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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 (they do not affect expansions).
589 Redirection operators and
590 their arguments (as described below) are stripped
591 off and saved for processing.
593 The remaining words are expanded as described in
595 .Sx Word Expansions ,
596 and the first remaining word is considered the command
597 name and the command is located.
599 words are considered the arguments of the command.
600 If no command name resulted, then the
602 variable assignments recognized in 1) affect the
605 Redirections are performed as described in
609 Redirections are used to change where a command reads its input
611 In general, redirections open, close, or
612 duplicate an existing reference to a file.
614 used for redirection is:
616 .D1 Oo Ar n Oc Ar redir-op file
620 is one of the redirection operators mentioned
622 The following gives some examples of how these
623 operators can be used.
624 Note that stdin and stdout are commonly used abbreviations
625 for standard input and standard output respectively.
626 .Bl -tag -width "1234567890XX" -offset indent
627 .It Oo Ar n Oc Ns Li > Ar file
628 redirect stdout (or file descriptor
632 .It Oo Ar n Oc Ns Li >| Ar file
633 same as above, but override the
636 .It Oo Ar n Oc Ns Li >> Ar file
637 append stdout (or file descriptor
641 .It Oo Ar n Oc Ns Li < Ar file
642 redirect stdin (or file descriptor
646 .It Oo Ar n Oc Ns Li <> Ar file
647 redirect stdin (or file descriptor
651 .It Oo Ar n1 Oc Ns Li <& Ns Ar n2
652 duplicate stdin (or file descriptor
656 .It Oo Ar n Oc Ns Li <&-
657 close stdin (or file descriptor
659 .It Oo Ar n1 Oc Ns Li >& Ns Ar n2
660 duplicate stdout (or file descriptor
664 .It Oo Ar n Oc Ns Li >&-
665 close stdout (or file descriptor
669 The following redirection is often called a
671 .Bd -unfilled -offset indent
672 .Oo Ar n Oc Ns Li << Ar delimiter
678 All the text on successive lines up to the delimiter is
679 saved away and made available to the command on standard
680 input, or file descriptor
685 as specified on the initial line is quoted, then the
687 is treated literally, otherwise the text is subjected to
688 parameter expansion, command substitution, and arithmetic
689 expansion (as described in the section on
690 .Sx Word Expansions ) .
699 .Ss Search and Execution
700 There are three types of commands: shell functions,
701 built-in commands, and normal programs.
702 The command is searched for (by name) in that order.
703 The three types of commands are all executed in a different way.
705 When a shell function is executed, all of the shell positional
708 which remains unchanged) are
709 set to the arguments of the shell function.
710 The variables which are explicitly placed in the environment of
711 the command (by placing assignments to them before the
712 function name) are made local to the function and are set
714 Then the command given in the function definition is executed.
715 The positional parameters are restored to their original values
716 when the command completes.
717 This all occurs within the current shell.
719 Shell built-in commands are executed internally to the shell, without
720 spawning a new process.
721 There are two kinds of built-in commands: regular and special.
722 Assignments before special builtins persist after they finish
723 executing and assignment errors, redirection errors and certain
724 operand errors cause a script to be aborted.
725 Special builtins cannot be overridden with a function.
726 Both regular and special builtins can affect the shell in ways
727 normal programs cannot.
729 Otherwise, if the command name does not match a function
730 or built-in command, the command is searched for as a normal
731 program in the file system (as described in the next section).
732 When a normal program is executed, the shell runs the program,
733 passing the arguments and the environment to the program.
734 If the program is not a normal executable file
735 (i.e., if it does not begin with the
745 but appears to be a text file,
746 the shell will run a new instance of
750 Note that previous versions of this document
751 and the source code itself misleadingly and sporadically
752 refer to a shell script without a magic number
754 .Dq "shell procedure" .
756 When locating a command, the shell first looks to see if
757 it has a shell function by that name.
759 built-in command by that name.
760 If a built-in command is not found,
761 one of two things happen:
764 Command names containing a slash are simply executed without
765 performing any searches.
767 The shell searches each entry in the
770 in turn for the command.
773 variable should be a series of
774 entries separated by colons.
775 Each entry consists of a
777 The current directory
778 may be indicated implicitly by an empty directory name,
779 or explicitly by a single period.
781 .Ss Command Exit Status
782 Each command has an exit status that can influence the behavior
783 of other shell commands.
784 The paradigm is that a command exits
785 with zero for normal or success, and non-zero for failure,
786 error, or a false indication.
787 The man page for each command
788 should indicate the various exit codes and what they mean.
