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32 .\" from: @(#)sh.1 8.6 (Berkeley) 5/4/95
40 .Nd command interpreter (shell)
43 .Op Fl /+abCEefIimnPpTuVvx
44 .Op Fl /+o Ar longname
50 .Op Fl /+abCEefIimnPpTuVvx
51 .Op Fl /+o Ar longname
58 .Op Fl /+abCEefIimnPpTuVvx
59 .Op Fl /+o Ar longname
65 utility is the standard command interpreter for the system.
66 The current version of
70 specification for the shell.
71 It only supports features
74 plus a few Berkeley extensions.
75 This man page is not intended to be a tutorial nor a complete
76 specification of the shell.
78 The shell is a command that reads lines from
79 either a file or the terminal, interprets them, and
80 generally executes other commands.
81 It is the program that is started when a user logs into the system,
82 although a user can select a different shell with the
86 implements a language that has flow control constructs,
87 a macro facility that provides a variety of features in
88 addition to data storage, along with built-in history and line
90 It incorporates many features to
91 aid interactive use and has the advantage that the interpretative
92 language is common to both interactive and non-interactive
94 That is, commands can be typed directly
95 to the running shell or can be put into a file,
96 which can be executed directly by the shell.
99 .\" XXX This next sentence is incredibly confusing.
101 If no arguments are present and if the standard input of the shell
102 is connected to a terminal
106 the shell is considered an interactive shell.
108 generally prompts before each command and handles programming
109 and command errors differently (as described below).
110 When first starting, the shell inspects argument 0, and
111 if it begins with a dash
113 the shell is also considered a login shell.
114 This is normally done automatically by the system
115 when the user first logs in.
116 A login shell first reads commands
121 in a user's home directory,
123 If the environment variable
125 is set on entry to a shell, or is set in the
127 of a login shell, the shell then subjects its value to parameter expansion
128 and arithmetic expansion and reads commands from the named file.
129 Therefore, a user should place commands that are to be executed only
132 file, and commands that are executed for every shell inside the
137 variable to some file by placing the following line in the file
139 in the home directory,
142 the filename desired:
144 .Dl "ENV=$HOME/.shinit; export ENV"
146 The first non-option argument specified on the command line
147 will be treated as the
148 name of a file from which to read commands (a shell script), and
149 the remaining arguments are set as the positional parameters
153 Otherwise, the shell reads commands
154 from its standard input.
156 Unlike older versions of
160 script is only sourced on invocation of interactive shells.
162 closes a well-known, and sometimes easily exploitable security
163 hole related to poorly thought out
166 .Ss Argument List Processing
167 All of the single letter options to
169 have a corresponding long name,
170 with the exception of
174 These long names are provided next to the single letter options
175 in the descriptions below.
176 The long name for an option may be specified as an argument to the
180 Once the shell is running,
181 the long name for an option may be specified as an argument to the
186 (described later in the section called
187 .Sx Built-in Commands ) .
188 Introducing an option with a dash
198 will stop option processing and will force the remaining
199 words on the command line to be treated as arguments.
204 options do not have long names.
205 They take arguments and are described after the single letter options.
206 .Bl -tag -width indent
207 .It Fl a Li allexport
208 Flag variables for export when assignments are made to them.
210 Enable asynchronous notification of background job
213 .It Fl C Li noclobber
214 Do not overwrite existing files with
219 command line editor (disables the
221 option if it has been set;
222 set automatically when interactive on terminals).
224 Exit immediately if any untested command fails in non-interactive mode.
225 The exit status of a command is considered to be
226 explicitly tested if the command is part of the list used to control
228 .Ic if , elif , while ,
231 if the command is the left
236 operator; or if the command is a pipeline preceded by the
239 If a shell function is executed and its exit status is explicitly
240 tested, all commands of the function are considered to be tested as
243 Disable pathname expansion.
245 A do-nothing option for
248 .It Fl I Li ignoreeof
251 from input when in interactive mode.
252 .It Fl i Li interactive
253 Force the shell to behave interactively.
255 Turn on job control (set automatically when interactive).
257 If not interactive, read commands but do not
259 This is useful for checking the
260 syntax of shell scripts.
262 Change the default for the
268 (logical directory layout)
271 (physical directory layout).
272 .It Fl p Li privileged
273 Turn on privileged mode.
274 This mode is enabled on startup
275 if either the effective user or group ID is not equal to the
276 real user or group ID.
277 Turning this mode off sets the
278 effective user and group IDs to the real user and group IDs.
279 When this mode is enabled for interactive shells, the file
280 .Pa /etc/suid_profile
281 is sourced instead of
285 is sourced, and the contents of the
287 variable are ignored.
289 Read commands from standard input (set automatically
290 if no file arguments are present).
292 no effect when set after the shell has already started
293 running (i.e., when set with the
296 .It Fl T Li trapsasync
297 When waiting for a child, execute traps immediately.
298 If this option is not set,
299 traps are executed after the child exits,
302 This nonstandard option is useful for putting guarding shells around
303 children that block signals.
304 The surrounding shell may kill the child
305 or it may just return control to the tty and leave the child alone,
307 .Bd -literal -offset indent
308 sh -T -c "trap 'exit 1' 2 ; some-blocking-program"
311 Write a message to standard error when attempting
312 to expand a variable, a positional parameter or
313 the special parameter
315 that is not set, and if the
316 shell is not interactive, exit immediately.
320 command line editor (disables
324 The shell writes its input to standard error
326 Useful for debugging.
329 (preceded by the value of the
331 variable subjected to parameter expansion and arithmetic expansion)
332 to standard error before it is executed.
333 Useful for debugging.
338 option causes the commands to be read from the
340 operand instead of from the standard input.
341 Keep in mind that this option only accepts a single string as its
342 argument, hence multi-word strings must be quoted.
346 option takes as its only argument the long name of an option
347 to be enabled or disabled.
348 For example, the following two invocations of
350 both enable the built-in
353 .Bd -literal -offset indent
358 If used without an argument, the
360 option displays the current option settings in a human-readable format.
363 is used without an argument, the current option settings are output
364 in a format suitable for re-input into the shell.
365 .Ss Lexical Structure
366 The shell reads input in terms of lines from a file and breaks
367 it up into words at whitespace (blanks and tabs), and at
371 which are special to the shell.
372 There are two types of operators: control operators and
373 redirection operators (their meaning is discussed later).
374 The following is a list of valid operators:
375 .Bl -tag -width indent
376 .It Control operators:
377 .Bl -column "XXX" "XXX" "XXX" "XXX" "XXX" -offset center -compact
378 .It Li & Ta Li && Ta Li \&( Ta Li \&) Ta Li \en
379 .It Li ;; Ta Li ;& Ta Li \&; Ta Li \&| Ta Li ||
381 .It Redirection operators:
382 .Bl -column "XXX" "XXX" "XXX" "XXX" "XXX" -offset center -compact
383 .It Li < Ta Li > Ta Li << Ta Li >> Ta Li <>
384 .It Li <& Ta Li >& Ta Li <<- Ta Li >| Ta \&
390 introduces a comment if used at the beginning of a word.
