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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 >|
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 References to open files.
1046 Positional parameters and variables.
1055 These are copied from the parent shell environment,
1056 except that trapped (but not ignored) signals are reset to the default action
1057 and known jobs are cleared.
1058 Any changes do not affect the parent shell environment.
1060 A subshell environment may be implemented as a child process or differently.
1061 If job control is enabled in an interactive shell,
1062 commands grouped in parentheses can be suspended and continued as a unit.
1064 The second form never forks another shell,
1065 so it is slightly more efficient.
1066 Grouping commands together this way allows the user to
1067 redirect their output as though they were one program:
1068 .Bd -literal -offset indent
1069 { echo -n "hello"; echo " world"; } > greeting
1072 The syntax of a function definition is
1074 .D1 Ar name Li \&( \&) Ar command
1076 A function definition is an executable statement; when
1077 executed it installs a function named
1080 exit status of zero.
1089 Variables may be declared to be local to a function by
1093 This should appear as the first statement of a function,
1096 .D1 Ic local Oo Ar variable ... Oc Op Fl
1100 command is implemented as a built-in command.
1102 When a variable is made local, it inherits the initial
1103 value and exported and readonly flags from the variable
1104 with the same name in the surrounding scope, if there is
1106 Otherwise, the variable is initially unset.
1108 uses dynamic scoping, so that if the variable
1110 is made local to function
1112 which then calls function
1114 references to the variable
1118 will refer to the variable
1122 not to the global variable named
1125 The only special parameter that can be made local is
1129 local causes any shell options that are
1132 command inside the function to be
1133 restored to their original values when the function
1140 .D1 Ic return Op Ar exitstatus
1142 It terminates the current executional scope, returning from the previous
1143 nested function, sourced script, or shell instance, in that order.
1146 command is implemented as a special built-in command.
1147 .Ss Variables and Parameters
1148 The shell maintains a set of parameters.
1150 denoted by a name is called a variable.
1152 the shell turns all the environment variables into shell
1154 New variables can be set using the form
1156 .D1 Ar name Ns = Ns Ar value
1158 Variables set by the user must have a name consisting solely
1159 of alphabetics, numerics, and underscores.
1160 The first letter of a variable name must not be numeric.
1161 A parameter can also be denoted by a number
1162 or a special character as explained below.
1164 Assignments are expanded differently from other words:
1165 tilde expansion is also performed after the equals sign and after any colon
1166 and usernames are also terminated by colons,
1167 and field splitting and pathname expansion are not performed.
1168 .Ss Positional Parameters
1169 A positional parameter is a parameter denoted by a number greater than zero.
1170 The shell sets these initially to the values of its command line
1171 arguments that follow the name of the shell script.
1174 built-in command can also be used to set or reset them.
1175 .Ss Special Parameters
1176 Special parameters are parameters denoted by a single special character
1178 They are shown in the following list, exactly as they would appear in input
1179 typed by the user or in the source of a shell script.
1182 Expands to the positional parameters, starting from one.
1184 the expansion occurs within a double-quoted string
1185 it expands to a single field with the value of each parameter
1186 separated by the first character of the
1193 Expands to the positional parameters, starting from one.
1195 the expansion occurs within double-quotes, each positional
1196 parameter expands as a separate argument.
1197 If there are no positional parameters, the
1200 generates zero arguments, even when
1203 What this basically means, for example, is
1216 .Bd -literal -offset indent
1220 Expands to the number of positional parameters.
1222 Expands to the exit status of the most recent pipeline.
1224 (hyphen) Expands to the current option flags (the single-letter
1225 option names concatenated into a string) as specified on
1228 built-in command, or implicitly
1231 Expands to the process ID of the invoked shell.
1233 retains the same value of
1237 Expands to the process ID of the most recent background
1238 command executed from the current shell.
1240 pipeline, the process ID is that of the last command in the
1242 If this parameter is referenced, the shell will remember
1243 the process ID and its exit status until the
1245 built-in command reports completion of the process.
1247 (zero) Expands to the name of the shell script if passed on the command line,
1250 operand if given (with
1252 or otherwise argument 0 passed to the shell.