789 Additionally, the built-in commands return exit codes, as does
790 an executed shell function.
792 If a command is terminated by a signal, its exit status is 128 plus
794 Signal numbers are defined in the header file
797 Complex commands are combinations of simple commands
798 with control operators or keywords, together creating a larger complex
800 More generally, a command is one of the following:
801 .Bl -item -offset indent
807 list or compound-list
814 Unless otherwise stated, the exit status of a command is
815 that of the last simple command executed by the command.
817 A pipeline is a sequence of one or more commands separated
818 by the control operator
820 The standard output of all but
821 the last command is connected to the standard input
823 The standard output of the last
824 command is inherited from the shell, as usual.
826 The format for a pipeline is:
828 .D1 Oo Li \&! Oc Ar command1 Op Li \&| Ar command2 ...
830 The standard output of
832 is connected to the standard input of
834 The standard input, standard output, or
835 both of a command is considered to be assigned by the
836 pipeline before any redirection specified by redirection
837 operators that are part of the command.
839 Note that unlike some other shells,
841 executes each process in a pipeline with more than one command
842 in a subshell environment and as a child of the
846 If the pipeline is not in the background (discussed later),
847 the shell waits for all commands to complete.
851 does not precede the pipeline, the
852 exit status is the exit status of the last command specified
854 Otherwise, the exit status is the logical
855 NOT of the exit status of the last command.
857 the last command returns zero, the exit status is 1; if
858 the last command returns greater than zero, the exit status
861 Because pipeline assignment of standard input or standard
862 output or both takes place before redirection, it can be
863 modified by redirection.
866 .Dl "command1 2>&1 | command2"
868 sends both the standard output and standard error of
870 to the standard input of
875 or newline terminator causes the preceding
877 (described below in the section called
878 .Sx Short-Circuit List Operators )
879 to be executed sequentially;
882 causes asynchronous execution of the preceding AND-OR-list.
883 .Ss Background Commands (&)
884 If a command is terminated by the control operator ampersand
886 the shell executes the command in a subshell environment (see
887 .Sx Grouping Commands Together
888 below) and asynchronously;
889 the shell does not wait for the command to finish
890 before executing the next command.
892 The format for running a command in background is:
894 .D1 Ar command1 Li & Op Ar command2 Li & Ar ...
896 If the shell is not interactive, the standard input of an
897 asynchronous command is set to
899 .Ss Lists (Generally Speaking)
900 A list is a sequence of zero or more commands separated by
901 newlines, semicolons, or ampersands,
902 and optionally terminated by one of these three characters.
904 list are executed in the order they are written.
905 If command is followed by an ampersand, the shell starts the
906 command and immediately proceeds onto the next command;
907 otherwise it waits for the command to terminate before
908 proceeding to the next one.
909 .Ss Short-Circuit List Operators
913 are AND-OR list operators.
915 executes the first command, and then executes the second command
916 if the exit status of the first command is zero.
918 is similar, but executes the second command if the exit
919 status of the first command is nonzero.
923 both have the same priority.
924 .Ss Flow-Control Constructs (if, while, for, case)
928 .Bd -unfilled -offset indent -compact
932 .Ic then Ar list Oc Ar ...
940 .Bd -unfilled -offset indent -compact
946 The two lists are executed repeatedly while the exit status of the
950 command is similar, but has the word
955 repeat until the exit status of the first list is zero.
960 .Bd -unfilled -offset indent -compact
961 .Ic for Ar variable Op Ic in Ar word ...
968 and the following words are omitted,
971 The words are expanded, and then the list is executed
972 repeatedly with the variable set to each word in turn.
977 commands may be replaced with
987 .D1 Ic break Op Ar num
988 .D1 Ic continue Op Ar num
992 command terminates the
1001 command continues with the next iteration of the innermost loop.
1002 These are implemented as special built-in commands.
1007 .Bd -unfilled -offset indent -compact
1008 .Ic case Ar word Ic in
1009 .Ar pattern Ns Li ) Ar list Li ;;
1014 The pattern can actually be one or more patterns
1021 Tilde expansion, parameter expansion, command substitution,
1022 arithmetic expansion and quote removal are applied to the word.
1023 Then, each pattern is expanded in turn using tilde expansion,
1024 parameter expansion, command substitution and arithmetic expansion and
1025 the expanded form of the word is checked against it.
1026 If a match is found, the corresponding list is executed.
1027 If the selected list is terminated by the control operator
1031 execution continues with the next list,
1032 continuing until a list terminated with
1037 The exit code of the
1039 command is the exit code of the last command executed in the list or
1040 zero if no patterns were matched.
