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44 .Nd command interpreter (shell)
47 .Op Fl /+abCEefIimnPpTuVvx
48 .Op Fl /+o Ar longname
54 .Op Fl /+abCEefIimnPpTuVvx
55 .Op Fl /+o Ar longname
62 .Op Fl /+abCEefIimnPpTuVvx
63 .Op Fl /+o Ar longname
69 utility is the standard command interpreter for the system.
70 The current version of
74 specification for the shell.
75 It only supports features
78 plus a few Berkeley extensions.
79 This man page is not intended to be a tutorial nor a complete
80 specification of the shell.
82 The shell is a command that reads lines from
83 either a file or the terminal, interprets them, and
84 generally executes other commands.
85 It is the program that is started when a user logs into the system,
86 although a user can select a different shell with the
90 implements a language that has flow control constructs,
91 a macro facility that provides a variety of features in
92 addition to data storage, along with built-in history and line
94 It incorporates many features to
95 aid interactive use and has the advantage that the interpretative
96 language is common to both interactive and non-interactive
98 That is, commands can be typed directly
99 to the running shell or can be put into a file,
100 which can be executed directly by the shell.
103 .\" XXX This next sentence is incredibly confusing.
105 If no arguments are present and if the standard input of the shell
106 is connected to a terminal
110 the shell is considered an interactive shell.
112 generally prompts before each command and handles programming
113 and command errors differently (as described below).
114 When first starting, the shell inspects argument 0, and
115 if it begins with a dash
117 the shell is also considered a login shell.
118 This is normally done automatically by the system
119 when the user first logs in.
120 A login shell first reads commands
125 in a user's home directory,
127 If the environment variable
129 is set on entry to a shell, or is set in the
131 of a login shell, the shell then subjects its value to parameter expansion
132 and arithmetic expansion and reads commands from the named file.
133 Therefore, a user should place commands that are to be executed only
136 file, and commands that are executed for every shell inside the
141 variable to some file by placing the following line in the file
143 in the home directory,
146 the filename desired:
148 .Dl "ENV=$HOME/.shrc; export ENV"
150 The first non-option argument specified on the command line
151 will be treated as the
152 name of a file from which to read commands (a shell script), and
153 the remaining arguments are set as the positional parameters
157 Otherwise, the shell reads commands
158 from its standard input.
160 Unlike older versions of
164 script is only sourced on invocation of interactive shells.
166 closes a well-known, and sometimes easily exploitable security
167 hole related to poorly thought out
170 .Ss Argument List Processing
171 All of the single letter options to
173 have a corresponding long name,
174 with the exception of
178 These long names are provided next to the single letter options
179 in the descriptions below.
180 The long name for an option may be specified as an argument to the
184 Once the shell is running,
185 the long name for an option may be specified as an argument to the
190 (described later in the section called
191 .Sx Built-in Commands ) .
192 Introducing an option with a dash
202 will stop option processing and will force the remaining
203 words on the command line to be treated as arguments.
208 options do not have long names.
209 They take arguments and are described after the single letter options.
210 .Bl -tag -width indent
211 .It Fl a Li allexport
212 Flag variables for export when assignments are made to them.
214 Enable asynchronous notification of background job
217 .It Fl C Li noclobber
218 Do not overwrite existing files with
223 command line editor (disables the
225 option if it has been set;
226 set automatically when interactive on terminals).
228 Exit immediately if any untested command fails in non-interactive mode.
229 The exit status of a command is considered to be
230 explicitly tested if the command is part of the list used to control
232 .Ic if , elif , while ,
235 if the command is the left
240 operator; or if the command is a pipeline preceded by the
243 If a shell function is executed and its exit status is explicitly
244 tested, all commands of the function are considered to be tested as
247 Disable pathname expansion.
249 A do-nothing option for
252 .It Fl I Li ignoreeof
255 from input when in interactive mode.
256 .It Fl i Li interactive
257 Force the shell to behave interactively.
259 Turn on job control (set automatically when interactive).
261 If not interactive, read commands but do not
263 This is useful for checking the
264 syntax of shell scripts.
266 Change the default for the
272 (logical directory layout)
275 (physical directory layout).
276 .It Fl p Li privileged
277 Turn on privileged mode.
278 This mode is enabled on startup
279 if either the effective user or group ID is not equal to the
280 real user or group ID.
281 Turning this mode off sets the
282 effective user and group IDs to the real user and group IDs.
283 When this mode is enabled for interactive shells, the file
284 .Pa /etc/suid_profile
285 is sourced instead of
289 is sourced, and the contents of the
291 variable are ignored.
293 Read commands from standard input (set automatically
294 if no file arguments are present).
296 no effect when set after the shell has already started
297 running (i.e., when set with the
300 .It Fl T Li trapsasync
301 When waiting for a child, execute traps immediately.
302 If this option is not set,
303 traps are executed after the child exits,
306 This nonstandard option is useful for putting guarding shells around
307 children that block signals.
308 The surrounding shell may kill the child
309 or it may just return control to the tty and leave the child alone,
311 .Bd -literal -offset indent
312 sh -T -c "trap 'exit 1' 2 ; some-blocking-program"
315 Write a message to standard error when attempting
316 to expand a variable, a positional parameter or
317 the special parameter
319 that is not set, and if the
320 shell is not interactive, exit immediately.
324 command line editor (disables
328 The shell writes its input to standard error
330 Useful for debugging.
333 (preceded by the value of the
335 variable subjected to parameter expansion and arithmetic expansion)
336 to standard error before it is executed.
337 Useful for debugging.
338 .It "\ \ " Em tabcomplete
339 Enables filename completion in the command line editor.
340 Typing a tab character will extend the current input word to match a
342 If more than one filename matches it is only extended to be the common prefix.
343 Typing a second tab character will list all the matching names.
344 Turned on by default in an interactive shell.
349 option causes the commands to be read from the
351 operand instead of from the standard input.
352 Keep in mind that this option only accepts a single string as its
353 argument, hence multi-word strings must be quoted.
357 option takes as its only argument the long name of an option
358 to be enabled or disabled.
359 For example, the following two invocations of
361 both enable the built-in
364 .Bd -literal -offset indent
369 If used without an argument, the
371 option displays the current option settings in a human-readable format.
374 is used without an argument, the current option settings are output
375 in a format suitable for re-input into the shell.
376 .Ss Lexical Structure
377 The shell reads input in terms of lines from a file and breaks
378 it up into words at whitespace (blanks and tabs), and at
382 which are special to the shell.
383 There are two types of operators: control operators and
384 redirection operators (their meaning is discussed later).
