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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:
490 .Bl -column "XXX" "XXX" "XXX" "XXX" "XXX" -offset center -compact
491 .It Li $ Ta Li ` Ta Li \&" Ta Li \e\ Ta Li \en
494 A backslash preserves the literal meaning of the following
495 character, with the exception of the newline character
497 A backslash preceding a newline is treated as a line continuation.
500 Keywords or reserved words are words that have special meaning to the
501 shell and are recognized at the beginning of a line and
502 after a control operator.
503 The following are keywords:
504 .Bl -column "doneXX" "elifXX" "elseXX" "untilXX" "whileX" -offset center
505 .It Li \&! Ta { Ta } Ta Ic case Ta Ic do
506 .It Ic done Ta Ic elif Ta Ic else Ta Ic esac Ta Ic fi
507 .It Ic for Ta Ic if Ta Ic then Ta Ic until Ta Ic while
510 An alias is a name and corresponding value set using the
513 Wherever the command word of a simple command may occur,
514 and after checking for keywords if a keyword may occur, the shell
515 checks the word to see if it matches an alias.
516 If it does, it replaces it in the input stream with its value.
517 For example, if there is an alias called
529 Aliases provide a convenient way for naive users to
530 create shorthands for commands without having to learn how
531 to create functions with arguments.
532 Using aliases in scripts is discouraged
533 because the command that defines them must be executed
534 before the code that uses them is parsed.
535 This is fragile and not portable.
537 An alias name may be escaped in a command line, so that it is not
538 replaced by its alias value, by using quoting characters within or
539 adjacent to the alias name.
540 This is most often done by prefixing
541 an alias name with a backslash to execute a function, built-in, or
542 normal program with the same name.
547 The shell interprets the words it reads according to a
548 language, the specification of which is outside the scope
549 of this man page (refer to the BNF in the
552 Essentially though, a line is read and if
553 the first word of the line (or after a control operator)
554 is not a keyword, then the shell has recognized a
556 Otherwise, a complex command or some
557 other special construct may have been recognized.
559 If a simple command has been recognized, the shell performs
560 the following actions:
563 Leading words of the form
565 are stripped off and assigned to the environment of
567 Redirection operators and
568 their arguments (as described below) are stripped
569 off and saved for processing.
571 The remaining words are expanded as described in
573 .Sx Word Expansions ,
574 and the first remaining word is considered the command
575 name and the command is located.
577 words are considered the arguments of the command.
578 If no command name resulted, then the
580 variable assignments recognized in 1) affect the
583 Redirections are performed as described in
587 Redirections are used to change where a command reads its input
589 In general, redirections open, close, or
590 duplicate an existing reference to a file.
592 used for redirection is:
594 .D1 Oo Ar n Oc Ar redir-op file
598 is one of the redirection operators mentioned
600 The following gives some examples of how these
601 operators can be used.
602 Note that stdin and stdout are commonly used abbreviations
603 for standard input and standard output respectively.
604 .Bl -tag -width "1234567890XX" -offset indent
605 .It Oo Ar n Oc Ns Li > Ar file
606 redirect stdout (or file descriptor
610 .It Oo Ar n Oc Ns Li >| Ar file
611 same as above, but override the
614 .It Oo Ar n Oc Ns Li >> Ar file
615 append stdout (or file descriptor
619 .It Oo Ar n Oc Ns Li < Ar file
620 redirect stdin (or file descriptor
624 .It Oo Ar n Oc Ns Li <> Ar file
625 redirect stdin (or file descriptor
629 .It Oo Ar n1 Oc Ns Li <& Ns Ar n2
630 duplicate stdin (or file descriptor
634 .It Oo Ar n Oc Ns Li <&-
635 close stdin (or file descriptor
637 .It Oo Ar n1 Oc Ns Li >& Ns Ar n2
638 duplicate stdout (or file descriptor
642 .It Oo Ar n Oc Ns Li >&-
643 close stdout (or file descriptor
647 The following redirection is often called a
649 .Bd -unfilled -offset indent
650 .Oo Ar n Oc Ns Li << Ar delimiter
656 All the text on successive lines up to the delimiter is
657 saved away and made available to the command on standard
658 input, or file descriptor
663 as specified on the initial line is quoted, then the
665 is treated literally, otherwise the text is subjected to
666 parameter expansion, command substitution, and arithmetic
667 expansion (as described in the section on
668 .Sx Word Expansions ) .
677 .Ss Search and Execution
678 There are three types of commands: shell functions,
679 built-in commands, and normal programs.
680 The command is searched for (by name) in that order.
681 The three types of commands are all executed in a different way.
683 When a shell function is executed, all of the shell positional
686 which remains unchanged) are
687 set to the arguments of the shell function.
688 The variables which are explicitly placed in the environment of
689 the command (by placing assignments to them before the
690 function name) are made local to the function and are set
692 Then the command given in the function definition is executed.
693 The positional parameters are restored to their original values
694 when the command completes.
695 This all occurs within the current shell.
697 Shell built-in commands are executed internally to the shell, without
698 spawning a new process.
699 There are two kinds of built-in commands: regular and special.
700 Assignments before special builtins persist after they finish
701 executing and assignment errors, redirection errors and certain
702 operand errors cause a script to be aborted.
703 Special builtins cannot be overridden with a function.
704 Both regular and special builtins can affect the shell in ways
705 normal programs cannot.
707 Otherwise, if the command name does not match a function
708 or built-in command, the command is searched for as a normal
709 program in the file system (as described in the next section).
710 When a normal program is executed, the shell runs the program,
711 passing the arguments and the environment to the program.
