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32 .\" from: @(#)sh.1 8.6 (Berkeley) 5/4/95
40 .Nd command interpreter (shell)
43 .Op Fl /+abCEefhIimnPpTuVvx
44 .Op Fl /+o Ar longname
50 .Op Fl /+abCEefhIimnPpTuVvx
51 .Op Fl /+o Ar longname
58 .Op Fl /+abCEefhIimnPpTuVvx
59 .Op Fl /+o Ar longname
65 utility is the standard command interpreter for the system.
66 The current version of
70 specification for the shell.
71 It only supports features
74 plus a few Berkeley extensions.
75 This man page is not intended to be a tutorial nor a complete
76 specification of the shell.
78 The shell is a command that reads lines from
79 either a file or the terminal, interprets them, and
80 generally executes other commands.
81 It is the program that is started when a user logs into the system,
82 although a user can select a different shell with the
86 implements a language that has flow control constructs,
87 a macro facility that provides a variety of features in
88 addition to data storage, along with built-in history and line
90 It incorporates many features to
91 aid interactive use and has the advantage that the interpretative
92 language is common to both interactive and non-interactive
94 That is, commands can be typed directly
95 to the running shell or can be put into a file,
96 which can be executed directly by the shell.
99 .\" XXX This next sentence is incredibly confusing.
101 If no arguments are present and if the standard input of the shell
102 is connected to a terminal
106 the shell is considered an interactive shell.
108 generally prompts before each command and handles programming
109 and command errors differently (as described below).
110 When first starting, the shell inspects argument 0, and
111 if it begins with a dash
113 the shell is also considered a login shell.
114 This is normally done automatically by the system
115 when the user first logs in.
116 A login shell first reads commands
121 in a user's home directory,
123 If the environment variable
125 is set on entry to a shell, or is set in the
127 of a login shell, the shell then subjects its value to parameter expansion
128 and arithmetic expansion and reads commands from the named file.
129 Therefore, a user should place commands that are to be executed only
132 file, and commands that are executed for every shell inside the
137 variable to some file by placing the following line in the file
139 in the home directory,
142 the filename desired:
144 .Dl "ENV=$HOME/.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 >|
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:
1033 The current working directory as set by
1036 The file creation mask as set by
1039 Resource limits as set by
1042 References to open files.
1049 Positional parameters and variables.
1058 These are copied from the parent shell environment,
1059 except that trapped (but not ignored) signals are reset to the default action
1060 and known jobs are cleared.
1061 Any changes do not affect the parent shell environment.
1063 A subshell environment may be implemented as a child process or differently.
1064 If job control is enabled in an interactive shell,
1065 commands grouped in parentheses can be suspended and continued as a unit.
1067 For compatibility with other shells,
1068 two open parentheses in sequence should be separated by whitespace.
1070 The second form never forks another shell,
1071 so it is slightly more efficient.
1072 Grouping commands together this way allows the user to
1073 redirect their output as though they were one program:
1074 .Bd -literal -offset indent
1075 { echo -n "hello"; echo " world"; } > greeting
1078 The syntax of a function definition is
1080 .D1 Ar name Li \&( \&) Ar command
1082 A function definition is an executable statement; when
1083 executed it installs a function named
1086 exit status of zero.
1095 Variables may be declared to be local to a function by
1099 This should appear as the first statement of a function,
1102 .D1 Ic local Oo Ar variable ... Oc Op Fl
1106 command is implemented as a built-in command.
1108 When a variable is made local, it inherits the initial
1109 value and exported and readonly flags from the variable
1110 with the same name in the surrounding scope, if there is
1112 Otherwise, the variable is initially unset.
1114 uses dynamic scoping, so that if the variable
1116 is made local to function
1118 which then calls function
1120 references to the variable
1124 will refer to the variable
1128 not to the global variable named
1131 The only special parameter that can be made local is
1135 local causes any shell options that are
1138 command inside the function to be
1139 restored to their original values when the function
1146 .D1 Ic return Op Ar exitstatus
1148 It terminates the current executional scope, returning from the previous
1149 nested function, sourced script, or shell instance, in that order.
1152 command is implemented as a special built-in command.
1153 .Ss Variables and Parameters
1154 The shell maintains a set of parameters.
1156 denoted by a name is called a variable.
1158 the shell turns all the environment variables into shell
1160 New variables can be set using the form
1162 .D1 Ar name Ns = Ns Ar value
1164 Variables set by the user must have a name consisting solely
1165 of alphabetics, numerics, and underscores.
1166 The first letter of a variable name must not be numeric.
1167 A parameter can also be denoted by a number
1168 or a special character as explained below.