385 The following is a list of valid operators:
386 .Bl -tag -width indent
387 .It Control operators:
388 .Bl -column "XXX" "XXX" "XXX" "XXX" "XXX" -offset center -compact
389 .It Li & Ta Li && Ta Li \&( Ta Li \&) Ta Li \en
390 .It Li ;; Ta Li ;& Ta Li \&; Ta Li \&| Ta Li ||
392 .It Redirection operators:
393 .Bl -column "XXX" "XXX" "XXX" "XXX" "XXX" -offset center -compact
394 .It Li < Ta Li > Ta Li << Ta Li >> Ta Li <>
395 .It Li <& Ta Li >& Ta Li <<- Ta Li >| Ta \&
401 introduces a comment if used at the beginning of a word.
402 The word starting with
404 and the rest of the line are ignored.
408 characters (character code 0) are not allowed in shell input.
410 Quoting is used to remove the special meaning of certain characters
411 or words to the shell, such as operators, whitespace, keywords,
414 There are four types of quoting: matched single quotes,
415 dollar-single quotes,
416 matched double quotes, and backslash.
417 .Bl -tag -width indent
419 Enclosing characters in single quotes preserves the literal
420 meaning of all the characters (except single quotes, making
421 it impossible to put single-quotes in a single-quoted string).
422 .It Dollar-Single Quotes
423 Enclosing characters between
427 preserves the literal meaning of all characters
428 except backslashes and single quotes.
429 A backslash introduces a C-style escape sequence:
430 .Bl -tag -width xUnnnnnnnn
432 Alert (ring the terminal bell)
436 The control character denoted by
442 is a backslash, it must be doubled.
464 The byte whose octal value is
466 (one to three digits)
468 The byte whose hexadecimal value is
470 (one or more digits only the last two of which are used)
472 The Unicode code point
474 (four hexadecimal digits)
475 .It \eU Ns Ar nnnnnnnn
476 The Unicode code point
478 (eight hexadecimal digits)
481 The sequences for Unicode code points are currently only useful with
483 They reject code point 0 and UTF-16 surrogates.
485 If an escape sequence would produce a byte with value 0,
486 that byte and the rest of the string until the matching single-quote
489 Any other string starting with a backslash is an error.
491 Enclosing characters within double quotes preserves the literal
492 meaning of all characters except dollar sign
498 The backslash inside double quotes is historically weird.
499 It remains literal unless it precedes the following characters,
500 which it serves to quote:
502 .Bl -column "XXX" "XXX" "XXX" "XXX" "XXX" -offset center -compact
503 .It Li $ Ta Li ` Ta Li \&" Ta Li \e Ta Li \en
506 A backslash preserves the literal meaning of the following
507 character, with the exception of the newline character
509 A backslash preceding a newline is treated as a line continuation.
512 Keywords or reserved words are words that have special meaning to the
513 shell and are recognized at the beginning of a line and
514 after a control operator.
515 The following are keywords:
516 .Bl -column "doneXX" "elifXX" "elseXX" "untilXX" "whileX" -offset center
517 .It Li \&! Ta { Ta } Ta Ic case Ta Ic do
518 .It Ic done Ta Ic elif Ta Ic else Ta Ic esac Ta Ic fi
519 .It Ic for Ta Ic if Ta Ic then Ta Ic until Ta Ic while
522 An alias is a name and corresponding value set using the
525 Wherever the command word of a simple command may occur,
526 and after checking for keywords if a keyword may occur, the shell
527 checks the word to see if it matches an alias.
528 If it does, it replaces it in the input stream with its value.
529 For example, if there is an alias called
541 Aliases provide a convenient way for naive users to
542 create shorthands for commands without having to learn how
543 to create functions with arguments.
544 Using aliases in scripts is discouraged
545 because the command that defines them must be executed
546 before the code that uses them is parsed.
547 This is fragile and not portable.
549 An alias name may be escaped in a command line, so that it is not
550 replaced by its alias value, by using quoting characters within or
551 adjacent to the alias name.
552 This is most often done by prefixing
553 an alias name with a backslash to execute a function, built-in, or
554 normal program with the same name.
559 The shell interprets the words it reads according to a
560 language, the specification of which is outside the scope
561 of this man page (refer to the BNF in the
564 Essentially though, a line is read and if
565 the first word of the line (or after a control operator)
566 is not a keyword, then the shell has recognized a
568 Otherwise, a complex command or some
569 other special construct may have been recognized.
571 If a simple command has been recognized, the shell performs
572 the following actions:
575 Leading words of the form
577 are stripped off and assigned to the environment of
579 Redirection operators and
580 their arguments (as described below) are stripped
581 off and saved for processing.
583 The remaining words are expanded as described in
585 .Sx Word Expansions ,
586 and the first remaining word is considered the command
587 name and the command is located.
589 words are considered the arguments of the command.
590 If no command name resulted, then the
592 variable assignments recognized in 1) affect the
595 Redirections are performed as described in
599 Redirections are used to change where a command reads its input
601 In general, redirections open, close, or
602 duplicate an existing reference to a file.
604 used for redirection is:
606 .D1 Oo Ar n Oc Ar redir-op file
610 is one of the redirection operators mentioned
612 The following gives some examples of how these
613 operators can be used.
614 Note that stdin and stdout are commonly used abbreviations
615 for standard input and standard output respectively.
616 .Bl -tag -width "1234567890XX" -offset indent
617 .It Oo Ar n Oc Ns Li > Ar file
618 redirect stdout (or file descriptor
622 .It Oo Ar n Oc Ns Li >| Ar file
623 same as above, but override the
626 .It Oo Ar n Oc Ns Li >> Ar file
627 append stdout (or file descriptor
631 .It Oo Ar n Oc Ns Li < Ar file
632 redirect stdin (or file descriptor
636 .It Oo Ar n Oc Ns Li <> Ar file
637 redirect stdin (or file descriptor
641 .It Oo Ar n1 Oc Ns Li <& Ns Ar n2
642 duplicate stdin (or file descriptor
646 .It Oo Ar n Oc Ns Li <&-
647 close stdin (or file descriptor
649 .It Oo Ar n1 Oc Ns Li >& Ns Ar n2
650 duplicate stdout (or file descriptor
654 .It Oo Ar n Oc Ns Li >&-
655 close stdout (or file descriptor
659 The following redirection is often called a
661 .Bd -unfilled -offset indent
662 .Oo Ar n Oc Ns Li << Ar delimiter
668 All the text on successive lines up to the delimiter is
669 saved away and made available to the command on standard
670 input, or file descriptor
675 as specified on the initial line is quoted, then the
677 is treated literally, otherwise the text is subjected to
678 parameter expansion, command substitution, and arithmetic
679 expansion (as described in the section on
680 .Sx Word Expansions ) .
689 .Ss Search and Execution
690 There are three types of commands: shell functions,
691 built-in commands, and normal programs.
692 The command is searched for (by name) in that order.
693 The three types of commands are all executed in a different way.
695 When a shell function is executed, all of the shell positional
698 which remains unchanged) are
699 set to the arguments of the shell function.
