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32 .\" from: @(#)sh.1 8.6 (Berkeley) 5/4/95
39 .Nd command interpreter (shell)
42 .Op Fl /+abCEefhIimnPpTuVvx
43 .Op Fl /+o Ar longname
49 .Op Fl /+abCEefhIimnPpTuVvx
50 .Op Fl /+o Ar longname
57 .Op Fl /+abCEefhIimnPpTuVvx
58 .Op Fl /+o Ar longname
64 utility is the standard command interpreter for the system.
65 The current version of
69 specification for the shell.
70 It only supports features
72 plus a few Berkeley extensions.
73 This man page is not intended to be a tutorial nor a complete
74 specification of the shell.
76 The shell is a command that reads lines from
77 either a file or the terminal, interprets them, and
78 generally executes other commands.
79 It is the program that is started when a user logs into the system,
80 although a user can select a different shell with the
84 implements a language that has flow control constructs,
85 a macro facility that provides a variety of features in
86 addition to data storage, along with built-in history and line
88 It incorporates many features to
89 aid interactive use and has the advantage that the interpretative
90 language is common to both interactive and non-interactive
92 That is, commands can be typed directly
93 to the running shell or can be put into a file,
94 which can be executed directly by the shell.
97 .\" XXX This next sentence is incredibly confusing.
99 If no arguments are present and if the standard input of the shell
100 is connected to a terminal
104 the shell is considered an interactive shell.
106 generally prompts before each command and handles programming
107 and command errors differently (as described below).
108 When first starting, the shell inspects argument 0, and
109 if it begins with a dash
111 the shell is also considered a login shell.
112 This is normally done automatically by the system
113 when the user first logs in.
114 A login shell first reads commands
119 in a user's home directory,
121 If the environment variable
123 is set on entry to a shell, or is set in the
125 of a login shell, the shell then subjects its value to parameter expansion
126 and arithmetic expansion and reads commands from the named file.
127 Therefore, a user should place commands that are to be executed only
130 file, and commands that are executed for every shell inside the
135 variable to some file by placing the following line in the file
137 in the home directory,
140 the filename desired:
142 .Dl "ENV=$HOME/.shrc; export ENV"
144 The first non-option argument specified on the command line
145 will be treated as the
146 name of a file from which to read commands (a shell script), and
147 the remaining arguments are set as the positional parameters
151 Otherwise, the shell reads commands
152 from its standard input.
154 Unlike older versions of
158 script is only sourced on invocation of interactive shells.
160 closes a well-known, and sometimes easily exploitable security
161 hole related to poorly thought out
164 .Ss Argument List Processing
165 All of the single letter options to
167 have a corresponding long name,
168 with the exception of
172 These long names are provided next to the single letter options
173 in the descriptions below.
174 The long name for an option may be specified as an argument to the
178 Once the shell is running,
179 the long name for an option may be specified as an argument to the
184 (described later in the section called
185 .Sx Built-in Commands ) .
186 Introducing an option with a dash
196 will stop option processing and will force the remaining
197 words on the command line to be treated as arguments.
202 options do not have long names.
203 They take arguments and are described after the single letter options.
204 .Bl -tag -width indent
205 .It Fl a Li allexport
206 Flag variables for export when assignments are made to them.
208 Enable asynchronous notification of background job
211 .It Fl C Li noclobber
212 Do not overwrite existing files with
216 .Xr emacs 1 Pq Pa ports/editors/emacs
217 command line editor (disables the
219 option if it has been set;
220 set automatically when interactive on terminals).
222 Exit immediately if any untested command fails in non-interactive mode.
223 The exit status of a command is considered to be
224 explicitly tested if the command is part of the list used to control
226 .Ic if , elif , while ,
229 if the command is the left
234 operator; or if the command is a pipeline preceded by the
237 If a shell function is executed and its exit status is explicitly
238 tested, all commands of the function are considered to be tested as
241 It is recommended to check for failures explicitly
242 instead of relying on
244 because it tends to behave in unexpected ways,
245 particularly in larger scripts.
247 Disable pathname expansion.
249 A do-nothing option for POSIX compliance.
250 .It Fl I Li ignoreeof
253 from input when in interactive mode.
254 .It Fl i Li interactive
255 Force the shell to behave interactively.
257 Turn on job control (set automatically when interactive).
258 A new process group is created for each pipeline (called a job).
259 It is possible to suspend jobs or to have them run in the foreground or
261 In a non-interactive shell,
262 this option can be set even if no terminal is available
263 and is useful to place processes in separate process groups.
265 If not interactive, read commands but do not
267 This is useful for checking the
268 syntax of shell scripts.
270 Change the default for the
276 (logical directory layout)
279 (physical directory layout).
280 .It Fl p Li privileged
281 Turn on privileged mode.
282 This mode is enabled on startup
283 if either the effective user or group ID is not equal to the
284 real user or group ID.
285 Turning this mode off sets the
286 effective user and group IDs to the real user and group IDs.
287 When this mode is enabled for interactive shells, the file
288 .Pa /etc/suid_profile
289 is sourced instead of
293 is sourced, and the contents of the
295 variable are ignored.
297 Read commands from standard input (set automatically
298 if no file arguments are present).
300 no effect when set after the shell has already started
301 running (i.e., when set with the
304 .It Fl T Li trapsasync
305 When waiting for a child, execute traps immediately.
306 If this option is not set,
307 traps are executed after the child exits,
310 This nonstandard option is useful for putting guarding shells around
311 children that block signals.
312 The surrounding shell may kill the child
313 or it may just return control to the tty and leave the child alone,
315 .Bd -literal -offset indent
316 sh -T -c "trap 'exit 1' 2 ; some-blocking-program"
319 Write a message to standard error when attempting
320 to expand a variable, a positional parameter or
321 the special parameter
323 that is not set, and if the
324 shell is not interactive, exit immediately.
328 command line editor (disables
332 The shell writes its input to standard error
334 Useful for debugging.
337 (preceded by the value of the
339 variable subjected to parameter expansion and arithmetic expansion)
340 to standard error before it is executed.
341 Useful for debugging.
343 Another do-nothing option for POSIX compliance.
344 It only has a long name.
346 Change the exit status of a pipeline to the last non-zero exit status of
347 any command in the pipeline, if any.
350 counts as a non-zero exit status,
351 this option may cause non-zero exit status for successful pipelines
354 in the pipeline terminates with status 0 without reading its
356 This option only has a long name.
360 when sourcing files or loading profiles.
362 .\" .Xr mac_veriexec 4 . TODO Does not exist; write it.
367 option causes the commands to be read from the
369 operand instead of from the standard input.
370 Keep in mind that this option only accepts a single string as its
371 argument, hence multi-word strings must be quoted.
375 option takes as its only argument the long name of an option
376 to be enabled or disabled.
377 For example, the following two invocations of
379 both enable the built-in
380 .Xr emacs 1 Pq Pa ports/editors/emacs
382 .Bd -literal -offset indent
387 If used without an argument, the
389 option displays the current option settings in a human-readable format.
392 is used without an argument, the current option settings are output
393 in a format suitable for re-input into the shell.
394 .Ss Lexical Structure
395 The shell reads input in terms of lines from a file and breaks
396 it up into words at whitespace (blanks and tabs), and at
400 which are special to the shell.