712 If the program is not a normal executable file
713 (i.e., if it does not begin with the
723 but appears to be a text file,
724 the shell will run a new instance of
728 Note that previous versions of this document
729 and the source code itself misleadingly and sporadically
730 refer to a shell script without a magic number
732 .Dq "shell procedure" .
734 When locating a command, the shell first looks to see if
735 it has a shell function by that name.
737 built-in command by that name.
738 If a built-in command is not found,
739 one of two things happen:
742 Command names containing a slash are simply executed without
743 performing any searches.
745 The shell searches each entry in the
748 in turn for the command.
751 variable should be a series of
752 entries separated by colons.
753 Each entry consists of a
755 The current directory
756 may be indicated implicitly by an empty directory name,
757 or explicitly by a single period.
759 .Ss Command Exit Status
760 Each command has an exit status that can influence the behavior
761 of other shell commands.
762 The paradigm is that a command exits
763 with zero for normal or success, and non-zero for failure,
764 error, or a false indication.
765 The man page for each command
766 should indicate the various exit codes and what they mean.
767 Additionally, the built-in commands return exit codes, as does
768 an executed shell function.
770 If a command is terminated by a signal, its exit status is 128 plus
772 Signal numbers are defined in the header file
775 Complex commands are combinations of simple commands
776 with control operators or keywords, together creating a larger complex
778 More generally, a command is one of the following:
779 .Bl -item -offset indent
785 list or compound-list
792 Unless otherwise stated, the exit status of a command is
793 that of the last simple command executed by the command.
795 A pipeline is a sequence of one or more commands separated
796 by the control operator
798 The standard output of all but
799 the last command is connected to the standard input
801 The standard output of the last
802 command is inherited from the shell, as usual.
804 The format for a pipeline is:
806 .D1 Oo Li \&! Oc Ar command1 Op Li \&| Ar command2 ...
808 The standard output of
810 is connected to the standard input of
812 The standard input, standard output, or
813 both of a command is considered to be assigned by the
814 pipeline before any redirection specified by redirection
815 operators that are part of the command.
817 Note that unlike some other shells,
819 executes each process in a pipeline with more than one command
820 in a subshell environment and as a child of the
824 If the pipeline is not in the background (discussed later),
825 the shell waits for all commands to complete.
829 does not precede the pipeline, the
830 exit status is the exit status of the last command specified
832 Otherwise, the exit status is the logical
833 NOT of the exit status of the last command.
835 the last command returns zero, the exit status is 1; if
836 the last command returns greater than zero, the exit status
839 Because pipeline assignment of standard input or standard
840 output or both takes place before redirection, it can be
841 modified by redirection.
844 .Dl "command1 2>&1 | command2"
846 sends both the standard output and standard error of
848 to the standard input of
853 or newline terminator causes the preceding
855 (described below in the section called
856 .Sx Short-Circuit List Operators )
857 to be executed sequentially;
860 causes asynchronous execution of the preceding AND-OR-list.
861 .Ss Background Commands (&)
862 If a command is terminated by the control operator ampersand
864 the shell executes the command in a subshell environment (see
865 .Sx Grouping Commands Together
866 below) and asynchronously;
867 the shell does not wait for the command to finish
868 before executing the next command.
870 The format for running a command in background is:
872 .D1 Ar command1 Li & Op Ar command2 Li & Ar ...
874 If the shell is not interactive, the standard input of an
875 asynchronous command is set to
877 .Ss Lists (Generally Speaking)
878 A list is a sequence of zero or more commands separated by
879 newlines, semicolons, or ampersands,
880 and optionally terminated by one of these three characters.
882 list are executed in the order they are written.
883 If command is followed by an ampersand, the shell starts the
884 command and immediately proceeds onto the next command;
885 otherwise it waits for the command to terminate before
886 proceeding to the next one.
887 .Ss Short-Circuit List Operators
891 are AND-OR list operators.
893 executes the first command, and then executes the second command
894 if the exit status of the first command is zero.
896 is similar, but executes the second command if the exit
897 status of the first command is nonzero.
901 both have the same priority.
902 .Ss Flow-Control Constructs (if, while, for, case)
906 .Bd -unfilled -offset indent -compact
910 .Ic then Ar list Oc Ar ...
918 .Bd -unfilled -offset indent -compact
924 The two lists are executed repeatedly while the exit status of the
928 command is similar, but has the word
933 repeat until the exit status of the first list is zero.
938 .Bd -unfilled -offset indent -compact
939 .Ic for Ar variable Op Ic in Ar word ...
946 and the following words are omitted,
949 The words are expanded, and then the list is executed
950 repeatedly with the variable set to each word in turn.
955 commands may be replaced with
965 .D1 Ic break Op Ar num
966 .D1 Ic continue Op Ar num
970 command terminates the
979 command continues with the next iteration of the innermost loop.
980 These are implemented as special built-in commands.
985 .Bd -unfilled -offset indent -compact
986 .Ic case Ar word Ic in
987 .Ar pattern Ns Li ) Ar list Li ;;
992 The pattern can actually be one or more patterns
999 Tilde expansion, parameter expansion, command substitution,
1000 arithmetic expansion and quote removal are applied to the word.
1001 Then, each pattern is expanded in turn using tilde expansion,
1002 parameter expansion, command substitution and arithmetic expansion and
1003 the expanded form of the word is checked against it.
1004 If a match is found, the corresponding list is executed.
1005 If the selected list is terminated by the control operator
1009 execution continues with the next list,
1010 continuing until a list terminated with
1015 The exit code of the
1017 command is the exit code of the last command executed in the list or
1018 zero if no patterns were matched.