700 The variables which are explicitly placed in the environment of
701 the command (by placing assignments to them before the
702 function name) are made local to the function and are set
704 Then the command given in the function definition is executed.
705 The positional parameters are restored to their original values
706 when the command completes.
707 This all occurs within the current shell.
709 Shell built-in commands are executed internally to the shell, without
710 spawning a new process.
711 There are two kinds of built-in commands: regular and special.
712 Assignments before special builtins persist after they finish
713 executing and assignment errors, redirection errors and certain
714 operand errors cause a script to be aborted.
715 Special builtins cannot be overridden with a function.
716 Both regular and special builtins can affect the shell in ways
717 normal programs cannot.
719 Otherwise, if the command name does not match a function
720 or built-in command, the command is searched for as a normal
721 program in the file system (as described in the next section).
722 When a normal program is executed, the shell runs the program,
723 passing the arguments and the environment to the program.
724 If the program is not a normal executable file
725 (i.e., if it does not begin with the
735 but appears to be a text file,
736 the shell will run a new instance of
740 Note that previous versions of this document
741 and the source code itself misleadingly and sporadically
742 refer to a shell script without a magic number
744 .Dq "shell procedure" .
746 When locating a command, the shell first looks to see if
747 it has a shell function by that name.
749 built-in command by that name.
750 If a built-in command is not found,
751 one of two things happen:
754 Command names containing a slash are simply executed without
755 performing any searches.
757 The shell searches each entry in the
760 in turn for the command.
763 variable should be a series of
764 entries separated by colons.
765 Each entry consists of a
767 The current directory
768 may be indicated implicitly by an empty directory name,
769 or explicitly by a single period.
771 .Ss Command Exit Status
772 Each command has an exit status that can influence the behavior
773 of other shell commands.
774 The paradigm is that a command exits
775 with zero for normal or success, and non-zero for failure,
776 error, or a false indication.
777 The man page for each command
778 should indicate the various exit codes and what they mean.
779 Additionally, the built-in commands return exit codes, as does
780 an executed shell function.
782 If a command is terminated by a signal, its exit status is 128 plus
784 Signal numbers are defined in the header file
787 Complex commands are combinations of simple commands
788 with control operators or keywords, together creating a larger complex
790 More generally, a command is one of the following:
791 .Bl -item -offset indent
797 list or compound-list
804 Unless otherwise stated, the exit status of a command is
805 that of the last simple command executed by the command.
807 A pipeline is a sequence of one or more commands separated
808 by the control operator
810 The standard output of all but
811 the last command is connected to the standard input
813 The standard output of the last
814 command is inherited from the shell, as usual.
816 The format for a pipeline is:
818 .D1 Oo Li \&! Oc Ar command1 Op Li \&| Ar command2 ...
820 The standard output of
822 is connected to the standard input of
824 The standard input, standard output, or
825 both of a command is considered to be assigned by the
826 pipeline before any redirection specified by redirection
827 operators that are part of the command.
829 Note that unlike some other shells,
831 executes each process in a pipeline with more than one command
832 in a subshell environment and as a child of the
836 If the pipeline is not in the background (discussed later),
837 the shell waits for all commands to complete.
841 does not precede the pipeline, the
842 exit status is the exit status of the last command specified
844 Otherwise, the exit status is the logical
845 NOT of the exit status of the last command.
847 the last command returns zero, the exit status is 1; if
848 the last command returns greater than zero, the exit status
851 Because pipeline assignment of standard input or standard
852 output or both takes place before redirection, it can be
853 modified by redirection.
856 .Dl "command1 2>&1 | command2"
858 sends both the standard output and standard error of
860 to the standard input of
865 or newline terminator causes the preceding
867 (described below in the section called
868 .Sx Short-Circuit List Operators )
869 to be executed sequentially;
872 causes asynchronous execution of the preceding AND-OR-list.
873 .Ss Background Commands (&)
874 If a command is terminated by the control operator ampersand
876 the shell executes the command in a subshell environment (see
877 .Sx Grouping Commands Together
878 below) and asynchronously;
879 the shell does not wait for the command to finish
880 before executing the next command.
882 The format for running a command in background is:
884 .D1 Ar command1 Li & Op Ar command2 Li & Ar ...
886 If the shell is not interactive, the standard input of an
887 asynchronous command is set to
889 .Ss Lists (Generally Speaking)
890 A list is a sequence of zero or more commands separated by
891 newlines, semicolons, or ampersands,
892 and optionally terminated by one of these three characters.
894 list are executed in the order they are written.
895 If command is followed by an ampersand, the shell starts the
896 command and immediately proceeds onto the next command;
897 otherwise it waits for the command to terminate before
898 proceeding to the next one.
899 .Ss Short-Circuit List Operators
903 are AND-OR list operators.
905 executes the first command, and then executes the second command
906 if the exit status of the first command is zero.
908 is similar, but executes the second command if the exit
909 status of the first command is nonzero.
913 both have the same priority.
914 .Ss Flow-Control Constructs (if, while, for, case)
918 .Bd -unfilled -offset indent -compact
922 .Ic then Ar list Oc Ar ...
930 .Bd -unfilled -offset indent -compact
936 The two lists are executed repeatedly while the exit status of the
940 command is similar, but has the word
945 repeat until the exit status of the first list is zero.
950 .Bd -unfilled -offset indent -compact
951 .Ic for Ar variable Op Ic in Ar word ...
958 and the following words are omitted,
961 The words are expanded, and then the list is executed
962 repeatedly with the variable set to each word in turn.
967 commands may be replaced with
977 .D1 Ic break Op Ar num
978 .D1 Ic continue Op Ar num
982 command terminates the
991 command continues with the next iteration of the innermost loop.
992 These are implemented as special built-in commands.
997 .Bd -unfilled -offset indent -compact
998 .Ic case Ar word Ic in
999 .Ar pattern Ns Li ) Ar list Li ;;
1004 The pattern can actually be one or more patterns
1011 Tilde expansion, parameter expansion, command substitution,
1012 arithmetic expansion and quote removal are applied to the word.
1013 Then, each pattern is expanded in turn using tilde expansion,
1014 parameter expansion, command substitution and arithmetic expansion and
1015 the expanded form of the word is checked against it.
1016 If a match is found, the corresponding list is executed.
1017 If the selected list is terminated by the control operator
1021 execution continues with the next list,
1022 continuing until a list terminated with
1027 The exit code of the
1029 command is the exit code of the last command executed in the list or
1030 zero if no patterns were matched.
