobs.
2371 .It Ic local Oo Ar variable ... Oc Op Fl
2376 A built-in equivalent of
2378 .It Ic pwd Op Fl L | P
2379 Print the path of the current directory.
2380 The built-in command may
2381 differ from the program of the same name because the
2382 built-in command remembers what the current directory
2383 is rather than recomputing it each time.
2386 However, if the current directory is
2388 the built-in version of
2390 will continue to print the old name for the directory.
2394 option is specified, symbolic links are resolved.
2397 option is specified, the shell's notion of the current directory
2398 is printed (symbolic links are not resolved).
2399 This is the default.
2400 .It Ic read Oo Fl p Ar prompt Oc Oo
2401 .Fl t Ar timeout Oc Oo Fl er Oc Ar variable ...
2407 and the standard input is a terminal.
2409 read from the standard input.
2410 The trailing newline
2411 is deleted from the line and the line is split as
2412 described in the section on
2413 .Sx White Space Splitting (Field Splitting)
2415 the pieces are assigned to the variables in order.
2416 If there are more pieces than variables, the remaining
2417 pieces (along with the characters in
2419 that separated them)
2420 are assigned to the last variable.
2421 If there are more variables than pieces, the remaining
2422 variables are assigned the null string.
2424 Backslashes are treated specially, unless the
2428 If a backslash is followed by
2429 a newline, the backslash and the newline will be
2431 If a backslash is followed by any other
2432 character, the backslash will be deleted and the following
2433 character will be treated as though it were not in
2439 option is specified and the
2441 elapses before a complete line of input is supplied,
2444 command will return an exit status as if terminated by
2446 without assigning any values.
2449 value may optionally be followed by one of
2454 to explicitly specify seconds, minutes or hours.
2455 If none is supplied,
2461 option exists only for backward compatibility with older scripts.
2463 The exit status is 0 on success, 1 on end of file,
2464 between 2 and 128 if an error occurs
2465 and greater than 128 if a trapped signal interrupts
2467 .It Ic readonly Oo Fl p Oc Op Ar name ...
2470 is marked as read only,
2471 so that it cannot be subsequently modified or unset.
2472 The shell allows the value of a variable to be set
2473 at the same time as it is marked read only
2474 by using the following form:
2476 .D1 Ic readonly Ar name Ns = Ns Ar value
2478 With no arguments the
2480 command lists the names of all read only variables.
2483 option is specified, the read-only variables are printed as
2484 .Dq Ic readonly Ar name Ns = Ns Ar value
2485 lines, suitable for re-input to the shell.
2486 .It Ic return Op Ar exitstatus
2490 .It Ic set Oo Fl /+abCEefIimnpTuVvx Oc Oo Fl /+o Ar longname Oc Oo
2491 .Fl c Ar string Oc Op Fl - Ar arg ...
2494 command performs three different functions:
2497 With no arguments, it lists the values of all shell variables.
2499 If options are given,
2500 either in short form or using the long
2501 .Dq Fl /+o Ar longname
2503 it sets or clears the specified options as described in the section called
2504 .Sx Argument List Processing .
2508 option is specified,
2510 will replace the shell's positional parameters with the subsequent
2512 If no arguments follow the
2515 all the positional parameters will be cleared,
2516 which is equivalent to executing the command
2520 flag may be omitted when specifying arguments to be used
2521 as positional replacement parameters.
2522 This is not recommended,
2523 because the first argument may begin with a dash
2529 command will interpret as a request to enable or disable options.
2531 .It Ic setvar Ar variable value
2532 Assigns the specified
2538 command is intended to be used in functions that
2539 assign values to variables whose names are passed as parameters.
2540 In general it is better to write
2541 .Dq Ar variable Ns = Ns Ar value
2544 .It Ic shift Op Ar n
2545 Shift the positional parameters
2550 A shift sets the value of
2559 decreasing the value of
2562 For portability, shifting if there are zero positional parameters
2563 should be avoided, since the shell may abort.
2565 A built-in equivalent of
2568 Print the amount of time spent executing the shell process and its children.
2569 The first output line shows the user and system times for the shell process
2570 itself, the second one contains the user and system times for the
2572 .It Ic trap Oo Ar action Oc Ar signal ...
2574 Cause the shell to parse and execute
2579 The signals are specified by name or number.
2580 In addition, the pseudo-signal
2582 may be used to specify an
2584 that is performed when the shell terminates.
2587 may be an empty string or a dash
2589 the former causes the specified signal to be ignored
2590 and the latter causes the default action to be taken.
2593 and using only signal numbers is another way to request the default action.
2594 In a subshell or utility environment,
2595 the shell resets trapped (but not ignored) signals to the default action.
2598 command has no effect on signals that were ignored on entry to the shell.
2604 command to display a list of valid signal names.
2606 A null command that returns a 0 (true) exit value.
2607 .It Ic type Op Ar name ...
2610 as a command and print the resolution of the command search.
2611 Possible resolutions are:
2612 shell keyword, alias, special shell builtin, shell builtin, command,
2615 For aliases the alias expansion is printed;
2616 for commands and tracked aliases
2617 the complete pathname of the command is printed.