1019 .Ss Grouping Commands Together
1020 Commands may be grouped by writing either
1022 .D1 Li \&( Ns Ar list Ns Li \%)
1026 .D1 Li { Ar list Ns Li \&; }
1028 The first form executes the commands in a subshell environment.
1029 A subshell environment has its own copy of:
1032 The current working directory as set by
1035 The file creation mask as set by
1038 References to open files.
1045 Positional parameters and variables.
1054 These are copied from the parent shell environment,
1055 except that trapped (but not ignored) signals are reset to the default action
1056 and known jobs are cleared.
1057 Any changes do not affect the parent shell environment.
1059 A subshell environment may be implemented as a child process or differently.
1060 If job control is enabled in an interactive shell,
1061 commands grouped in parentheses can be suspended and continued as a unit.
1063 The second form never forks another shell,
1064 so it is slightly more efficient.
1065 Grouping commands together this way allows the user to
1066 redirect their output as though they were one program:
1067 .Bd -literal -offset indent
1068 { echo -n "hello"; echo " world"; } > greeting
1071 The syntax of a function definition is
1073 .D1 Ar name Li \&( \&) Ar command
1075 A function definition is an executable statement; when
1076 executed it installs a function named
1079 exit status of zero.
1088 Variables may be declared to be local to a function by
1092 This should appear as the first statement of a function,
1095 .D1 Ic local Oo Ar variable ... Oc Op Fl
1099 command is implemented as a built-in command.
1101 When a variable is made local, it inherits the initial
1102 value and exported and readonly flags from the variable
1103 with the same name in the surrounding scope, if there is
1105 Otherwise, the variable is initially unset.
1107 uses dynamic scoping, so that if the variable
1109 is made local to function
1111 which then calls function
1113 references to the variable
1117 will refer to the variable
1121 not to the global variable named
1124 The only special parameter that can be made local is
1128 local causes any shell options that are
1131 command inside the function to be
1132 restored to their original values when the function
1139 .D1 Ic return Op Ar exitstatus
1141 It terminates the current executional scope, returning from the previous
1142 nested function, sourced script, or shell instance, in that order.
1145 command is implemented as a special built-in command.
1146 .Ss Variables and Parameters
1147 The shell maintains a set of parameters.
1149 denoted by a name is called a variable.
1151 the shell turns all the environment variables into shell
1153 New variables can be set using the form
1155 .D1 Ar name Ns = Ns Ar value
1157 Variables set by the user must have a name consisting solely
1158 of alphabetics, numerics, and underscores.
1159 The first letter of a variable name must not be numeric.
1160 A parameter can also be denoted by a number
1161 or a special character as explained below.
1163 Assignments are expanded differently from other words:
1164 tilde expansion is also performed after the equals sign and after any colon
1165 and usernames are also terminated by colons,
1166 and field splitting and pathname expansion are not performed.
1167 .Ss Positional Parameters
1168 A positional parameter is a parameter denoted by a number greater than zero.
1169 The shell sets these initially to the values of its command line
1170 arguments that follow the name of the shell script.
1173 built-in command can also be used to set or reset them.
1174 .Ss Special Parameters
1175 Special parameters are parameters denoted by a single special character
1177 They are shown in the following list, exactly as they would appear in input
1178 typed by the user or in the source of a shell script.
1181 Expands to the positional parameters, starting from one.
1183 the expansion occurs within a double-quoted string
1184 it expands to a single field with the value of each parameter
1185 separated by the first character of the
1192 Expands to the positional parameters, starting from one.
1194 the expansion occurs within double-quotes, each positional
1195 parameter expands as a separate argument.
1196 If there are no positional parameters, the
1199 generates zero arguments, even when
1202 What this basically means, for example, is
1215 .Bd -literal -offset indent
1219 Expands to the number of positional parameters.
1221 Expands to the exit status of the most recent pipeline.
1223 (hyphen) Expands to the current option flags (the single-letter
1224 option names concatenated into a string) as specified on
1227 built-in command, or implicitly
1230 Expands to the process ID of the invoked shell.
1232 retains the same value of
1236 Expands to the process ID of the most recent background
1237 command executed from the current shell.
1239 pipeline, the process ID is that of the last command in the
1241 If this parameter is referenced, the shell will remember
1242 the process ID and its exit status until the
1244 built-in command reports completion of the process.
1246 (zero) Expands to the name of the shell script if passed on the command line,
1249 operand if given (with
1251 or otherwise argument 0 passed to the shell.
1253 .Ss Special Variables
1254 The following variables are set by the shell or
1255 have special meaning to it:
1256 .Bl -tag -width ".Va HISTSIZE"
1258 The search path used with the
1262 The fallback editor used with the
1265 If not set, the default editor is
1268 The default editor used with the
1272 The number of previous commands that are accessible.
1274 The user's home directory,
1275 used in tilde expansion and as a default directory for the
1279 Input Field Separators.
1280 The default value is
1286 This default also applies if
1288 is unset, but not if it is set to the empty string.
1290 .Sx White Space Splitting
1291 section for more details.
1293 The current line number in the script or function.
1295 The name of a mail file, that will be checked for the arrival of new
1302 separated list of file names, for the shell to check for incoming
1304 This variable overrides the
1307 There is a maximum of 10 mailboxes that can be monitored at once.
1309 The default search path for executables.
1312 section for details.
1314 The parent process ID of the invoked shell.
1315 This is set at startup
1316 unless this variable is in the environment.
1317 A later change of parent process ID is not reflected.
1318 A subshell retains the same value of
1321 The primary prompt string, which defaults to
1323 unless you are the superuser, in which case it defaults to
1326 The secondary prompt string, which defaults to
1329 The prefix for the trace output (if
1336 This clause describes the various expansions that are
1338 Not all expansions are performed on
1339 every word, as explained later.