1254 .Ss Special Variables
1255 The following variables are set by the shell or
1256 have special meaning to it:
1257 .Bl -tag -width ".Va HISTSIZE"
1259 The search path used with the
1263 The fallback editor used with the
1266 If not set, the default editor is
1269 The default editor used with the
1273 The number of previous commands that are accessible.
1275 The user's home directory,
1276 used in tilde expansion and as a default directory for the
1280 Input Field Separators.
1281 The default value is
1287 This default also applies if
1289 is unset, but not if it is set to the empty string.
1291 .Sx White Space Splitting
1292 section for more details.
1294 The current line number in the script or function.
1296 The name of a mail file, that will be checked for the arrival of new
1303 separated list of file names, for the shell to check for incoming
1305 This variable overrides the
1308 There is a maximum of 10 mailboxes that can be monitored at once.
1310 The default search path for executables.
1313 section for details.
1315 The parent process ID of the invoked shell.
1316 This is set at startup
1317 unless this variable is in the environment.
1318 A later change of parent process ID is not reflected.
1319 A subshell retains the same value of
1322 The primary prompt string, which defaults to
1324 unless you are the superuser, in which case it defaults to
1327 The secondary prompt string, which defaults to
1330 The prefix for the trace output (if
1337 This clause describes the various expansions that are
1339 Not all expansions are performed on
1340 every word, as explained later.
1342 Tilde expansions, parameter expansions, command substitutions,
1343 arithmetic expansions, and quote removals that occur within
1344 a single word expand to a single field.
1346 splitting or pathname expansion that can create multiple
1347 fields from a single word.
1348 The single exception to this rule is
1349 the expansion of the special parameter
1351 within double-quotes,
1352 as was described above.
1354 The order of word expansion is:
1357 Tilde Expansion, Parameter Expansion, Command Substitution,
1358 Arithmetic Expansion (these all occur at the same time).
1360 Field Splitting is performed on fields generated by step (1)
1365 Pathname Expansion (unless the
1367 option is in effect).
1374 character is used to introduce parameter expansion, command
1375 substitution, or arithmetic expansion.
1376 .Ss Tilde Expansion (substituting a user's home directory)
1377 A word beginning with an unquoted tilde character
1380 subjected to tilde expansion.
1381 All the characters up to a slash
1383 or the end of the word are treated as a username
1384 and are replaced with the user's home directory.
1386 username is missing (as in
1388 the tilde is replaced with the value of the
1390 variable (the current user's home directory).
1391 .Ss Parameter Expansion
1392 The format for parameter expansion is as follows:
1394 .D1 Li ${ Ns Ar expression Ns Li }
1398 consists of all characters until the matching
1402 escaped by a backslash or within a single-quoted or double-quoted
1403 string, and characters in
1404 embedded arithmetic expansions, command substitutions, and variable
1405 expansions, are not examined in determining the matching
1407 If the variants with
1413 occur within a double-quoted string,
1414 as an extension there may be unquoted parts
1415 (via double-quotes inside the expansion);
1417 within such parts are also not examined in determining the matching
1420 The simplest form for parameter expansion is:
1422 .D1 Li ${ Ns Ar parameter Ns Li }
1424 The value, if any, of
1428 The parameter name or symbol can be enclosed in braces, which are
1429 optional except for positional parameters with more than one digit or
1430 when parameter is followed by a character that could be interpreted as
1432 If a parameter expansion occurs inside double-quotes:
1435 Field splitting is not performed on the results of the
1436 expansion, with the exception of the special parameter
1439 Pathname expansion is not performed on the results of the
1443 In addition, a parameter expansion can be modified by using one of the
1445 .Bl -tag -width indent
1446 .It Li ${ Ns Ar parameter Ns Li :- Ns Ar word Ns Li }
1450 is unset or null, the expansion of
1452 is substituted; otherwise, the value of
1455 .It Li ${ Ns Ar parameter Ns Li := Ns Ar word Ns Li }
1456 Assign Default Values.
1459 is unset or null, the expansion of
1469 does not prevent field splitting or pathname expansion.
1470 Only variables, not positional
1471 parameters or special parameters, can be
1472 assigned in this way.
1473 .It Li ${ Ns Ar parameter Ns Li :? Ns Oo Ar word Oc Ns Li }
1474 Indicate Error if Null or Unset.
1477 is unset or null, the expansion of
1479 (or a message indicating it is unset if
1481 is omitted) is written to standard
1482 error and the shell exits with a nonzero
1484 Otherwise, the value of
1488 interactive shell need not exit.
