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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/.shrc; 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 It is recommended to check for failures explicitly
244 instead of relying on
246 because it tends to behave in unexpected ways,
247 particularly in larger scripts.
249 Disable pathname expansion.
251 A do-nothing option for
254 .It Fl I Li ignoreeof
257 from input when in interactive mode.
258 .It Fl i Li interactive
259 Force the shell to behave interactively.
261 Turn on job control (set automatically when interactive).
263 If not interactive, read commands but do not
265 This is useful for checking the
266 syntax of shell scripts.
268 Change the default for the
274 (logical directory layout)
277 (physical directory layout).
278 .It Fl p Li privileged
279 Turn on privileged mode.
280 This mode is enabled on startup
281 if either the effective user or group ID is not equal to the
282 real user or group ID.
283 Turning this mode off sets the
284 effective user and group IDs to the real user and group IDs.
285 When this mode is enabled for interactive shells, the file
286 .Pa /etc/suid_profile
287 is sourced instead of
291 is sourced, and the contents of the
293 variable are ignored.
295 Read commands from standard input (set automatically
296 if no file arguments are present).
298 no effect when set after the shell has already started
299 running (i.e., when set with the
302 .It Fl T Li trapsasync
303 When waiting for a child, execute traps immediately.
304 If this option is not set,
305 traps are executed after the child exits,
308 This nonstandard option is useful for putting guarding shells around
309 children that block signals.
310 The surrounding shell may kill the child
311 or it may just return control to the tty and leave the child alone,
313 .Bd -literal -offset indent
314 sh -T -c "trap 'exit 1' 2 ; some-blocking-program"
317 Write a message to standard error when attempting
318 to expand a variable, a positional parameter or
319 the special parameter
321 that is not set, and if the
322 shell is not interactive, exit immediately.
326 command line editor (disables
330 The shell writes its input to standard error
332 Useful for debugging.
335 (preceded by the value of the
337 variable subjected to parameter expansion and arithmetic expansion)
338 to standard error before it is executed.
339 Useful for debugging.
344 option causes the commands to be read from the
346 operand instead of from the standard input.
347 Keep in mind that this option only accepts a single string as its
348 argument, hence multi-word strings must be quoted.
352 option takes as its only argument the long name of an option
353 to be enabled or disabled.
354 For example, the following two invocations of
356 both enable the built-in
359 .Bd -literal -offset indent
364 If used without an argument, the
366 option displays the current option settings in a human-readable format.
369 is used without an argument, the current option settings are output
370 in a format suitable for re-input into the shell.
371 .Ss Lexical Structure
372 The shell reads input in terms of lines from a file and breaks
373 it up into words at whitespace (blanks and tabs), and at
377 which are special to the shell.
378 There are two types of operators: control operators and
379 redirection operators (their meaning is discussed later).
380 The following is a list of valid operators:
381 .Bl -tag -width indent
382 .It Control operators:
383 .Bl -column "XXX" "XXX" "XXX" "XXX" "XXX" -offset center -compact
384 .It Li & Ta Li && Ta Li \&( Ta Li \&) Ta Li \en
385 .It Li ;; Ta Li ;& Ta Li \&; Ta Li \&| Ta Li ||
387 .It Redirection operators:
388 .Bl -column "XXX" "XXX" "XXX" "XXX" "XXX" -offset center -compact
389 .It Li < Ta Li > Ta Li << Ta Li >> Ta Li <>
390 .It Li <& Ta Li >& Ta Li <<- Ta Li >| Ta \&
396 introduces a comment if used at the beginning of a word.
397 The word starting with
399 and the rest of the line are ignored.
403 characters (character code 0) are not allowed in shell input.
405 Quoting is used to remove the special meaning of certain characters
406 or words to the shell, such as operators, whitespace, keywords,
409 There are four types of quoting: matched single quotes,
410 dollar-single quotes,
411 matched double quotes, and backslash.
412 .Bl -tag -width indent
414 Enclosing characters in single quotes preserves the literal
415 meaning of all the characters (except single quotes, making
416 it impossible to put single-quotes in a single-quoted string).
417 .It Dollar-Single Quotes
418 Enclosing characters between
422 preserves the literal meaning of all characters
423 except backslashes and single quotes.
424 A backslash introduces a C-style escape sequence:
425 .Bl -tag -width xUnnnnnnnn
427 Alert (ring the terminal bell)
431 The control character denoted by
437 is a backslash, it must be doubled.
459 The byte whose octal value is
461 (one to three digits)
463 The byte whose hexadecimal value is
465 (one or more digits only the last two of which are used)
467 The Unicode code point
469 (four hexadecimal digits)
470 .It \eU Ns Ar nnnnnnnn
471 The Unicode code point
473 (eight hexadecimal digits)
476 The sequences for Unicode code points are currently only useful with
478 They reject code point 0 and UTF-16 surrogates.
480 If an escape sequence would produce a byte with value 0,
481 that byte and the rest of the string until the matching single-quote
484 Any other string starting with a backslash is an error.
486 Enclosing characters within double quotes preserves the literal
487 meaning of all characters except dollar sign
493 The backslash inside double quotes is historically weird.
494 It remains literal unless it precedes the following characters,
495 which it serves to quote:
497 .Bl -column "XXX" "XXX" "XXX" "XXX" "XXX" -offset center -compact
498 .It Li $ Ta Li ` Ta Li \&" Ta Li \e Ta Li \en
501 A backslash preserves the literal meaning of the following
502 character, with the exception of the newline character
504 A backslash preceding a newline is treated as a line continuation.
507 Keywords or reserved words are words that have special meaning to the
508 shell and are recognized at the beginning of a line and
509 after a control operator.
510 The following are keywords:
511 .Bl -column "doneXX" "elifXX" "elseXX" "untilXX" "whileX" -offset center
512 .It Li \&! Ta { Ta } Ta Ic case Ta Ic do
513 .It Ic done Ta Ic elif Ta Ic else Ta Ic esac Ta Ic fi
514 .It Ic for Ta Ic if Ta Ic then Ta Ic until Ta Ic while
517 An alias is a name and corresponding value set using the
520 Wherever the command word of a simple command may occur,
521 and after checking for keywords if a keyword may occur, the shell
522 checks the word to see if it matches an alias.
523 If it does, it replaces it in the input stream with its value.
524 For example, if there is an alias called
536 Aliases are also recognized after an alias
537 whose value ends with a space or tab.