391 The word starting with
393 and the rest of the line are ignored.
397 characters (character code 0) are not allowed in shell input.
399 Quoting is used to remove the special meaning of certain characters
400 or words to the shell, such as operators, whitespace, keywords,
403 There are four types of quoting: matched single quotes,
404 dollar-single quotes,
405 matched double quotes, and backslash.
406 .Bl -tag -width indent
408 Enclosing characters in single quotes preserves the literal
409 meaning of all the characters (except single quotes, making
410 it impossible to put single-quotes in a single-quoted string).
411 .It Dollar-Single Quotes
412 Enclosing characters between
416 preserves the literal meaning of all characters
417 except backslashes and single quotes.
418 A backslash introduces a C-style escape sequence:
419 .Bl -tag -width xUnnnnnnnn
421 Alert (ring the terminal bell)
425 The control character denoted by
431 is a backslash, it must be doubled.
453 The byte whose octal value is
455 (one to three digits)
457 The byte whose hexadecimal value is
459 (one or more digits only the last two of which are used)
461 The Unicode code point
463 (four hexadecimal digits)
464 .It \eU Ns Ar nnnnnnnn
465 The Unicode code point
467 (eight hexadecimal digits)
470 The sequences for Unicode code points are currently only useful with
472 They reject code point 0 and UTF-16 surrogates.
474 If an escape sequence would produce a byte with value 0,
475 that byte and the rest of the string until the matching single-quote
478 Any other string starting with a backslash is an error.
480 Enclosing characters within double quotes preserves the literal
481 meaning of all characters except dollar sign
487 The backslash inside double quotes is historically weird.
488 It remains literal unless it precedes the following characters,
489 which it serves to quote:
491 .Bl -column "XXX" "XXX" "XXX" "XXX" "XXX" -offset center -compact
492 .It Li $ Ta Li ` Ta Li \&" Ta Li \e Ta Li \en
495 A backslash preserves the literal meaning of the following
496 character, with the exception of the newline character
498 A backslash preceding a newline is treated as a line continuation.
501 Keywords or reserved words are words that have special meaning to the
502 shell and are recognized at the beginning of a line and
503 after a control operator.
504 The following are keywords:
505 .Bl -column "doneXX" "elifXX" "elseXX" "untilXX" "whileX" -offset center
506 .It Li \&! Ta { Ta } Ta Ic case Ta Ic do
507 .It Ic done Ta Ic elif Ta Ic else Ta Ic esac Ta Ic fi
508 .It Ic for Ta Ic if Ta Ic then Ta Ic until Ta Ic while
511 An alias is a name and corresponding value set using the
514 Wherever the command word of a simple command may occur,
515 and after checking for keywords if a keyword may occur, the shell
516 checks the word to see if it matches an alias.
517 If it does, it replaces it in the input stream with its value.
518 For example, if there is an alias called
530 Aliases provide a convenient way for naive users to
531 create shorthands for commands without having to learn how
532 to create functions with arguments.
533 Using aliases in scripts is discouraged
534 because the command that defines them must be executed
535 before the code that uses them is parsed.
536 This is fragile and not portable.
538 An alias name may be escaped in a command line, so that it is not
539 replaced by its alias value, by using quoting characters within or
540 adjacent to the alias name.
541 This is most often done by prefixing
542 an alias name with a backslash to execute a function, built-in, or
543 normal program with the same name.
548 The shell interprets the words it reads according to a
549 language, the specification of which is outside the scope
550 of this man page (refer to the BNF in the
553 Essentially though, a line is read and if
554 the first word of the line (or after a control operator)
555 is not a keyword, then the shell has recognized a
557 Otherwise, a complex command or some
558 other special construct may have been recognized.
560 If a simple command has been recognized, the shell performs
561 the following actions:
564 Leading words of the form
566 are stripped off and assigned to the environment of
568 Redirection operators and
569 their arguments (as described below) are stripped
570 off and saved for processing.
572 The remaining words are expanded as described in
574 .Sx Word Expansions ,
575 and the first remaining word is considered the command
576 name and the command is located.
578 words are considered the arguments of the command.
579 If no command name resulted, then the
581 variable assignments recognized in 1) affect the
584 Redirections are performed as described in
588 Redirections are used to change where a command reads its input
590 In general, redirections open, close, or
591 duplicate an existing reference to a file.
593 used for redirection is:
595 .D1 Oo Ar n Oc Ar redir-op file
599 is one of the redirection operators mentioned
601 The following gives some examples of how these
602 operators can be used.
603 Note that stdin and stdout are commonly used abbreviations
604 for standard input and standard output respectively.
605 .Bl -tag -width "1234567890XX" -offset indent
606 .It Oo Ar n Oc Ns Li > Ar file
607 redirect stdout (or file descriptor
611 .It Oo Ar n Oc Ns Li >| Ar file
612 same as above, but override the
615 .It Oo Ar n Oc Ns Li >> Ar file
616 append stdout (or file descriptor
620 .It Oo Ar n Oc Ns Li < Ar file
621 redirect stdin (or file descriptor
625 .It Oo Ar n Oc Ns Li <> Ar file
626 redirect stdin (or file descriptor
630 .It Oo Ar n1 Oc Ns Li <& Ns Ar n2
631 duplicate stdin (or file descriptor
635 .It Oo Ar n Oc Ns Li <&-
636 close stdin (or file descriptor
638 .It Oo Ar n1 Oc Ns Li >& Ns Ar n2
639 duplicate stdout (or file descriptor
643 .It Oo Ar n Oc Ns Li >&-
644 close stdout (or file descriptor
648 The following redirection is often called a
650 .Bd -unfilled -offset indent
651 .Oo Ar n Oc Ns Li << Ar delimiter
657 All the text on successive lines up to the delimiter is
658 saved away and made available to the command on standard
659 input, or file descriptor
664 as specified on the initial line is quoted, then the
666 is treated literally, otherwise the text is subjected to
667 parameter expansion, command substitution, and arithmetic
668 expansion (as described in the section on
669 .Sx Word Expansions ) .
678 .Ss Search and Execution
679 There are three types of commands: shell functions,
680 built-in commands, and normal programs.
681 The command is searched for (by name) in that order.
682 The three types of commands are all executed in a different way.
684 When a shell function is executed, all of the shell positional
687 which remains unchanged) are
688 set to the arguments of the shell function.