1031 .Ss Grouping Commands Together
1032 Commands may be grouped by writing either
1034 .D1 Li \&( Ns Ar list Ns Li \%)
1038 .D1 Li { Ar list Ns Li \&; }
1040 The first form executes the commands in a subshell environment.
1041 A subshell environment has its own copy of:
1044 The current working directory as set by
1047 The file creation mask as set by
1050 References to open files.
1057 Positional parameters and variables.
1066 These are copied from the parent shell environment,
1067 except that trapped (but not ignored) signals are reset to the default action
1068 and known jobs are cleared.
1069 Any changes do not affect the parent shell environment.
1071 A subshell environment may be implemented as a child process or differently.
1072 If job control is enabled in an interactive shell,
1073 commands grouped in parentheses can be suspended and continued as a unit.
1075 The second form never forks another shell,
1076 so it is slightly more efficient.
1077 Grouping commands together this way allows the user to
1078 redirect their output as though they were one program:
1079 .Bd -literal -offset indent
1080 { echo -n "hello"; echo " world"; } > greeting
1083 The syntax of a function definition is
1085 .D1 Ar name Li \&( \&) Ar command
1087 A function definition is an executable statement; when
1088 executed it installs a function named
1091 exit status of zero.
1100 Variables may be declared to be local to a function by
1104 This should appear as the first statement of a function,
1107 .D1 Ic local Oo Ar variable ... Oc Op Fl
1111 command is implemented as a built-in command.
1113 When a variable is made local, it inherits the initial
1114 value and exported and readonly flags from the variable
1115 with the same name in the surrounding scope, if there is
1117 Otherwise, the variable is initially unset.
1119 uses dynamic scoping, so that if the variable
1121 is made local to function
1123 which then calls function
1125 references to the variable
1129 will refer to the variable
1133 not to the global variable named
1136 The only special parameter that can be made local is
1140 local causes any shell options that are
1143 command inside the function to be
1144 restored to their original values when the function
1151 .D1 Ic return Op Ar exitstatus
1153 It terminates the current executional scope, returning from the previous
1154 nested function, sourced script, or shell instance, in that order.
1157 command is implemented as a special built-in command.
1158 .Ss Variables and Parameters
1159 The shell maintains a set of parameters.
1161 denoted by a name is called a variable.
1163 the shell turns all the environment variables into shell
1165 New variables can be set using the form
1167 .D1 Ar name Ns = Ns Ar value
1169 Variables set by the user must have a name consisting solely
1170 of alphabetics, numerics, and underscores.
1171 The first letter of a variable name must not be numeric.
1172 A parameter can also be denoted by a number
1173 or a special character as explained below.
1175 Assignments are expanded differently from other words:
1176 tilde expansion is also performed after the equals sign and after any colon
1177 and usernames are also terminated by colons,
1178 and field splitting and pathname expansion are not performed.
1180 This special expansion applies not only to assignments that form a simple
1181 command by themselves or precede a command word,
1182 but also to words passed to the
1187 built-in commands that have this form.
1188 For this, the builtin's name must be literal
1189 (not the result of an expansion)
1190 and may optionally be preceded by one or more literal instances of
1193 .Ss Positional Parameters
1194 A positional parameter is a parameter denoted by a number greater than zero.
1195 The shell sets these initially to the values of its command line
1196 arguments that follow the name of the shell script.
1199 built-in command can also be used to set or reset them.
1200 .Ss Special Parameters
1201 Special parameters are parameters denoted by a single special character
1203 They are shown in the following list, exactly as they would appear in input
1204 typed by the user or in the source of a shell script.
1207 Expands to the positional parameters, starting from one.
1209 the expansion occurs within a double-quoted string
1210 it expands to a single field with the value of each parameter
1211 separated by the first character of the
1218 Expands to the positional parameters, starting from one.
1220 the expansion occurs within double-quotes, each positional
1221 parameter expands as a separate argument.
1222 If there are no positional parameters, the
1225 generates zero arguments, even when
1228 What this basically means, for example, is
1241 .Bd -literal -offset indent
1245 Expands to the number of positional parameters.
1247 Expands to the exit status of the most recent pipeline.
1249 (hyphen) Expands to the current option flags (the single-letter
1250 option names concatenated into a string) as specified on
1253 built-in command, or implicitly
1256 Expands to the process ID of the invoked shell.
1258 retains the same value of
1262 Expands to the process ID of the most recent background
1263 command executed from the current shell.
1265 pipeline, the process ID is that of the last command in the
1267 If this parameter is referenced, the shell will remember
1268 the process ID and its exit status until the
1270 built-in command reports completion of the process.
1272 (zero) Expands to the name of the shell script if passed on the command line,
1275 operand if given (with
1277 or otherwise argument 0 passed to the shell.
1279 .Ss Special Variables
1280 The following variables are set by the shell or
1281 have special meaning to it:
1282 .Bl -tag -width ".Va HISTSIZE"
1284 The search path used with the
1288 The fallback editor used with the
1291 If not set, the default editor is
1294 The default editor used with the
1298 The number of previous commands that are accessible.
1300 The user's home directory,
1301 used in tilde expansion and as a default directory for the
1305 Input Field Separators.
1306 The default value is
1312 This default also applies if
1314 is unset, but not if it is set to the empty string.
1316 .Sx White Space Splitting
1317 section for more details.
1319 The current line number in the script or function.
1321 The name of a mail file, that will be checked for the arrival of new
1328 separated list of file names, for the shell to check for incoming
1330 This variable overrides the
1333 There is a maximum of 10 mailboxes that can be monitored at once.
1335 The default search path for executables.
1338 section for details.
1340 The parent process ID of the invoked shell.
1341 This is set at startup
1342 unless this variable is in the environment.
1343 A later change of parent process ID is not reflected.
1344 A subshell retains the same value of
1347 The primary prompt string, which defaults to
1349 unless you are the superuser, in which case it defaults to
1352 The secondary prompt string, which defaults to
1355 The prefix for the trace output (if
1362 This clause describes the various expansions that are
1364 Not all expansions are performed on
1365 every word, as explained later.
1367 Tilde expansions, parameter expansions, command substitutions,
1368 arithmetic expansions, and quote removals that occur within
1369 a single word expand to a single field.
1371 splitting or pathname expansion that can create multiple
1372 fields from a single word.
1373 The single exception to this rule is
1374 the expansion of the special parameter
1376 within double-quotes,
1377 as was described above.
1379 The order of word expansion is:
1382 Tilde Expansion, Parameter Expansion, Command Substitution,
1383 Arithmetic Expansion (these all occur at the same time).
1385 Field Splitting is performed on fields generated by step (1)
1390 Pathname Expansion (unless the
1392 option is in effect).
1399 character is used to introduce parameter expansion, command
1400 substitution, or arithmetic expansion.
1401 .Ss Tilde Expansion (substituting a user's home directory)
1402 A word beginning with an unquoted tilde character
1405 subjected to tilde expansion.
1406 All the characters up to a slash
1408 or the end of the word are treated as a username
1409 and are replaced with the user's home directory.