538 For example, if there is also an alias called
544 .Dl "nohup lf foobar"
548 .Dl "nohup ls -F foobar"
550 Aliases provide a convenient way for naive users to
551 create shorthands for commands without having to learn how
552 to create functions with arguments.
553 Using aliases in scripts is discouraged
554 because the command that defines them must be executed
555 before the code that uses them is parsed.
556 This is fragile and not portable.
558 An alias name may be escaped in a command line, so that it is not
559 replaced by its alias value, by using quoting characters within or
560 adjacent to the alias name.
561 This is most often done by prefixing
562 an alias name with a backslash to execute a function, built-in, or
563 normal program with the same name.
568 The shell interprets the words it reads according to a
569 language, the specification of which is outside the scope
570 of this man page (refer to the BNF in the
573 Essentially though, a line is read and if
574 the first word of the line (or after a control operator)
575 is not a keyword, then the shell has recognized a
577 Otherwise, a complex command or some
578 other special construct may have been recognized.
580 If a simple command has been recognized, the shell performs
581 the following actions:
584 Leading words of the form
586 are stripped off and assigned to the environment of
588 Redirection operators and
589 their arguments (as described below) are stripped
590 off and saved for processing.
592 The remaining words are expanded as described in
594 .Sx Word Expansions ,
595 and the first remaining word is considered the command
596 name and the command is located.
598 words are considered the arguments of the command.
599 If no command name resulted, then the
601 variable assignments recognized in 1) affect the
604 Redirections are performed as described in
608 Redirections are used to change where a command reads its input
610 In general, redirections open, close, or
611 duplicate an existing reference to a file.
613 used for redirection is:
615 .D1 Oo Ar n Oc Ar redir-op file
619 is one of the redirection operators mentioned
621 The following gives some examples of how these
622 operators can be used.
623 Note that stdin and stdout are commonly used abbreviations
624 for standard input and standard output respectively.
625 .Bl -tag -width "1234567890XX" -offset indent
626 .It Oo Ar n Oc Ns Li > Ar file
627 redirect stdout (or file descriptor
631 .It Oo Ar n Oc Ns Li >| Ar file
632 same as above, but override the
635 .It Oo Ar n Oc Ns Li >> Ar file
636 append stdout (or file descriptor
640 .It Oo Ar n Oc Ns Li < Ar file
641 redirect stdin (or file descriptor
645 .It Oo Ar n Oc Ns Li <> Ar file
646 redirect stdin (or file descriptor
650 .It Oo Ar n1 Oc Ns Li <& Ns Ar n2
651 duplicate stdin (or file descriptor
655 .It Oo Ar n Oc Ns Li <&-
656 close stdin (or file descriptor
658 .It Oo Ar n1 Oc Ns Li >& Ns Ar n2
659 duplicate stdout (or file descriptor
663 .It Oo Ar n Oc Ns Li >&-
664 close stdout (or file descriptor
668 The following redirection is often called a
670 .Bd -unfilled -offset indent
671 .Oo Ar n Oc Ns Li << Ar delimiter
677 All the text on successive lines up to the delimiter is
678 saved away and made available to the command on standard
679 input, or file descriptor
684 as specified on the initial line is quoted, then the
686 is treated literally, otherwise the text is subjected to
687 parameter expansion, command substitution, and arithmetic
688 expansion (as described in the section on
689 .Sx Word Expansions ) .
698 .Ss Search and Execution
699 There are three types of commands: shell functions,
700 built-in commands, and normal programs.
701 The command is searched for (by name) in that order.
702 The three types of commands are all executed in a different way.
704 When a shell function is executed, all of the shell positional
707 which remains unchanged) are
708 set to the arguments of the shell function.
709 The variables which are explicitly placed in the environment of
710 the command (by placing assignments to them before the
711 function name) are made local to the function and are set
713 Then the command given in the function definition is executed.
714 The positional parameters are restored to their original values
715 when the command completes.
716 This all occurs within the current shell.
718 Shell built-in commands are executed internally to the shell, without
719 spawning a new process.
720 There are two kinds of built-in commands: regular and special.
721 Assignments before special builtins persist after they finish
722 executing and assignment errors, redirection errors and certain
723 operand errors cause a script to be aborted.
724 Special builtins cannot be overridden with a function.
725 Both regular and special builtins can affect the shell in ways
726 normal programs cannot.
728 Otherwise, if the command name does not match a function
729 or built-in command, the command is searched for as a normal
730 program in the file system (as described in the next section).
731 When a normal program is executed, the shell runs the program,
732 passing the arguments and the environment to the program.
733 If the program is not a normal executable file
734 (i.e., if it does not begin with the
744 but appears to be a text file,
745 the shell will run a new instance of
749 Note that previous versions of this document
750 and the source code itself misleadingly and sporadically
751 refer to a shell script without a magic number
753 .Dq "shell procedure" .
755 When locating a command, the shell first looks to see if
756 it has a shell function by that name.
758 built-in command by that name.
759 If a built-in command is not found,
760 one of two things happen:
763 Command names containing a slash are simply executed without
764 performing any searches.
766 The shell searches each entry in the
769 in turn for the command.
772 variable should be a series of
773 entries separated by colons.
774 Each entry consists of a
776 The current directory
777 may be indicated implicitly by an empty directory name,
778 or explicitly by a single period.
780 .Ss Command Exit Status
781 Each command has an exit status that can influence the behavior
782 of other shell commands.
783 The paradigm is that a command exits
784 with zero for normal or success, and non-zero for failure,
785 error, or a false indication.
786 The man page for each command
787 should indicate the various exit codes and what they mean.
788 Additionally, the built-in commands return exit codes, as does
789 an executed shell function.
791 If a command is terminated by a signal, its exit status is 128 plus
793 Signal numbers are defined in the header file
796 Complex commands are combinations of simple commands
797 with control operators or keywords, together creating a larger complex
799 More generally, a command is one of the following:
800 .Bl -item -offset indent
806 list or compound-list
813 Unless otherwise stated, the exit status of a command is
814 that of the last simple command executed by the command.
816 A pipeline is a sequence of one or more commands separated
817 by the control operator
819 The standard output of all but
820 the last command is connected to the standard input
822 The standard output of the last
823 command is inherited from the shell, as usual.
825 The format for a pipeline is:
827 .D1 Oo Li \&! Oc Ar command1 Op Li \&| Ar command2 ...
829 The standard output of
831 is connected to the standard input of
833 The standard input, standard output, or
834 both of a command is considered to be assigned by the
835 pipeline before any redirection specified by redirection
836 operators that are part of the command.