689 The variables which are explicitly placed in the environment of
690 the command (by placing assignments to them before the
691 function name) are made local to the function and are set
693 Then the command given in the function definition is executed.
694 The positional parameters are restored to their original values
695 when the command completes.
696 This all occurs within the current shell.
698 Shell built-in commands are executed internally to the shell, without
699 spawning a new process.
700 There are two kinds of built-in commands: regular and special.
701 Assignments before special builtins persist after they finish
702 executing and assignment errors, redirection errors and certain
703 operand errors cause a script to be aborted.
704 Special builtins cannot be overridden with a function.
705 Both regular and special builtins can affect the shell in ways
706 normal programs cannot.
708 Otherwise, if the command name does not match a function
709 or built-in command, the command is searched for as a normal
710 program in the file system (as described in the next section).
711 When a normal program is executed, the shell runs the program,
712 passing the arguments and the environment to the program.
713 If the program is not a normal executable file
714 (i.e., if it does not begin with the
724 but appears to be a text file,
725 the shell will run a new instance of
729 Note that previous versions of this document
730 and the source code itself misleadingly and sporadically
731 refer to a shell script without a magic number
733 .Dq "shell procedure" .
735 When locating a command, the shell first looks to see if
736 it has a shell function by that name.
738 built-in command by that name.
739 If a built-in command is not found,
740 one of two things happen:
743 Command names containing a slash are simply executed without
744 performing any searches.
746 The shell searches each entry in the
749 in turn for the command.
752 variable should be a series of
753 entries separated by colons.
754 Each entry consists of a
756 The current directory
757 may be indicated implicitly by an empty directory name,
758 or explicitly by a single period.
760 .Ss Command Exit Status
761 Each command has an exit status that can influence the behavior
762 of other shell commands.
763 The paradigm is that a command exits
764 with zero for normal or success, and non-zero for failure,
765 error, or a false indication.
766 The man page for each command
767 should indicate the various exit codes and what they mean.
768 Additionally, the built-in commands return exit codes, as does
769 an executed shell function.
771 If a command is terminated by a signal, its exit status is 128 plus
773 Signal numbers are defined in the header file
776 Complex commands are combinations of simple commands
777 with control operators or keywords, together creating a larger complex
779 More generally, a command is one of the following:
780 .Bl -item -offset indent
786 list or compound-list
793 Unless otherwise stated, the exit status of a command is
794 that of the last simple command executed by the command.
796 A pipeline is a sequence of one or more commands separated
797 by the control operator
799 The standard output of all but
800 the last command is connected to the standard input
802 The standard output of the last
803 command is inherited from the shell, as usual.
805 The format for a pipeline is:
807 .D1 Oo Li \&! Oc Ar command1 Op Li \&| Ar command2 ...
809 The standard output of
811 is connected to the standard input of
813 The standard input, standard output, or
814 both of a command is considered to be assigned by the
815 pipeline before any redirection specified by redirection
816 operators that are part of the command.
818 Note that unlike some other shells,
820 executes each process in a pipeline with more than one command
821 in a subshell environment and as a child of the
825 If the pipeline is not in the background (discussed later),
826 the shell waits for all commands to complete.
830 does not precede the pipeline, the
831 exit status is the exit status of the last command specified
833 Otherwise, the exit status is the logical
834 NOT of the exit status of the last command.
836 the last command returns zero, the exit status is 1; if
837 the last command returns greater than zero, the exit status
840 Because pipeline assignment of standard input or standard
841 output or both takes place before redirection, it can be
842 modified by redirection.
845 .Dl "command1 2>&1 | command2"
847 sends both the standard output and standard error of
849 to the standard input of
854 or newline terminator causes the preceding
856 (described below in the section called
857 .Sx Short-Circuit List Operators )
858 to be executed sequentially;
861 causes asynchronous execution of the preceding AND-OR-list.
862 .Ss Background Commands (&)
863 If a command is terminated by the control operator ampersand
865 the shell executes the command in a subshell environment (see
866 .Sx Grouping Commands Together
867 below) and asynchronously;
868 the shell does not wait for the command to finish
869 before executing the next command.
871 The format for running a command in background is:
873 .D1 Ar command1 Li & Op Ar command2 Li & Ar ...
875 If the shell is not interactive, the standard input of an
876 asynchronous command is set to
878 .Ss Lists (Generally Speaking)
879 A list is a sequence of zero or more commands separated by
880 newlines, semicolons, or ampersands,
881 and optionally terminated by one of these three characters.
883 list are executed in the order they are written.
884 If command is followed by an ampersand, the shell starts the
885 command and immediately proceeds onto the next command;
886 otherwise it waits for the command to terminate before
887 proceeding to the next one.
888 .Ss Short-Circuit List Operators
892 are AND-OR list operators.
894 executes the first command, and then executes the second command
895 if the exit status of the first command is zero.
897 is similar, but executes the second command if the exit
898 status of the first command is nonzero.
902 both have the same priority.
903 .Ss Flow-Control Constructs (if, while, for, case)
907 .Bd -unfilled -offset indent -compact
911 .Ic then Ar list Oc Ar ...
919 .Bd -unfilled -offset indent -compact
925 The two lists are executed repeatedly while the exit status of the
929 command is similar, but has the word
934 repeat until the exit status of the first list is zero.
939 .Bd -unfilled -offset indent -compact
940 .Ic for Ar variable Op Ic in Ar word ...
947 and the following words are omitted,
950 The words are expanded, and then the list is executed
951 repeatedly with the variable set to each word in turn.
956 commands may be replaced with
966 .D1 Ic break Op Ar num
967 .D1 Ic continue Op Ar num
971 command terminates the
980 command continues with the next iteration of the innermost loop.
981 These are implemented as special built-in commands.
986 .Bd -unfilled -offset indent -compact
987 .Ic case Ar word Ic in
988 .Ar pattern Ns Li ) Ar list Li ;;
993 The pattern can actually be one or more patterns
1000 Tilde expansion, parameter expansion, command substitution,
1001 arithmetic expansion and quote removal are applied to the word.
1002 Then, each pattern is expanded in turn using tilde expansion,
1003 parameter expansion, command substitution and arithmetic expansion and
1004 the expanded form of the word is checked against it.
1005 If a match is found, the corresponding list is executed.
1006 If the selected list is terminated by the control operator
1010 execution continues with the next list,
1011 continuing until a list terminated with
1016 The exit code of the
1018 command is the exit code of the last command executed in the list or
1019 zero if no patterns were matched.
1020 .Ss Grouping Commands Together
1021 Commands may be grouped by writing either
1023 .D1 Li \&( Ns Ar list Ns Li \%)
1027 .D1 Li { Ar list Ns Li \&; }
1029 The first form executes the commands in a subshell environment.
1030 A subshell environment has its own copy of:
1033 The current working directory as set by
1036 The file creation mask as set by
1039 References to open files.
1046 Positional parameters and variables.
1055 These are copied from the parent shell environment,
1056 except that trapped (but not ignored) signals are reset to the default action
1057 and known jobs are cleared.