1341 Tilde expansions, parameter expansions, command substitutions,
1342 arithmetic expansions, and quote removals that occur within
1343 a single word expand to a single field.
1345 splitting or pathname expansion that can create multiple
1346 fields from a single word.
1347 The single exception to this rule is
1348 the expansion of the special parameter
1350 within double-quotes,
1351 as was described above.
1353 The order of word expansion is:
1356 Tilde Expansion, Parameter Expansion, Command Substitution,
1357 Arithmetic Expansion (these all occur at the same time).
1359 Field Splitting is performed on fields generated by step (1)
1364 Pathname Expansion (unless the
1366 option is in effect).
1373 character is used to introduce parameter expansion, command
1374 substitution, or arithmetic expansion.
1375 .Ss Tilde Expansion (substituting a user's home directory)
1376 A word beginning with an unquoted tilde character
1379 subjected to tilde expansion.
1380 All the characters up to a slash
1382 or the end of the word are treated as a username
1383 and are replaced with the user's home directory.
1385 username is missing (as in
1387 the tilde is replaced with the value of the
1389 variable (the current user's home directory).
1390 .Ss Parameter Expansion
1391 The format for parameter expansion is as follows:
1393 .D1 Li ${ Ns Ar expression Ns Li }
1397 consists of all characters until the matching
1401 escaped by a backslash or within a single-quoted or double-quoted
1402 string, and characters in
1403 embedded arithmetic expansions, command substitutions, and variable
1404 expansions, are not examined in determining the matching
1406 If the variants with
1412 occur within a double-quoted string,
1413 as an extension there may be unquoted parts
1414 (via double-quotes inside the expansion);
1416 within such parts are also not examined in determining the matching
1419 The simplest form for parameter expansion is:
1421 .D1 Li ${ Ns Ar parameter Ns Li }
1423 The value, if any, of
1427 The parameter name or symbol can be enclosed in braces, which are
1428 optional except for positional parameters with more than one digit or
1429 when parameter is followed by a character that could be interpreted as
1431 If a parameter expansion occurs inside double-quotes:
1434 Field splitting is not performed on the results of the
1435 expansion, with the exception of the special parameter
1438 Pathname expansion is not performed on the results of the
1442 In addition, a parameter expansion can be modified by using one of the
1444 .Bl -tag -width indent
1445 .It Li ${ Ns Ar parameter Ns Li :- Ns Ar word Ns Li }
1449 is unset or null, the expansion of
1451 is substituted; otherwise, the value of
1454 .It Li ${ Ns Ar parameter Ns Li := Ns Ar word Ns Li }
1455 Assign Default Values.
1458 is unset or null, the expansion of
1468 does not prevent field splitting or pathname expansion.
1469 Only variables, not positional
1470 parameters or special parameters, can be
1471 assigned in this way.
1472 .It Li ${ Ns Ar parameter Ns Li :? Ns Oo Ar word Oc Ns Li }
1473 Indicate Error if Null or Unset.
1476 is unset or null, the expansion of
1478 (or a message indicating it is unset if
1480 is omitted) is written to standard
1481 error and the shell exits with a nonzero
1483 Otherwise, the value of
1487 interactive shell need not exit.
1488 .It Li ${ Ns Ar parameter Ns Li :+ Ns Ar word Ns Li }
1489 Use Alternate Value.
1492 is unset or null, null is substituted;
1493 otherwise, the expansion of
1498 In the parameter expansions shown previously, use of the colon in the
1499 format results in a test for a parameter that is unset or null; omission
1500 of the colon results in a test for a parameter that is only unset.
1504 inherits the type of quoting
1505 (unquoted, double-quoted or here-document)
1506 from the surroundings,
1507 with the exception that a backslash that quotes a closing brace is removed
1508 during quote removal.
1509 .Bl -tag -width indent
1510 .It Li ${# Ns Ar parameter Ns Li }
1512 The length in characters of
1517 The following four varieties of parameter expansion provide for substring
1519 In each case, pattern matching notation
1521 .Sx Shell Patterns ) ,
1522 rather than regular expression notation,
1523 is used to evaluate the patterns.
1524 If parameter is one of the special parameters
1528 the result of the expansion is unspecified.
1529 Enclosing the full parameter expansion string in double-quotes does not
1530 cause the following four varieties of pattern characters to be quoted,
1531 whereas quoting characters within the braces has this effect.
1532 .Bl -tag -width indent
1533 .It Li ${ Ns Ar parameter Ns Li % Ns Ar word Ns Li }
1534 Remove Smallest Suffix Pattern.
1537 is expanded to produce a pattern.
1539 parameter expansion then results in
1541 with the smallest portion of the
1542 suffix matched by the pattern deleted.
1543 .It Li ${ Ns Ar parameter Ns Li %% Ns Ar word Ns Li }
1544 Remove Largest Suffix Pattern.
1547 is expanded to produce a pattern.
1549 parameter expansion then results in
1551 with the largest portion of the
1552 suffix matched by the pattern deleted.
1553 .It Li ${ Ns Ar parameter Ns Li # Ns Ar word Ns Li }
1554 Remove Smallest Prefix Pattern.
1557 is expanded to produce a pattern.
1559 parameter expansion then results in
1561 with the smallest portion of the
1562 prefix matched by the pattern deleted.
1563 .It Li ${ Ns Ar parameter Ns Li ## Ns Ar word Ns Li }
1564 Remove Largest Prefix Pattern.
1567 is expanded to produce a pattern.
1569 parameter expansion then results in
1571 with the largest portion of the
1572 prefix matched by the pattern deleted.