1170 Assignments are expanded differently from other words:
1171 tilde expansion is also performed after the equals sign and after any colon
1172 and usernames are also terminated by colons,
1173 and field splitting and pathname expansion are not performed.
1175 This special expansion applies not only to assignments that form a simple
1176 command by themselves or precede a command word,
1177 but also to words passed to the
1182 built-in commands that have this form.
1183 For this, the builtin's name must be literal
1184 (not the result of an expansion)
1185 and may optionally be preceded by one or more literal instances of
1188 .Ss Positional Parameters
1189 A positional parameter is a parameter denoted by a number greater than zero.
1190 The shell sets these initially to the values of its command line
1191 arguments that follow the name of the shell script.
1194 built-in command can also be used to set or reset them.
1195 .Ss Special Parameters
1196 Special parameters are parameters denoted by a single special character
1198 They are shown in the following list, exactly as they would appear in input
1199 typed by the user or in the source of a shell script.
1202 Expands to the positional parameters, starting from one.
1204 the expansion occurs within a double-quoted string
1205 it expands to a single field with the value of each parameter
1206 separated by the first character of the
1213 Expands to the positional parameters, starting from one.
1215 the expansion occurs within double-quotes, each positional
1216 parameter expands as a separate argument.
1217 If there are no positional parameters, the
1220 generates zero arguments, even when
1223 What this basically means, for example, is
1236 .Bd -literal -offset indent
1240 Expands to the number of positional parameters.
1242 Expands to the exit status of the most recent pipeline.
1244 (hyphen) Expands to the current option flags (the single-letter
1245 option names concatenated into a string) as specified on
1248 built-in command, or implicitly
1251 Expands to the process ID of the invoked shell.
1253 retains the same value of
1257 Expands to the process ID of the most recent background
1258 command executed from the current shell.
1260 pipeline, the process ID is that of the last command in the
1262 If this parameter is referenced, the shell will remember
1263 the process ID and its exit status until the
1265 built-in command reports completion of the process.
1267 (zero) Expands to the name of the shell script if passed on the command line,
1270 operand if given (with
1272 or otherwise argument 0 passed to the shell.
1274 .Ss Special Variables
1275 The following variables are set by the shell or
1276 have special meaning to it:
1277 .Bl -tag -width ".Va HISTSIZE"
1279 The search path used with the
1283 The fallback editor used with the
1286 If not set, the default editor is
1289 The default editor used with the
1293 The number of previous commands that are accessible.
1295 The user's home directory,
1296 used in tilde expansion and as a default directory for the
1300 Input Field Separators.
1301 The default value is
1307 This default also applies if
1309 is unset, but not if it is set to the empty string.
1311 .Sx White Space Splitting
1312 section for more details.
1314 The current line number in the script or function.
1316 The name of a mail file, that will be checked for the arrival of new
1323 separated list of file names, for the shell to check for incoming
1325 This variable overrides the
1328 There is a maximum of 10 mailboxes that can be monitored at once.
1330 The default search path for executables.
1333 section for details.
1335 The parent process ID of the invoked shell.
1336 This is set at startup
1337 unless this variable is in the environment.
1338 A later change of parent process ID is not reflected.
1339 A subshell retains the same value of
1342 The primary prompt string, which defaults to
1344 unless you are the superuser, in which case it defaults to
1347 The secondary prompt string, which defaults to
1350 The prefix for the trace output (if
1357 This clause describes the various expansions that are
1359 Not all expansions are performed on
1360 every word, as explained later.
1362 Tilde expansions, parameter expansions, command substitutions,
1363 arithmetic expansions, and quote removals that occur within
1364 a single word expand to a single field.
1366 splitting or pathname expansion that can create multiple
1367 fields from a single word.
1368 The single exception to this rule is
1369 the expansion of the special parameter
1371 within double-quotes,
1372 as was described above.
1374 The order of word expansion is:
1377 Tilde Expansion, Parameter Expansion, Command Substitution,
1378 Arithmetic Expansion (these all occur at the same time).
1380 Field Splitting is performed on fields generated by step (1)
1385 Pathname Expansion (unless the
1387 option is in effect).
1394 character is used to introduce parameter expansion, command
1395 substitution, or arithmetic expansion.
1396 .Ss Tilde Expansion (substituting a user's home directory)
1397 A word beginning with an unquoted tilde character
1400 subjected to tilde expansion.
1401 All the characters up to a slash
1403 or the end of the word are treated as a username
1404 and are replaced with the user's home directory.