1058 Any changes do not affect the parent shell environment.
1060 A subshell environment may be implemented as a child process or differently.
1061 If job control is enabled in an interactive shell,
1062 commands grouped in parentheses can be suspended and continued as a unit.
1064 The second form never forks another shell,
1065 so it is slightly more efficient.
1066 Grouping commands together this way allows the user to
1067 redirect their output as though they were one program:
1068 .Bd -literal -offset indent
1069 { echo -n "hello"; echo " world"; } > greeting
1072 The syntax of a function definition is
1074 .D1 Ar name Li \&( \&) Ar command
1076 A function definition is an executable statement; when
1077 executed it installs a function named
1080 exit status of zero.
1089 Variables may be declared to be local to a function by
1093 This should appear as the first statement of a function,
1096 .D1 Ic local Oo Ar variable ... Oc Op Fl
1100 command is implemented as a built-in command.
1102 When a variable is made local, it inherits the initial
1103 value and exported and readonly flags from the variable
1104 with the same name in the surrounding scope, if there is
1106 Otherwise, the variable is initially unset.
1108 uses dynamic scoping, so that if the variable
1110 is made local to function
1112 which then calls function
1114 references to the variable
1118 will refer to the variable
1122 not to the global variable named
1125 The only special parameter that can be made local is
1129 local causes any shell options that are
1132 command inside the function to be
1133 restored to their original values when the function
1140 .D1 Ic return Op Ar exitstatus
1142 It terminates the current executional scope, returning from the previous
1143 nested function, sourced script, or shell instance, in that order.
1146 command is implemented as a special built-in command.
1147 .Ss Variables and Parameters
1148 The shell maintains a set of parameters.
1150 denoted by a name is called a variable.
1152 the shell turns all the environment variables into shell
1154 New variables can be set using the form
1156 .D1 Ar name Ns = Ns Ar value
1158 Variables set by the user must have a name consisting solely
1159 of alphabetics, numerics, and underscores.
1160 The first letter of a variable name must not be numeric.
1161 A parameter can also be denoted by a number
1162 or a special character as explained below.
1164 Assignments are expanded differently from other words:
1165 tilde expansion is also performed after the equals sign and after any colon
1166 and usernames are also terminated by colons,
1167 and field splitting and pathname expansion are not performed.
1169 This special expansion applies not only to assignments that form a simple
1170 command by themselves or precede a command word,
1171 but also to words passed to the
1176 built-in commands that have this form.
1177 For this, the builtin's name must be literal
1178 (not the result of an expansion)
1179 and may optionally be preceded by one or more literal instances of
1182 .Ss Positional Parameters
1183 A positional parameter is a parameter denoted by a number greater than zero.
1184 The shell sets these initially to the values of its command line
1185 arguments that follow the name of the shell script.
1188 built-in command can also be used to set or reset them.
1189 .Ss Special Parameters
1190 Special parameters are parameters denoted by a single special character
1192 They are shown in the following list, exactly as they would appear in input
1193 typed by the user or in the source of a shell script.
1196 Expands to the positional parameters, starting from one.
1198 the expansion occurs within a double-quoted string
1199 it expands to a single field with the value of each parameter
1200 separated by the first character of the
1207 Expands to the positional parameters, starting from one.
1209 the expansion occurs within double-quotes, each positional
1210 parameter expands as a separate argument.
1211 If there are no positional parameters, the
1214 generates zero arguments, even when
1217 What this basically means, for example, is
1230 .Bd -literal -offset indent
1234 Expands to the number of positional parameters.
1236 Expands to the exit status of the most recent pipeline.
1238 (hyphen) Expands to the current option flags (the single-letter
1239 option names concatenated into a string) as specified on
1242 built-in command, or implicitly
1245 Expands to the process ID of the invoked shell.
1247 retains the same value of
1251 Expands to the process ID of the most recent background
1252 command executed from the current shell.
1254 pipeline, the process ID is that of the last command in the
1256 If this parameter is referenced, the shell will remember
1257 the process ID and its exit status until the
1259 built-in command reports completion of the process.
1261 (zero) Expands to the name of the shell script if passed on the command line,
1264 operand if given (with
1266 or otherwise argument 0 passed to the shell.
1268 .Ss Special Variables
1269 The following variables are set by the shell or
1270 have special meaning to it:
1271 .Bl -tag -width ".Va HISTSIZE"
1273 The search path used with the
1277 The fallback editor used with the
1280 If not set, the default editor is
1283 The default editor used with the
1287 The number of previous commands that are accessible.
1289 The user's home directory,
1290 used in tilde expansion and as a default directory for the
1294 Input Field Separators.
1295 The default value is
1301 This default also applies if
1303 is unset, but not if it is set to the empty string.
1305 .Sx White Space Splitting
1306 section for more details.
1308 The current line number in the script or function.
1310 The name of a mail file, that will be checked for the arrival of new
1317 separated list of file names, for the shell to check for incoming
1319 This variable overrides the
1322 There is a maximum of 10 mailboxes that can be monitored at once.
1324 The default search path for executables.
1327 section for details.
1329 The parent process ID of the invoked shell.
1330 This is set at startup
1331 unless this variable is in the environment.
1332 A later change of parent process ID is not reflected.
1333 A subshell retains the same value of
1336 The primary prompt string, which defaults to
1338 unless you are the superuser, in which case it defaults to
1341 The secondary prompt string, which defaults to
1344 The prefix for the trace output (if
1351 This clause describes the various expansions that are
1353 Not all expansions are performed on
1354 every word, as explained later.
1356 Tilde expansions, parameter expansions, command substitutions,
1357 arithmetic expansions, and quote removals that occur within
1358 a single word expand to a single field.
1360 splitting or pathname expansion that can create multiple
1361 fields from a single word.
1362 The single exception to this rule is
1363 the expansion of the special parameter
1365 within double-quotes,
1366 as was described above.
1368 The order of word expansion is:
1371 Tilde Expansion, Parameter Expansion, Command Substitution,
1372 Arithmetic Expansion (these all occur at the same time).
1374 Field Splitting is performed on fields generated by step (1)
1379 Pathname Expansion (unless the
1381 option is in effect).
1388 character is used to introduce parameter expansion, command
1389 substitution, or arithmetic expansion.
1390 .Ss Tilde Expansion (substituting a user's home directory)
1391 A word beginning with an unquoted tilde character
1394 subjected to tilde expansion.
1395 All the characters up to a slash
1397 or the end of the word are treated as a username
1398 and are replaced with the user's home directory.