1489 .It Li ${ Ns Ar parameter Ns Li :+ Ns Ar word Ns Li }
1490 Use Alternate Value.
1493 is unset or null, null is substituted;
1494 otherwise, the expansion of
1499 In the parameter expansions shown previously, use of the colon in the
1500 format results in a test for a parameter that is unset or null; omission
1501 of the colon results in a test for a parameter that is only unset.
1505 inherits the type of quoting
1506 (unquoted, double-quoted or here-document)
1507 from the surroundings,
1508 with the exception that a backslash that quotes a closing brace is removed
1509 during quote removal.
1510 .Bl -tag -width indent
1511 .It Li ${# Ns Ar parameter Ns Li }
1513 The length in characters of
1518 The following four varieties of parameter expansion provide for substring
1520 In each case, pattern matching notation
1522 .Sx Shell Patterns ) ,
1523 rather than regular expression notation,
1524 is used to evaluate the patterns.
1525 If parameter is one of the special parameters
1529 the result of the expansion is unspecified.
1530 Enclosing the full parameter expansion string in double-quotes does not
1531 cause the following four varieties of pattern characters to be quoted,
1532 whereas quoting characters within the braces has this effect.
1533 .Bl -tag -width indent
1534 .It Li ${ Ns Ar parameter Ns Li % Ns Ar word Ns Li }
1535 Remove Smallest Suffix Pattern.
1538 is expanded to produce a pattern.
1540 parameter expansion then results in
1542 with the smallest portion of the
1543 suffix matched by the pattern deleted.
1544 .It Li ${ Ns Ar parameter Ns Li %% Ns Ar word Ns Li }
1545 Remove Largest Suffix Pattern.
1548 is expanded to produce a pattern.
1550 parameter expansion then results in
1552 with the largest portion of the
1553 suffix matched by the pattern deleted.
1554 .It Li ${ Ns Ar parameter Ns Li # Ns Ar word Ns Li }
1555 Remove Smallest Prefix Pattern.
1558 is expanded to produce a pattern.
1560 parameter expansion then results in
1562 with the smallest portion of the
1563 prefix matched by the pattern deleted.
1564 .It Li ${ Ns Ar parameter Ns Li ## Ns Ar word Ns Li }
1565 Remove Largest Prefix Pattern.
1568 is expanded to produce a pattern.
1570 parameter expansion then results in
1572 with the largest portion of the
1573 prefix matched by the pattern deleted.
1575 .Ss Command Substitution
1576 Command substitution allows the output of a command to be substituted in
1577 place of the command name itself.
1578 Command substitution occurs when
1579 the command is enclosed as follows:
1581 .D1 Li $( Ns Ar command Ns Li )\&
1583 or the backquoted version:
1585 .D1 Li ` Ns Ar command Ns Li `
1587 The shell expands the command substitution by executing command
1588 and replacing the command substitution
1589 with the standard output of the command,
1590 removing sequences of one or more newlines at the end of the substitution.
1591 Embedded newlines before the end of the output are not removed;
1592 however, during field splitting, they may be translated into spaces
1593 depending on the value of
1595 and the quoting that is in effect.
1596 The command is executed in a subshell environment,
1597 except that the built-in commands
1602 return information about the parent shell environment
1605 returns information about the same process
1606 if they are the only command in a command substitution.
1607 .Ss Arithmetic Expansion
1608 Arithmetic expansion provides a mechanism for evaluating an arithmetic
1609 expression and substituting its value.
1610 The format for arithmetic expansion is as follows:
1612 .D1 Li $(( Ns Ar expression Ns Li ))
1616 is treated as if it were in double-quotes, except
1617 that a double-quote inside the expression is not treated specially.
1619 shell expands all tokens in the
1621 for parameter expansion,
1622 command substitution,
1623 arithmetic expansion
1626 The allowed expressions are a subset of C expressions,
1628 .Bl -tag -width "Variables" -offset indent
1630 All values are of type
1633 Decimal, octal (starting with
1635 and hexadecimal (starting with
1639 Shell variables can be read and written
1640 and contain integer constants.