838 Note that unlike some other shells,
840 executes each process in a pipeline with more than one command
841 in a subshell environment and as a child of the
845 If the pipeline is not in the background (discussed later),
846 the shell waits for all commands to complete.
850 does not precede the pipeline, the
851 exit status is the exit status of the last command specified
853 Otherwise, the exit status is the logical
854 NOT of the exit status of the last command.
856 the last command returns zero, the exit status is 1; if
857 the last command returns greater than zero, the exit status
860 Because pipeline assignment of standard input or standard
861 output or both takes place before redirection, it can be
862 modified by redirection.
865 .Dl "command1 2>&1 | command2"
867 sends both the standard output and standard error of
869 to the standard input of
874 or newline terminator causes the preceding
876 (described below in the section called
877 .Sx Short-Circuit List Operators )
878 to be executed sequentially;
881 causes asynchronous execution of the preceding AND-OR-list.
882 .Ss Background Commands (&)
883 If a command is terminated by the control operator ampersand
885 the shell executes the command in a subshell environment (see
886 .Sx Grouping Commands Together
887 below) and asynchronously;
888 the shell does not wait for the command to finish
889 before executing the next command.
891 The format for running a command in background is:
893 .D1 Ar command1 Li & Op Ar command2 Li & Ar ...
895 If the shell is not interactive, the standard input of an
896 asynchronous command is set to
898 .Ss Lists (Generally Speaking)
899 A list is a sequence of zero or more commands separated by
900 newlines, semicolons, or ampersands,
901 and optionally terminated by one of these three characters.
903 list are executed in the order they are written.
904 If command is followed by an ampersand, the shell starts the
905 command and immediately proceeds onto the next command;
906 otherwise it waits for the command to terminate before
907 proceeding to the next one.
908 .Ss Short-Circuit List Operators
912 are AND-OR list operators.
914 executes the first command, and then executes the second command
915 if the exit status of the first command is zero.
917 is similar, but executes the second command if the exit
918 status of the first command is nonzero.
922 both have the same priority.
923 .Ss Flow-Control Constructs (if, while, for, case)
927 .Bd -unfilled -offset indent -compact
931 .Ic then Ar list Oc Ar ...
939 .Bd -unfilled -offset indent -compact
945 The two lists are executed repeatedly while the exit status of the
949 command is similar, but has the word
954 repeat until the exit status of the first list is zero.
959 .Bd -unfilled -offset indent -compact
960 .Ic for Ar variable Op Ic in Ar word ...
967 and the following words are omitted,
970 The words are expanded, and then the list is executed
971 repeatedly with the variable set to each word in turn.
976 commands may be replaced with
986 .D1 Ic break Op Ar num
987 .D1 Ic continue Op Ar num
991 command terminates the
1000 command continues with the next iteration of the innermost loop.
1001 These are implemented as special built-in commands.
1006 .Bd -unfilled -offset indent -compact
1007 .Ic case Ar word Ic in
1008 .Ar pattern Ns Li ) Ar list Li ;;
1013 The pattern can actually be one or more patterns
1020 Tilde expansion, parameter expansion, command substitution,
1021 arithmetic expansion and quote removal are applied to the word.
1022 Then, each pattern is expanded in turn using tilde expansion,
1023 parameter expansion, command substitution and arithmetic expansion and
1024 the expanded form of the word is checked against it.
1025 If a match is found, the corresponding list is executed.
1026 If the selected list is terminated by the control operator
1030 execution continues with the next list,
1031 continuing until a list terminated with
1036 The exit code of the
1038 command is the exit code of the last command executed in the list or
1039 zero if no patterns were matched.
1040 .Ss Grouping Commands Together
1041 Commands may be grouped by writing either
1043 .D1 Li \&( Ns Ar list Ns Li \%)
1047 .D1 Li { Ar list Ns Li \&; }
1049 The first form executes the commands in a subshell environment.
1050 A subshell environment has its own copy of:
1053 The current working directory as set by
1056 The file creation mask as set by
1059 Resource limits as set by
1062 References to open files.
1069 Positional parameters and variables.
1078 These are copied from the parent shell environment,
1079 except that trapped (but not ignored) signals are reset to the default action
1080 and known jobs are cleared.
1081 Any changes do not affect the parent shell environment.
1083 A subshell environment may be implemented as a child process or differently.
1084 If job control is enabled in an interactive shell,
1085 commands grouped in parentheses can be suspended and continued as a unit.
1087 For compatibility with other shells,
1088 two open parentheses in sequence should be separated by whitespace.
1090 The second form never forks another shell,
1091 so it is slightly more efficient.
1092 Grouping commands together this way allows the user to
1093 redirect their output as though they were one program:
1094 .Bd -literal -offset indent
1095 { echo -n "hello"; echo " world"; } > greeting
1098 The syntax of a function definition is
1100 .D1 Ar name Li \&( \&) Ar command
1102 A function definition is an executable statement; when
1103 executed it installs a function named
1106 exit status of zero.
1115 Variables may be declared to be local to a function by
1119 This should appear as the first statement of a function,
1122 .D1 Ic local Oo Ar variable ... Oc Op Fl
1126 command is implemented as a built-in command.
1128 When a variable is made local, it inherits the initial
1129 value and exported and readonly flags from the variable
1130 with the same name in the surrounding scope, if there is
1132 Otherwise, the variable is initially unset.
1134 uses dynamic scoping, so that if the variable
1136 is made local to function
1138 which then calls function
1140 references to the variable
1144 will refer to the variable
1148 not to the global variable named
1151 The only special parameter that can be made local is
1155 local causes any shell options that are
1158 command inside the function to be
1159 restored to their original values when the function
1166 .D1 Ic return Op Ar exitstatus
1168 It terminates the current executional scope, returning from the closest
1169 nested function or sourced script;
1170 if no function or sourced script is being executed,
1171 it exits the shell instance.
1174 command is implemented as a special built-in command.
1175 .Ss Variables and Parameters
1176 The shell maintains a set of parameters.
1178 denoted by a name is called a variable.
1180 the shell turns all the environment variables into shell
1182 New variables can be set using the form
1184 .D1 Ar name Ns = Ns Ar value
1186 Variables set by the user must have a name consisting solely
1187 of alphabetics, numerics, and underscores.
1188 The first letter of a variable name must not be numeric.
1189 A parameter can also be denoted by a number
1190 or a special character as explained below.