1400 username is missing (as in
1402 the tilde is replaced with the value of the
1404 variable (the current user's home directory).
1405 .Ss Parameter Expansion
1406 The format for parameter expansion is as follows:
1408 .D1 Li ${ Ns Ar expression Ns Li }
1412 consists of all characters until the matching
1416 escaped by a backslash or within a single-quoted or double-quoted
1417 string, and characters in
1418 embedded arithmetic expansions, command substitutions, and variable
1419 expansions, are not examined in determining the matching
1421 If the variants with
1427 occur within a double-quoted string,
1428 as an extension there may be unquoted parts
1429 (via double-quotes inside the expansion);
1431 within such parts are also not examined in determining the matching
1434 The simplest form for parameter expansion is:
1436 .D1 Li ${ Ns Ar parameter Ns Li }
1438 The value, if any, of
1442 The parameter name or symbol can be enclosed in braces, which are
1443 optional except for positional parameters with more than one digit or
1444 when parameter is followed by a character that could be interpreted as
1446 If a parameter expansion occurs inside double-quotes:
1449 Field splitting is not performed on the results of the
1450 expansion, with the exception of the special parameter
1453 Pathname expansion is not performed on the results of the
1457 In addition, a parameter expansion can be modified by using one of the
1459 .Bl -tag -width indent
1460 .It Li ${ Ns Ar parameter Ns Li :- Ns Ar word Ns Li }
1464 is unset or null, the expansion of
1466 is substituted; otherwise, the value of
1469 .It Li ${ Ns Ar parameter Ns Li := Ns Ar word Ns Li }
1470 Assign Default Values.
1473 is unset or null, the expansion of
1483 does not prevent field splitting or pathname expansion.
1484 Only variables, not positional
1485 parameters or special parameters, can be
1486 assigned in this way.
1487 .It Li ${ Ns Ar parameter Ns Li :? Ns Oo Ar word Oc Ns Li }
1488 Indicate Error if Null or Unset.
1491 is unset or null, the expansion of
1493 (or a message indicating it is unset if
1495 is omitted) is written to standard
1496 error and the shell exits with a nonzero
1498 Otherwise, the value of
1502 interactive shell need not exit.
1503 .It Li ${ Ns Ar parameter Ns Li :+ Ns Ar word Ns Li }
1504 Use Alternate Value.
1507 is unset or null, null is substituted;
1508 otherwise, the expansion of
1513 In the parameter expansions shown previously, use of the colon in the
1514 format results in a test for a parameter that is unset or null; omission
1515 of the colon results in a test for a parameter that is only unset.
1519 inherits the type of quoting
1520 (unquoted, double-quoted or here-document)
1521 from the surroundings,
1522 with the exception that a backslash that quotes a closing brace is removed
1523 during quote removal.
1524 .Bl -tag -width indent
1525 .It Li ${# Ns Ar parameter Ns Li }
1527 The length in characters of
1532 The following four varieties of parameter expansion provide for substring
1534 In each case, pattern matching notation
1536 .Sx Shell Patterns ) ,
1537 rather than regular expression notation,
1538 is used to evaluate the patterns.
1539 If parameter is one of the special parameters
1543 the result of the expansion is unspecified.
1544 Enclosing the full parameter expansion string in double-quotes does not
1545 cause the following four varieties of pattern characters to be quoted,
1546 whereas quoting characters within the braces has this effect.
1547 .Bl -tag -width indent
1548 .It Li ${ Ns Ar parameter Ns Li % Ns Ar word Ns Li }
1549 Remove Smallest Suffix Pattern.
1552 is expanded to produce a pattern.
1554 parameter expansion then results in
1556 with the smallest portion of the
1557 suffix matched by the pattern deleted.
1558 .It Li ${ Ns Ar parameter Ns Li %% Ns Ar word Ns Li }
1559 Remove Largest Suffix Pattern.
1562 is expanded to produce a pattern.
1564 parameter expansion then results in
1566 with the largest portion of the
1567 suffix matched by the pattern deleted.
1568 .It Li ${ Ns Ar parameter Ns Li # Ns Ar word Ns Li }
1569 Remove Smallest Prefix Pattern.
1572 is expanded to produce a pattern.
1574 parameter expansion then results in
1576 with the smallest portion of the
1577 prefix matched by the pattern deleted.
1578 .It Li ${ Ns Ar parameter Ns Li ## Ns Ar word Ns Li }
1579 Remove Largest Prefix Pattern.
1582 is expanded to produce a pattern.
1584 parameter expansion then results in
1586 with the largest portion of the
1587 prefix matched by the pattern deleted.
1589 .Ss Command Substitution
1590 Command substitution allows the output of a command to be substituted in
1591 place of the command name itself.
1592 Command substitution occurs when
1593 the command is enclosed as follows:
1595 .D1 Li $( Ns Ar command Ns Li )\&
1597 or the backquoted version:
1599 .D1 Li ` Ns Ar command Ns Li `
1601 The shell expands the command substitution by executing command
1602 and replacing the command substitution
1603 with the standard output of the command,
1604 removing sequences of one or more newlines at the end of the substitution.
1605 Embedded newlines before the end of the output are not removed;
1606 however, during field splitting, they may be translated into spaces
1607 depending on the value of
1609 and the quoting that is in effect.
1610 The command is executed in a subshell environment,
1611 except that the built-in commands
1616 return information about the parent shell environment
1619 returns information about the same process
1620 if they are the only command in a command substitution.
1621 .Ss Arithmetic Expansion
1622 Arithmetic expansion provides a mechanism for evaluating an arithmetic
1623 expression and substituting its value.
1624 The format for arithmetic expansion is as follows:
1626 .D1 Li $(( Ns Ar expression Ns Li ))
1630 is treated as if it were in double-quotes, except
1631 that a double-quote inside the expression is not treated specially.
1633 shell expands all tokens in the
1635 for parameter expansion,
1636 command substitution,
1637 arithmetic expansion
1640 The allowed expressions are a subset of C expressions,
1642 .Bl -tag -width "Variables" -offset indent
1644 All values are of type
1647 Decimal, octal (starting with
1649 and hexadecimal (starting with
1653 Shell variables can be read and written
1654 and contain integer constants.
1657 .It Binary operators
1658 .Li "* / % + - << >> < <= > >= == != & ^ | && ||"
1659 .It Assignment operators
1660 .Li "= += -= *= /= %= <<= >>= &= ^= |="
1661 .It Conditional operator
1665 The result of the expression is substituted in decimal.
1666 .Ss White Space Splitting (Field Splitting)
1667 In certain contexts,
1668 after parameter expansion, command substitution, and
1669 arithmetic expansion the shell scans the results of
1670 expansions and substitutions that did not occur in double-quotes for
1671 field splitting and multiple fields can result.
1682 are treated differently from other characters in
1687 at the beginning or end of a word is discarded.