1643 .It Binary operators
1644 .Li "* / % + - << >> < <= > >= == != & ^ | && ||"
1645 .It Assignment operators
1646 .Li "= += -= *= /= %= <<= >>= &= ^= |="
1647 .It Conditional operator
1651 The result of the expression is substituted in decimal.
1652 .Ss White Space Splitting (Field Splitting)
1653 In certain contexts,
1654 after parameter expansion, command substitution, and
1655 arithmetic expansion the shell scans the results of
1656 expansions and substitutions that did not occur in double-quotes for
1657 field splitting and multiple fields can result.
1668 are treated differently from other characters in
1673 at the beginning or end of a word is discarded.
1675 Subsequently, a field is delimited by either
1678 a non-whitespace character in
1680 with any whitespace in
1684 one or more whitespace characters in
1688 If a word ends with a non-whitespace character in
1690 there is no empty field after this character.
1692 If no field is delimited, the word is discarded.
1693 In particular, if a word consists solely of an unquoted substitution
1694 and the result of the substitution is null,
1695 it is removed by field splitting even if
1698 .Ss Pathname Expansion (File Name Generation)
1702 file name generation is performed
1703 after word splitting is complete.
1705 viewed as a series of patterns, separated by slashes.
1707 process of expansion replaces the word with the names of
1708 all existing files whose names can be formed by replacing
1709 each pattern with a string that matches the specified pattern.
1710 There are two restrictions on this: first, a pattern cannot match
1711 a string containing a slash, and second,
1712 a pattern cannot match a string starting with a period
1713 unless the first character of the pattern is a period.
1714 The next section describes the patterns used for
1716 the four varieties of parameter expansion for substring processing and the
1720 A pattern consists of normal characters, which match themselves,
1721 and meta-characters.
1722 The meta-characters are
1727 These characters lose their special meanings if they are quoted.
1728 When command or variable substitution is performed and the dollar sign
1729 or back quotes are not double-quoted, the value of the
1730 variable or the output of the command is scanned for these
1731 characters and they are turned into meta-characters.
1735 matches any string of characters.
1738 matches any single character.
1741 introduces a character class.
1742 The end of the character class is indicated by a
1750 rather than introducing a character class.
1751 A character class matches any of the characters between the square brackets.
1752 A locale-dependent range of characters may be specified using a minus sign.
1753 A named class of characters (see
1755 may be specified by surrounding the name with
1760 .Ql \&[\&[:alpha:\&]\&]
1761 is a shell pattern that matches a single letter.
1762 The character class may be complemented by making an exclamation point
1764 the first character of the character class.
1767 has the same effect but is non-standard.
1771 in a character class, make it the first character listed
1779 make it the first or last character listed.
1780 .Ss Built-in Commands
1781 This section lists the built-in commands.
1782 .Bl -tag -width indent
1784 A null command that returns a 0 (true) exit value.
1786 The commands in the specified file are read and executed by the shell.
1789 command may be used to return to the
1796 characters, it is used as is.
1797 Otherwise, the shell searches the
1800 If it is not found in the
1802 it is sought in the current working directory.
1804 A built-in equivalent of
1806 .It Ic alias Oo Ar name Ns Oo = Ns Ar string Oc ... Oc
1808 .Ar name Ns = Ns Ar string
1809 is specified, the shell defines the alias
1815 is specified, the value of the alias
1818 With no arguments, the
1820 built-in command prints the names and values of all defined aliases
1823 Alias values are written with appropriate quoting so that they are
1824 suitable for re-input to the shell.
1828 .It Ic bg Op Ar job ...
1829 Continue the specified jobs
1830 (or the current job if no jobs are given)
1832 .It Ic bind Oo Fl aeklrsv Oc Oo Ar key Oo Ar command Oc Oc
1833 List or alter key bindings for the line editor.
1834 This command is documented in
1836 .It Ic break Op Ar num
1838 .Sx Flow-Control Constructs
1840 .It Ic builtin Ar cmd Op Ar arg ...
1841 Execute the specified built-in command,
1843 This is useful when the user wishes to override a shell function
1844 with the same name as a built-in command.