1192 Assignments are expanded differently from other words:
1193 tilde expansion is also performed after the equals sign and after any colon
1194 and usernames are also terminated by colons,
1195 and field splitting and pathname expansion are not performed.
1197 This special expansion applies not only to assignments that form a simple
1198 command by themselves or precede a command word,
1199 but also to words passed to the
1204 built-in commands that have this form.
1205 For this, the builtin's name must be literal
1206 (not the result of an expansion)
1207 and may optionally be preceded by one or more literal instances of
1210 .Ss Positional Parameters
1211 A positional parameter is a parameter denoted by a number greater than zero.
1212 The shell sets these initially to the values of its command line
1213 arguments that follow the name of the shell script.
1216 built-in command can also be used to set or reset them.
1217 .Ss Special Parameters
1218 Special parameters are parameters denoted by a single special character
1220 They are shown in the following list, exactly as they would appear in input
1221 typed by the user or in the source of a shell script.
1224 Expands to the positional parameters, starting from one.
1226 the expansion occurs within a double-quoted string
1227 it expands to a single field with the value of each parameter
1228 separated by the first character of the
1235 Expands to the positional parameters, starting from one.
1237 the expansion occurs within double-quotes, each positional
1238 parameter expands as a separate argument.
1239 If there are no positional parameters, the
1242 generates zero arguments, even when
1245 What this basically means, for example, is
1258 .Bd -literal -offset indent
1262 Expands to the number of positional parameters.
1264 Expands to the exit status of the most recent pipeline.
1266 (hyphen) Expands to the current option flags (the single-letter
1267 option names concatenated into a string) as specified on
1270 built-in command, or implicitly
1273 Expands to the process ID of the invoked shell.
1275 retains the same value of
1279 Expands to the process ID of the most recent background
1280 command executed from the current shell.
1282 pipeline, the process ID is that of the last command in the
1284 If this parameter is referenced, the shell will remember
1285 the process ID and its exit status until the
1287 built-in command reports completion of the process.
1289 (zero) Expands to the name of the shell script if passed on the command line,
1292 operand if given (with
1294 or otherwise argument 0 passed to the shell.
1296 .Ss Special Variables
1297 The following variables are set by the shell or
1298 have special meaning to it:
1299 .Bl -tag -width ".Va HISTSIZE"
1301 The search path used with the
1305 The fallback editor used with the
1308 If not set, the default editor is
1311 The default editor used with the
1315 The number of previous commands that are accessible.
1317 The user's home directory,
1318 used in tilde expansion and as a default directory for the
1322 Input Field Separators.
1323 The default value is
1329 This default also applies if
1331 is unset, but not if it is set to the empty string.
1333 .Sx White Space Splitting
1334 section for more details.
1336 The current line number in the script or function.
1338 The name of a mail file, that will be checked for the arrival of new
1345 separated list of file names, for the shell to check for incoming
1347 This variable overrides the
1350 There is a maximum of 10 mailboxes that can be monitored at once.
1352 The default search path for executables.
1355 section for details.
1357 The parent process ID of the invoked shell.
1358 This is set at startup
1359 unless this variable is in the environment.
1360 A later change of parent process ID is not reflected.
1361 A subshell retains the same value of
1364 The primary prompt string, which defaults to
1366 unless you are the superuser, in which case it defaults to
1369 may include any of the following formatting sequences,
1370 which are replaced by the given information:
1371 .Bl -tag -width indent
1375 The fully-qualified hostname.
1377 The final component of the current working directory.
1379 The entire path of the current working directory.
1383 for normal users and
1387 A literal backslash.
1390 The secondary prompt string, which defaults to
1393 may include any of the formatting sequences from
1396 The prefix for the trace output (if
1403 This clause describes the various expansions that are
1405 Not all expansions are performed on
1406 every word, as explained later.
1408 Tilde expansions, parameter expansions, command substitutions,
1409 arithmetic expansions, and quote removals that occur within
1410 a single word expand to a single field.
1412 splitting or pathname expansion that can create multiple
1413 fields from a single word.
1414 The single exception to this rule is
1415 the expansion of the special parameter
1417 within double-quotes,
1418 as was described above.
1420 The order of word expansion is:
1423 Tilde Expansion, Parameter Expansion, Command Substitution,
1424 Arithmetic Expansion (these all occur at the same time).
1426 Field Splitting is performed on fields generated by step (1)
1431 Pathname Expansion (unless the
1433 option is in effect).
1440 character is used to introduce parameter expansion, command
1441 substitution, or arithmetic expansion.
1442 .Ss Tilde Expansion (substituting a user's home directory)
1443 A word beginning with an unquoted tilde character
1446 subjected to tilde expansion.
1447 All the characters up to a slash
1449 or the end of the word are treated as a username
1450 and are replaced with the user's home directory.
1452 username is missing (as in
1454 the tilde is replaced with the value of the
1456 variable (the current user's home directory).
1457 .Ss Parameter Expansion
1458 The format for parameter expansion is as follows:
1460 .D1 Li ${ Ns Ar expression Ns Li }
1464 consists of all characters until the matching
1468 escaped by a backslash or within a single-quoted or double-quoted
1469 string, and characters in
1470 embedded arithmetic expansions, command substitutions, and variable
1471 expansions, are not examined in determining the matching
1473 If the variants with
1479 occur within a double-quoted string,
1480 as an extension there may be unquoted parts
1481 (via double-quotes inside the expansion);
1483 within such parts are also not examined in determining the matching
1486 The simplest form for parameter expansion is:
1488 .D1 Li ${ Ns Ar parameter Ns Li }
1490 The value, if any, of
1494 The parameter name or symbol can be enclosed in braces, which are
1495 optional except for positional parameters with more than one digit or
1496 when parameter is followed by a character that could be interpreted as
1498 If a parameter expansion occurs inside double-quotes:
1501 Field splitting is not performed on the results of the
1502 expansion, with the exception of the special parameter
1505 Pathname expansion is not performed on the results of the
1509 In addition, a parameter expansion can be modified by using one of the
1511 .Bl -tag -width indent
1512 .It Li ${ Ns Ar parameter Ns Li :- Ns Ar word Ns Li }
1516 is unset or null, the expansion of
1518 is substituted; otherwise, the value of
1521 .It Li ${ Ns Ar parameter Ns Li := Ns Ar word Ns Li }
1522 Assign Default Values.
1525 is unset or null, the expansion of
1535 does not prevent field splitting or pathname expansion.
1536 Only variables, not positional
1537 parameters or special parameters, can be
1538 assigned in this way.