401 There are two types of operators: control operators and
402 redirection operators (their meaning is discussed later).
403 The following is a list of valid operators:
404 .Bl -tag -width indent
405 .It Control operators:
406 .Bl -column "XXX" "XXX" "XXX" "XXX" "XXX" -offset center -compact
407 .It Li & Ta Li && Ta Li \&( Ta Li \&) Ta Li \en
408 .It Li ;; Ta Li ;& Ta Li \&; Ta Li \&| Ta Li ||
410 .It Redirection operators:
411 .Bl -column "XXX" "XXX" "XXX" "XXX" "XXX" -offset center -compact
412 .It Li < Ta Li > Ta Li << Ta Li >> Ta Li <>
413 .It Li <& Ta Li >& Ta Li <<- Ta Li >| Ta \&
419 introduces a comment if used at the beginning of a word.
420 The word starting with
422 and the rest of the line are ignored.
426 characters (character code 0) are not allowed in shell input.
428 Quoting is used to remove the special meaning of certain characters
429 or words to the shell, such as operators, whitespace, keywords,
432 There are four types of quoting: matched single quotes,
433 dollar-single quotes,
434 matched double quotes, and backslash.
435 .Bl -tag -width indent
437 Enclosing characters in single quotes preserves the literal
438 meaning of all the characters (except single quotes, making
439 it impossible to put single-quotes in a single-quoted string).
440 .It Dollar-Single Quotes
441 Enclosing characters between
445 preserves the literal meaning of all characters
446 except backslashes and single quotes.
447 A backslash introduces a C-style escape sequence:
448 .Bl -tag -width xUnnnnnnnn
450 Alert (ring the terminal bell)
454 The control character denoted by
460 is a backslash, it must be doubled.
462 The ESC character (ASCII 0x1b)
480 The byte whose octal value is
482 (one to three digits)
484 The byte whose hexadecimal value is
486 (one or more digits only the last two of which are used)
488 The Unicode code point
490 (four hexadecimal digits)
491 .It \eU Ns Ar nnnnnnnn
492 The Unicode code point
494 (eight hexadecimal digits)
497 The sequences for Unicode code points are currently only useful with
499 They reject code point 0 and UTF-16 surrogates.
501 If an escape sequence would produce a byte with value 0,
502 that byte and the rest of the string until the matching single-quote
505 Any other string starting with a backslash is an error.
507 Enclosing characters within double quotes preserves the literal
508 meaning of all characters except dollar sign
514 The backslash inside double quotes is historically weird.
515 It remains literal unless it precedes the following characters,
516 which it serves to quote:
518 .Bl -column "XXX" "XXX" "XXX" "XXX" "XXX" -offset center -compact
519 .It Li $ Ta Li ` Ta Li \&" Ta Li \e Ta Li \en
522 A backslash preserves the literal meaning of the following
523 character, with the exception of the newline character
525 A backslash preceding a newline is treated as a line continuation.
528 Keywords or reserved words are words that have special meaning to the
529 shell and are recognized at the beginning of a line and
530 after a control operator.
531 The following are keywords:
532 .Bl -column "doneXX" "elifXX" "elseXX" "untilXX" "whileX" -offset center
533 .It Li \&! Ta { Ta } Ta Ic case Ta Ic do
534 .It Ic done Ta Ic elif Ta Ic else Ta Ic esac Ta Ic fi
535 .It Ic for Ta Ic if Ta Ic then Ta Ic until Ta Ic while
538 An alias is a name and corresponding value set using the
541 Wherever the command word of a simple command may occur,
542 and after checking for keywords if a keyword may occur, the shell
543 checks the word to see if it matches an alias.
544 If it does, it replaces it in the input stream with its value.
545 For example, if there is an alias called
557 Aliases are also recognized after an alias
558 whose value ends with a space or tab.
559 For example, if there is also an alias called
565 .Dl "nohup lf foobar"
569 .Dl "nohup ls -F foobar"
571 Aliases provide a convenient way for naive users to
572 create shorthands for commands without having to learn how
573 to create functions with arguments.
574 Using aliases in scripts is discouraged
575 because the command that defines them must be executed
576 before the code that uses them is parsed.
577 This is fragile and not portable.
579 An alias name may be escaped in a command line, so that it is not
580 replaced by its alias value, by using quoting characters within or
581 adjacent to the alias name.
582 This is most often done by prefixing
583 an alias name with a backslash to execute a function, built-in, or
584 normal program with the same name.
589 The shell interprets the words it reads according to a
590 language, the specification of which is outside the scope
591 of this man page (refer to the BNF in the
594 Essentially though, a line is read and if
595 the first word of the line (or after a control operator)
596 is not a keyword, then the shell has recognized a
598 Otherwise, a complex command or some
599 other special construct may have been recognized.
601 If a simple command has been recognized, the shell performs
602 the following actions:
605 Leading words of the form
607 are stripped off and assigned to the environment of
609 (they do not affect expansions).
610 Redirection operators and
611 their arguments (as described below) are stripped
612 off and saved for processing.
614 The remaining words are expanded as described in
616 .Sx Word Expansions ,
617 and the first remaining word is considered the command
618 name and the command is located.
620 words are considered the arguments of the command.
621 If no command name resulted, then the
623 variable assignments recognized in 1) affect the
626 Redirections are performed as described in
630 Redirections are used to change where a command reads its input
632 In general, redirections open, close, or
633 duplicate an existing reference to a file.
635 used for redirection is:
637 .D1 Oo Ar n Oc Ar redir-op file
641 is one of the redirection operators mentioned
643 The following gives some examples of how these
644 operators can be used.
645 Note that stdin and stdout are commonly used abbreviations
646 for standard input and standard output respectively.
647 .Bl -tag -width "1234567890XX" -offset indent
648 .It Oo Ar n Oc Ns Li > Ar file
649 redirect stdout (or file descriptor
653 .It Oo Ar n Oc Ns Li >| Ar file
654 same as above, but override the
657 .It Oo Ar n Oc Ns Li >> Ar file
658 append stdout (or file descriptor
662 .It Oo Ar n Oc Ns Li < Ar file
663 redirect stdin (or file descriptor
667 .It Oo Ar n Oc Ns Li <> Ar file
668 redirect stdin (or file descriptor
672 .It Oo Ar n1 Oc Ns Li <& Ns Ar n2
673 duplicate stdin (or file descriptor
677 .It Oo Ar n Oc Ns Li <&-
678 close stdin (or file descriptor
680 .It Oo Ar n1 Oc Ns Li >& Ns Ar n2
681 duplicate stdout (or file descriptor
685 .It Oo Ar n Oc Ns Li >&-
686 close stdout (or file descriptor
690 The following redirection is often called a
692 .Bd -unfilled -offset indent
693 .Oo Ar n Oc Ns Li << Ar delimiter
699 All the text on successive lines up to the delimiter is
700 saved away and made available to the command on standard
701 input, or file descriptor
706 as specified on the initial line is quoted, then the
708 is treated literally, otherwise the text is subjected to
709 parameter expansion, command substitution, and arithmetic
710 expansion (as described in the section on
711 .Sx Word Expansions ) .
720 .Ss Search and Execution
721 There are three types of commands: shell functions,
722 built-in commands, and normal programs.