1406 username is missing (as in
1408 the tilde is replaced with the value of the
1410 variable (the current user's home directory).
1411 .Ss Parameter Expansion
1412 The format for parameter expansion is as follows:
1414 .D1 Li ${ Ns Ar expression Ns Li }
1418 consists of all characters until the matching
1422 escaped by a backslash or within a single-quoted or double-quoted
1423 string, and characters in
1424 embedded arithmetic expansions, command substitutions, and variable
1425 expansions, are not examined in determining the matching
1427 If the variants with
1433 occur within a double-quoted string,
1434 as an extension there may be unquoted parts
1435 (via double-quotes inside the expansion);
1437 within such parts are also not examined in determining the matching
1440 The simplest form for parameter expansion is:
1442 .D1 Li ${ Ns Ar parameter Ns Li }
1444 The value, if any, of
1448 The parameter name or symbol can be enclosed in braces, which are
1449 optional except for positional parameters with more than one digit or
1450 when parameter is followed by a character that could be interpreted as
1452 If a parameter expansion occurs inside double-quotes:
1455 Field splitting is not performed on the results of the
1456 expansion, with the exception of the special parameter
1459 Pathname expansion is not performed on the results of the
1463 In addition, a parameter expansion can be modified by using one of the
1465 .Bl -tag -width indent
1466 .It Li ${ Ns Ar parameter Ns Li :- Ns Ar word Ns Li }
1470 is unset or null, the expansion of
1472 is substituted; otherwise, the value of
1475 .It Li ${ Ns Ar parameter Ns Li := Ns Ar word Ns Li }
1476 Assign Default Values.
1479 is unset or null, the expansion of
1489 does not prevent field splitting or pathname expansion.
1490 Only variables, not positional
1491 parameters or special parameters, can be
1492 assigned in this way.
1493 .It Li ${ Ns Ar parameter Ns Li :? Ns Oo Ar word Oc Ns Li }
1494 Indicate Error if Null or Unset.
1497 is unset or null, the expansion of
1499 (or a message indicating it is unset if
1501 is omitted) is written to standard
1502 error and the shell exits with a nonzero
1504 Otherwise, the value of
1508 interactive shell need not exit.
1509 .It Li ${ Ns Ar parameter Ns Li :+ Ns Ar word Ns Li }
1510 Use Alternate Value.
1513 is unset or null, null is substituted;
1514 otherwise, the expansion of
1519 In the parameter expansions shown previously, use of the colon in the
1520 format results in a test for a parameter that is unset or null; omission
1521 of the colon results in a test for a parameter that is only unset.
1525 inherits the type of quoting
1526 (unquoted, double-quoted or here-document)
1527 from the surroundings,
1528 with the exception that a backslash that quotes a closing brace is removed
1529 during quote removal.
1530 .Bl -tag -width indent
1531 .It Li ${# Ns Ar parameter Ns Li }
1533 The length in characters of
1538 The following four varieties of parameter expansion provide for substring
1540 In each case, pattern matching notation
1542 .Sx Shell Patterns ) ,
1543 rather than regular expression notation,
1544 is used to evaluate the patterns.
1545 If parameter is one of the special parameters
1549 the result of the expansion is unspecified.
1550 Enclosing the full parameter expansion string in double-quotes does not
1551 cause the following four varieties of pattern characters to be quoted,
1552 whereas quoting characters within the braces has this effect.
1553 .Bl -tag -width indent
1554 .It Li ${ Ns Ar parameter Ns Li % Ns Ar word Ns Li }
1555 Remove Smallest Suffix Pattern.
1558 is expanded to produce a pattern.
1560 parameter expansion then results in
1562 with the smallest portion of the
1563 suffix matched by the pattern deleted.
1564 .It Li ${ Ns Ar parameter Ns Li %% Ns Ar word Ns Li }
1565 Remove Largest Suffix Pattern.
1568 is expanded to produce a pattern.
1570 parameter expansion then results in
1572 with the largest portion of the
1573 suffix matched by the pattern deleted.
1574 .It Li ${ Ns Ar parameter Ns Li # Ns Ar word Ns Li }
1575 Remove Smallest Prefix Pattern.
1578 is expanded to produce a pattern.
1580 parameter expansion then results in
1582 with the smallest portion of the
1583 prefix matched by the pattern deleted.
1584 .It Li ${ Ns Ar parameter Ns Li ## Ns Ar word Ns Li }
1585 Remove Largest Prefix Pattern.
1588 is expanded to produce a pattern.
1590 parameter expansion then results in
1592 with the largest portion of the
1593 prefix matched by the pattern deleted.