1574 .Ss Command Substitution
1575 Command substitution allows the output of a command to be substituted in
1576 place of the command name itself.
1577 Command substitution occurs when
1578 the command is enclosed as follows:
1580 .D1 Li $( Ns Ar command Ns Li )\&
1582 or the backquoted version:
1584 .D1 Li ` Ns Ar command Ns Li `
1586 The shell expands the command substitution by executing command
1587 and replacing the command substitution
1588 with the standard output of the command,
1589 removing sequences of one or more newlines at the end of the substitution.
1590 Embedded newlines before the end of the output are not removed;
1591 however, during field splitting, they may be translated into spaces
1592 depending on the value of
1594 and the quoting that is in effect.
1595 The command is executed in a subshell environment,
1596 except that the built-in commands
1601 return information about the parent shell environment
1604 returns information about the same process
1605 if they are the only command in a command substitution.
1606 .Ss Arithmetic Expansion
1607 Arithmetic expansion provides a mechanism for evaluating an arithmetic
1608 expression and substituting its value.
1609 The format for arithmetic expansion is as follows:
1611 .D1 Li $(( Ns Ar expression Ns Li ))
1615 is treated as if it were in double-quotes, except
1616 that a double-quote inside the expression is not treated specially.
1618 shell expands all tokens in the
1620 for parameter expansion,
1621 command substitution,
1622 arithmetic expansion
1625 The allowed expressions are a subset of C expressions,
1627 .Bl -tag -width "Variables" -offset indent
1629 All values are of type
1632 Decimal, octal (starting with
1634 and hexadecimal (starting with
1638 Shell variables can be read and written
1639 and contain integer constants.
1642 .It Binary operators
1643 .Li "* / % + - << >> < <= > >= == != & ^ | && ||"
1644 .It Assignment operators
1645 .Li "= += -= *= /= %= <<= >>= &= ^= |="
1646 .It Conditional operator
1650 The result of the expression is substituted in decimal.
1651 .Ss White Space Splitting (Field Splitting)
1652 In certain contexts,
1653 after parameter expansion, command substitution, and
1654 arithmetic expansion the shell scans the results of
1655 expansions and substitutions that did not occur in double-quotes for
1656 field splitting and multiple fields can result.
1667 are treated differently from other characters in
1672 at the beginning or end of a word is discarded.
1674 Subsequently, a field is delimited by either
1677 a non-whitespace character in
1679 with any whitespace in
1683 one or more whitespace characters in
1687 If a word ends with a non-whitespace character in
1689 there is no empty field after this character.
1691 If no field is delimited, the word is discarded.
1692 In particular, if a word consists solely of an unquoted substitution
1693 and the result of the substitution is null,
1694 it is removed by field splitting even if
1697 .Ss Pathname Expansion (File Name Generation)
1701 file name generation is performed
1702 after word splitting is complete.
1704 viewed as a series of patterns, separated by slashes.
1706 process of expansion replaces the word with the names of
1707 all existing files whose names can be formed by replacing
1708 each pattern with a string that matches the specified pattern.
1709 There are two restrictions on this: first, a pattern cannot match
1710 a string containing a slash, and second,
1711 a pattern cannot match a string starting with a period
1712 unless the first character of the pattern is a period.
1713 The next section describes the patterns used for
1715 the four varieties of parameter expansion for substring processing and the
1719 A pattern consists of normal characters, which match themselves,
1720 and meta-characters.
1721 The meta-characters are
1726 These characters lose their special meanings if they are quoted.
1727 When command or variable substitution is performed and the dollar sign
1728 or back quotes are not double-quoted, the value of the
1729 variable or the output of the command is scanned for these
1730 characters and they are turned into meta-characters.
1734 matches any string of characters.
1737 matches any single character.
1740 introduces a character class.
1741 The end of the character class is indicated by a
1749 rather than introducing a character class.
1750 A character class matches any of the characters between the square brackets.
1751 A locale-dependent range of characters may be specified using a minus sign.
1752 A named class of characters (see
1754 may be specified by surrounding the name with
1759 .Ql \&[\&[:alpha:\&]\&]
1760 is a shell pattern that matches a single letter.
1761 The character class may be complemented by making an exclamation point
1763 the first character of the character class.
1766 has the same effect but is non-standard.
1770 in a character class, make it the first character listed
1778 make it the first or last character listed.
1779 .Ss Built-in Commands
1780 This section lists the built-in commands.
1781 .Bl -tag -width indent
1783 A null command that returns a 0 (true) exit value.
1785 The commands in the specified file are read and executed by the shell.
1788 command may be used to return to the
1795 characters, it is used as is.
1796 Otherwise, the shell searches the
1799 If it is not found in the
1801 it is sought in the current working directory.
1803 A built-in equivalent of
1805 .It Ic alias Oo Ar name Ns Oo = Ns Ar string Oc ... Oc
1807 .Ar name Ns = Ns Ar string
1808 is specified, the shell defines the alias
1814 is specified, the value of the alias
1817 With no arguments, the
1819 built-in command prints the names and values of all defined aliases
1822 Alias values are written with appropriate quoting so that they are
1823 suitable for re-input to the shell.
1827 .It Ic bg Op Ar job ...
1828 Continue the specified jobs
1829 (or the current job if no jobs are given)
1831 .It Ic bind Oo Fl aeklrsv Oc Oo Ar key Oo Ar command Oc Oc
1832 List or alter key bindings for the line editor.
1833 This command is documented in
1835 .It Ic break Op Ar num
1837 .Sx Flow-Control Constructs
1839 .It Ic builtin Ar cmd Op Ar arg ...
1840 Execute the specified built-in command,
1842 This is useful when the user wishes to override a shell function
1843 with the same name as a built-in command.