723 The command is searched for (by name) in that order.
724 The three types of commands are all executed in a different way.
726 When a shell function is executed, all of the shell positional
729 which remains unchanged) are
730 set to the arguments of the shell function.
731 The variables which are explicitly placed in the environment of
732 the command (by placing assignments to them before the
733 function name) are made local to the function and are set
735 Then the command given in the function definition is executed.
736 The positional parameters are restored to their original values
737 when the command completes.
738 This all occurs within the current shell.
740 Shell built-in commands are executed internally to the shell, without
741 spawning a new process.
742 There are two kinds of built-in commands: regular and special.
743 Assignments before special builtins persist after they finish
744 executing and assignment errors, redirection errors and certain
745 operand errors cause a script to be aborted.
746 Special builtins cannot be overridden with a function.
747 Both regular and special builtins can affect the shell in ways
748 normal programs cannot.
750 Otherwise, if the command name does not match a function
751 or built-in command, the command is searched for as a normal
752 program in the file system (as described in the next section).
753 When a normal program is executed, the shell runs the program,
754 passing the arguments and the environment to the program.
755 If the program is not a normal executable file
756 (i.e., if it does not begin with the
758 whose ASCII representation is
764 but appears to be a text file,
765 the shell will run a new instance of
769 Note that previous versions of this document
770 and the source code itself misleadingly and sporadically
771 refer to a shell script without a magic number
773 .Dq "shell procedure" .
775 When locating a command, the shell first looks to see if
776 it has a shell function by that name.
778 built-in command by that name.
779 If a built-in command is not found,
780 one of two things happen:
783 Command names containing a slash are simply executed without
784 performing any searches.
786 The shell searches each entry in the
789 in turn for the command.
792 variable should be a series of
793 entries separated by colons.
794 Each entry consists of a
796 The current directory
797 may be indicated implicitly by an empty directory name,
798 or explicitly by a single period.
800 .Ss Command Exit Status
801 Each command has an exit status that can influence the behavior
802 of other shell commands.
803 The paradigm is that a command exits
804 with zero for normal or success, and non-zero for failure,
805 error, or a false indication.
806 The man page for each command
807 should indicate the various exit codes and what they mean.
808 Additionally, the built-in commands return exit codes, as does
809 an executed shell function.
811 If a command is terminated by a signal, its exit status is greater than 128.
812 The signal name can be found by passing the exit status to
815 If there is no command word,
816 the exit status is the exit status of the last command substitution executed,
817 or zero if the command does not contain any command substitutions.
819 Complex commands are combinations of simple commands
820 with control operators or keywords, together creating a larger complex
822 More generally, a command is one of the following:
823 .Bl -item -offset indent
829 list or compound-list
836 Unless otherwise stated, the exit status of a command is
837 that of the last simple command executed by the command,
838 or zero if no simple command was executed.
840 A pipeline is a sequence of one or more commands separated
841 by the control operator
843 The standard output of all but
844 the last command is connected to the standard input
846 The standard output of the last
847 command is inherited from the shell, as usual.
849 The format for a pipeline is:
851 .D1 Oo Li \&! Oc Ar command1 Op Li \&| Ar command2 ...
853 The standard output of
855 is connected to the standard input of
857 The standard input, standard output, or
858 both of a command is considered to be assigned by the
859 pipeline before any redirection specified by redirection
860 operators that are part of the command.
862 Note that unlike some other shells,
864 executes each process in a pipeline with more than one command
865 in a subshell environment and as a child of the
869 If the pipeline is not in the background (discussed later),
870 the shell waits for all commands to complete.
874 does not precede the pipeline, the
875 exit status is the exit status of the last command specified
876 in the pipeline if the
878 option is not set or all commands returned zero,
879 or the last non-zero exit status of any command in the pipeline otherwise.
880 Otherwise, the exit status is the logical
881 NOT of that exit status.
883 that status is zero, the exit status is 1; if
884 that status is greater than zero, the exit status
887 Because pipeline assignment of standard input or standard
888 output or both takes place before redirection, it can be
889 modified by redirection.
892 .Dl "command1 2>&1 | command2"
894 sends both the standard output and standard error of
896 to the standard input of
901 or newline terminator causes the preceding
903 (described below in the section called
904 .Sx Short-Circuit List Operators )
905 to be executed sequentially;
908 causes asynchronous execution of the preceding AND-OR-list.
909 .Ss Background Commands (&)
910 If a command is terminated by the control operator ampersand
912 the shell executes the command in a subshell environment (see
913 .Sx Grouping Commands Together
914 below) and asynchronously;
915 the shell does not wait for the command to finish
916 before executing the next command.
918 The format for running a command in background is:
920 .D1 Ar command1 Li & Op Ar command2 Li & Ar ...
922 If the shell is not interactive, the standard input of an
923 asynchronous command is set to
926 The exit status is zero.
927 .Ss Lists (Generally Speaking)
928 A list is a sequence of zero or more commands separated by
929 newlines, semicolons, or ampersands,
930 and optionally terminated by one of these three characters.
932 list are executed in the order they are written.
933 If command is followed by an ampersand, the shell starts the
934 command and immediately proceeds onto the next command;
935 otherwise it waits for the command to terminate before
936 proceeding to the next one.
937 .Ss Short-Circuit List Operators
941 are AND-OR list operators.
943 executes the first command, and then executes the second command
944 if the exit status of the first command is zero.
946 is similar, but executes the second command if the exit
947 status of the first command is nonzero.
951 both have the same priority.
952 .Ss Flow-Control Constructs (if, while, for, case)
956 .Bd -unfilled -offset indent -compact
960 .Ic then Ar list Oc Ar ...
965 The exit status is that of selected
970 or zero if no list was selected.
975 .Bd -unfilled -offset indent -compact
981 The two lists are executed repeatedly while the exit status of the
985 command is similar, but has the word
990 repeat until the exit status of the first list is zero.
992 The exit status is that of the last execution of the second list,
993 or zero if it was never executed.
998 .Bd -unfilled -offset indent -compact
999 .Ic for Ar variable Op Ic in Ar word ...
1006 and the following words are omitted,
1009 The words are expanded, and then the list is executed
1010 repeatedly with the variable set to each word in turn.
1015 commands may be replaced with
1025 .D1 Ic break Op Ar num
1026 .D1 Ic continue Op Ar num
1030 command terminates the
1039 command continues with the next iteration of the innermost loop.
1040 These are implemented as special built-in commands.
1045 .Bd -unfilled -offset indent -compact
1046 .Ic case Ar word Ic in
1047 .Ar pattern ) Ar list Li ;;
1052 The pattern can actually be one or more patterns
1059 Tilde expansion, parameter expansion, command substitution,
1060 arithmetic expansion and quote removal are applied to the word.
1061 Then, each pattern is expanded in turn using tilde expansion,
1062 parameter expansion, command substitution and arithmetic expansion and
1063 the expanded form of the word is checked against it.