1539 .It Li ${ Ns Ar parameter Ns Li :? Ns Oo Ar word Oc Ns Li }
1540 Indicate Error if Null or Unset.
1543 is unset or null, the expansion of
1545 (or a message indicating it is unset if
1547 is omitted) is written to standard
1548 error and the shell exits with a nonzero
1550 Otherwise, the value of
1554 interactive shell need not exit.
1555 .It Li ${ Ns Ar parameter Ns Li :+ Ns Ar word Ns Li }
1556 Use Alternate Value.
1559 is unset or null, null is substituted;
1560 otherwise, the expansion of
1565 In the parameter expansions shown previously, use of the colon in the
1566 format results in a test for a parameter that is unset or null; omission
1567 of the colon results in a test for a parameter that is only unset.
1571 inherits the type of quoting
1572 (unquoted, double-quoted or here-document)
1573 from the surroundings,
1574 with the exception that a backslash that quotes a closing brace is removed
1575 during quote removal.
1576 .Bl -tag -width indent
1577 .It Li ${# Ns Ar parameter Ns Li }
1579 The length in characters of
1584 The following four varieties of parameter expansion provide for substring
1586 In each case, pattern matching notation
1588 .Sx Shell Patterns ) ,
1589 rather than regular expression notation,
1590 is used to evaluate the patterns.
1591 If parameter is one of the special parameters
1595 the result of the expansion is unspecified.
1596 Enclosing the full parameter expansion string in double-quotes does not
1597 cause the following four varieties of pattern characters to be quoted,
1598 whereas quoting characters within the braces has this effect.
1599 .Bl -tag -width indent
1600 .It Li ${ Ns Ar parameter Ns Li % Ns Ar word Ns Li }
1601 Remove Smallest Suffix Pattern.
1604 is expanded to produce a pattern.
1606 parameter expansion then results in
1608 with the smallest portion of the
1609 suffix matched by the pattern deleted.
1610 .It Li ${ Ns Ar parameter Ns Li %% Ns Ar word Ns Li }
1611 Remove Largest Suffix Pattern.
1614 is expanded to produce a pattern.
1616 parameter expansion then results in
1618 with the largest portion of the
1619 suffix matched by the pattern deleted.
1620 .It Li ${ Ns Ar parameter Ns Li # Ns Ar word Ns Li }
1621 Remove Smallest Prefix Pattern.
1624 is expanded to produce a pattern.
1626 parameter expansion then results in
1628 with the smallest portion of the
1629 prefix matched by the pattern deleted.
1630 .It Li ${ Ns Ar parameter Ns Li ## Ns Ar word Ns Li }
1631 Remove Largest Prefix Pattern.
1634 is expanded to produce a pattern.
1636 parameter expansion then results in
1638 with the largest portion of the
1639 prefix matched by the pattern deleted.
1641 .Ss Command Substitution
1642 Command substitution allows the output of a command to be substituted in
1643 place of the command name itself.
1644 Command substitution occurs when
1645 the command is enclosed as follows:
1647 .D1 Li $( Ns Ar command Ns Li )\&
1649 or the backquoted version:
1651 .D1 Li ` Ns Ar command Ns Li `
1653 The shell expands the command substitution by executing command
1654 and replacing the command substitution
1655 with the standard output of the command,
1656 removing sequences of one or more newlines at the end of the substitution.
1657 Embedded newlines before the end of the output are not removed;
1658 however, during field splitting, they may be translated into spaces
1659 depending on the value of
1661 and the quoting that is in effect.
1662 The command is executed in a subshell environment,
1663 except that the built-in commands
1668 return information about the parent shell environment
1671 returns information about the same process
1672 if they are the only command in a command substitution.
1674 If a command substitution of the
1676 form begins with a subshell,
1681 must be separated by whitespace
1682 to avoid ambiguity with arithmetic expansion.
1683 .Ss Arithmetic Expansion
1684 Arithmetic expansion provides a mechanism for evaluating an arithmetic
1685 expression and substituting its value.
1686 The format for arithmetic expansion is as follows:
1688 .D1 Li $(( Ns Ar expression Ns Li ))
1692 is treated as if it were in double-quotes, except
1693 that a double-quote inside the expression is not treated specially.
1695 shell expands all tokens in the
1697 for parameter expansion,
1698 command substitution,
1699 arithmetic expansion
1702 The allowed expressions are a subset of C expressions,
1704 .Bl -tag -width "Variables" -offset indent
1706 All values are of type
1709 Decimal, octal (starting with
1711 and hexadecimal (starting with
1715 Shell variables can be read and written
1716 and contain integer constants.
1719 .It Binary operators
1720 .Li "* / % + - << >> < <= > >= == != & ^ | && ||"
1721 .It Assignment operators
1722 .Li "= += -= *= /= %= <<= >>= &= ^= |="
1723 .It Conditional operator
1727 The result of the expression is substituted in decimal.
1728 .Ss White Space Splitting (Field Splitting)
1729 In certain contexts,
1730 after parameter expansion, command substitution, and
1731 arithmetic expansion the shell scans the results of
1732 expansions and substitutions that did not occur in double-quotes for
1733 field splitting and multiple fields can result.
1744 are treated differently from other characters in
1749 at the beginning or end of a word is discarded.
1751 Subsequently, a field is delimited by either
1754 a non-whitespace character in
1756 with any whitespace in
1760 one or more whitespace characters in
1764 If a word ends with a non-whitespace character in
1766 there is no empty field after this character.
1768 If no field is delimited, the word is discarded.
1769 In particular, if a word consists solely of an unquoted substitution
1770 and the result of the substitution is null,
1771 it is removed by field splitting even if
1774 .Ss Pathname Expansion (File Name Generation)
1778 file name generation is performed
1779 after word splitting is complete.
1781 viewed as a series of patterns, separated by slashes.
1783 process of expansion replaces the word with the names of
1784 all existing files whose names can be formed by replacing
1785 each pattern with a string that matches the specified pattern.
1786 There are two restrictions on this: first, a pattern cannot match
1787 a string containing a slash, and second,
1788 a pattern cannot match a string starting with a period
1789 unless the first character of the pattern is a period.
1790 The next section describes the patterns used for
1792 the four varieties of parameter expansion for substring processing and the
1796 A pattern consists of normal characters, which match themselves,
1797 and meta-characters.