1844 .It Ic cd Oo Fl L | P Oc Oo Fl e Oc Op Ar directory
1845 Switch to the specified
1847 or to the directory specified in the
1849 environment variable if no
1858 then the directories listed in the
1861 searched for the specified
1865 is unset, the current directory is searched.
1868 is the same as that of
1870 In an interactive shell,
1873 command will print out the name of the directory
1874 that it actually switched to
1875 if this is different from the name that the user gave.
1876 These may be different either because the
1878 mechanism was used or because a symbolic link was crossed.
1882 option is specified,
1884 is handled physically and symbolic links are resolved before
1886 components are processed.
1889 option is specified,
1891 is handled logically.
1892 This is the default.
1898 to return exit status 1 if the full pathname of the new directory
1899 cannot be determined reliably or at all.
1900 Normally this is not considered an error,
1901 although a warning is printed.
1906 .It Ic command Oo Fl p Oc Op Ar utility Op Ar argument ...
1907 .It Ic command Oo Fl p Oc Fl v Ar utility
1908 .It Ic command Oo Fl p Oc Fl V Ar utility
1909 The first form of invocation executes the specified
1911 ignoring shell functions in the search.
1914 is a special builtin,
1915 it is executed as if it were a regular builtin.
1919 option is specified, the command search is performed using a
1922 that is guaranteed to find all of the standard utilities.
1926 option is specified,
1928 is not executed but a description of its interpretation by the shell is
1930 For ordinary commands the output is the path name; for shell built-in
1931 commands, shell functions and keywords only the name is written.
1932 Aliases are printed as
1933 .Dq Ic alias Ar name Ns = Ns Ar value .
1937 option is identical to
1939 except for the output.
1941 .Dq Ar utility Ic is Ar description
1947 a special shell builtin,
1954 .It Ic continue Op Ar num
1956 .Sx Flow-Control Constructs
1958 .It Ic echo Oo Fl e | n Oc Op Ar string ...
1959 Print a space-separated list of the arguments to the standard output
1960 and append a newline character.
1961 .Bl -tag -width indent
1963 Suppress the output of the trailing newline.
1965 Process C-style backslash escape sequences.
1968 command understands the following character escapes:
1969 .Bl -tag -width indent
1971 Alert (ring the terminal bell)
1975 Suppress the trailing newline (this has the side-effect of truncating the
1976 line if it is not the last character)
1994 (Zero) The character whose octal value is
2000 is not enclosed in quotes then the backslash itself must be escaped
2001 with a backslash to protect it from the shell.
2003 .Bd -literal -offset indent
2012 $ echo -e a\e\e\e\eb
2021 options may be specified.
2022 .It Ic eval Ar string ...
2023 Concatenate all the arguments with spaces.
2024 Then re-parse and execute the command.
2025 .It Ic exec Op Ar command Op arg ...
2029 the shell process is replaced with the specified program
2030 (which must be a real program, not a shell built-in command or function).
2031 Any redirections on the
2033 command are marked as permanent,
2034 so that they are not undone when the
2037 .It Ic exit Op Ar exitstatus
2038 Terminate the shell process.
2042 it is used as the exit status of the shell.
2043 Otherwise, if the shell is executing an
2045 trap, the exit status of the last command before the trap is used;
2046 if the shell is executing a trap for a signal,
2047 the shell exits by resending the signal to itself.
2048 Otherwise, the exit status of the preceding command is used.
2049 The exit status should be an integer between 0 and 255.
2050 .It Ic export Ar name ...
2051 .It Ic export Op Fl p
2052 The specified names are exported so that they will
2053 appear in the environment of subsequent commands.
2054 The only way to un-export a variable is to
2057 The shell allows the value of a variable to be set
2058 at the same time as it is exported by writing
2060 .D1 Ic export Ar name Ns = Ns Ar value
2062 With no arguments the
2064 command lists the names
2065 of all exported variables.
2068 option is specified, the exported variables are printed as
2069 .Dq Ic export Ar name Ns = Ns Ar value
2070 lines, suitable for re-input to the shell.
2072 A null command that returns a non-zero (false) exit value.
2073 .It Ic fc Oo Fl e Ar editor Oc Op Ar first Op Ar last
2074 .It Ic fc Fl l Oo Fl nr Oc Op Ar first Op Ar last
2075 .It Ic fc Fl s Oo Ar old Ns = Ns Ar new Oc Op Ar first
2078 built-in command lists, or edits and re-executes,
2079 commands previously entered to an interactive shell.
2080 .Bl -tag -width indent
2082 Use the editor named by
2084 to edit the commands.
2087 string is a command name,
2088 subject to search via the
2093 variable is used as a default when
2098 is null or unset, the value of the
2105 is used as the editor.
2107 List the commands rather than invoking
2109 The commands are written in the
2110 sequence indicated by the
2114 operands, as affected by
2116 with each command preceded by the command number.
2118 Suppress command numbers when listing with
2121 Reverse the order of the commands listed
2130 Re-execute the command without invoking an editor.
2133 Select the commands to list or edit.
2134 The number of previous commands that can be accessed
2135 are determined by the value of the
2142 or both are one of the following:
2143 .Bl -tag -width indent
2144 .It Oo Cm + Oc Ns Ar num
2145 A positive number representing a command number;
2146 command numbers can be displayed with the
2150 A negative decimal number representing the
2151 command that was executed
2154 commands previously.
2155 For example, \-1 is the immediately previous command.
2157 A string indicating the most recently entered command
2158 that begins with that string.
2160 .Ar old Ns = Ns Ar new
2161 operand is not also specified with
2163 the string form of the first operand cannot contain an embedded equal sign.