1041 .Ss Grouping Commands Together
1042 Commands may be grouped by writing either
1044 .D1 Li \&( Ns Ar list Ns Li \%)
1048 .D1 Li { Ar list Ns Li \&; }
1050 The first form executes the commands in a subshell environment.
1051 A subshell environment has its own copy of:
1054 The current working directory as set by
1057 The file creation mask as set by
1060 Resource limits as set by
1063 References to open files.
1070 Positional parameters and variables.
1079 These are copied from the parent shell environment,
1080 except that trapped (but not ignored) signals are reset to the default action
1081 and known jobs are cleared.
1082 Any changes do not affect the parent shell environment.
1084 A subshell environment may be implemented as a child process or differently.
1085 If job control is enabled in an interactive shell,
1086 commands grouped in parentheses can be suspended and continued as a unit.
1088 For compatibility with other shells,
1089 two open parentheses in sequence should be separated by whitespace.
1091 The second form never forks another shell,
1092 so it is slightly more efficient.
1093 Grouping commands together this way allows the user to
1094 redirect their output as though they were one program:
1095 .Bd -literal -offset indent
1096 { echo -n "hello"; echo " world"; } > greeting
1099 The syntax of a function definition is
1101 .D1 Ar name Li \&( \&) Ar command
1103 A function definition is an executable statement; when
1104 executed it installs a function named
1107 exit status of zero.
1116 Variables may be declared to be local to a function by
1120 This should appear as the first statement of a function,
1123 .D1 Ic local Oo Ar variable ... Oc Op Fl
1127 command is implemented as a built-in command.
1129 When a variable is made local, it inherits the initial
1130 value and exported and readonly flags from the variable
1131 with the same name in the surrounding scope, if there is
1133 Otherwise, the variable is initially unset.
1135 uses dynamic scoping, so that if the variable
1137 is made local to function
1139 which then calls function
1141 references to the variable
1145 will refer to the variable
1149 not to the global variable named
1152 The only special parameter that can be made local is
1156 local causes any shell options that are
1159 command inside the function to be
1160 restored to their original values when the function
1167 .D1 Ic return Op Ar exitstatus
1169 It terminates the current executional scope, returning from the closest
1170 nested function or sourced script;
1171 if no function or sourced script is being executed,
1172 it exits the shell instance.
1175 command is implemented as a special built-in command.
1176 .Ss Variables and Parameters
1177 The shell maintains a set of parameters.
1179 denoted by a name is called a variable.
1181 the shell turns all the environment variables into shell
1183 New variables can be set using the form
1185 .D1 Ar name Ns = Ns Ar value
1187 Variables set by the user must have a name consisting solely
1188 of alphabetics, numerics, and underscores.
1189 The first letter of a variable name must not be numeric.
1190 A parameter can also be denoted by a number
1191 or a special character as explained below.
1193 Assignments are expanded differently from other words:
1194 tilde expansion is also performed after the equals sign and after any colon
1195 and usernames are also terminated by colons,
1196 and field splitting and pathname expansion are not performed.
1198 This special expansion applies not only to assignments that form a simple
1199 command by themselves or precede a command word,
1200 but also to words passed to the
1205 built-in commands that have this form.
1206 For this, the builtin's name must be literal
1207 (not the result of an expansion)
1208 and may optionally be preceded by one or more literal instances of
1211 .Ss Positional Parameters
1212 A positional parameter is a parameter denoted by a number greater than zero.
1213 The shell sets these initially to the values of its command line
1214 arguments that follow the name of the shell script.
1217 built-in command can also be used to set or reset them.
1218 .Ss Special Parameters
1219 Special parameters are parameters denoted by a single special character
1221 They are shown in the following list, exactly as they would appear in input
1222 typed by the user or in the source of a shell script.
1225 Expands to the positional parameters, starting from one.
1227 the expansion occurs within a double-quoted string
1228 it expands to a single field with the value of each parameter
1229 separated by the first character of the
1236 Expands to the positional parameters, starting from one.
1238 the expansion occurs within double-quotes, each positional
1239 parameter expands as a separate argument.
1240 If there are no positional parameters, the
1243 generates zero arguments, even when
1246 What this basically means, for example, is
1259 .Bd -literal -offset indent
1263 Expands to the number of positional parameters.
1265 Expands to the exit status of the most recent pipeline.
1267 (hyphen) Expands to the current option flags (the single-letter
1268 option names concatenated into a string) as specified on
1271 built-in command, or implicitly
1274 Expands to the process ID of the invoked shell.
1276 retains the same value of
1280 Expands to the process ID of the most recent background
1281 command executed from the current shell.