1411 username is missing (as in
1413 the tilde is replaced with the value of the
1415 variable (the current user's home directory).
1416 .Ss Parameter Expansion
1417 The format for parameter expansion is as follows:
1419 .D1 Li ${ Ns Ar expression Ns Li }
1423 consists of all characters until the matching
1427 escaped by a backslash or within a single-quoted or double-quoted
1428 string, and characters in
1429 embedded arithmetic expansions, command substitutions, and variable
1430 expansions, are not examined in determining the matching
1432 If the variants with
1438 occur within a double-quoted string,
1439 as an extension there may be unquoted parts
1440 (via double-quotes inside the expansion);
1442 within such parts are also not examined in determining the matching
1445 The simplest form for parameter expansion is:
1447 .D1 Li ${ Ns Ar parameter Ns Li }
1449 The value, if any, of
1453 The parameter name or symbol can be enclosed in braces, which are
1454 optional except for positional parameters with more than one digit or
1455 when parameter is followed by a character that could be interpreted as
1457 If a parameter expansion occurs inside double-quotes:
1460 Field splitting is not performed on the results of the
1461 expansion, with the exception of the special parameter
1464 Pathname expansion is not performed on the results of the
1468 In addition, a parameter expansion can be modified by using one of the
1470 .Bl -tag -width indent
1471 .It Li ${ Ns Ar parameter Ns Li :- Ns Ar word Ns Li }
1475 is unset or null, the expansion of
1477 is substituted; otherwise, the value of
1480 .It Li ${ Ns Ar parameter Ns Li := Ns Ar word Ns Li }
1481 Assign Default Values.
1484 is unset or null, the expansion of
1494 does not prevent field splitting or pathname expansion.
1495 Only variables, not positional
1496 parameters or special parameters, can be
1497 assigned in this way.
1498 .It Li ${ Ns Ar parameter Ns Li :? Ns Oo Ar word Oc Ns Li }
1499 Indicate Error if Null or Unset.
1502 is unset or null, the expansion of
1504 (or a message indicating it is unset if
1506 is omitted) is written to standard
1507 error and the shell exits with a nonzero
1509 Otherwise, the value of
1513 interactive shell need not exit.
1514 .It Li ${ Ns Ar parameter Ns Li :+ Ns Ar word Ns Li }
1515 Use Alternate Value.
1518 is unset or null, null is substituted;
1519 otherwise, the expansion of
1524 In the parameter expansions shown previously, use of the colon in the
1525 format results in a test for a parameter that is unset or null; omission
1526 of the colon results in a test for a parameter that is only unset.
1530 inherits the type of quoting
1531 (unquoted, double-quoted or here-document)
1532 from the surroundings,
1533 with the exception that a backslash that quotes a closing brace is removed
1534 during quote removal.
1535 .Bl -tag -width indent
1536 .It Li ${# Ns Ar parameter Ns Li }
1538 The length in characters of
1543 The following four varieties of parameter expansion provide for substring
1545 In each case, pattern matching notation
1547 .Sx Shell Patterns ) ,
1548 rather than regular expression notation,
1549 is used to evaluate the patterns.
1550 If parameter is one of the special parameters
1554 the result of the expansion is unspecified.
1555 Enclosing the full parameter expansion string in double-quotes does not
1556 cause the following four varieties of pattern characters to be quoted,
1557 whereas quoting characters within the braces has this effect.
1558 .Bl -tag -width indent
1559 .It Li ${ Ns Ar parameter Ns Li % Ns Ar word Ns Li }
1560 Remove Smallest Suffix Pattern.
1563 is expanded to produce a pattern.
1565 parameter expansion then results in
1567 with the smallest portion of the
1568 suffix matched by the pattern deleted.
1569 .It Li ${ Ns Ar parameter Ns Li %% Ns Ar word Ns Li }
1570 Remove Largest Suffix Pattern.
1573 is expanded to produce a pattern.
1575 parameter expansion then results in
1577 with the largest portion of the
1578 suffix matched by the pattern deleted.
1579 .It Li ${ Ns Ar parameter Ns Li # Ns Ar word Ns Li }
1580 Remove Smallest Prefix Pattern.
1583 is expanded to produce a pattern.
1585 parameter expansion then results in
1587 with the smallest portion of the
1588 prefix matched by the pattern deleted.
1589 .It Li ${ Ns Ar parameter Ns Li ## Ns Ar word Ns Li }
1590 Remove Largest Prefix Pattern.
1593 is expanded to produce a pattern.
1595 parameter expansion then results in
1597 with the largest portion of the
1598 prefix matched by the pattern deleted.
1600 .Ss Command Substitution
1601 Command substitution allows the output of a command to be substituted in
1602 place of the command name itself.
1603 Command substitution occurs when
1604 the command is enclosed as follows:
1606 .D1 Li $( Ns Ar command Ns Li )\&
1608 or the backquoted version:
1610 .D1 Li ` Ns Ar command Ns Li `
1612 The shell expands the command substitution by executing command
1613 and replacing the command substitution
1614 with the standard output of the command,
1615 removing sequences of one or more newlines at the end of the substitution.
1616 Embedded newlines before the end of the output are not removed;
1617 however, during field splitting, they may be translated into spaces
1618 depending on the value of
1620 and the quoting that is in effect.
1621 The command is executed in a subshell environment,
1622 except that the built-in commands
1627 return information about the parent shell environment
1630 returns information about the same process
1631 if they are the only command in a command substitution.
1632 .Ss Arithmetic Expansion
1633 Arithmetic expansion provides a mechanism for evaluating an arithmetic
1634 expression and substituting its value.
1635 The format for arithmetic expansion is as follows:
1637 .D1 Li $(( Ns Ar expression Ns Li ))
1641 is treated as if it were in double-quotes, except
1642 that a double-quote inside the expression is not treated specially.
1644 shell expands all tokens in the
1646 for parameter expansion,
1647 command substitution,
1648 arithmetic expansion
1651 The allowed expressions are a subset of C expressions,
1653 .Bl -tag -width "Variables" -offset indent
1655 All values are of type
1658 Decimal, octal (starting with
1660 and hexadecimal (starting with
1664 Shell variables can be read and written
1665 and contain integer constants.
1668 .It Binary operators
1669 .Li "* / % + - << >> < <= > >= == != & ^ | && ||"
1670 .It Assignment operators
1671 .Li "= += -= *= /= %= <<= >>= &= ^= |="
1672 .It Conditional operator
1676 The result of the expression is substituted in decimal.
1677 .Ss White Space Splitting (Field Splitting)
1678 In certain contexts,
1679 after parameter expansion, command substitution, and
1680 arithmetic expansion the shell scans the results of
1681 expansions and substitutions that did not occur in double-quotes for
1682 field splitting and multiple fields can result.