1595 .Ss Command Substitution
1596 Command substitution allows the output of a command to be substituted in
1597 place of the command name itself.
1598 Command substitution occurs when
1599 the command is enclosed as follows:
1601 .D1 Li $( Ns Ar command Ns Li )\&
1603 or the backquoted version:
1605 .D1 Li ` Ns Ar command Ns Li `
1607 The shell expands the command substitution by executing command
1608 and replacing the command substitution
1609 with the standard output of the command,
1610 removing sequences of one or more newlines at the end of the substitution.
1611 Embedded newlines before the end of the output are not removed;
1612 however, during field splitting, they may be translated into spaces
1613 depending on the value of
1615 and the quoting that is in effect.
1616 The command is executed in a subshell environment,
1617 except that the built-in commands
1622 return information about the parent shell environment
1625 returns information about the same process
1626 if they are the only command in a command substitution.
1628 If a command substitution of the
1630 form begins with a subshell,
1635 must be separated by whitespace
1636 to avoid ambiguity with arithmetic expansion.
1637 .Ss Arithmetic Expansion
1638 Arithmetic expansion provides a mechanism for evaluating an arithmetic
1639 expression and substituting its value.
1640 The format for arithmetic expansion is as follows:
1642 .D1 Li $(( Ns Ar expression Ns Li ))
1646 is treated as if it were in double-quotes, except
1647 that a double-quote inside the expression is not treated specially.
1649 shell expands all tokens in the
1651 for parameter expansion,
1652 command substitution,
1653 arithmetic expansion
1656 The allowed expressions are a subset of C expressions,
1658 .Bl -tag -width "Variables" -offset indent
1660 All values are of type
1663 Decimal, octal (starting with
1665 and hexadecimal (starting with
1669 Shell variables can be read and written
1670 and contain integer constants.
1673 .It Binary operators
1674 .Li "* / % + - << >> < <= > >= == != & ^ | && ||"
1675 .It Assignment operators
1676 .Li "= += -= *= /= %= <<= >>= &= ^= |="
1677 .It Conditional operator
1681 The result of the expression is substituted in decimal.
1682 .Ss White Space Splitting (Field Splitting)
1683 In certain contexts,
1684 after parameter expansion, command substitution, and
1685 arithmetic expansion the shell scans the results of
1686 expansions and substitutions that did not occur in double-quotes for
1687 field splitting and multiple fields can result.
1698 are treated differently from other characters in
1703 at the beginning or end of a word is discarded.
1705 Subsequently, a field is delimited by either
1708 a non-whitespace character in
1710 with any whitespace in
1714 one or more whitespace characters in
1718 If a word ends with a non-whitespace character in
1720 there is no empty field after this character.
1722 If no field is delimited, the word is discarded.
1723 In particular, if a word consists solely of an unquoted substitution
1724 and the result of the substitution is null,
1725 it is removed by field splitting even if
1728 .Ss Pathname Expansion (File Name Generation)
1732 file name generation is performed
1733 after word splitting is complete.
1735 viewed as a series of patterns, separated by slashes.
1737 process of expansion replaces the word with the names of
1738 all existing files whose names can be formed by replacing
1739 each pattern with a string that matches the specified pattern.
1740 There are two restrictions on this: first, a pattern cannot match
1741 a string containing a slash, and second,
1742 a pattern cannot match a string starting with a period
1743 unless the first character of the pattern is a period.
1744 The next section describes the patterns used for
1746 the four varieties of parameter expansion for substring processing and the
1750 A pattern consists of normal characters, which match themselves,
1751 and meta-characters.
1752 The meta-characters are
1757 These characters lose their special meanings if they are quoted.
1758 When command or variable substitution is performed and the dollar sign
1759 or back quotes are not double-quoted, the value of the
1760 variable or the output of the command is scanned for these
1761 characters and they are turned into meta-characters.
1765 matches any string of characters.
1768 matches any single character.
1771 introduces a character class.
1772 The end of the character class is indicated by a
1780 rather than introducing a character class.
1781 A character class matches any of the characters between the square brackets.
1782 A locale-dependent range of characters may be specified using a minus sign.
1783 A named class of characters (see
1785 may be specified by surrounding the name with
1790 .Ql \&[\&[:alpha:\&]\&]
1791 is a shell pattern that matches a single letter.
1792 The character class may be complemented by making an exclamation point
1794 the first character of the character class.
1797 has the same effect but is non-standard.
1801 in a character class, make it the first character listed
1809 make it the first or last character listed.