1845 .It Ic cd Oo Fl L | P Oc Oo Fl e Oc Op Ar directory
1846 Switch to the specified
1848 or to the directory specified in the
1850 environment variable if no
1859 then the directories listed in the
1862 searched for the specified
1866 is unset, the current directory is searched.
1869 is the same as that of
1871 In an interactive shell,
1874 command will print out the name of the directory
1875 that it actually switched to
1876 if this is different from the name that the user gave.
1877 These may be different either because the
1879 mechanism was used or because a symbolic link was crossed.
1883 option is specified,
1885 is handled physically and symbolic links are resolved before
1887 components are processed.
1890 option is specified,
1892 is handled logically.
1893 This is the default.
1899 to return exit status 1 if the full pathname of the new directory
1900 cannot be determined reliably or at all.
1901 Normally this is not considered an error,
1902 although a warning is printed.
1907 .It Ic command Oo Fl p Oc Op Ar utility Op Ar argument ...
1908 .It Ic command Oo Fl p Oc Fl v Ar utility
1909 .It Ic command Oo Fl p Oc Fl V Ar utility
1910 The first form of invocation executes the specified
1912 ignoring shell functions in the search.
1915 is a special builtin,
1916 it is executed as if it were a regular builtin.
1920 option is specified, the command search is performed using a
1923 that is guaranteed to find all of the standard utilities.
1927 option is specified,
1929 is not executed but a description of its interpretation by the shell is
1931 For ordinary commands the output is the path name; for shell built-in
1932 commands, shell functions and keywords only the name is written.
1933 Aliases are printed as
1934 .Dq Ic alias Ar name Ns = Ns Ar value .
1938 option is identical to
1940 except for the output.
1942 .Dq Ar utility Ic is Ar description
1948 a special shell builtin,
1955 .It Ic continue Op Ar num
1957 .Sx Flow-Control Constructs
1959 .It Ic echo Oo Fl e | n Oc Op Ar string ...
1960 Print a space-separated list of the arguments to the standard output
1961 and append a newline character.
1962 .Bl -tag -width indent
1964 Suppress the output of the trailing newline.
1966 Process C-style backslash escape sequences.
1969 command understands the following character escapes:
1970 .Bl -tag -width indent
1972 Alert (ring the terminal bell)
1976 Suppress the trailing newline (this has the side-effect of truncating the
1977 line if it is not the last character)
1995 (Zero) The character whose octal value is
2001 is not enclosed in quotes then the backslash itself must be escaped
2002 with a backslash to protect it from the shell.
2004 .Bd -literal -offset indent
2013 $ echo -e a\e\e\e\eb
2022 options may be specified.
2023 .It Ic eval Ar string ...
2024 Concatenate all the arguments with spaces.
2025 Then re-parse and execute the command.
2026 .It Ic exec Op Ar command Op arg ...
2030 the shell process is replaced with the specified program
2031 (which must be a real program, not a shell built-in command or function).
2032 Any redirections on the
2034 command are marked as permanent,
2035 so that they are not undone when the
2038 .It Ic exit Op Ar exitstatus
2039 Terminate the shell process.
2043 it is used as the exit status of the shell.
2044 Otherwise, if the shell is executing an
2046 trap, the exit status of the last command before the trap is used;
2047 if the shell is executing a trap for a signal,
2048 the shell exits by resending the signal to itself.
2049 Otherwise, the exit status of the preceding command is used.
2050 The exit status should be an integer between 0 and 255.
2051 .It Ic export Ar name ...
2052 .It Ic export Op Fl p
2053 The specified names are exported so that they will
2054 appear in the environment of subsequent commands.
2055 The only way to un-export a variable is to
2058 The shell allows the value of a variable to be set
2059 at the same time as it is exported by writing
2061 .D1 Ic export Ar name Ns = Ns Ar value
2063 With no arguments the
2065 command lists the names
2066 of all exported variables.
2069 option is specified, the exported variables are printed as
2070 .Dq Ic export Ar name Ns = Ns Ar value
2071 lines, suitable for re-input to the shell.
2073 A null command that returns a non-zero (false) exit value.
2074 .It Ic fc Oo Fl e Ar editor Oc Op Ar first Op Ar last
2075 .It Ic fc Fl l Oo Fl nr Oc Op Ar first Op Ar last
2076 .It Ic fc Fl s Oo Ar old Ns = Ns Ar new Oc Op Ar first
2079 built-in command lists, or edits and re-executes,
2080 commands previously entered to an interactive shell.