2167 The following variables affect the execution of
2169 .Bl -tag -width ".Va HISTSIZE"
2171 Name of the editor to use for history editing.
2173 The number of previous commands that are accessible.
2178 or the current job to the foreground.
2179 .It Ic getopts Ar optstring var
2186 command deprecates the older
2189 The first argument should be a series of letters, each possibly
2190 followed by a colon which indicates that the option takes an argument.
2191 The specified variable is set to the parsed option.
2193 the next argument is placed into the shell variable
2195 If an option takes an argument, it is placed into the shell variable
2197 If an invalid option is encountered,
2201 It returns a false value (1) when it encounters the end of the options.
2202 .It Ic hash Oo Fl rv Oc Op Ar command ...
2203 The shell maintains a hash table which remembers the locations of commands.
2204 With no arguments whatsoever, the
2206 command prints out the contents of this table.
2207 Entries which have not been looked at since the last
2209 command are marked with an asterisk;
2210 it is possible for these entries to be invalid.
2214 command removes each specified
2216 from the hash table (unless they are functions) and then locates it.
2221 prints the locations of the commands as it finds them.
2226 command to delete all the entries in the hash table except for functions.
2227 .It Ic jobid Op Ar job
2228 Print the process IDs of the processes in the specified
2232 argument is omitted, use the current job.
2233 .It Ic jobs Oo Fl lps Oc Op Ar job ...
2234 Print information about the specified jobs, or all jobs if no
2237 The information printed includes job ID, status and command name.
2241 option is specified, the PID of each job is also printed.
2244 option is specified, only the process IDs for the process group leaders
2245 are printed, one per line.
2248 option is specified, only the PIDs of the job commands are printed, one per
2251 A built-in equivalent of
2253 that additionally supports sending signals to jobs.
2254 .It Ic local Oo Ar variable ... Oc Op Fl
2259 A built-in equivalent of
2261 .It Ic pwd Op Fl L | P
2262 Print the path of the current directory.
2263 The built-in command may
2264 differ from the program of the same name because the
2265 built-in command remembers what the current directory
2266 is rather than recomputing it each time.
2269 However, if the current directory is
2271 the built-in version of
2273 will continue to print the old name for the directory.
2277 option is specified, symbolic links are resolved.
2280 option is specified, the shell's notion of the current directory
2281 is printed (symbolic links are not resolved).
2282 This is the default.
2283 .It Ic read Oo Fl p Ar prompt Oc Oo
2284 .Fl t Ar timeout Oc Oo Fl er Oc Ar variable ...
2290 and the standard input is a terminal.
2292 read from the standard input.
2293 The trailing newline
2294 is deleted from the line and the line is split as
2295 described in the section on
2296 .Sx White Space Splitting (Field Splitting)
2298 the pieces are assigned to the variables in order.
2299 If there are more pieces than variables, the remaining
2300 pieces (along with the characters in
2302 that separated them)
2303 are assigned to the last variable.
2304 If there are more variables than pieces, the remaining
2305 variables are assigned the null string.
2307 Backslashes are treated specially, unless the
2311 If a backslash is followed by
2312 a newline, the backslash and the newline will be
2314 If a backslash is followed by any other
2315 character, the backslash will be deleted and the following
2316 character will be treated as though it were not in
2322 option is specified and the
2324 elapses before a complete line of input is supplied,
2327 command will return an exit status of 1 without assigning any values.
2330 value may optionally be followed by one of
2335 to explicitly specify seconds, minutes or hours.
2336 If none is supplied,
2342 option exists only for backward compatibility with older scripts.
2343 .It Ic readonly Oo Fl p Oc Op Ar name ...
2346 is marked as read only,
2347 so that it cannot be subsequently modified or unset.
2348 The shell allows the value of a variable to be set
2349 at the same time as it is marked read only
2350 by using the following form:
2352 .D1 Ic readonly Ar name Ns = Ns Ar value
2354 With no arguments the
2356 command lists the names of all read only variables.
2359 option is specified, the read-only variables are printed as
2360 .Dq Ic readonly Ar name Ns = Ns Ar value
2361 lines, suitable for re-input to the shell.
2362 .It Ic return Op Ar exitstatus
2366 .It Ic set Oo Fl /+abCEefIimnpTuVvx Oc Oo Fl /+o Ar longname Oc Oo
2367 .Fl c Ar string Oc Op Fl - Ar arg ...
2370 command performs three different functions:
2373 With no arguments, it lists the values of all shell variables.
2375 If options are given,
2376 either in short form or using the long
2377 .Dq Fl /+o Ar longname
2379 it sets or clears the specified options as described in the section called
2380 .Sx Argument List Processing .
2384 option is specified,
2386 will replace the shell's positional parameters with the subsequent
2388 If no arguments follow the
2391 all the positional parameters will be cleared,
2392 which is equivalent to executing the command
2396 flag may be omitted when specifying arguments to be used
2397 as positional replacement parameters.
2398 This is not recommended,
2399 because the first argument may begin with a dash
2405 command will interpret as a request to enable or disable options.
2407 .It Ic setvar Ar variable value
2408 Assigns the specified
2414 command is intended to be used in functions that
2415 assign values to variables whose names are passed as parameters.
2416 In general it is better to write
2417 .Dq Ar variable Ns = Ns Ar value
2420 .It Ic shift Op Ar n
2421 Shift the positional parameters
2426 A shift sets the value of
2435 decreasing the value of
2438 If there are zero positional parameters, shifting does not do anything.
2440 A built-in equivalent of
2443 Print the amount of time spent executing the shell process and its children.
2444 The first output line shows the user and system times for the shell process
2445 itself, the second one contains the user and system times for the
2447 .It Ic trap Oo Ar action Oc Ar signal ...