1064 If a match is found, the corresponding list is executed.
1065 If the selected list is terminated by the control operator
1069 execution continues with the next list,
1070 continuing until a list terminated with
1075 .Ss Grouping Commands Together
1076 Commands may be grouped by writing either
1079 .Bd -literal -offset -ident
1085 .Bd -literal -offset -ident
1089 The first form executes the commands in a subshell environment.
1090 A subshell environment has its own copy of:
1093 The current working directory as set by
1096 The file creation mask as set by
1099 Resource limits as set by
1102 References to open files.
1109 Positional parameters and variables.
1118 These are copied from the parent shell environment,
1119 except that trapped (but not ignored) signals are reset to the default action
1120 and known jobs are cleared.
1121 Any changes do not affect the parent shell environment.
1123 A subshell environment may be implemented as a child process or differently.
1124 If job control is enabled in an interactive shell,
1125 commands grouped in parentheses can be suspended and continued as a unit.
1127 For compatibility with other shells,
1128 two open parentheses in sequence should be separated by whitespace.
1130 The second form never forks another shell,
1131 so it is slightly more efficient.
1132 Grouping commands together this way allows the user to
1133 redirect their output as though they were one program:
1134 .Bd -literal -offset indent
1135 { echo -n "hello"; echo " world"; } > greeting
1138 The syntax of a function definition is
1140 .D1 Ar name Li \&( \&) Ar command
1142 A function definition is an executable statement; when
1143 executed it installs a function named
1146 exit status of zero.
1155 Variables may be declared to be local to a function by
1159 This should appear as the first statement of a function,
1162 .D1 Ic local Oo Ar variable ... Oc Op Fl
1166 command is implemented as a built-in command.
1167 The exit status is zero
1168 unless the command is not in a function or a variable name is invalid.
1170 When a variable is made local, it inherits the initial
1171 value and exported and readonly flags from the variable
1172 with the same name in the surrounding scope, if there is
1174 Otherwise, the variable is initially unset.
1176 uses dynamic scoping, so that if the variable
1178 is made local to function
1180 which then calls function
1182 references to the variable
1186 will refer to the variable
1190 not to the global variable named
1193 The only special parameter that can be made local is
1197 local causes any shell options
1198 (including those that only have long names)
1202 command inside the function to be
1203 restored to their original values when the function
1210 .D1 Ic return Op Ar exitstatus
1212 It terminates the current executional scope, returning from the closest
1213 nested function or sourced script;
1214 if no function or sourced script is being executed,
1215 it exits the shell instance.
1218 command is implemented as a special built-in command.
1219 .Ss Variables and Parameters
1220 The shell maintains a set of parameters.
1224 of alphabetics, numerics, and underscores,
1225 and starting with an alphabetic or an underscore)
1226 is called a variable.
1228 the shell turns all environment variables with valid names into shell
1230 New variables can be set using the form
1232 .D1 Ar name Ns = Ns Ar value
1234 A parameter can also be denoted by a number
1235 or a special character as explained below.
1237 Assignments are expanded differently from other words:
1238 tilde expansion is also performed after the equals sign and after any colon
1239 and usernames are also terminated by colons,
1240 and field splitting and pathname expansion are not performed.
1242 This special expansion applies not only to assignments that form a simple
1243 command by themselves or precede a command word,
1244 but also to words passed to the
1249 built-in commands that have this form.
1250 For this, the builtin's name must be literal
1251 (not the result of an expansion)
1252 and may optionally be preceded by one or more literal instances of
1255 .Ss Positional Parameters
1256 A positional parameter is a parameter denoted by a number greater than zero.
1257 The shell sets these initially to the values of its command line
1258 arguments that follow the name of the shell script.
1261 built-in command can also be used to set or reset them.
1262 .Ss Special Parameters
1263 Special parameters are parameters denoted by a single special character
1265 They are shown in the following list, exactly as they would appear in input
1266 typed by the user or in the source of a shell script.
1269 Expands to the positional parameters, starting from one.
1271 the expansion occurs within a double-quoted string
1272 it expands to a single field with the value of each parameter
1273 separated by the first character of the
1280 Expands to the positional parameters, starting from one.
1282 the expansion occurs within double-quotes, each positional
1283 parameter expands as a separate argument.
1284 If there are no positional parameters, the
1287 generates zero arguments, even when
1290 What this basically means, for example, is
1303 .Bd -literal -offset indent
1307 Expands to the number of positional parameters.
1309 Expands to the exit status of the most recent pipeline.
1311 (hyphen) Expands to the current option flags (the single-letter
1312 option names concatenated into a string) as specified on
1315 built-in command, or implicitly
1318 Expands to the process ID of the invoked shell.
1320 retains the same value of
1324 Expands to the process ID of the most recent background
1325 command executed from the current shell.
1327 pipeline, the process ID is that of the last command in the
1329 If this parameter is referenced, the shell will remember
1330 the process ID and its exit status until the
1332 built-in command reports completion of the process.
1334 (zero) Expands to the name of the shell script if passed on the command line,
1337 operand if given (with
1339 or otherwise argument 0 passed to the shell.
1341 .Ss Special Variables
1342 The following variables are set by the shell or
1343 have special meaning to it:
1344 .Bl -tag -width ".Va HISTSIZE"
1346 The search path used with the
1350 The fallback editor used with the
1353 If not set, the default editor is
1356 The default editor used with the
1360 File used for persistent history storage.
1367 the shell will not load and save the history.
1369 The number of previous commands that are accessible.
1371 The user's home directory,
1372 used in tilde expansion and as a default directory for the
1376 Input Field Separators.
1377 This is initialized at startup to
1383 This value also applies if
1385 is unset, but not if it is set to the empty string.
1387 .Sx White Space Splitting
1388 section for more details.
1390 The current line number in the script or function.
1392 The name of a mail file, that will be checked for the arrival of new
1399 separated list of file names, for the shell to check for incoming
1401 This variable overrides the
1404 There is a maximum of 10 mailboxes that can be monitored at once.
1406 The index of the next argument to be processed by
1408 This is initialized to 1 at startup.
1410 The default search path for executables.
1413 section for details.
1415 The parent process ID of the invoked shell.
1416 This is set at startup
1417 unless this variable is in the environment.
1418 A later change of parent process ID is not reflected.
1419 A subshell retains the same value of
1422 The primary prompt string, which defaults to
1424 unless you are the superuser, in which case it defaults to
1427 may include any of the following formatting sequences,
1428 which are replaced by the given information:
1429 .Bl -tag -width indent
1434 The braces are required.
1439 national representation of the time.
1441 This system's fully-qualified hostname (FQDN).
1443 This system's hostname.
1447 The final component of the current working directory.
1449 The entire path of the current working directory.
1453 for normal users and
1457 A literal backslash.
1459 Start of a sequence of non-printing characters (used, for example,
1460 to embed ANSI CSI sequences into the prompt).
1462 End of a sequence of non-printing characters.
1465 The following special and non-printing characters are supported
1466 within the sequence of non-printing characters:
1467 .Bl -tag -width indent
1469 Emits ASCII BEL (0x07, 007) character.
1471 Emits ASCII ESC (0x1b, 033) character.
1473 Emits ASCII CR (0x0d, 015) character.
1475 Emits CRLF sequence.
1478 The secondary prompt string, which defaults to
1481 may include any of the formatting sequences from
1484 The prefix for the trace output (if
1491 This clause describes the various expansions that are
1493 Not all expansions are performed on
1494 every word, as explained later.