1693 are treated differently from other characters in
1698 at the beginning or end of a word is discarded.
1700 Subsequently, a field is delimited by either
1703 a non-whitespace character in
1705 with any whitespace in
1709 one or more whitespace characters in
1713 If a word ends with a non-whitespace character in
1715 there is no empty field after this character.
1717 If no field is delimited, the word is discarded.
1718 In particular, if a word consists solely of an unquoted substitution
1719 and the result of the substitution is null,
1720 it is removed by field splitting even if
1723 .Ss Pathname Expansion (File Name Generation)
1727 file name generation is performed
1728 after word splitting is complete.
1730 viewed as a series of patterns, separated by slashes.
1732 process of expansion replaces the word with the names of
1733 all existing files whose names can be formed by replacing
1734 each pattern with a string that matches the specified pattern.
1735 There are two restrictions on this: first, a pattern cannot match
1736 a string containing a slash, and second,
1737 a pattern cannot match a string starting with a period
1738 unless the first character of the pattern is a period.
1739 The next section describes the patterns used for
1741 the four varieties of parameter expansion for substring processing and the
1745 A pattern consists of normal characters, which match themselves,
1746 and meta-characters.
1747 The meta-characters are
1752 These characters lose their special meanings if they are quoted.
1753 When command or variable substitution is performed and the dollar sign
1754 or back quotes are not double-quoted, the value of the
1755 variable or the output of the command is scanned for these
1756 characters and they are turned into meta-characters.
1760 matches any string of characters.
1763 matches any single character.
1766 introduces a character class.
1767 The end of the character class is indicated by a
1775 rather than introducing a character class.
1776 A character class matches any of the characters between the square brackets.
1777 A locale-dependent range of characters may be specified using a minus sign.
1778 A named class of characters (see
1780 may be specified by surrounding the name with
1785 .Ql \&[\&[:alpha:\&]\&]
1786 is a shell pattern that matches a single letter.
1787 The character class may be complemented by making an exclamation point
1789 the first character of the character class.
1792 has the same effect but is non-standard.
1796 in a character class, make it the first character listed
1804 make it the first or last character listed.
1805 .Ss Built-in Commands
1806 This section lists the built-in commands.
1807 .Bl -tag -width indent
1809 A null command that returns a 0 (true) exit value.
1811 The commands in the specified file are read and executed by the shell.
1814 command may be used to return to the
1821 characters, it is used as is.
1822 Otherwise, the shell searches the
1825 If it is not found in the
1827 it is sought in the current working directory.
1829 A built-in equivalent of
1831 .It Ic alias Oo Ar name Ns Oo = Ns Ar string Oc Ar ... Oc
1833 .Ar name Ns = Ns Ar string
1834 is specified, the shell defines the alias
1840 is specified, the value of the alias
1843 With no arguments, the
1845 built-in command prints the names and values of all defined aliases
1848 Alias values are written with appropriate quoting so that they are
1849 suitable for re-input to the shell.
1853 .It Ic bg Op Ar job ...
1854 Continue the specified jobs
1855 (or the current job if no jobs are given)
1857 .It Ic bind Oo Fl aeklrsv Oc Oo Ar key Oo Ar command Oc Oc
1858 List or alter key bindings for the line editor.
1859 This command is documented in
1861 .It Ic break Op Ar num
1863 .Sx Flow-Control Constructs
1865 .It Ic builtin Ar cmd Op Ar arg ...
1866 Execute the specified built-in command,
1868 This is useful when the user wishes to override a shell function
1869 with the same name as a built-in command.
1870 .It Ic cd Oo Fl L | P Oc Oo Fl e Oc Op Ar directory
1871 Switch to the specified
1873 or to the directory specified in the
1875 environment variable if no
1884 then the directories listed in the
1887 searched for the specified
1891 is unset, the current directory is searched.
1894 is the same as that of
1896 In an interactive shell,
1899 command will print out the name of the directory
1900 that it actually switched to
1901 if this is different from the name that the user gave.
1902 These may be different either because the
1904 mechanism was used or because a symbolic link was crossed.
1908 option is specified,
1910 is handled physically and symbolic links are resolved before
1912 components are processed.
1915 option is specified,
1917 is handled logically.
1918 This is the default.
1924 to return exit status 1 if the full pathname of the new directory
1925 cannot be determined reliably or at all.
1926 Normally this is not considered an error,
1927 although a warning is printed.
1932 .It Ic command Oo Fl p Oc Op Ar utility Op Ar argument ...
1933 .It Ic command Oo Fl p Oc Fl v Ar utility
1934 .It Ic command Oo Fl p Oc Fl V Ar utility
1935 The first form of invocation executes the specified
1937 ignoring shell functions in the search.
1940 is a special builtin,
1941 it is executed as if it were a regular builtin.
1945 option is specified, the command search is performed using a
1948 that is guaranteed to find all of the standard utilities.
1952 option is specified,
1954 is not executed but a description of its interpretation by the shell is
1956 For ordinary commands the output is the path name; for shell built-in
1957 commands, shell functions and keywords only the name is written.
1958 Aliases are printed as
1959 .Dq Ic alias Ar name Ns = Ns Ar value .
1963 option is identical to
1965 except for the output.
1967 .Dq Ar utility Ic is Ar description
1973 a special shell builtin,
1980 .It Ic continue Op Ar num
1982 .Sx Flow-Control Constructs
1984 .It Ic echo Oo Fl e | n Oc Op Ar string ...
1985 Print a space-separated list of the arguments to the standard output
1986 and append a newline character.
1987 .Bl -tag -width indent
1989 Suppress the output of the trailing newline.
1991 Process C-style backslash escape sequences.
1994 command understands the following character escapes:
1995 .Bl -tag -width indent
1997 Alert (ring the terminal bell)
2001 Suppress the trailing newline (this has the side-effect of truncating the
2002 line if it is not the last character)
2020 (Zero) The character whose octal value is
2026 is not enclosed in quotes then the backslash itself must be escaped
2027 with a backslash to protect it from the shell.
2029 .Bd -literal -offset indent
2038 $ echo -e a\e\e\e\eb
2047 options may be specified.
2048 .It Ic eval Ar string ...
2049 Concatenate all the arguments with spaces.
2050 Then re-parse and execute the command.
2051 .It Ic exec Op Ar command Op Ar arg ...
2055 the shell process is replaced with the specified program
2056 (which must be a real program, not a shell built-in command or function).
2057 Any redirections on the
2059 command are marked as permanent,
2060 so that they are not undone when the
2063 .It Ic exit Op Ar exitstatus
2064 Terminate the shell process.
2068 it is used as the exit status of the shell.
2069 Otherwise, if the shell is executing an
2071 trap, the exit status of the last command before the trap is used;
2072 if the shell is executing a trap for a signal,
2073 the shell exits by resending the signal to itself.