2081 .Bl -tag -width indent
2083 Use the editor named by
2085 to edit the commands.
2088 string is a command name,
2089 subject to search via the
2094 variable is used as a default when
2099 is null or unset, the value of the
2106 is used as the editor.
2108 List the commands rather than invoking
2110 The commands are written in the
2111 sequence indicated by the
2115 operands, as affected by
2117 with each command preceded by the command number.
2119 Suppress command numbers when listing with
2122 Reverse the order of the commands listed
2131 Re-execute the command without invoking an editor.
2134 Select the commands to list or edit.
2135 The number of previous commands that can be accessed
2136 are determined by the value of the
2143 or both are one of the following:
2144 .Bl -tag -width indent
2145 .It Oo Cm + Oc Ns Ar num
2146 A positive number representing a command number;
2147 command numbers can be displayed with the
2151 A negative decimal number representing the
2152 command that was executed
2155 commands previously.
2156 For example, \-1 is the immediately previous command.
2158 A string indicating the most recently entered command
2159 that begins with that string.
2161 .Ar old Ns = Ns Ar new
2162 operand is not also specified with
2164 the string form of the first operand cannot contain an embedded equal sign.
2168 The following variables affect the execution of
2170 .Bl -tag -width ".Va HISTSIZE"
2172 Name of the editor to use for history editing.
2174 The number of previous commands that are accessible.
2179 or the current job to the foreground.
2180 .It Ic getopts Ar optstring var
2187 command deprecates the older
2190 The first argument should be a series of letters, each possibly
2191 followed by a colon which indicates that the option takes an argument.
2192 The specified variable is set to the parsed option.
2194 the next argument is placed into the shell variable
2196 If an option takes an argument, it is placed into the shell variable
2198 If an invalid option is encountered,
2202 It returns a false value (1) when it encounters the end of the options.
2203 .It Ic hash Oo Fl rv Oc Op Ar command ...
2204 The shell maintains a hash table which remembers the locations of commands.
2205 With no arguments whatsoever, the
2207 command prints out the contents of this table.
2208 Entries which have not been looked at since the last
2210 command are marked with an asterisk;
2211 it is possible for these entries to be invalid.
2215 command removes each specified
2217 from the hash table (unless they are functions) and then locates it.
2222 prints the locations of the commands as it finds them.
2227 command to delete all the entries in the hash table except for functions.
2228 .It Ic jobid Op Ar job
2229 Print the process IDs of the processes in the specified
2233 argument is omitted, use the current job.
2234 .It Ic jobs Oo Fl lps Oc Op Ar job ...
2235 Print information about the specified jobs, or all jobs if no
2238 The information printed includes job ID, status and command name.
2242 option is specified, the PID of each job is also printed.
2245 option is specified, only the process IDs for the process group leaders
2246 are printed, one per line.
2249 option is specified, only the PIDs of the job commands are printed, one per
2252 A built-in equivalent of
2254 that additionally supports sending signals to jobs.
2255 .It Ic local Oo Ar variable ... Oc Op Fl
2260 A built-in equivalent of
2262 .It Ic pwd Op Fl L | P
2263 Print the path of the current directory.
2264 The built-in command may
2265 differ from the program of the same name because the
2266 built-in command remembers what the current directory
2267 is rather than recomputing it each time.
2270 However, if the current directory is
2272 the built-in version of
2274 will continue to print the old name for the directory.
2278 option is specified, symbolic links are resolved.
2281 option is specified, the shell's notion of the current directory
2282 is printed (symbolic links are not resolved).
2283 This is the default.
2284 .It Ic read Oo Fl p Ar prompt Oc Oo
2285 .Fl t Ar timeout Oc Oo Fl er Oc Ar variable ...
2291 and the standard input is a terminal.
2293 read from the standard input.
2294 The trailing newline
2295 is deleted from the line and the line is split as
2296 described in the section on
2297 .Sx White Space Splitting (Field Splitting)
2299 the pieces are assigned to the variables in order.
2300 If there are more pieces than variables, the remaining
2301 pieces (along with the characters in
2303 that separated them)
2304 are assigned to the last variable.