1689 Subsequently, a field is delimited by either
1692 a non-whitespace character in
1694 with any whitespace in
1698 one or more whitespace characters in
1702 If a word ends with a non-whitespace character in
1704 there is no empty field after this character.
1706 If no field is delimited, the word is discarded.
1707 In particular, if a word consists solely of an unquoted substitution
1708 and the result of the substitution is null,
1709 it is removed by field splitting even if
1712 .Ss Pathname Expansion (File Name Generation)
1716 file name generation is performed
1717 after word splitting is complete.
1719 viewed as a series of patterns, separated by slashes.
1721 process of expansion replaces the word with the names of
1722 all existing files whose names can be formed by replacing
1723 each pattern with a string that matches the specified pattern.
1724 There are two restrictions on this: first, a pattern cannot match
1725 a string containing a slash, and second,
1726 a pattern cannot match a string starting with a period
1727 unless the first character of the pattern is a period.
1728 The next section describes the patterns used for
1730 the four varieties of parameter expansion for substring processing and the
1734 A pattern consists of normal characters, which match themselves,
1735 and meta-characters.
1736 The meta-characters are
1741 These characters lose their special meanings if they are quoted.
1742 When command or variable substitution is performed and the dollar sign
1743 or back quotes are not double-quoted, the value of the
1744 variable or the output of the command is scanned for these
1745 characters and they are turned into meta-characters.
1749 matches any string of characters.
1752 matches any single character.
1755 introduces a character class.
1756 The end of the character class is indicated by a
1764 rather than introducing a character class.
1765 A character class matches any of the characters between the square brackets.
1766 A locale-dependent range of characters may be specified using a minus sign.
1767 A named class of characters (see
1769 may be specified by surrounding the name with
1774 .Ql \&[\&[:alpha:\&]\&]
1775 is a shell pattern that matches a single letter.
1776 The character class may be complemented by making an exclamation point
1778 the first character of the character class.
1781 has the same effect but is non-standard.
1785 in a character class, make it the first character listed
1793 make it the first or last character listed.
1794 .Ss Built-in Commands
1795 This section lists the built-in commands.
1796 .Bl -tag -width indent
1798 A null command that returns a 0 (true) exit value.
1800 The commands in the specified file are read and executed by the shell.
1803 command may be used to return to the
1810 characters, it is used as is.
1811 Otherwise, the shell searches the
1814 If it is not found in the
1816 it is sought in the current working directory.
1818 A built-in equivalent of
1820 .It Ic alias Oo Ar name Ns Oo = Ns Ar string Oc ... Oc
1822 .Ar name Ns = Ns Ar string
1823 is specified, the shell defines the alias
1829 is specified, the value of the alias
1832 With no arguments, the
1834 built-in command prints the names and values of all defined aliases
1837 Alias values are written with appropriate quoting so that they are
1838 suitable for re-input to the shell.
1842 .It Ic bg Op Ar job ...
1843 Continue the specified jobs
1844 (or the current job if no jobs are given)
1846 .It Ic bind Oo Fl aeklrsv Oc Oo Ar key Oo Ar command Oc Oc
1847 List or alter key bindings for the line editor.
1848 This command is documented in
1850 .It Ic break Op Ar num
1852 .Sx Flow-Control Constructs
1854 .It Ic builtin Ar cmd Op Ar arg ...
1855 Execute the specified built-in command,
1857 This is useful when the user wishes to override a shell function
1858 with the same name as a built-in command.
1859 .It Ic cd Oo Fl L | P Oc Oo Fl e Oc Op Ar directory
1860 Switch to the specified
1862 or to the directory specified in the
1864 environment variable if no
1873 then the directories listed in the
1876 searched for the specified
1880 is unset, the current directory is searched.
1883 is the same as that of
1885 In an interactive shell,
1888 command will print out the name of the directory
1889 that it actually switched to
1890 if this is different from the name that the user gave.
1891 These may be different either because the
1893 mechanism was used or because a symbolic link was crossed.
1897 option is specified,
1899 is handled physically and symbolic links are resolved before
1901 components are processed.
1904 option is specified,
1906 is handled logically.
1907 This is the default.
1913 to return exit status 1 if the full pathname of the new directory
1914 cannot be determined reliably or at all.
1915 Normally this is not considered an error,
1916 although a warning is printed.
1921 .It Ic command Oo Fl p Oc Op Ar utility Op Ar argument ...
1922 .It Ic command Oo Fl p Oc Fl v Ar utility
1923 .It Ic command Oo Fl p Oc Fl V Ar utility
1924 The first form of invocation executes the specified
1926 ignoring shell functions in the search.
1929 is a special builtin,
1930 it is executed as if it were a regular builtin.
1934 option is specified, the command search is performed using a
1937 that is guaranteed to find all of the standard utilities.
1941 option is specified,
1943 is not executed but a description of its interpretation by the shell is
1945 For ordinary commands the output is the path name; for shell built-in
1946 commands, shell functions and keywords only the name is written.
1947 Aliases are printed as
1948 .Dq Ic alias Ar name Ns = Ns Ar value .
1952 option is identical to
1954 except for the output.
1956 .Dq Ar utility Ic is Ar description
1962 a special shell builtin,
1969 .It Ic continue Op Ar num
1971 .Sx Flow-Control Constructs
1973 .It Ic echo Oo Fl e | n Oc Op Ar string ...
1974 Print a space-separated list of the arguments to the standard output
1975 and append a newline character.
1976 .Bl -tag -width indent
1978 Suppress the output of the trailing newline.
1980 Process C-style backslash escape sequences.
1983 command understands the following character escapes:
1984 .Bl -tag -width indent
1986 Alert (ring the terminal bell)
1990 Suppress the trailing newline (this has the side-effect of truncating the
1991 line if it is not the last character)
2009 (Zero) The character whose octal value is
2015 is not enclosed in quotes then the backslash itself must be escaped
2016 with a backslash to protect it from the shell.
2018 .Bd -literal -offset indent
2027 $ echo -e a\e\e\e\eb
2036 options may be specified.
2037 .It Ic eval Ar string ...
2038 Concatenate all the arguments with spaces.
2039 Then re-parse and execute the command.
2040 .It Ic exec Op Ar command Op arg ...
2044 the shell process is replaced with the specified program
2045 (which must be a real program, not a shell built-in command or function).
2046 Any redirections on the
2048 command are marked as permanent,
2049 so that they are not undone when the
2052 .It Ic exit Op Ar exitstatus
2053 Terminate the shell process.
2057 it is used as the exit status of the shell.
2058 Otherwise, if the shell is executing an
2060 trap, the exit status of the last command before the trap is used;
2061 if the shell is executing a trap for a signal,
2062 the shell exits by resending the signal to itself.