1810 .Ss Built-in Commands
1811 This section lists the built-in commands.
1812 .Bl -tag -width indent
1814 A null command that returns a 0 (true) exit value.
1816 The commands in the specified file are read and executed by the shell.
1819 command may be used to return to the
1826 characters, it is used as is.
1827 Otherwise, the shell searches the
1830 If it is not found in the
1832 it is sought in the current working directory.
1834 A built-in equivalent of
1836 .It Ic alias Oo Ar name Ns Oo = Ns Ar string Oc ... Oc
1838 .Ar name Ns = Ns Ar string
1839 is specified, the shell defines the alias
1845 is specified, the value of the alias
1848 With no arguments, the
1850 built-in command prints the names and values of all defined aliases
1853 Alias values are written with appropriate quoting so that they are
1854 suitable for re-input to the shell.
1858 .It Ic bg Op Ar job ...
1859 Continue the specified jobs
1860 (or the current job if no jobs are given)
1862 .It Ic bind Oo Fl aeklrsv Oc Oo Ar key Oo Ar command Oc Oc
1863 List or alter key bindings for the line editor.
1864 This command is documented in
1866 .It Ic break Op Ar num
1868 .Sx Flow-Control Constructs
1870 .It Ic builtin Ar cmd Op Ar arg ...
1871 Execute the specified built-in command,
1873 This is useful when the user wishes to override a shell function
1874 with the same name as a built-in command.
1875 .It Ic cd Oo Fl L | P Oc Oo Fl e Oc Op Ar directory
1876 Switch to the specified
1878 or to the directory specified in the
1880 environment variable if no
1889 then the directories listed in the
1892 searched for the specified
1896 is unset, the current directory is searched.
1899 is the same as that of
1901 In an interactive shell,
1904 command will print out the name of the directory
1905 that it actually switched to
1906 if this is different from the name that the user gave.
1907 These may be different either because the
1909 mechanism was used or because a symbolic link was crossed.
1913 option is specified,
1915 is handled physically and symbolic links are resolved before
1917 components are processed.
1920 option is specified,
1922 is handled logically.
1923 This is the default.
1929 to return exit status 1 if the full pathname of the new directory
1930 cannot be determined reliably or at all.
1931 Normally this is not considered an error,
1932 although a warning is printed.
1937 .It Ic command Oo Fl p Oc Op Ar utility Op Ar argument ...
1938 .It Ic command Oo Fl p Oc Fl v Ar utility
1939 .It Ic command Oo Fl p Oc Fl V Ar utility
1940 The first form of invocation executes the specified
1942 ignoring shell functions in the search.
1945 is a special builtin,
1946 it is executed as if it were a regular builtin.
1950 option is specified, the command search is performed using a
1953 that is guaranteed to find all of the standard utilities.
1957 option is specified,
1959 is not executed but a description of its interpretation by the shell is
1961 For ordinary commands the output is the path name; for shell built-in
1962 commands, shell functions and keywords only the name is written.
1963 Aliases are printed as
1964 .Dq Ic alias Ar name Ns = Ns Ar value .
1968 option is identical to
1970 except for the output.
1972 .Dq Ar utility Ic is Ar description
1978 a special shell builtin,
1985 .It Ic continue Op Ar num
1987 .Sx Flow-Control Constructs
1989 .It Ic echo Oo Fl e | n Oc Op Ar string ...
1990 Print a space-separated list of the arguments to the standard output
1991 and append a newline character.
1992 .Bl -tag -width indent
1994 Suppress the output of the trailing newline.
1996 Process C-style backslash escape sequences.
1999 command understands the following character escapes:
2000 .Bl -tag -width indent
2002 Alert (ring the terminal bell)
2006 Suppress the trailing newline (this has the side-effect of truncating the
2007 line if it is not the last character)
2025 (Zero) The character whose octal value is
2031 is not enclosed in quotes then the backslash itself must be escaped
2032 with a backslash to protect it from the shell.
2034 .Bd -literal -offset indent
2043 $ echo -e a\e\e\e\eb
2052 options may be specified.
2053 .It Ic eval Ar string ...
2054 Concatenate all the arguments with spaces.
2055 Then re-parse and execute the command.
2056 .It Ic exec Op Ar command Op arg ...
2060 the shell process is replaced with the specified program
2061 (which must be a real program, not a shell built-in command or function).
2062 Any redirections on the
2064 command are marked as permanent,
2065 so that they are not undone when the
2068 .It Ic exit Op Ar exitstatus
2069 Terminate the shell process.
2073 it is used as the exit status of the shell.
2074 Otherwise, if the shell is executing an
2076 trap, the exit status of the last command before the trap is used;
2077 if the shell is executing a trap for a signal,
2078 the shell exits by resending the signal to itself.