2074 Otherwise, the exit status of the preceding command is used.
2075 The exit status should be an integer between 0 and 255.
2076 .It Ic export Ar name ...
2077 .It Ic export Op Fl p
2078 The specified names are exported so that they will
2079 appear in the environment of subsequent commands.
2080 The only way to un-export a variable is to
2083 The shell allows the value of a variable to be set
2084 at the same time as it is exported by writing
2086 .D1 Ic export Ar name Ns = Ns Ar value
2088 With no arguments the
2090 command lists the names
2091 of all exported variables.
2094 option is specified, the exported variables are printed as
2095 .Dq Ic export Ar name Ns = Ns Ar value
2096 lines, suitable for re-input to the shell.
2098 A null command that returns a non-zero (false) exit value.
2099 .It Ic fc Oo Fl e Ar editor Oc Op Ar first Op Ar last
2100 .It Ic fc Fl l Oo Fl nr Oc Op Ar first Op Ar last
2101 .It Ic fc Fl s Oo Ar old Ns = Ns Ar new Oc Op Ar first
2104 built-in command lists, or edits and re-executes,
2105 commands previously entered to an interactive shell.
2106 .Bl -tag -width indent
2108 Use the editor named by
2110 to edit the commands.
2113 string is a command name,
2114 subject to search via the
2119 variable is used as a default when
2124 is null or unset, the value of the
2131 is used as the editor.
2133 List the commands rather than invoking
2135 The commands are written in the
2136 sequence indicated by the
2140 operands, as affected by
2142 with each command preceded by the command number.
2144 Suppress command numbers when listing with
2147 Reverse the order of the commands listed
2156 Re-execute the command without invoking an editor.
2159 Select the commands to list or edit.
2160 The number of previous commands that can be accessed
2161 are determined by the value of the
2168 or both are one of the following:
2169 .Bl -tag -width indent
2170 .It Oo Cm + Oc Ns Ar num
2171 A positive number representing a command number;
2172 command numbers can be displayed with the
2176 A negative decimal number representing the
2177 command that was executed
2180 commands previously.
2181 For example, \-1 is the immediately previous command.
2183 A string indicating the most recently entered command
2184 that begins with that string.
2186 .Ar old Ns = Ns Ar new
2187 operand is not also specified with
2189 the string form of the first operand cannot contain an embedded equal sign.
2193 The following variables affect the execution of
2195 .Bl -tag -width ".Va HISTSIZE"
2197 Name of the editor to use for history editing.
2199 The number of previous commands that are accessible.
2204 or the current job to the foreground.
2205 .It Ic getopts Ar optstring var
2212 command deprecates the older
2215 The first argument should be a series of letters, each possibly
2216 followed by a colon which indicates that the option takes an argument.
2217 The specified variable is set to the parsed option.
2219 the next argument is placed into the shell variable
2221 If an option takes an argument, it is placed into the shell variable
2223 If an invalid option is encountered,
2227 It returns a false value (1) when it encounters the end of the options.
2228 .It Ic hash Oo Fl rv Oc Op Ar command ...
2229 The shell maintains a hash table which remembers the locations of commands.
2230 With no arguments whatsoever, the
2232 command prints out the contents of this table.
2236 command removes each specified
2238 from the hash table (unless they are functions) and then locates it.
2243 prints the locations of the commands as it finds them.
2248 command to delete all the entries in the hash table except for functions.
2249 .It Ic jobid Op Ar job
2250 Print the process IDs of the processes in the specified
2254 argument is omitted, use the current job.
2255 .It Ic jobs Oo Fl lps Oc Op Ar job ...
2256 Print information about the specified jobs, or all jobs if no
2259 The information printed includes job ID, status and command name.
2263 option is specified, the PID of each job is also printed.
2266 option is specified, only the process IDs for the process group leaders
2267 are printed, one per line.
2270 option is specified, only the PIDs of the job commands are printed, one per
2273 A built-in equivalent of
2275 that additionally supports sending signals to jobs.
2276 .It Ic local Oo Ar variable ... Oc Op Fl
2281 A built-in equivalent of
2283 .It Ic pwd Op Fl L | P
2284 Print the path of the current directory.
2285 The built-in command may
2286 differ from the program of the same name because the
2287 built-in command remembers what the current directory
2288 is rather than recomputing it each time.
2291 However, if the current directory is
2293 the built-in version of
2295 will continue to print the old name for the directory.
2299 option is specified, symbolic links are resolved.
2302 option is specified, the shell's notion of the current directory
2303 is printed (symbolic links are not resolved).
2304 This is the default.
2305 .It Ic read Oo Fl p Ar prompt Oc Oo
2306 .Fl t Ar timeout Oc Oo Fl er Oc Ar variable ...
2312 and the standard input is a terminal.
2314 read from the standard input.
2315 The trailing newline
2316 is deleted from the line and the line is split as
2317 described in the section on
2318 .Sx White Space Splitting (Field Splitting)
2320 the pieces are assigned to the variables in order.
2321 If there are more pieces than variables, the remaining
2322 pieces (along with the characters in
2324 that separated them)
2325 are assigned to the last variable.
2326 If there are more variables than pieces, the remaining
2327 variables are assigned the null string.
2329 Backslashes are treated specially, unless the
2333 If a backslash is followed by
2334 a newline, the backslash and the newline will be
2336 If a backslash is followed by any other
2337 character, the backslash will be deleted and the following
2338 character will be treated as though it were not in
2344 option is specified and the
2346 elapses before a complete line of input is supplied,
2349 command will return an exit status of 1 without assigning any values.
2352 value may optionally be followed by one of
2357 to explicitly specify seconds, minutes or hours.
2358 If none is supplied,
2364 option exists only for backward compatibility with older scripts.
2365 .It Ic readonly Oo Fl p Oc Op Ar name ...
2368 is marked as read only,
2369 so that it cannot be subsequently modified or unset.
2370 The shell allows the value of a variable to be set
2371 at the same time as it is marked read only
2372 by using the following form:
2374 .D1 Ic readonly Ar name Ns = Ns Ar value
2376 With no arguments the
2378 command lists the names of all read only variables.
2381 option is specified, the read-only variables are printed as
2382 .Dq Ic readonly Ar name Ns = Ns Ar value
2383 lines, suitable for re-input to the shell.
2384 .It Ic return Op Ar exitstatus
2388 .It Ic set Oo Fl /+abCEefIimnpTuVvx Oc Oo Fl /+o Ar longname Oc Oo
2389 .Fl c Ar string Oc Op Fl - Ar arg ...
2392 command performs three different functions:
2395 With no arguments, it lists the values of all shell variables.
2397 If options are given,
2398 either in short form or using the long
2399 .Dq Fl /+o Ar longname
2401 it sets or clears the specified options as described in the section called
2402 .Sx Argument List Processing .