2449 Cause the shell to parse and execute
2454 The signals are specified by name or number.
2455 In addition, the pseudo-signal
2457 may be used to specify an
2459 that is performed when the shell terminates.
2462 may be an empty string or a dash
2464 the former causes the specified signal to be ignored
2465 and the latter causes the default action to be taken.
2468 is another way to request the default action, for compatibility reasons this
2469 usage is not recommended though.
2470 In a subshell or utility environment,
2471 the shell resets trapped (but not ignored) signals to the default action.
2474 command has no effect on signals that were ignored on entry to the shell.
2480 command to display a list of valid signal names.
2482 A null command that returns a 0 (true) exit value.
2483 .It Ic type Op Ar name ...
2486 as a command and print the resolution of the command search.
2487 Possible resolutions are:
2488 shell keyword, alias, special shell builtin, shell builtin, command,
2491 For aliases the alias expansion is printed;
2492 for commands and tracked aliases
2493 the complete pathname of the command is printed.
2494 .It Ic ulimit Oo Fl HSabcdflmnpstuvw Oc Op Ar limit
2495 Set or display resource limits (see
2499 is specified, the named resource will be set;
2500 otherwise the current resource value will be displayed.
2504 is specified, the hard limits will be set or displayed.
2505 While everybody is allowed to reduce a hard limit,
2506 only the superuser can increase it.
2510 specifies the soft limits instead.
2511 When displaying limits,
2517 The default is to display the soft limits,
2518 and to set both the hard and the soft limits.
2524 command to display all resources.
2527 is not acceptable in this mode.
2529 The remaining options specify which resource value is to be
2530 displayed or modified.
2531 They are mutually exclusive.
2532 .Bl -tag -width indent
2534 The maximum size of socket buffer usage, in bytes.
2535 .It Fl c Ar coredumpsize
2536 The maximal size of core dump files, in 512-byte blocks.
2537 .It Fl d Ar datasize
2538 The maximal size of the data segment of a process, in kilobytes.
2539 .It Fl f Ar filesize
2540 The maximal size of a file, in 512-byte blocks.
2541 .It Fl l Ar lockedmem
2542 The maximal size of memory that can be locked by a process, in
2544 .It Fl m Ar memoryuse
2545 The maximal resident set size of a process, in kilobytes.
2547 The maximal number of descriptors that could be opened by a process.
2548 .It Fl p Ar pseudoterminals
2549 The maximal number of pseudo-terminals for this user ID.
2550 .It Fl s Ar stacksize
2551 The maximal size of the stack segment, in kilobytes.
2553 The maximal amount of CPU time to be used by each process, in seconds.
2554 .It Fl u Ar userproc
2555 The maximal number of simultaneous processes for this user ID.
2556 .It Fl v Ar virtualmem
2557 The maximal virtual size of a process, in kilobytes.
2559 The maximum amount of swap space reserved or used for this user ID,
2562 .It Ic umask Oo Fl S Oc Op Ar mask
2563 Set the file creation mask (see
2565 to the octal or symbolic (see
2569 If the argument is omitted, the current mask value is printed.
2572 option is specified, the output is symbolic, otherwise the output is octal.
2573 .It Ic unalias Oo Fl a Oc Op Ar name ...
2574 The specified alias names are removed.
2577 is specified, all aliases are removed.
2578 .It Ic unset Oo Fl fv Oc Ar name ...
2579 The specified variables or functions are unset and unexported.
2582 option is specified or no options are given, the
2584 arguments are treated as variable names.
2587 option is specified, the
2589 arguments are treated as function names.
2590 .It Ic wait Op Ar job
2591 Wait for the specified
2593 to complete and return the exit status of the last process in the
2595 If the argument is omitted, wait for all jobs to complete
2596 and return an exit status of zero.
2598 .Ss Commandline Editing
2601 is being used interactively from a terminal, the current command
2602 and the command history
2606 .Sx Built-in Commands )
2609 command line editing.
2610 This mode uses commands similar
2611 to a subset of those described in the
2629 can be switched between insert mode and command mode by typing
2633 while in command mode will pass the line to the shell.
2636 .Dq Li "set -o emacs"
2639 command can be used to enable a subset of
2641 command line editing features.
2643 The following environment variables affect the execution of
2645 .Bl -tag -width ".Ev LANGXXXXXX"
2647 Initialization file for interactive shells.
2648 .It Ev LANG , Ev LC_*
2650 These are inherited by children of the shell,
2651 and is used in a limited manner by the shell itself.
2653 An absolute pathname for the current directory,
2654 possibly containing symbolic links.
2655 This is used and updated by the shell.
2657 The default terminal setting for the shell.
2658 This is inherited by children of the shell, and is used in the history
2662 Additionally, all environment variables are turned into shell variables
2664 which may affect the shell as described under
2665 .Sx Special Variables .
2667 Errors that are detected by the shell, such as a syntax error, will
2668 cause the shell to exit with a non-zero exit status.
2669 If the shell is not an interactive shell, the execution of the shell
2670 file will be aborted.
2671 Otherwise the shell will return the exit status of the last command
2674 builtin is used with a numeric argument, it
2675 will return the argument.
2695 command, the Thompson shell, appeared in
2697 It was superseded in
2699 by the Bourne shell, which inherited the name
2704 was rewritten in 1989 under the
2706 license after the Bourne shell from
2711 was originally written by
2712 .An Kenneth Almquist .
2716 utility does not recognize multibyte characters other than UTF-8.
2719 and the line editing library
2721 do not recognize multibyte characters.
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