2618 .It Ic ulimit Oo Fl HSabcdfklmnopstuvw Oc Op Ar limit
2619 Set or display resource limits (see
2623 is specified, the named resource will be set;
2624 otherwise the current resource value will be displayed.
2628 is specified, the hard limits will be set or displayed.
2629 While everybody is allowed to reduce a hard limit,
2630 only the superuser can increase it.
2634 specifies the soft limits instead.
2635 When displaying limits,
2641 The default is to display the soft limits,
2642 and to set both the hard and the soft limits.
2648 command to display all resources.
2651 is not acceptable in this mode.
2653 The remaining options specify which resource value is to be
2654 displayed or modified.
2655 They are mutually exclusive.
2656 .Bl -tag -width indent
2658 The maximum size of socket buffer usage, in bytes.
2659 .It Fl c Ar coredumpsize
2660 The maximal size of core dump files, in 512-byte blocks.
2661 .It Fl d Ar datasize
2662 The maximal size of the data segment of a process, in kilobytes.
2663 .It Fl f Ar filesize
2664 The maximal size of a file, in 512-byte blocks.
2666 The maximal number of kqueues
2670 .It Fl l Ar lockedmem
2671 The maximal size of memory that can be locked by a process, in
2673 .It Fl m Ar memoryuse
2674 The maximal resident set size of a process, in kilobytes.
2676 The maximal number of descriptors that could be opened by a process.
2678 The maximal number of process-shared locks
2682 .It Fl p Ar pseudoterminals
2683 The maximal number of pseudo-terminals for this user ID.
2684 .It Fl s Ar stacksize
2685 The maximal size of the stack segment, in kilobytes.
2687 The maximal amount of CPU time to be used by each process, in seconds.
2688 .It Fl u Ar userproc
2689 The maximal number of simultaneous processes for this user ID.
2690 .It Fl v Ar virtualmem
2691 The maximal virtual size of a process, in kilobytes.
2693 The maximum amount of swap space reserved or used for this user ID,
2696 .It Ic umask Oo Fl S Oc Op Ar mask
2697 Set the file creation mask (see
2699 to the octal or symbolic (see
2703 If the argument is omitted, the current mask value is printed.
2706 option is specified, the output is symbolic, otherwise the output is octal.
2707 .It Ic unalias Oo Fl a Oc Op Ar name ...
2708 The specified alias names are removed.
2711 is specified, all aliases are removed.
2712 .It Ic unset Oo Fl fv Oc Ar name ...
2713 The specified variables or functions are unset and unexported.
2716 option is specified or no options are given, the
2718 arguments are treated as variable names.
2721 option is specified, the
2723 arguments are treated as function names.
2724 .It Ic wait Op Ar job ...
2725 Wait for each specified
2727 to complete and return the exit status of the last process in the
2732 specified is unknown to the shell, it is treated as if it
2733 were a known job that exited with exit status 127.
2734 If no operands are given, wait for all jobs to complete
2735 and return an exit status of zero.
2737 .Ss Commandline Editing
2740 is being used interactively from a terminal, the current command
2741 and the command history
2745 .Sx Built-in Commands )
2748 command line editing.
2749 This mode uses commands similar
2750 to a subset of those described in the
2768 can be switched between insert mode and command mode by typing
2772 while in command mode will pass the line to the shell.
2775 .Dq Li "set -o emacs"
2778 command can be used to enable a subset of
2780 command line editing features.
2782 The following environment variables affect the execution of
2784 .Bl -tag -width ".Ev LANGXXXXXX"
2786 Initialization file for interactive shells.
2787 .It Ev LANG , Ev LC_*
2789 These are inherited by children of the shell,
2790 and is used in a limited manner by the shell itself.
2792 The previous current directory.
2793 This is used and updated by
2796 An absolute pathname for the current directory,
2797 possibly containing symbolic links.
2798 This is used and updated by the shell.
2800 The default terminal setting for the shell.
2801 This is inherited by children of the shell, and is used in the history
2805 Additionally, environment variables are turned into shell variables
2807 which may affect the shell as described under
2808 .Sx Special Variables .
2810 .Bl -tag -width "/etc/suid_profileXX" -compact
2812 User's login profile.
2814 System login profile.
2817 .It Pa /etc/suid_profile
2818 Privileged shell profile.
2821 Errors that are detected by the shell, such as a syntax error, will
2822 cause the shell to exit with a non-zero exit status.
2823 If the shell is not an interactive shell, the execution of the shell
2824 file will be aborted.
2825 Otherwise the shell will return the exit status of the last command
2828 builtin is used with a numeric argument, it
2829 will return the argument.
2850 command, the Thompson shell, appeared in
2852 It was superseded in
2854 by the Bourne shell, which inherited the name
2859 was rewritten in 1989 under the
2861 license after the Bourne shell from
2866 was originally written by
2867 .An Kenneth Almquist .
2871 utility does not recognize multibyte characters other than UTF-8.
2874 does not recognize multibyte characters.
projects / FreeBSD / FreeBSD.git / blob