1496 Tilde expansions, parameter expansions, command substitutions,
1497 arithmetic expansions, and quote removals that occur within
1498 a single word expand to a single field.
1500 splitting or pathname expansion that can create multiple
1501 fields from a single word.
1502 The single exception to this rule is
1503 the expansion of the special parameter
1505 within double-quotes,
1506 as was described above.
1508 The order of word expansion is:
1511 Tilde Expansion, Parameter Expansion, Command Substitution,
1512 Arithmetic Expansion (these all occur at the same time).
1514 Field Splitting is performed on fields generated by step (1)
1519 Pathname Expansion (unless the
1521 option is in effect).
1528 character is used to introduce parameter expansion, command
1529 substitution, or arithmetic expansion.
1530 .Ss Tilde Expansion (substituting a user's home directory)
1531 A word beginning with an unquoted tilde character
1534 subjected to tilde expansion.
1535 All the characters up to a slash
1537 or the end of the word are treated as a username
1538 and are replaced with the user's home directory.
1540 username is missing (as in
1542 the tilde is replaced with the value of the
1544 variable (the current user's home directory).
1545 .Ss Parameter Expansion
1546 The format for parameter expansion is as follows:
1548 .D1 Li ${ Ns Ar expression Ns Li }
1552 consists of all characters until the matching
1556 escaped by a backslash or within a single-quoted or double-quoted
1557 string, and characters in
1558 embedded arithmetic expansions, command substitutions, and variable
1559 expansions, are not examined in determining the matching
1561 If the variants with
1567 occur within a double-quoted string,
1568 as an extension there may be unquoted parts
1569 (via double-quotes inside the expansion);
1571 within such parts are also not examined in determining the matching
1574 The simplest form for parameter expansion is:
1576 .D1 Li ${ Ns Ar parameter Ns Li }
1578 The value, if any, of
1582 The parameter name or symbol can be enclosed in braces, which are
1583 optional except for positional parameters with more than one digit or
1584 when parameter is followed by a character that could be interpreted as
1586 If a parameter expansion occurs inside double-quotes:
1589 Field splitting is not performed on the results of the
1590 expansion, with the exception of the special parameter
1593 Pathname expansion is not performed on the results of the
1597 In addition, a parameter expansion can be modified by using one of the
1599 .Bl -tag -width indent
1600 .It Li ${ Ns Ar parameter Ns Li :- Ns Ar word Ns Li }
1604 is unset or null, the expansion of
1606 is substituted; otherwise, the value of
1609 .It Li ${ Ns Ar parameter Ns Li := Ns Ar word Ns Li }
1610 Assign Default Values.
1613 is unset or null, the expansion of
1623 does not prevent field splitting or pathname expansion.
1624 Only variables, not positional
1625 parameters or special parameters, can be
1626 assigned in this way.
1627 .It Li ${ Ns Ar parameter Ns Li :? Ns Oo Ar word Oc Ns Li }
1628 Indicate Error if Null or Unset.
1631 is unset or null, the expansion of
1633 (or a message indicating it is unset if
1635 is omitted) is written to standard
1636 error and the shell exits with a nonzero
1638 Otherwise, the value of
1642 interactive shell need not exit.
1643 .It Li ${ Ns Ar parameter Ns Li :+ Ns Ar word Ns Li }
1644 Use Alternate Value.
1647 is unset or null, null is substituted;
1648 otherwise, the expansion of
1653 In the parameter expansions shown previously, use of the colon in the
1654 format results in a test for a parameter that is unset or null; omission
1655 of the colon results in a test for a parameter that is only unset.
1659 inherits the type of quoting
1660 (unquoted, double-quoted or here-document)
1661 from the surroundings,
1662 with the exception that a backslash that quotes a closing brace is removed
1663 during quote removal.
1664 .Bl -tag -width indent
1665 .It Li ${# Ns Ar parameter Ns Li }
1667 The length in characters of
1672 The following four varieties of parameter expansion provide for substring
1674 In each case, pattern matching notation
1676 .Sx Shell Patterns ) ,
1677 rather than regular expression notation,
1678 is used to evaluate the patterns.
1679 If parameter is one of the special parameters
1683 the result of the expansion is unspecified.
1684 Enclosing the full parameter expansion string in double-quotes does not
1685 cause the following four varieties of pattern characters to be quoted,
1686 whereas quoting characters within the braces has this effect.
1687 .Bl -tag -width indent
1688 .It Li ${ Ns Ar parameter Ns Li % Ns Ar word Ns Li }
1689 Remove Smallest Suffix Pattern.
1692 is expanded to produce a pattern.
1694 parameter expansion then results in
1696 with the smallest portion of the
1697 suffix matched by the pattern deleted.
1698 .It Li ${ Ns Ar parameter Ns Li %% Ns Ar word Ns Li }
1699 Remove Largest Suffix Pattern.
1702 is expanded to produce a pattern.
1704 parameter expansion then results in
1706 with the largest portion of the
1707 suffix matched by the pattern deleted.
1708 .It Li ${ Ns Ar parameter Ns Li # Ns Ar word Ns Li }
1709 Remove Smallest Prefix Pattern.
1712 is expanded to produce a pattern.
1714 parameter expansion then results in
1716 with the smallest portion of the
1717 prefix matched by the pattern deleted.
1718 .It Li ${ Ns Ar parameter Ns Li ## Ns Ar word Ns Li }
1719 Remove Largest Prefix Pattern.
1722 is expanded to produce a pattern.
1724 parameter expansion then results in
1726 with the largest portion of the
1727 prefix matched by the pattern deleted.
1729 .Ss Command Substitution
1730 Command substitution allows the output of a command to be substituted in
1731 place of the command name itself.
1732 Command substitution occurs when
1733 the command is enclosed as follows:
1735 .D1 Li $( Ns Ar command Ns Li )\&
1737 or the backquoted version:
1739 .D1 Li ` Ns Ar command Ns Li `
1741 The shell expands the command substitution by executing command
1742 and replacing the command substitution
1743 with the standard output of the command,
1744 removing sequences of one or more newlines at the end of the substitution.
1745 Embedded newlines before the end of the output are not removed;
1746 however, during field splitting, they may be translated into spaces
1747 depending on the value of
1749 and the quoting that is in effect.
1750 The command is executed in a subshell environment,
1751 except that the built-in commands
1756 return information about the parent shell environment
1759 returns information about the same process
1760 if they are the only command in a command substitution.
1762 If a command substitution of the
1764 form begins with a subshell,
1769 must be separated by whitespace
1770 to avoid ambiguity with arithmetic expansion.
1771 .Ss Arithmetic Expansion
1772 Arithmetic expansion provides a mechanism for evaluating an arithmetic
1773 expression and substituting its value.
1774 The format for arithmetic expansion is as follows:
1776 .D1 Li $(( Ns Ar expression Ns Li ))
1780 is treated as if it were in double-quotes, except
1781 that a double-quote inside the expression is not treated specially.
1783 shell expands all tokens in the
1785 for parameter expansion,
1786 command substitution,
1787 arithmetic expansion
1790 The allowed expressions are a subset of C expressions,
1792 .Bl -tag -width "Variables" -offset indent
1794 All values are of type
1797 Decimal, octal (starting with
1799 and hexadecimal (starting with
1803 Shell variables can be read and written
1804 and contain integer constants.