2079 Otherwise, the exit status of the preceding command is used.
2080 The exit status should be an integer between 0 and 255.
2081 .It Ic export Ar name ...
2082 .It Ic export Op Fl p
2083 The specified names are exported so that they will
2084 appear in the environment of subsequent commands.
2085 The only way to un-export a variable is to
2088 The shell allows the value of a variable to be set
2089 at the same time as it is exported by writing
2091 .D1 Ic export Ar name Ns = Ns Ar value
2093 With no arguments the
2095 command lists the names
2096 of all exported variables.
2099 option is specified, the exported variables are printed as
2100 .Dq Ic export Ar name Ns = Ns Ar value
2101 lines, suitable for re-input to the shell.
2103 A null command that returns a non-zero (false) exit value.
2104 .It Ic fc Oo Fl e Ar editor Oc Op Ar first Op Ar last
2105 .It Ic fc Fl l Oo Fl nr Oc Op Ar first Op Ar last
2106 .It Ic fc Fl s Oo Ar old Ns = Ns Ar new Oc Op Ar first
2109 built-in command lists, or edits and re-executes,
2110 commands previously entered to an interactive shell.
2111 .Bl -tag -width indent
2113 Use the editor named by
2115 to edit the commands.
2118 string is a command name,
2119 subject to search via the
2124 variable is used as a default when
2129 is null or unset, the value of the
2136 is used as the editor.
2138 List the commands rather than invoking
2140 The commands are written in the
2141 sequence indicated by the
2145 operands, as affected by
2147 with each command preceded by the command number.
2149 Suppress command numbers when listing with
2152 Reverse the order of the commands listed
2161 Re-execute the command without invoking an editor.
2164 Select the commands to list or edit.
2165 The number of previous commands that can be accessed
2166 are determined by the value of the
2173 or both are one of the following:
2174 .Bl -tag -width indent
2175 .It Oo Cm + Oc Ns Ar num
2176 A positive number representing a command number;
2177 command numbers can be displayed with the
2181 A negative decimal number representing the
2182 command that was executed
2185 commands previously.
2186 For example, \-1 is the immediately previous command.
2188 A string indicating the most recently entered command
2189 that begins with that string.
2191 .Ar old Ns = Ns Ar new
2192 operand is not also specified with
2194 the string form of the first operand cannot contain an embedded equal sign.
2198 The following variables affect the execution of
2200 .Bl -tag -width ".Va HISTSIZE"
2202 Name of the editor to use for history editing.
2204 The number of previous commands that are accessible.
2209 or the current job to the foreground.
2210 .It Ic getopts Ar optstring var
2217 command deprecates the older
2220 The first argument should be a series of letters, each possibly
2221 followed by a colon which indicates that the option takes an argument.
2222 The specified variable is set to the parsed option.
2224 the next argument is placed into the shell variable
2226 If an option takes an argument, it is placed into the shell variable
2228 If an invalid option is encountered,
2232 It returns a false value (1) when it encounters the end of the options.
2233 .It Ic hash Oo Fl rv Oc Op Ar command ...
2234 The shell maintains a hash table which remembers the locations of commands.
2235 With no arguments whatsoever, the
2237 command prints out the contents of this table.
2238 Entries which have not been looked at since the last
2240 command are marked with an asterisk;
2241 it is possible for these entries to be invalid.
2245 command removes each specified
2247 from the hash table (unless they are functions) and then locates it.
2252 prints the locations of the commands as it finds them.
2257 command to delete all the entries in the hash table except for functions.
2258 .It Ic jobid Op Ar job
2259 Print the process IDs of the processes in the specified
2263 argument is omitted, use the current job.
2264 .It Ic jobs Oo Fl lps Oc Op Ar job ...
2265 Print information about the specified jobs, or all jobs if no
2268 The information printed includes job ID, status and command name.
2272 option is specified, the PID of each job is also printed.
2275 option is specified, only the process IDs for the process group leaders
2276 are printed, one per line.
2279 option is specified, only the PIDs of the job commands are printed, one per
2282 A built-in equivalent of
2284 that additionally supports sending signals to jobs.
2285 .It Ic local Oo Ar variable ... Oc Op Fl
2290 A built-in equivalent of
2292 .It Ic pwd Op Fl L | P
2293 Print the path of the current directory.
2294 The built-in command may
2295 differ from the program of the same name because the
2296 built-in command remembers what the current directory
2297 is rather than recomputing it each time.
2300 However, if the current directory is
2302 the built-in version of
2304 will continue to print the old name for the directory.