2305 If there are more variables than pieces, the remaining
2306 variables are assigned the null string.
2308 Backslashes are treated specially, unless the
2312 If a backslash is followed by
2313 a newline, the backslash and the newline will be
2315 If a backslash is followed by any other
2316 character, the backslash will be deleted and the following
2317 character will be treated as though it were not in
2323 option is specified and the
2325 elapses before a complete line of input is supplied,
2328 command will return an exit status of 1 without assigning any values.
2331 value may optionally be followed by one of
2336 to explicitly specify seconds, minutes or hours.
2337 If none is supplied,
2343 option exists only for backward compatibility with older scripts.
2344 .It Ic readonly Oo Fl p Oc Op Ar name ...
2347 is marked as read only,
2348 so that it cannot be subsequently modified or unset.
2349 The shell allows the value of a variable to be set
2350 at the same time as it is marked read only
2351 by using the following form:
2353 .D1 Ic readonly Ar name Ns = Ns Ar value
2355 With no arguments the
2357 command lists the names of all read only variables.
2360 option is specified, the read-only variables are printed as
2361 .Dq Ic readonly Ar name Ns = Ns Ar value
2362 lines, suitable for re-input to the shell.
2363 .It Ic return Op Ar exitstatus
2367 .It Ic set Oo Fl /+abCEefIimnpTuVvx Oc Oo Fl /+o Ar longname Oc Oo
2368 .Fl c Ar string Oc Op Fl - Ar arg ...
2371 command performs three different functions:
2374 With no arguments, it lists the values of all shell variables.
2376 If options are given,
2377 either in short form or using the long
2378 .Dq Fl /+o Ar longname
2380 it sets or clears the specified options as described in the section called
2381 .Sx Argument List Processing .
2385 option is specified,
2387 will replace the shell's positional parameters with the subsequent
2389 If no arguments follow the
2392 all the positional parameters will be cleared,
2393 which is equivalent to executing the command
2397 flag may be omitted when specifying arguments to be used
2398 as positional replacement parameters.
2399 This is not recommended,
2400 because the first argument may begin with a dash
2406 command will interpret as a request to enable or disable options.
2408 .It Ic setvar Ar variable value
2409 Assigns the specified
2415 command is intended to be used in functions that
2416 assign values to variables whose names are passed as parameters.
2417 In general it is better to write
2418 .Dq Ar variable Ns = Ns Ar value
2421 .It Ic shift Op Ar n
2422 Shift the positional parameters
2427 A shift sets the value of
2436 decreasing the value of
2439 If there are zero positional parameters, shifting does not do anything.
2441 A built-in equivalent of
2444 Print the amount of time spent executing the shell process and its children.
2445 The first output line shows the user and system times for the shell process
2446 itself, the second one contains the user and system times for the
2448 .It Ic trap Oo Ar action Oc Ar signal ...
2450 Cause the shell to parse and execute
2455 The signals are specified by name or number.
2456 In addition, the pseudo-signal
2458 may be used to specify an
2460 that is performed when the shell terminates.
2463 may be an empty string or a dash
2465 the former causes the specified signal to be ignored
2466 and the latter causes the default action to be taken.
2469 is another way to request the default action, for compatibility reasons this
2470 usage is not recommended though.
2471 In a subshell or utility environment,
2472 the shell resets trapped (but not ignored) signals to the default action.
2475 command has no effect on signals that were ignored on entry to the shell.
2481 command to display a list of valid signal names.
2483 A null command that returns a 0 (true) exit value.
2484 .It Ic type Op Ar name ...
2487 as a command and print the resolution of the command search.
2488 Possible resolutions are:
2489 shell keyword, alias, special shell builtin, shell builtin, command,
2492 For aliases the alias expansion is printed;
2493 for commands and tracked aliases
2494 the complete pathname of the command is printed.
2495 .It Ic ulimit Oo Fl HSabcdflmnpstuvw Oc Op Ar limit
2496 Set or display resource limits (see
2500 is specified, the named resource will be set;
2501 otherwise the current resource value will be displayed.
2505 is specified, the hard limits will be set or displayed.
2506 While everybody is allowed to reduce a hard limit,
2507 only the superuser can increase it.
2511 specifies the soft limits instead.