1807 .It Binary operators
1808 .Li "* / % + - << >> < <= > >= == != & ^ | && ||"\&
1809 .It Assignment operators
1810 .Li "= += -= *= /= %= <<= >>= &= ^= |="
1811 .It Conditional operator
1815 The result of the expression is substituted in decimal.
1816 .Ss White Space Splitting (Field Splitting)
1817 In certain contexts,
1818 after parameter expansion, command substitution, and
1819 arithmetic expansion the shell scans the results of
1820 expansions and substitutions that did not occur in double-quotes for
1821 field splitting and multiple fields can result.
1832 are treated differently from other characters in
1837 at the beginning or end of a word is discarded.
1839 Subsequently, a field is delimited by either
1842 a non-whitespace character in
1844 with any whitespace in
1848 one or more whitespace characters in
1852 If a word ends with a non-whitespace character in
1854 there is no empty field after this character.
1856 If no field is delimited, the word is discarded.
1857 In particular, if a word consists solely of an unquoted substitution
1858 and the result of the substitution is null,
1859 it is removed by field splitting even if
1862 .Ss Pathname Expansion (File Name Generation)
1866 file name generation is performed
1867 after word splitting is complete.
1869 viewed as a series of patterns, separated by slashes.
1871 process of expansion replaces the word with the names of
1872 all existing files whose names can be formed by replacing
1873 each pattern with a string that matches the specified pattern.
1874 There are two restrictions on this: first, a pattern cannot match
1875 a string containing a slash, and second,
1876 a pattern cannot match a string starting with a period
1877 unless the first character of the pattern is a period.
1878 The next section describes the patterns used for
1880 the four varieties of parameter expansion for substring processing and the
1884 A pattern consists of normal characters, which match themselves,
1885 and meta-characters.
1886 The meta-characters are
1891 These characters lose their special meanings if they are quoted.
1892 When command or variable substitution is performed and the dollar sign
1893 or back quotes are not double-quoted, the value of the
1894 variable or the output of the command is scanned for these
1895 characters and they are turned into meta-characters.
1899 matches any string of characters.
1902 matches any single character.
1905 introduces a character class.
1906 The end of the character class is indicated by a
1914 rather than introducing a character class.
1915 A character class matches any of the characters between the square brackets.
1916 A locale-dependent range of characters may be specified using a minus sign.
1917 A named class of characters (see
1919 may be specified by surrounding the name with
1924 .Ql \&[\&[:alpha:\&]\&]
1925 is a shell pattern that matches a single letter.
1926 The character class may be complemented by making an exclamation point
1928 the first character of the character class.
1931 has the same effect but is non-standard.
1935 in a character class, make it the first character listed
1943 make it the first or last character listed.
1944 .Ss Built-in Commands
1945 This section lists the built-in commands.
1946 .Bl -tag -width indent
1948 A null command that returns a 0 (true) exit value.
1950 The commands in the specified file are read and executed by the shell.
1953 command may be used to return to the
1960 characters, it is used as is.
1961 Otherwise, the shell searches the
1964 If it is not found in the
1966 it is sought in the current working directory.
1968 A built-in equivalent of
1970 .It Ic alias Oo Ar name Ns Oo = Ns Ar string Oc ... Oc
1972 .Ar name Ns = Ns Ar string
1973 is specified, the shell defines the alias
1979 is specified, the value of the alias
1982 With no arguments, the
1984 built-in command prints the names and values of all defined aliases
1987 Alias values are written with appropriate quoting so that they are
1988 suitable for re-input to the shell.
1992 .It Ic bg Op Ar job ...
1993 Continue the specified jobs
1994 (or the current job if no jobs are given)
1996 .It Ic bind Oo Fl aeklrsv Oc Oo Ar key Oo Ar command Oc Oc
1997 List or alter key bindings for the line editor.
1998 This command is documented in
2000 .It Ic break Op Ar num
2002 .Sx Flow-Control Constructs
2004 .It Ic builtin Ar cmd Op Ar arg ...
2005 Execute the specified built-in command,
2007 This is useful when the user wishes to override a shell function
2008 with the same name as a built-in command.
2009 .It Ic cd Oo Fl L | P Oc Oo Fl e Oc Op Ar directory
2011 Switch to the specified
2013 to the directory specified in the
2015 environment variable if no
2018 to the directory specified in the
2020 environment variable if
2030 then the directories listed in the
2033 searched for the specified
2037 is unset, the current directory is searched.
2040 is the same as that of
2042 In an interactive shell,
2045 command will print out the name of the directory
2046 that it actually switched to
2049 mechanism was used or if
2056 option is specified,
2058 is handled physically and symbolic links are resolved before
2060 components are processed.
2063 option is specified,
2065 is handled logically.
2066 This is the default.
2072 to return exit status 1 if the full pathname of the new directory
2073 cannot be determined reliably or at all.
2074 Normally this is not considered an error,
2075 although a warning is printed.
2077 If changing the directory fails, the exit status is greater than 1.
2078 If the directory is changed, the exit status is 0, or also 1 if
2085 .It Ic command Oo Fl p Oc Op Ar utility Op Ar argument ...
2086 .It Ic command Oo Fl p Oc Fl v Ar utility
2087 .It Ic command Oo Fl p Oc Fl V Ar utility
2088 The first form of invocation executes the specified
2090 ignoring shell functions in the search.
2093 is a special builtin,
2094 it is executed as if it were a regular builtin.
2098 option is specified, the command search is performed using a
2101 that is guaranteed to find all of the standard utilities.
2105 option is specified,
2107 is not executed but a description of its interpretation by the shell is
2109 For ordinary commands the output is the path name; for shell built-in
2110 commands, shell functions and keywords only the name is written.
2111 Aliases are printed as
2112 .Dq Ic alias Ar name Ns = Ns Ar value .
2116 option is identical to
2118 except for the output.
2120 .Dq Ar utility Ic is Ar description
2126 a special shell builtin,
2133 .It Ic continue Op Ar num
2135 .Sx Flow-Control Constructs
2137 .It Ic echo Oo Fl e | n Oc Op Ar string ...
2138 Print a space-separated list of the arguments to the standard output
2139 and append a newline character.
2140 .Bl -tag -width indent
2142 Suppress the output of the trailing newline.
2144 Process C-style backslash escape sequences.
2147 command understands the following character escapes:
2148 .Bl -tag -width indent
2150 Alert (ring the terminal bell)
2154 Suppress the trailing newline (this has the side-effect of truncating the
2155 line if it is not the last character)
2157 The ESC character (ASCII 0x1b)
2171 (Zero) The character whose octal value is
2177 is not enclosed in quotes then the backslash itself must be escaped
2178 with a backslash to protect it from the shell.
2180 .Bd -literal -offset indent
2189 $ echo -e a\e\e\e\eb
2198 options may be specified.
2199 .It Ic eval Ar string ...
2200 Concatenate all the arguments with spaces.
2201 Then re-parse and execute the command.
2202 .It Ic exec Op Ar command Op arg ...
2206 the shell process is replaced with the specified program
2207 (which must be a real program, not a shell built-in command or function).
2208 Any redirections on the
2210 command are marked as permanent,
2211 so that they are not undone when the
2214 .It Ic exit Op Ar exitstatus
2215 Terminate the shell process.
2219 it is used as the exit status of the shell.