2063 Otherwise, the exit status of the preceding command is used.
2064 The exit status should be an integer between 0 and 255.
2065 .It Ic export Ar name ...
2066 .It Ic export Op Fl p
2067 The specified names are exported so that they will
2068 appear in the environment of subsequent commands.
2069 The only way to un-export a variable is to
2072 The shell allows the value of a variable to be set
2073 at the same time as it is exported by writing
2075 .D1 Ic export Ar name Ns = Ns Ar value
2077 With no arguments the
2079 command lists the names
2080 of all exported variables.
2083 option is specified, the exported variables are printed as
2084 .Dq Ic export Ar name Ns = Ns Ar value
2085 lines, suitable for re-input to the shell.
2087 A null command that returns a non-zero (false) exit value.
2088 .It Ic fc Oo Fl e Ar editor Oc Op Ar first Op Ar last
2089 .It Ic fc Fl l Oo Fl nr Oc Op Ar first Op Ar last
2090 .It Ic fc Fl s Oo Ar old Ns = Ns Ar new Oc Op Ar first
2093 built-in command lists, or edits and re-executes,
2094 commands previously entered to an interactive shell.
2095 .Bl -tag -width indent
2097 Use the editor named by
2099 to edit the commands.
2102 string is a command name,
2103 subject to search via the
2108 variable is used as a default when
2113 is null or unset, the value of the
2120 is used as the editor.
2122 List the commands rather than invoking
2124 The commands are written in the
2125 sequence indicated by the
2129 operands, as affected by
2131 with each command preceded by the command number.
2133 Suppress command numbers when listing with
2136 Reverse the order of the commands listed
2145 Re-execute the command without invoking an editor.
2148 Select the commands to list or edit.
2149 The number of previous commands that can be accessed
2150 are determined by the value of the
2157 or both are one of the following:
2158 .Bl -tag -width indent
2159 .It Oo Cm + Oc Ns Ar num
2160 A positive number representing a command number;
2161 command numbers can be displayed with the
2165 A negative decimal number representing the
2166 command that was executed
2169 commands previously.
2170 For example, \-1 is the immediately previous command.
2172 A string indicating the most recently entered command
2173 that begins with that string.
2175 .Ar old Ns = Ns Ar new
2176 operand is not also specified with
2178 the string form of the first operand cannot contain an embedded equal sign.
2182 The following variables affect the execution of
2184 .Bl -tag -width ".Va HISTSIZE"
2186 Name of the editor to use for history editing.
2188 The number of previous commands that are accessible.
2193 or the current job to the foreground.
2194 .It Ic getopts Ar optstring var
2201 command deprecates the older
2204 The first argument should be a series of letters, each possibly
2205 followed by a colon which indicates that the option takes an argument.
2206 The specified variable is set to the parsed option.
2208 the next argument is placed into the shell variable
2210 If an option takes an argument, it is placed into the shell variable
2212 If an invalid option is encountered,
2216 It returns a false value (1) when it encounters the end of the options.
2217 .It Ic hash Oo Fl rv Oc Op Ar command ...
2218 The shell maintains a hash table which remembers the locations of commands.
2219 With no arguments whatsoever, the
2221 command prints out the contents of this table.
2222 Entries which have not been looked at since the last
2224 command are marked with an asterisk;
2225 it is possible for these entries to be invalid.
2229 command removes each specified
2231 from the hash table (unless they are functions) and then locates it.
2236 prints the locations of the commands as it finds them.
2241 command to delete all the entries in the hash table except for functions.
2242 .It Ic jobid Op Ar job
2243 Print the process IDs of the processes in the specified
2247 argument is omitted, use the current job.
2248 .It Ic jobs Oo Fl lps Oc Op Ar job ...
2249 Print information about the specified jobs, or all jobs if no
2252 The information printed includes job ID, status and command name.
2256 option is specified, the PID of each job is also printed.
2259 option is specified, only the process IDs for the process group leaders
2260 are printed, one per line.
2263 option is specified, only the PIDs of the job commands are printed, one per
2266 A built-in equivalent of
2268 that additionally supports sending signals to jobs.
2269 .It Ic local Oo Ar variable ... Oc Op Fl
2274 A built-in equivalent of
2276 .It Ic pwd Op Fl L | P
2277 Print the path of the current directory.
2278 The built-in command may
2279 differ from the program of the same name because the
2280 built-in command remembers what the current directory
2281 is rather than recomputing it each time.
2284 However, if the current directory is
2286 the built-in version of
2288 will continue to print the old name for the directory.
2292 option is specified, symbolic links are resolved.
2295 option is specified, the shell's notion of the current directory
2296 is printed (symbolic links are not resolved).
2297 This is the default.
2298 .It Ic read Oo Fl p Ar prompt Oc Oo
2299 .Fl t Ar timeout Oc Oo Fl er Oc Ar variable ...
2305 and the standard input is a terminal.
2307 read from the standard input.
2308 The trailing newline
2309 is deleted from the line and the line is split as
2310 described in the section on
2311 .Sx White Space Splitting (Field Splitting)
2313 the pieces are assigned to the variables in order.
2314 If there are more pieces than variables, the remaining
2315 pieces (along with the characters in
2317 that separated them)
2318 are assigned to the last variable.
2319 If there are more variables than pieces, the remaining
2320 variables are assigned the null string.
2322 Backslashes are treated specially, unless the
2326 If a backslash is followed by
2327 a newline, the backslash and the newline will be
2329 If a backslash is followed by any other
2330 character, the backslash will be deleted and the following
2331 character will be treated as though it were not in
2337 option is specified and the
2339 elapses before a complete line of input is supplied,
2342 command will return an exit status of 1 without assigning any values.
2345 value may optionally be followed by one of
2350 to explicitly specify seconds, minutes or hours.
2351 If none is supplied,
2357 option exists only for backward compatibility with older scripts.
2358 .It Ic readonly Oo Fl p Oc Op Ar name ...
2361 is marked as read only,
2362 so that it cannot be subsequently modified or unset.
2363 The shell allows the value of a variable to be set
2364 at the same time as it is marked read only
2365 by using the following form:
2367 .D1 Ic readonly Ar name Ns = Ns Ar value
2369 With no arguments the
2371 command lists the names of all read only variables.
2374 option is specified, the read-only variables are printed as
2375 .Dq Ic readonly Ar name Ns = Ns Ar value
2376 lines, suitable for re-input to the shell.
2377 .It Ic return Op Ar exitstatus
2381 .It Ic set Oo Fl /+abCEefIimnpTuVvx Oc Oo Fl /+o Ar longname Oc Oo
2382 .Fl c Ar string Oc Op Fl - Ar arg ...