1798 The meta-characters are
1803 These characters lose their special meanings if they are quoted.
1804 When command or variable substitution is performed and the dollar sign
1805 or back quotes are not double-quoted, the value of the
1806 variable or the output of the command is scanned for these
1807 characters and they are turned into meta-characters.
1811 matches any string of characters.
1814 matches any single character.
1817 introduces a character class.
1818 The end of the character class is indicated by a
1826 rather than introducing a character class.
1827 A character class matches any of the characters between the square brackets.
1828 A locale-dependent range of characters may be specified using a minus sign.
1829 A named class of characters (see
1831 may be specified by surrounding the name with
1836 .Ql \&[\&[:alpha:\&]\&]
1837 is a shell pattern that matches a single letter.
1838 The character class may be complemented by making an exclamation point
1840 the first character of the character class.
1843 has the same effect but is non-standard.
1847 in a character class, make it the first character listed
1855 make it the first or last character listed.
1856 .Ss Built-in Commands
1857 This section lists the built-in commands.
1858 .Bl -tag -width indent
1860 A null command that returns a 0 (true) exit value.
1862 The commands in the specified file are read and executed by the shell.
1865 command may be used to return to the
1872 characters, it is used as is.
1873 Otherwise, the shell searches the
1876 If it is not found in the
1878 it is sought in the current working directory.
1880 A built-in equivalent of
1882 .It Ic alias Oo Ar name Ns Oo = Ns Ar string Oc ... Oc
1884 .Ar name Ns = Ns Ar string
1885 is specified, the shell defines the alias
1891 is specified, the value of the alias
1894 With no arguments, the
1896 built-in command prints the names and values of all defined aliases
1899 Alias values are written with appropriate quoting so that they are
1900 suitable for re-input to the shell.
1904 .It Ic bg Op Ar job ...
1905 Continue the specified jobs
1906 (or the current job if no jobs are given)
1908 .It Ic bind Oo Fl aeklrsv Oc Oo Ar key Oo Ar command Oc Oc
1909 List or alter key bindings for the line editor.
1910 This command is documented in
1912 .It Ic break Op Ar num
1914 .Sx Flow-Control Constructs
1916 .It Ic builtin Ar cmd Op Ar arg ...
1917 Execute the specified built-in command,
1919 This is useful when the user wishes to override a shell function
1920 with the same name as a built-in command.
1921 .It Ic cd Oo Fl L | P Oc Oo Fl e Oc Op Ar directory
1922 Switch to the specified
1924 or to the directory specified in the
1926 environment variable if no
1935 then the directories listed in the
1938 searched for the specified
1942 is unset, the current directory is searched.
1945 is the same as that of
1947 In an interactive shell,
1950 command will print out the name of the directory
1951 that it actually switched to
1952 if this is different from the name that the user gave.
1953 These may be different either because the
1955 mechanism was used or because a symbolic link was crossed.
1959 option is specified,
1961 is handled physically and symbolic links are resolved before
1963 components are processed.
1966 option is specified,
1968 is handled logically.
1969 This is the default.
1975 to return exit status 1 if the full pathname of the new directory
1976 cannot be determined reliably or at all.
1977 Normally this is not considered an error,
1978 although a warning is printed.
1983 .It Ic command Oo Fl p Oc Op Ar utility Op Ar argument ...
1984 .It Ic command Oo Fl p Oc Fl v Ar utility
1985 .It Ic command Oo Fl p Oc Fl V Ar utility
1986 The first form of invocation executes the specified
1988 ignoring shell functions in the search.
1991 is a special builtin,
1992 it is executed as if it were a regular builtin.
1996 option is specified, the command search is performed using a
1999 that is guaranteed to find all of the standard utilities.
2003 option is specified,
2005 is not executed but a description of its interpretation by the shell is
2007 For ordinary commands the output is the path name; for shell built-in
2008 commands, shell functions and keywords only the name is written.
2009 Aliases are printed as
2010 .Dq Ic alias Ar name Ns = Ns Ar value .
2014 option is identical to
2016 except for the output.
2018 .Dq Ar utility Ic is Ar description
2024 a special shell builtin,
2031 .It Ic continue Op Ar num
2033 .Sx Flow-Control Constructs
2035 .It Ic echo Oo Fl e | n Oc Op Ar string ...
2036 Print a space-separated list of the arguments to the standard output
2037 and append a newline character.
2038 .Bl -tag -width indent
2040 Suppress the output of the trailing newline.
2042 Process C-style backslash escape sequences.
2045 command understands the following character escapes:
2046 .Bl -tag -width indent
2048 Alert (ring the terminal bell)
2052 Suppress the trailing newline (this has the side-effect of truncating the
2053 line if it is not the last character)
2071 (Zero) The character whose octal value is
2077 is not enclosed in quotes then the backslash itself must be escaped
2078 with a backslash to protect it from the shell.
2080 .Bd -literal -offset indent
2089 $ echo -e a\e\e\e\eb
2098 options may be specified.
2099 .It Ic eval Ar string ...
2100 Concatenate all the arguments with spaces.
2101 Then re-parse and execute the command.
2102 .It Ic exec Op Ar command Op arg ...
2106 the shell process is replaced with the specified program
2107 (which must be a real program, not a shell built-in command or function).
2108 Any redirections on the
2110 command are marked as permanent,
2111 so that they are not undone when the
2114 .It Ic exit Op Ar exitstatus
2115 Terminate the shell process.
2119 it is used as the exit status of the shell.
2120 Otherwise, if the shell is executing an
2122 trap, the exit status of the last command before the trap is used;
2123 if the shell is executing a trap for a signal,
2124 the shell exits by resending the signal to itself.
2125 Otherwise, the exit status of the preceding command is used.
2126 The exit status should be an integer between 0 and 255.
2127 .It Ic export Ar name ...
2128 .It Ic export Op Fl p
2129 The specified names are exported so that they will
2130 appear in the environment of subsequent commands.
2131 The only way to un-export a variable is to
2134 The shell allows the value of a variable to be set
2135 at the same time as it is exported by writing
2137 .D1 Ic export Ar name Ns = Ns Ar value
2139 With no arguments the
2141 command lists the names
2142 of all exported variables.
2145 option is specified, the exported variables are printed as
2146 .Dq Ic export Ar name Ns = Ns Ar value
2147 lines, suitable for re-input to the shell.
2149 A null command that returns a non-zero (false) exit value.
2150 .It Ic fc Oo Fl e Ar editor Oc Op Ar first Op Ar last
2151 .It Ic fc Fl l Oo Fl nr Oc Op Ar first Op Ar last
2152 .It Ic fc Fl s Oo Ar old Ns = Ns Ar new Oc Op Ar first
2155 built-in command lists, or edits and re-executes,
2156 commands previously entered to an interactive shell.