2308 option is specified, symbolic links are resolved.
2311 option is specified, the shell's notion of the current directory
2312 is printed (symbolic links are not resolved).
2313 This is the default.
2314 .It Ic read Oo Fl p Ar prompt Oc Oo
2315 .Fl t Ar timeout Oc Oo Fl er Oc Ar variable ...
2321 and the standard input is a terminal.
2323 read from the standard input.
2324 The trailing newline
2325 is deleted from the line and the line is split as
2326 described in the section on
2327 .Sx White Space Splitting (Field Splitting)
2329 the pieces are assigned to the variables in order.
2330 If there are more pieces than variables, the remaining
2331 pieces (along with the characters in
2333 that separated them)
2334 are assigned to the last variable.
2335 If there are more variables than pieces, the remaining
2336 variables are assigned the null string.
2338 Backslashes are treated specially, unless the
2342 If a backslash is followed by
2343 a newline, the backslash and the newline will be
2345 If a backslash is followed by any other
2346 character, the backslash will be deleted and the following
2347 character will be treated as though it were not in
2353 option is specified and the
2355 elapses before a complete line of input is supplied,
2358 command will return an exit status of 1 without assigning any values.
2361 value may optionally be followed by one of
2366 to explicitly specify seconds, minutes or hours.
2367 If none is supplied,
2373 option exists only for backward compatibility with older scripts.
2374 .It Ic readonly Oo Fl p Oc Op Ar name ...
2377 is marked as read only,
2378 so that it cannot be subsequently modified or unset.
2379 The shell allows the value of a variable to be set
2380 at the same time as it is marked read only
2381 by using the following form:
2383 .D1 Ic readonly Ar name Ns = Ns Ar value
2385 With no arguments the
2387 command lists the names of all read only variables.
2390 option is specified, the read-only variables are printed as
2391 .Dq Ic readonly Ar name Ns = Ns Ar value
2392 lines, suitable for re-input to the shell.
2393 .It Ic return Op Ar exitstatus
2397 .It Ic set Oo Fl /+abCEefIimnpTuVvx Oc Oo Fl /+o Ar longname Oc Oo
2398 .Fl c Ar string Oc Op Fl - Ar arg ...
2401 command performs three different functions:
2404 With no arguments, it lists the values of all shell variables.
2406 If options are given,
2407 either in short form or using the long
2408 .Dq Fl /+o Ar longname
2410 it sets or clears the specified options as described in the section called
2411 .Sx Argument List Processing .
2415 option is specified,
2417 will replace the shell's positional parameters with the subsequent
2419 If no arguments follow the
2422 all the positional parameters will be cleared,
2423 which is equivalent to executing the command
2427 flag may be omitted when specifying arguments to be used
2428 as positional replacement parameters.
2429 This is not recommended,
2430 because the first argument may begin with a dash
2436 command will interpret as a request to enable or disable options.
2438 .It Ic setvar Ar variable value
2439 Assigns the specified
2445 command is intended to be used in functions that
2446 assign values to variables whose names are passed as parameters.
2447 In general it is better to write
2448 .Dq Ar variable Ns = Ns Ar value
2451 .It Ic shift Op Ar n
2452 Shift the positional parameters
2457 A shift sets the value of
2466 decreasing the value of
2469 If there are zero positional parameters, shifting does not do anything.
2471 A built-in equivalent of
2474 Print the amount of time spent executing the shell process and its children.
2475 The first output line shows the user and system times for the shell process
2476 itself, the second one contains the user and system times for the
2478 .It Ic trap Oo Ar action Oc Ar signal ...
2480 Cause the shell to parse and execute
2485 The signals are specified by name or number.
2486 In addition, the pseudo-signal
2488 may be used to specify an
2490 that is performed when the shell terminates.
2493 may be an empty string or a dash
2495 the former causes the specified signal to be ignored
2496 and the latter causes the default action to be taken.
2499 is another way to request the default action, for compatibility reasons this
2500 usage is not recommended though.
2501 In a subshell or utility environment,
2502 the shell resets trapped (but not ignored) signals to the default action.
2505 command has no effect on signals that were ignored on entry to the shell.
2511 command to display a list of valid signal names.
2513 A null command that returns a 0 (true) exit value.
2514 .It Ic type Op Ar name ...
2517 as a command and print the resolution of the command search.
2518 Possible resolutions are:
2519 shell keyword, alias, special shell builtin, shell builtin, command,
2522 For aliases the alias expansion is printed;
2523 for commands and tracked aliases
2524 the complete pathname of the command is printed.