2385 command performs three different functions:
2388 With no arguments, it lists the values of all shell variables.
2390 If options are given,
2391 either in short form or using the long
2392 .Dq Fl /+o Ar longname
2394 it sets or clears the specified options as described in the section called
2395 .Sx Argument List Processing .
2399 option is specified,
2401 will replace the shell's positional parameters with the subsequent
2403 If no arguments follow the
2406 all the positional parameters will be cleared,
2407 which is equivalent to executing the command
2411 flag may be omitted when specifying arguments to be used
2412 as positional replacement parameters.
2413 This is not recommended,
2414 because the first argument may begin with a dash
2420 command will interpret as a request to enable or disable options.
2422 .It Ic setvar Ar variable value
2423 Assigns the specified
2429 command is intended to be used in functions that
2430 assign values to variables whose names are passed as parameters.
2431 In general it is better to write
2432 .Dq Ar variable Ns = Ns Ar value
2435 .It Ic shift Op Ar n
2436 Shift the positional parameters
2441 A shift sets the value of
2450 decreasing the value of
2453 If there are zero positional parameters, shifting does not do anything.
2455 A built-in equivalent of
2458 Print the amount of time spent executing the shell process and its children.
2459 The first output line shows the user and system times for the shell process
2460 itself, the second one contains the user and system times for the
2462 .It Ic trap Oo Ar action Oc Ar signal ...
2464 Cause the shell to parse and execute
2469 The signals are specified by name or number.
2470 In addition, the pseudo-signal
2472 may be used to specify an
2474 that is performed when the shell terminates.
2477 may be an empty string or a dash
2479 the former causes the specified signal to be ignored
2480 and the latter causes the default action to be taken.
2483 is another way to request the default action, for compatibility reasons this
2484 usage is not recommended though.
2485 In a subshell or utility environment,
2486 the shell resets trapped (but not ignored) signals to the default action.
2489 command has no effect on signals that were ignored on entry to the shell.
2495 command to display a list of valid signal names.
2497 A null command that returns a 0 (true) exit value.
2498 .It Ic type Op Ar name ...
2501 as a command and print the resolution of the command search.
2502 Possible resolutions are:
2503 shell keyword, alias, special shell builtin, shell builtin, command,
2506 For aliases the alias expansion is printed;
2507 for commands and tracked aliases
2508 the complete pathname of the command is printed.
2509 .It Ic ulimit Oo Fl HSabcdflmnpstuvw Oc Op Ar limit
2510 Set or display resource limits (see
2514 is specified, the named resource will be set;
2515 otherwise the current resource value will be displayed.
2519 is specified, the hard limits will be set or displayed.
2520 While everybody is allowed to reduce a hard limit,
2521 only the superuser can increase it.
2525 specifies the soft limits instead.
2526 When displaying limits,
2532 The default is to display the soft limits,
2533 and to set both the hard and the soft limits.
2539 command to display all resources.
2542 is not acceptable in this mode.
2544 The remaining options specify which resource value is to be
2545 displayed or modified.
2546 They are mutually exclusive.
2547 .Bl -tag -width indent
2549 The maximum size of socket buffer usage, in bytes.
2550 .It Fl c Ar coredumpsize
2551 The maximal size of core dump files, in 512-byte blocks.
2552 .It Fl d Ar datasize
2553 The maximal size of the data segment of a process, in kilobytes.
2554 .It Fl f Ar filesize
2555 The maximal size of a file, in 512-byte blocks.
2556 .It Fl l Ar lockedmem
2557 The maximal size of memory that can be locked by a process, in
2559 .It Fl m Ar memoryuse
2560 The maximal resident set size of a process, in kilobytes.
2562 The maximal number of descriptors that could be opened by a process.
2563 .It Fl p Ar pseudoterminals
2564 The maximal number of pseudo-terminals for this user ID.
2565 .It Fl s Ar stacksize
2566 The maximal size of the stack segment, in kilobytes.
2568 The maximal amount of CPU time to be used by each process, in seconds.
2569 .It Fl u Ar userproc
2570 The maximal number of simultaneous processes for this user ID.
2571 .It Fl v Ar virtualmem
2572 The maximal virtual size of a process, in kilobytes.
2574 The maximum amount of swap space reserved or used for this user ID,
2577 .It Ic umask Oo Fl S Oc Op Ar mask
2578 Set the file creation mask (see
2580 to the octal or symbolic (see
2584 If the argument is omitted, the current mask value is printed.
2587 option is specified, the output is symbolic, otherwise the output is octal.
2588 .It Ic unalias Oo Fl a Oc Op Ar name ...
2589 The specified alias names are removed.
2592 is specified, all aliases are removed.
2593 .It Ic unset Oo Fl fv Oc Ar name ...
2594 The specified variables or functions are unset and unexported.
2597 option is specified or no options are given, the
2599 arguments are treated as variable names.
2602 option is specified, the
2604 arguments are treated as function names.
2605 .It Ic wait Op Ar job
2606 Wait for the specified
2608 to complete and return the exit status of the last process in the
2610 If the argument is omitted, wait for all jobs to complete
2611 and return an exit status of zero.
2613 .Ss Commandline Editing
2616 is being used interactively from a terminal, the current command
2617 and the command history
2621 .Sx Built-in Commands )
2624 command line editing.
2625 This mode uses commands similar
2626 to a subset of those described in the
2644 can be switched between insert mode and command mode by typing
2648 while in command mode will pass the line to the shell.
2651 .Dq Li "set -o emacs"
2654 command can be used to enable a subset of
2656 command line editing features.
2658 The following environment variables affect the execution of
2660 .Bl -tag -width ".Ev LANGXXXXXX"
2662 Initialization file for interactive shells.
2663 .It Ev LANG , Ev LC_*
2665 These are inherited by children of the shell,
2666 and is used in a limited manner by the shell itself.
2668 An absolute pathname for the current directory,
2669 possibly containing symbolic links.
2670 This is used and updated by the shell.
2672 The default terminal setting for the shell.
2673 This is inherited by children of the shell, and is used in the history
2677 Additionally, all environment variables are turned into shell variables
2679 which may affect the shell as described under
2680 .Sx Special Variables .
2682 Errors that are detected by the shell, such as a syntax error, will
2683 cause the shell to exit with a non-zero exit status.
2684 If the shell is not an interactive shell, the execution of the shell
2685 file will be aborted.
2686 Otherwise the shell will return the exit status of the last command
2689 builtin is used with a numeric argument, it
2690 will return the argument.
2710 command, the Thompson shell, appeared in
2712 It was superseded in
2714 by the Bourne shell, which inherited the name
2719 was rewritten in 1989 under the
2721 license after the Bourne shell from
2726 was originally written by
2727 .An Kenneth Almquist .
2731 utility does not recognize multibyte characters other than UTF-8.
2734 and the line editing library
2736 do not recognize multibyte characters.
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