2157 .Bl -tag -width indent
2159 Use the editor named by
2161 to edit the commands.
2164 string is a command name,
2165 subject to search via the
2170 variable is used as a default when
2175 is null or unset, the value of the
2182 is used as the editor.
2184 List the commands rather than invoking
2186 The commands are written in the
2187 sequence indicated by the
2191 operands, as affected by
2193 with each command preceded by the command number.
2195 Suppress command numbers when listing with
2198 Reverse the order of the commands listed
2207 Re-execute the command without invoking an editor.
2210 Select the commands to list or edit.
2211 The number of previous commands that can be accessed
2212 are determined by the value of the
2219 or both are one of the following:
2220 .Bl -tag -width indent
2221 .It Oo Cm + Oc Ns Ar num
2222 A positive number representing a command number;
2223 command numbers can be displayed with the
2227 A negative decimal number representing the
2228 command that was executed
2231 commands previously.
2232 For example, \-1 is the immediately previous command.
2234 A string indicating the most recently entered command
2235 that begins with that string.
2237 .Ar old Ns = Ns Ar new
2238 operand is not also specified with
2240 the string form of the first operand cannot contain an embedded equal sign.
2244 The following variables affect the execution of
2246 .Bl -tag -width ".Va HISTSIZE"
2248 Name of the editor to use for history editing.
2250 The number of previous commands that are accessible.
2255 or the current job to the foreground.
2256 .It Ic getopts Ar optstring var
2263 command deprecates the older
2266 The first argument should be a series of letters, each possibly
2267 followed by a colon which indicates that the option takes an argument.
2268 The specified variable is set to the parsed option.
2270 the next argument is placed into the shell variable
2272 If an option takes an argument, it is placed into the shell variable
2274 If an invalid option is encountered,
2278 It returns a false value (1) when it encounters the end of the options.
2279 .It Ic hash Oo Fl rv Oc Op Ar command ...
2280 The shell maintains a hash table which remembers the locations of commands.
2281 With no arguments whatsoever, the
2283 command prints out the contents of this table.
2287 command removes each specified
2289 from the hash table (unless they are functions) and then locates it.
2294 prints the locations of the commands as it finds them.
2299 command to delete all the entries in the hash table except for functions.
2300 .It Ic jobid Op Ar job
2301 Print the process IDs of the processes in the specified
2305 argument is omitted, use the current job.
2306 .It Ic jobs Oo Fl lps Oc Op Ar job ...
2307 Print information about the specified jobs, or all jobs if no
2310 The information printed includes job ID, status and command name.
2314 option is specified, the PID of each job is also printed.
2317 option is specified, only the process IDs for the process group leaders
2318 are printed, one per line.
2321 option is specified, only the PIDs of the job commands are printed, one per
2324 A built-in equivalent of
2326 that additionally supports sending signals to jobs.
2327 .It Ic local Oo Ar variable ... Oc Op Fl
2332 A built-in equivalent of
2334 .It Ic pwd Op Fl L | P
2335 Print the path of the current directory.
2336 The built-in command may
2337 differ from the program of the same name because the
2338 built-in command remembers what the current directory
2339 is rather than recomputing it each time.
2342 However, if the current directory is
2344 the built-in version of
2346 will continue to print the old name for the directory.
2350 option is specified, symbolic links are resolved.
2353 option is specified, the shell's notion of the current directory
2354 is printed (symbolic links are not resolved).
2355 This is the default.
2356 .It Ic read Oo Fl p Ar prompt Oc Oo
2357 .Fl t Ar timeout Oc Oo Fl er Oc Ar variable ...
2363 and the standard input is a terminal.
2365 read from the standard input.
2366 The trailing newline
2367 is deleted from the line and the line is split as
2368 described in the section on
2369 .Sx White Space Splitting (Field Splitting)
2371 the pieces are assigned to the variables in order.
2372 If there are more pieces than variables, the remaining
2373 pieces (along with the characters in
2375 that separated them)
2376 are assigned to the last variable.
2377 If there are more variables than pieces, the remaining
2378 variables are assigned the null string.
2380 Backslashes are treated specially, unless the
2384 If a backslash is followed by
2385 a newline, the backslash and the newline will be
2387 If a backslash is followed by any other
2388 character, the backslash will be deleted and the following
2389 character will be treated as though it were not in
2395 option is specified and the
2397 elapses before a complete line of input is supplied,
2400 command will return an exit status as if terminated by
2402 without assigning any values.
2405 value may optionally be followed by one of
2410 to explicitly specify seconds, minutes or hours.
2411 If none is supplied,
2417 option exists only for backward compatibility with older scripts.
2419 The exit status is 0 on success, 1 on end of file,
2420 between 2 and 128 if an error occurs
2421 and greater than 128 if a trapped signal interrupts
2423 .It Ic readonly Oo Fl p Oc Op Ar name ...
2426 is marked as read only,
2427 so that it cannot be subsequently modified or unset.
2428 The shell allows the value of a variable to be set
2429 at the same time as it is marked read only
2430 by using the following form:
2432 .D1 Ic readonly Ar name Ns = Ns Ar value
2434 With no arguments the
2436 command lists the names of all read only variables.
2439 option is specified, the read-only variables are printed as
2440 .Dq Ic readonly Ar name Ns = Ns Ar value
2441 lines, suitable for re-input to the shell.
2442 .It Ic return Op Ar exitstatus
2446 .It Ic set Oo Fl /+abCEefIimnpTuVvx Oc Oo Fl /+o Ar longname Oc Oo
2447 .Fl c Ar string Oc Op Fl - Ar arg ...
2450 command performs three different functions:
2453 With no arguments, it lists the values of all shell variables.
2455 If options are given,
2456 either in short form or using the long
2457 .Dq Fl /+o Ar longname
2459 it sets or clears the specified options as described in the section called
2460 .Sx Argument List Processing .
2464 option is specified,
2466 will replace the shell's positional parameters with the subsequent
2468 If no arguments follow the
2471 all the positional parameters will be cleared,
2472 which is equivalent to executing the command
2476 flag may be omitted when specifying arguments to be used
2477 as positional replacement parameters.
2478 This is not recommended,
2479 because the first argument may begin with a dash
2485 command will interpret as a request to enable or disable options.