2525 .It Ic ulimit Oo Fl HSabcdflmnpstuvw Oc Op Ar limit
2526 Set or display resource limits (see
2530 is specified, the named resource will be set;
2531 otherwise the current resource value will be displayed.
2535 is specified, the hard limits will be set or displayed.
2536 While everybody is allowed to reduce a hard limit,
2537 only the superuser can increase it.
2541 specifies the soft limits instead.
2542 When displaying limits,
2548 The default is to display the soft limits,
2549 and to set both the hard and the soft limits.
2555 command to display all resources.
2558 is not acceptable in this mode.
2560 The remaining options specify which resource value is to be
2561 displayed or modified.
2562 They are mutually exclusive.
2563 .Bl -tag -width indent
2565 The maximum size of socket buffer usage, in bytes.
2566 .It Fl c Ar coredumpsize
2567 The maximal size of core dump files, in 512-byte blocks.
2568 .It Fl d Ar datasize
2569 The maximal size of the data segment of a process, in kilobytes.
2570 .It Fl f Ar filesize
2571 The maximal size of a file, in 512-byte blocks.
2572 .It Fl l Ar lockedmem
2573 The maximal size of memory that can be locked by a process, in
2575 .It Fl m Ar memoryuse
2576 The maximal resident set size of a process, in kilobytes.
2578 The maximal number of descriptors that could be opened by a process.
2579 .It Fl p Ar pseudoterminals
2580 The maximal number of pseudo-terminals for this user ID.
2581 .It Fl s Ar stacksize
2582 The maximal size of the stack segment, in kilobytes.
2584 The maximal amount of CPU time to be used by each process, in seconds.
2585 .It Fl u Ar userproc
2586 The maximal number of simultaneous processes for this user ID.
2587 .It Fl v Ar virtualmem
2588 The maximal virtual size of a process, in kilobytes.
2590 The maximum amount of swap space reserved or used for this user ID,
2593 .It Ic umask Oo Fl S Oc Op Ar mask
2594 Set the file creation mask (see
2596 to the octal or symbolic (see
2600 If the argument is omitted, the current mask value is printed.
2603 option is specified, the output is symbolic, otherwise the output is octal.
2604 .It Ic unalias Oo Fl a Oc Op Ar name ...
2605 The specified alias names are removed.
2608 is specified, all aliases are removed.
2609 .It Ic unset Oo Fl fv Oc Ar name ...
2610 The specified variables or functions are unset and unexported.
2613 option is specified or no options are given, the
2615 arguments are treated as variable names.
2618 option is specified, the
2620 arguments are treated as function names.
2621 .It Ic wait Op Ar job
2622 Wait for the specified
2624 to complete and return the exit status of the last process in the
2626 If the argument is omitted, wait for all jobs to complete
2627 and return an exit status of zero.
2629 .Ss Commandline Editing
2632 is being used interactively from a terminal, the current command
2633 and the command history
2637 .Sx Built-in Commands )
2640 command line editing.
2641 This mode uses commands similar
2642 to a subset of those described in the
2660 can be switched between insert mode and command mode by typing
2664 while in command mode will pass the line to the shell.
2667 .Dq Li "set -o emacs"
2670 command can be used to enable a subset of
2672 command line editing features.
2674 The following environment variables affect the execution of
2676 .Bl -tag -width ".Ev LANGXXXXXX"
2678 Initialization file for interactive shells.
2679 .It Ev LANG , Ev LC_*
2681 These are inherited by children of the shell,
2682 and is used in a limited manner by the shell itself.
2684 An absolute pathname for the current directory,
2685 possibly containing symbolic links.
2686 This is used and updated by the shell.
2688 The default terminal setting for the shell.
2689 This is inherited by children of the shell, and is used in the history
2693 Additionally, all environment variables are turned into shell variables
2695 which may affect the shell as described under
2696 .Sx Special Variables .
2698 Errors that are detected by the shell, such as a syntax error, will
2699 cause the shell to exit with a non-zero exit status.
2700 If the shell is not an interactive shell, the execution of the shell
2701 file will be aborted.
2702 Otherwise the shell will return the exit status of the last command
2705 builtin is used with a numeric argument, it
2706 will return the argument.
2726 command, the Thompson shell, appeared in
2728 It was superseded in
2730 by the Bourne shell, which inherited the name
2735 was rewritten in 1989 under the
2737 license after the Bourne shell from
2742 was originally written by
2743 .An Kenneth Almquist .
2747 utility does not recognize multibyte characters other than UTF-8.
2750 and the line editing library
2752 do not recognize multibyte characters.
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