2406 option is specified,
2408 will replace the shell's positional parameters with the subsequent
2410 If no arguments follow the
2413 all the positional parameters will be cleared,
2414 which is equivalent to executing the command
2418 flag may be omitted when specifying arguments to be used
2419 as positional replacement parameters.
2420 This is not recommended,
2421 because the first argument may begin with a dash
2427 command will interpret as a request to enable or disable options.
2429 .It Ic setvar Ar variable value
2430 Assigns the specified
2436 command is intended to be used in functions that
2437 assign values to variables whose names are passed as parameters.
2438 In general it is better to write
2439 .Dq Ar variable Ns = Ns Ar value
2442 .It Ic shift Op Ar n
2443 Shift the positional parameters
2448 A shift sets the value of
2457 decreasing the value of
2460 If there are zero positional parameters, shifting does not do anything.
2462 A built-in equivalent of
2465 Print the amount of time spent executing the shell process and its children.
2466 The first output line shows the user and system times for the shell process
2467 itself, the second one contains the user and system times for the
2469 .It Ic trap Oo Ar action Oc Ar signal ...
2471 Cause the shell to parse and execute
2476 The signals are specified by name or number.
2477 In addition, the pseudo-signal
2479 may be used to specify an
2481 that is performed when the shell terminates.
2484 may be an empty string or a dash
2486 the former causes the specified signal to be ignored
2487 and the latter causes the default action to be taken.
2490 is another way to request the default action, for compatibility reasons this
2491 usage is not recommended though.
2492 In a subshell or utility environment,
2493 the shell resets trapped (but not ignored) signals to the default action.
2496 command has no effect on signals that were ignored on entry to the shell.
2502 command to display a list of valid signal names.
2504 A null command that returns a 0 (true) exit value.
2505 .It Ic type Op Ar name ...
2508 as a command and print the resolution of the command search.
2509 Possible resolutions are:
2510 shell keyword, alias, special shell builtin, shell builtin, command,
2513 For aliases the alias expansion is printed;
2514 for commands and tracked aliases
2515 the complete pathname of the command is printed.
2516 .It Ic ulimit Oo Fl HSabcdflmnstuv Oc Op Ar limit
2517 Set or display resource limits (see
2521 is specified, the named resource will be set;
2522 otherwise the current resource value will be displayed.
2526 is specified, the hard limits will be set or displayed.
2527 While everybody is allowed to reduce a hard limit,
2528 only the superuser can increase it.
2532 specifies the soft limits instead.
2533 When displaying limits,
2539 The default is to display the soft limits,
2540 and to set both the hard and the soft limits.
2546 command to display all resources.
2549 is not acceptable in this mode.
2551 The remaining options specify which resource value is to be
2552 displayed or modified.
2553 They are mutually exclusive.
2554 .Bl -tag -width indent
2556 The maximum size of socket buffer usage, in bytes.
2557 .It Fl c Ar coredumpsize
2558 The maximal size of core dump files, in 512-byte blocks.
2559 .It Fl d Ar datasize
2560 The maximal size of the data segment of a process, in kilobytes.
2561 .It Fl f Ar filesize
2562 The maximal size of a file, in 512-byte blocks.
2563 .It Fl l Ar lockedmem
2564 The maximal size of memory that can be locked by a process, in
2566 .It Fl m Ar memoryuse
2567 The maximal resident set size of a process, in kilobytes.
2569 The maximal number of descriptors that could be opened by a process.
2570 .It Fl s Ar stacksize
2571 The maximal size of the stack segment, in kilobytes.
2573 The maximal amount of CPU time to be used by each process, in seconds.
2574 .It Fl u Ar userproc
2575 The maximal number of simultaneous processes for this user ID.
2576 .It Fl v Ar virtualmem
2577 The maximal virtual size of a process, in kilobytes.
2579 .It Ic umask Oo Fl S Oc Op Ar mask
2580 Set the file creation mask (see
2582 to the octal or symbolic (see
2586 If the argument is omitted, the current mask value is printed.
2589 option is specified, the output is symbolic, otherwise the output is octal.
2590 .It Ic unalias Oo Fl a Oc Op Ar name ...
2591 The specified alias names are removed.
2594 is specified, all aliases are removed.
2595 .It Ic unset Oo Fl fv Oc Ar name ...
2596 The specified variables or functions are unset and unexported.
2599 option is specified or no options are given, the
2601 arguments are treated as variable names.
2604 option is specified, the
2606 arguments are treated as function names.
2607 .It Ic wait Op Ar job
2608 Wait for the specified
2610 to complete and return the exit status of the last process in the
2612 If the argument is omitted, wait for all jobs to complete
2613 and return an exit status of zero.
2615 .Ss Commandline Editing
2618 is being used interactively from a terminal, the current command
2619 and the command history
2623 .Sx Built-in Commands )
2626 command line editing.
2627 This mode uses commands similar
2628 to a subset of those described in the
2646 can be switched between insert mode and command mode by typing
2650 while in command mode will pass the line to the shell.
2653 .Dq Li "set -o emacs"
2656 command can be used to enable a subset of
2658 command line editing features.
2660 The following environment variables affect the execution of
2662 .Bl -tag -width ".Ev LANGXXXXXX"
2664 Initialization file for interactive shells.
2665 .It Ev LANG , Ev LC_*
2667 These are inherited by children of the shell,
2668 and is used in a limited manner by the shell itself.
2670 An absolute pathname for the current directory,
2671 possibly containing symbolic links.
2672 This is used and updated by the shell.
2674 The default terminal setting for the shell.
2675 This is inherited by children of the shell, and is used in the history
2679 Additionally, all environment variables are turned into shell variables
2681 which may affect the shell as described under
2682 .Sx Special Variables .
2684 .Bl -tag -width "/etc/suid_profileXX" -compact
2686 User's login profile.
2688 System login profile.
2691 .It Pa /etc/suid_profile
2692 Privileged shell profile.
2695 Errors that are detected by the shell, such as a syntax error, will
2696 cause the shell to exit with a non-zero exit status.
2697 If the shell is not an interactive shell, the execution of the shell
2698 file will be aborted.
2699 Otherwise the shell will return the exit status of the last command
2702 builtin is used with a numeric argument, it
2703 will return the argument.
2709 .Xr emacs 1 Pq Pa pkgsrc/editors/emacs ,
2725 command, the Thompson shell, appeared in
2727 It was superseded in
2729 by the Bourne shell, which inherited the name
2734 was rewritten in 1989 under the
2736 license after the Bourne shell from
2741 was originally written by
2742 .An Kenneth Almquist .
2746 utility does not recognize multibyte characters other than UTF-8.
2749 and the line editing library
2751 do not recognize multibyte characters.
2753 The characters generated by filename completion should probably be quoted
2754 to ensure that the filename is still valid after the input line has been
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