2512 When displaying limits,
2518 The default is to display the soft limits,
2519 and to set both the hard and the soft limits.
2525 command to display all resources.
2528 is not acceptable in this mode.
2530 The remaining options specify which resource value is to be
2531 displayed or modified.
2532 They are mutually exclusive.
2533 .Bl -tag -width indent
2535 The maximum size of socket buffer usage, in bytes.
2536 .It Fl c Ar coredumpsize
2537 The maximal size of core dump files, in 512-byte blocks.
2538 .It Fl d Ar datasize
2539 The maximal size of the data segment of a process, in kilobytes.
2540 .It Fl f Ar filesize
2541 The maximal size of a file, in 512-byte blocks.
2542 .It Fl l Ar lockedmem
2543 The maximal size of memory that can be locked by a process, in
2545 .It Fl m Ar memoryuse
2546 The maximal resident set size of a process, in kilobytes.
2548 The maximal number of descriptors that could be opened by a process.
2549 .It Fl p Ar pseudoterminals
2550 The maximal number of pseudo-terminals for this user ID.
2551 .It Fl s Ar stacksize
2552 The maximal size of the stack segment, in kilobytes.
2554 The maximal amount of CPU time to be used by each process, in seconds.
2555 .It Fl u Ar userproc
2556 The maximal number of simultaneous processes for this user ID.
2557 .It Fl v Ar virtualmem
2558 The maximal virtual size of a process, in kilobytes.
2560 The maximum amount of swap space reserved or used for this user ID,
2563 .It Ic umask Oo Fl S Oc Op Ar mask
2564 Set the file creation mask (see
2566 to the octal or symbolic (see
2570 If the argument is omitted, the current mask value is printed.
2573 option is specified, the output is symbolic, otherwise the output is octal.
2574 .It Ic unalias Oo Fl a Oc Op Ar name ...
2575 The specified alias names are removed.
2578 is specified, all aliases are removed.
2579 .It Ic unset Oo Fl fv Oc Ar name ...
2580 The specified variables or functions are unset and unexported.
2583 option is specified or no options are given, the
2585 arguments are treated as variable names.
2588 option is specified, the
2590 arguments are treated as function names.
2591 .It Ic wait Op Ar job
2592 Wait for the specified
2594 to complete and return the exit status of the last process in the
2596 If the argument is omitted, wait for all jobs to complete
2597 and return an exit status of zero.
2599 .Ss Commandline Editing
2602 is being used interactively from a terminal, the current command
2603 and the command history
2607 .Sx Built-in Commands )
2610 command line editing.
2611 This mode uses commands similar
2612 to a subset of those described in the
2630 can be switched between insert mode and command mode by typing
2634 while in command mode will pass the line to the shell.
2637 .Dq Li "set -o emacs"
2640 command can be used to enable a subset of
2642 command line editing features.
2644 The following environment variables affect the execution of
2646 .Bl -tag -width ".Ev LANGXXXXXX"
2648 Initialization file for interactive shells.
2649 .It Ev LANG , Ev LC_*
2651 These are inherited by children of the shell,
2652 and is used in a limited manner by the shell itself.
2654 An absolute pathname for the current directory,
2655 possibly containing symbolic links.
2656 This is used and updated by the shell.
2658 The default terminal setting for the shell.
2659 This is inherited by children of the shell, and is used in the history
2663 Additionally, all environment variables are turned into shell variables
2665 which may affect the shell as described under
2666 .Sx Special Variables .
2668 Errors that are detected by the shell, such as a syntax error, will
2669 cause the shell to exit with a non-zero exit status.
2670 If the shell is not an interactive shell, the execution of the shell
2671 file will be aborted.
2672 Otherwise the shell will return the exit status of the last command
2675 builtin is used with a numeric argument, it
2676 will return the argument.
2696 command, the Thompson shell, appeared in
2698 It was superseded in
2700 by the Bourne shell, which inherited the name
2705 was rewritten in 1989 under the
2707 license after the Bourne shell from
2712 was originally written by
2713 .An Kenneth Almquist .
2717 utility does not recognize multibyte characters other than UTF-8.
2720 and the line editing library
2722 do not recognize multibyte characters.
projects / FreeBSD / releng / 9.1.git / blob