2220 Otherwise, if the shell is executing an
2222 trap, the exit status of the last command before the trap is used;
2223 if the shell is executing a trap for a signal,
2224 the shell exits by resending the signal to itself.
2225 Otherwise, the exit status of the preceding command is used.
2226 The exit status should be an integer between 0 and 255.
2227 .It Ic export Ar name ...
2228 .It Ic export Op Fl p
2229 The specified names are exported so that they will
2230 appear in the environment of subsequent commands.
2231 The only way to un-export a variable is to
2234 The shell allows the value of a variable to be set
2235 at the same time as it is exported by writing
2237 .D1 Ic export Ar name Ns = Ns Ar value
2239 With no arguments the
2241 command lists the names
2242 of all exported variables.
2245 option is specified, the exported variables are printed as
2246 .Dq Ic export Ar name Ns = Ns Ar value
2247 lines, suitable for re-input to the shell.
2249 A null command that returns a non-zero (false) exit value.
2250 .It Ic fc Oo Fl e Ar editor Oc Op Ar first Op Ar last
2251 .It Ic fc Fl l Oo Fl nr Oc Op Ar first Op Ar last
2252 .It Ic fc Fl s Oo Ar old Ns = Ns Ar new Oc Op Ar first
2255 built-in command lists, or edits and re-executes,
2256 commands previously entered to an interactive shell.
2257 .Bl -tag -width indent
2259 Use the editor named by
2261 to edit the commands.
2264 string is a command name,
2265 subject to search via the
2270 variable is used as a default when
2275 is null or unset, the value of the
2282 is used as the editor.
2284 List the commands rather than invoking
2286 The commands are written in the
2287 sequence indicated by the
2291 operands, as affected by
2293 with each command preceded by the command number.
2295 Suppress command numbers when listing with
2298 Reverse the order of the commands listed
2307 Re-execute the command without invoking an editor.
2310 Select the commands to list or edit.
2311 The number of previous commands that can be accessed
2312 are determined by the value of the
2319 or both are one of the following:
2320 .Bl -tag -width indent
2321 .It Oo Cm + Oc Ns Ar num
2322 A positive number representing a command number;
2323 command numbers can be displayed with the
2327 A negative decimal number representing the
2328 command that was executed
2331 commands previously.
2332 For example, \-1 is the immediately previous command.
2334 A string indicating the most recently entered command
2335 that begins with that string.
2337 .Ar old Ns = Ns Ar new
2338 operand is not also specified with
2340 the string form of the first operand cannot contain an embedded equal sign.
2344 The following variables affect the execution of
2346 .Bl -tag -width ".Va HISTSIZE"
2348 Name of the editor to use for history editing.
2350 The number of previous commands that are accessible.
2355 or the current job to the foreground.
2356 .It Ic getopts Ar optstring var
2362 command deprecates the older
2365 The first argument should be a series of letters, each possibly
2366 followed by a colon which indicates that the option takes an argument.
2367 The specified variable is set to the parsed option.
2369 the next argument is placed into the shell variable
2371 If an option takes an argument, it is placed into the shell variable
2373 If an invalid option is encountered,
2377 It returns a false value (1) when it encounters the end of the options.
2378 A new set of arguments may be parsed by assigning
2380 .It Ic hash Oo Fl rv Oc Op Ar command ...
2381 The shell maintains a hash table which remembers the locations of commands.
2382 With no arguments whatsoever, the
2384 command prints out the contents of this table.
2388 command removes each specified
2390 from the hash table (unless they are functions) and then locates it.
2395 prints the locations of the commands as it finds them.
2400 command to delete all the entries in the hash table except for functions.
2401 .It Ic jobid Op Ar job
2402 Print the process IDs of the processes in the specified
2406 argument is omitted, use the current job.
2407 .It Ic jobs Oo Fl lps Oc Op Ar job ...
2408 Print information about the specified jobs, or all jobs if no
2411 The information printed includes job ID, status and command name.
2415 option is specified, the PID of each job is also printed.
2418 option is specified, only the process IDs for the process group leaders
2419 are printed, one per line.
2422 option is specified, only the PIDs of the job commands are printed, one per
2425 A built-in equivalent of
2427 that additionally supports sending signals to jobs.
2428 .It Ic local Oo Ar variable ... Oc Op Fl
2433 A built-in equivalent of
2435 .It Ic pwd Op Fl L | P
2436 Print the path of the current directory.
2437 The built-in command may
2438 differ from the program of the same name because the
2439 built-in command remembers what the current directory
2440 is rather than recomputing it each time.
2443 However, if the current directory is
2445 the built-in version of
2447 will continue to print the old name for the directory.
2451 option is specified, symbolic links are resolved.
2454 option is specified, the shell's notion of the current directory
2455 is printed (symbolic links are not resolved).
2456 This is the default.
2457 .It Ic read Oo Fl p Ar prompt Oc Oo
2458 .Fl t Ar timeout Oc Oo Fl er Oc Ar variable ...
2464 and the standard input is a terminal.
2466 read from the standard input.
2467 The trailing newline
2468 is deleted from the line and the line is split as
2469 described in the section on
2470 .Sx White Space Splitting (Field Splitting)\&
2472 the pieces are assigned to the variables in order.
2473 If there are more pieces than variables, the remaining
2474 pieces (along with the characters in
2476 that separated them)
2477 are assigned to the last variable.
2478 If there are more variables than pieces, the remaining
2479 variables are assigned the null string.
2481 Backslashes are treated specially, unless the
2485 If a backslash is followed by
2486 a newline, the backslash and the newline will be
2488 If a backslash is followed by any other
2489 character, the backslash will be deleted and the following
2490 character will be treated as though it were not in
2496 option is specified and the
2498 elapses before a complete line of input is supplied,
2501 command will return an exit status as if terminated by
2503 without assigning any values.
2506 value may optionally be followed by one of
2511 to explicitly specify seconds, minutes or hours.
2512 If none is supplied,
2518 option exists only for backward compatibility with older scripts.
2520 The exit status is 0 on success, 1 on end of file,
2521 between 2 and 128 if an error occurs
2522 and greater than 128 if a trapped signal interrupts
2524 .It Ic readonly Oo Fl p Oc Op Ar name ...
2527 is marked as read only,
2528 so that it cannot be subsequently modified or unset.
2529 The shell allows the value of a variable to be set
2530 at the same time as it is marked read only
2531 by using the following form:
2533 .D1 Ic readonly Ar name Ns = Ns Ar value
2535 With no arguments the
2537 command lists the names of all read only variables.
2540 option is specified, the read-only variables are printed as
2541 .Dq Ic readonly Ar name Ns = Ns Ar value
2542 lines, suitable for re-input to the shell.
2543 .It Ic return Op Ar exitstatus
2547 .It Ic set Oo Fl /+abCEefIimnpTuVvx Oc Oo Fl /+o Ar longname
2548 .Oc Op Fl - Ar arg ...
2551 command performs three different functions:
2554 With no arguments, it lists the values of all shell variables.
2556 If options are given,
2557 either in short form or using the long
2558 .Dq Fl /+o Ar longname
2560 it sets or clears the specified options as described in the section called
2561 .Sx Argument List Processing .