2487 .It Ic setvar Ar variable value
2488 Assigns the specified
2494 command is intended to be used in functions that
2495 assign values to variables whose names are passed as parameters.
2496 In general it is better to write
2497 .Dq Ar variable Ns = Ns Ar value
2500 .It Ic shift Op Ar n
2501 Shift the positional parameters
2506 A shift sets the value of
2515 decreasing the value of
2518 If there are zero positional parameters, shifting does not do anything.
2520 A built-in equivalent of
2523 Print the amount of time spent executing the shell process and its children.
2524 The first output line shows the user and system times for the shell process
2525 itself, the second one contains the user and system times for the
2527 .It Ic trap Oo Ar action Oc Ar signal ...
2529 Cause the shell to parse and execute
2534 The signals are specified by name or number.
2535 In addition, the pseudo-signal
2537 may be used to specify an
2539 that is performed when the shell terminates.
2542 may be an empty string or a dash
2544 the former causes the specified signal to be ignored
2545 and the latter causes the default action to be taken.
2548 is another way to request the default action, for compatibility reasons this
2549 usage is not recommended though.
2550 In a subshell or utility environment,
2551 the shell resets trapped (but not ignored) signals to the default action.
2554 command has no effect on signals that were ignored on entry to the shell.
2560 command to display a list of valid signal names.
2562 A null command that returns a 0 (true) exit value.
2563 .It Ic type Op Ar name ...
2566 as a command and print the resolution of the command search.
2567 Possible resolutions are:
2568 shell keyword, alias, special shell builtin, shell builtin, command,
2571 For aliases the alias expansion is printed;
2572 for commands and tracked aliases
2573 the complete pathname of the command is printed.
2574 .It Ic ulimit Oo Fl HSabcdflmnpstuvw Oc Op Ar limit
2575 Set or display resource limits (see
2579 is specified, the named resource will be set;
2580 otherwise the current resource value will be displayed.
2584 is specified, the hard limits will be set or displayed.
2585 While everybody is allowed to reduce a hard limit,
2586 only the superuser can increase it.
2590 specifies the soft limits instead.
2591 When displaying limits,
2597 The default is to display the soft limits,
2598 and to set both the hard and the soft limits.
2604 command to display all resources.
2607 is not acceptable in this mode.
2609 The remaining options specify which resource value is to be
2610 displayed or modified.
2611 They are mutually exclusive.
2612 .Bl -tag -width indent
2614 The maximum size of socket buffer usage, in bytes.
2615 .It Fl c Ar coredumpsize
2616 The maximal size of core dump files, in 512-byte blocks.
2617 .It Fl d Ar datasize
2618 The maximal size of the data segment of a process, in kilobytes.
2619 .It Fl f Ar filesize
2620 The maximal size of a file, in 512-byte blocks.
2621 .It Fl l Ar lockedmem
2622 The maximal size of memory that can be locked by a process, in
2624 .It Fl m Ar memoryuse
2625 The maximal resident set size of a process, in kilobytes.
2627 The maximal number of descriptors that could be opened by a process.
2628 .It Fl p Ar pseudoterminals
2629 The maximal number of pseudo-terminals for this user ID.
2630 .It Fl s Ar stacksize
2631 The maximal size of the stack segment, in kilobytes.
2633 The maximal amount of CPU time to be used by each process, in seconds.
2634 .It Fl u Ar userproc
2635 The maximal number of simultaneous processes for this user ID.
2636 .It Fl v Ar virtualmem
2637 The maximal virtual size of a process, in kilobytes.
2639 The maximum amount of swap space reserved or used for this user ID,
2642 .It Ic umask Oo Fl S Oc Op Ar mask
2643 Set the file creation mask (see
2645 to the octal or symbolic (see
2649 If the argument is omitted, the current mask value is printed.
2652 option is specified, the output is symbolic, otherwise the output is octal.
2653 .It Ic unalias Oo Fl a Oc Op Ar name ...
2654 The specified alias names are removed.
2657 is specified, all aliases are removed.
2658 .It Ic unset Oo Fl fv Oc Ar name ...
2659 The specified variables or functions are unset and unexported.
2662 option is specified or no options are given, the
2664 arguments are treated as variable names.
2667 option is specified, the
2669 arguments are treated as function names.
2670 .It Ic wait Op Ar job ...
2671 Wait for each specified
2673 to complete and return the exit status of the last process in the
2678 specified is unknown to the shell, it is treated as if it
2679 were a known job that exited with exit status 127.
2680 If no operands are given, wait for all jobs to complete
2681 and return an exit status of zero.
2683 .Ss Commandline Editing
2686 is being used interactively from a terminal, the current command
2687 and the command history
2691 .Sx Built-in Commands )
2694 command line editing.
2695 This mode uses commands similar
2696 to a subset of those described in the
2714 can be switched between insert mode and command mode by typing
2718 while in command mode will pass the line to the shell.
2721 .Dq Li "set -o emacs"
2724 command can be used to enable a subset of
2726 command line editing features.
2728 The following environment variables affect the execution of
2730 .Bl -tag -width ".Ev LANGXXXXXX"
2732 Initialization file for interactive shells.
2733 .It Ev LANG , Ev LC_*
2735 These are inherited by children of the shell,
2736 and is used in a limited manner by the shell itself.
2738 An absolute pathname for the current directory,
2739 possibly containing symbolic links.
2740 This is used and updated by the shell.
2742 The default terminal setting for the shell.
2743 This is inherited by children of the shell, and is used in the history
2747 Additionally, all environment variables are turned into shell variables
2749 which may affect the shell as described under
2750 .Sx Special Variables .
2752 .Bl -tag -width "/etc/suid_profileXX" -compact
2754 User's login profile.
2756 System login profile.
2759 .It Pa /etc/suid_profile
2760 Privileged shell profile.
2763 Errors that are detected by the shell, such as a syntax error, will
2764 cause the shell to exit with a non-zero exit status.
2765 If the shell is not an interactive shell, the execution of the shell
2766 file will be aborted.
2767 Otherwise the shell will return the exit status of the last command
2770 builtin is used with a numeric argument, it
2771 will return the argument.
2792 command, the Thompson shell, appeared in
2794 It was superseded in
2796 by the Bourne shell, which inherited the name
2801 was rewritten in 1989 under the
2803 license after the Bourne shell from
2808 was originally written by
2809 .An Kenneth Almquist .
2813 utility does not recognize multibyte characters other than UTF-8.
2816 and the line editing library
2818 do not recognize multibyte characters.
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