2565 option is specified,
2567 will replace the shell's positional parameters with the subsequent
2569 If no arguments follow the
2572 all the positional parameters will be cleared,
2573 which is equivalent to executing the command
2577 flag may be omitted when specifying arguments to be used
2578 as positional replacement parameters.
2579 This is not recommended,
2580 because the first argument may begin with a dash
2586 command will interpret as a request to enable or disable options.
2588 .It Ic setvar Ar variable value
2589 Assigns the specified
2595 command is intended to be used in functions that
2596 assign values to variables whose names are passed as parameters.
2597 In general it is better to write
2598 .Dq Ar variable Ns = Ns Ar value
2601 .It Ic shift Op Ar n
2602 Shift the positional parameters
2607 A shift sets the value of
2616 decreasing the value of
2619 For portability, shifting if there are zero positional parameters
2620 should be avoided, since the shell may abort.
2622 A built-in equivalent of
2625 Print the amount of time spent executing the shell process and its children.
2626 The first output line shows the user and system times for the shell process
2627 itself, the second one contains the user and system times for the
2629 .It Ic trap Oo Ar action Oc Ar signal ...
2631 Cause the shell to parse and execute
2636 The signals are specified by name or number.
2637 In addition, the pseudo-signal
2639 may be used to specify an
2641 that is performed when the shell terminates.
2644 may be an empty string or a dash
2646 the former causes the specified signal to be ignored
2647 and the latter causes the default action to be taken.
2650 and using only signal numbers is another way to request the default action.
2651 In a subshell or utility environment,
2652 the shell resets trapped (but not ignored) signals to the default action.
2655 command has no effect on signals that were ignored on entry to the shell.
2661 command to display a list of valid signal names.
2663 A null command that returns a 0 (true) exit value.
2664 .It Ic type Op Ar name ...
2667 as a command and print the resolution of the command search.
2668 Possible resolutions are:
2669 shell keyword, alias, special shell builtin, shell builtin, command,
2672 For aliases the alias expansion is printed;
2673 for commands and tracked aliases
2674 the complete pathname of the command is printed.
2675 .It Ic ulimit Oo Fl HSabcdfklmnopstuvw Oc Op Ar limit
2676 Set or display resource limits (see
2680 is specified, the named resource will be set;
2681 otherwise the current resource value will be displayed.
2685 is specified, the hard limits will be set or displayed.
2686 While everybody is allowed to reduce a hard limit,
2687 only the superuser can increase it.
2691 specifies the soft limits instead.
2692 When displaying limits,
2698 The default is to display the soft limits,
2699 and to set both the hard and the soft limits.
2705 command to display all resources.
2708 is not acceptable in this mode.
2710 The remaining options specify which resource value is to be
2711 displayed or modified.
2712 They are mutually exclusive.
2713 .Bl -tag -width indent
2715 The maximum size of socket buffer usage, in bytes.
2716 .It Fl c Ar coredumpsize
2717 The maximal size of core dump files, in 512-byte blocks.
2720 to 0 prevents core dump files from being created.
2721 .It Fl d Ar datasize
2722 The maximal size of the data segment of a process, in kilobytes.
2723 .It Fl f Ar filesize
2724 The maximal size of a file, in 512-byte blocks.
2726 The maximal number of kqueues
2730 .It Fl l Ar lockedmem
2731 The maximal size of memory that can be locked by a process, in
2733 .It Fl m Ar memoryuse
2734 The maximal resident set size of a process, in kilobytes.
2736 The maximal number of descriptors that could be opened by a process.
2738 The maximal number of process-shared locks
2742 .It Fl p Ar pseudoterminals
2743 The maximal number of pseudo-terminals for this user ID.
2744 .It Fl s Ar stacksize
2745 The maximal size of the stack segment, in kilobytes.
2747 The maximal amount of CPU time to be used by each process, in seconds.
2748 .It Fl u Ar userproc
2749 The maximal number of simultaneous processes for this user ID.
2750 .It Fl v Ar virtualmem
2751 The maximal virtual size of a process, in kilobytes.
2753 The maximum amount of swap space reserved or used for this user ID,
2756 .It Ic umask Oo Fl S Oc Op Ar mask
2757 Set the file creation mask (see
2759 to the octal or symbolic (see
2763 If the argument is omitted, the current mask value is printed.
2766 option is specified, the output is symbolic, otherwise the output is octal.
2767 .It Ic unalias Oo Fl a Oc Op Ar name ...
2768 The specified alias names are removed.
2771 is specified, all aliases are removed.
2772 .It Ic unset Oo Fl fv Oc Ar name ...
2773 The specified variables or functions are unset and unexported.
2776 option is specified or no options are given, the
2778 arguments are treated as variable names.
2781 option is specified, the
2783 arguments are treated as function names.
2784 .It Ic wait Op Ar job ...
2785 Wait for each specified
2787 to complete and return the exit status of the last process in the
2792 specified is unknown to the shell, it is treated as if it
2793 were a known job that exited with exit status 127.
2794 If no operands are given, wait for all jobs to complete
2795 and return an exit status of zero.
2797 .Ss Command Line Editing
2800 is being used interactively from a terminal, the current command
2801 and the command history
2805 .Sx Built-in Commands )
2808 command line editing.
2809 This mode uses commands similar
2810 to a subset of those described in the
2828 can be switched between insert mode and command mode by typing
2832 while in command mode will pass the line to the shell.
2835 .Dq Li "set -o emacs"
2838 command can be used to enable a subset of
2840 command line editing features.
2842 The following environment variables affect the execution of
2844 .Bl -tag -width ".Ev LANGXXXXXX"
2846 Initialization file for interactive shells.
2847 .It Ev LANG , Ev LC_*
2849 These are inherited by children of the shell,
2850 and is used in a limited manner by the shell itself.
2852 The previous current directory.
2853 This is used and updated by
2856 An absolute pathname for the current directory,
2857 possibly containing symbolic links.
2858 This is used and updated by the shell.
2860 The default terminal setting for the shell.
2861 This is inherited by children of the shell, and is used in the history
2865 Additionally, environment variables are turned into shell variables
2867 which may affect the shell as described under
2868 .Sx Special Variables .
2870 .Bl -tag -width "/etc/suid_profileXX" -compact
2872 User's login profile.
2874 System login profile.
2877 .It Pa /etc/suid_profile
2878 Privileged shell profile.
2883 cannot be found, the exit status will be 127;
2884 if it cannot be opened for another reason, the exit status will be 126.
2885 Other errors that are detected by the shell, such as a syntax error, will
2886 cause the shell to exit with a non-zero exit status.
2887 If the shell is not an interactive shell, the execution of the shell
2888 file will be aborted.
2889 Otherwise the shell will return the exit status of the last command
2892 builtin is used with a numeric argument, it
2893 will return the argument.
2899 .Xr emacs 1 Pq Pa ports/editors/emacs ,
2914 command, the Thompson shell, appeared in
2916 It was superseded in
2918 by the Bourne shell, which inherited the name
2923 was rewritten in 1989 under the
2925 license after the Bourne shell from
2930 was originally written by
2931 .An Kenneth Almquist .
2935 utility does not recognize multibyte characters other than UTF-8.
2938 does not recognize multibyte characters.