1283 pipeline, the process ID is that of the last command in the
1285 If this parameter is referenced, the shell will remember
1286 the process ID and its exit status until the
1288 built-in command reports completion of the process.
1290 (zero) Expands to the name of the shell script if passed on the command line,
1293 operand if given (with
1295 or otherwise argument 0 passed to the shell.
1297 .Ss Special Variables
1298 The following variables are set by the shell or
1299 have special meaning to it:
1300 .Bl -tag -width ".Va HISTSIZE"
1302 The search path used with the
1306 The fallback editor used with the
1309 If not set, the default editor is
1312 The default editor used with the
1316 The number of previous commands that are accessible.
1318 The user's home directory,
1319 used in tilde expansion and as a default directory for the
1323 Input Field Separators.
1324 The default value is
1330 This default also applies if
1332 is unset, but not if it is set to the empty string.
1334 .Sx White Space Splitting
1335 section for more details.
1337 The current line number in the script or function.
1339 The name of a mail file, that will be checked for the arrival of new
1346 separated list of file names, for the shell to check for incoming
1348 This variable overrides the
1351 There is a maximum of 10 mailboxes that can be monitored at once.
1353 The default search path for executables.
1356 section for details.
1358 The parent process ID of the invoked shell.
1359 This is set at startup
1360 unless this variable is in the environment.
1361 A later change of parent process ID is not reflected.
1362 A subshell retains the same value of
1365 The primary prompt string, which defaults to
1367 unless you are the superuser, in which case it defaults to
1370 may include any of the following formatting sequences,
1371 which are replaced by the given information:
1372 .Bl -tag -width indent
1374 This system's fully-qualified hostname (FQDN).
1376 This system's hostname.
1378 The final component of the current working directory.
1380 The entire path of the current working directory.
1384 for normal users and
1388 A literal backslash.
1391 The secondary prompt string, which defaults to
1394 may include any of the formatting sequences from
1397 The prefix for the trace output (if
1404 This clause describes the various expansions that are
1406 Not all expansions are performed on
1407 every word, as explained later.
1409 Tilde expansions, parameter expansions, command substitutions,
1410 arithmetic expansions, and quote removals that occur within
1411 a single word expand to a single field.
1413 splitting or pathname expansion that can create multiple
1414 fields from a single word.
1415 The single exception to this rule is
1416 the expansion of the special parameter
1418 within double-quotes,
1419 as was described above.
1421 The order of word expansion is:
1424 Tilde Expansion, Parameter Expansion, Command Substitution,
1425 Arithmetic Expansion (these all occur at the same time).
1427 Field Splitting is performed on fields generated by step (1)
1432 Pathname Expansion (unless the
1434 option is in effect).
1441 character is used to introduce parameter expansion, command
1442 substitution, or arithmetic expansion.
1443 .Ss Tilde Expansion (substituting a user's home directory)
1444 A word beginning with an unquoted tilde character
1447 subjected to tilde expansion.
1448 All the characters up to a slash
1450 or the end of the word are treated as a username
1451 and are replaced with the user's home directory.
1453 username is missing (as in
1455 the tilde is replaced with the value of the
1457 variable (the current user's home directory).
1458 .Ss Parameter Expansion
1459 The format for parameter expansion is as follows:
1461 .D1 Li ${ Ns Ar expression Ns Li }
1465 consists of all characters until the matching
1469 escaped by a backslash or within a single-quoted or double-quoted
1470 string, and characters in
1471 embedded arithmetic expansions, command substitutions, and variable
1472 expansions, are not examined in determining the matching
1474 If the variants with
1480 occur within a double-quoted string,
1481 as an extension there may be unquoted parts
1482 (via double-quotes inside the expansion);
1484 within such parts are also not examined in determining the matching
1487 The simplest form for parameter expansion is:
1489 .D1 Li ${ Ns Ar parameter Ns Li }
1491 The value, if any, of
1495 The parameter name or symbol can be enclosed in braces, which are
1496 optional except for positional parameters with more than one digit or
1497 when parameter is followed by a character that could be interpreted as
1499 If a parameter expansion occurs inside double-quotes:
1502 Field splitting is not performed on the results of the
1503 expansion, with the exception of the special parameter
1506 Pathname expansion is not performed on the results of the
1510 In addition, a parameter expansion can be modified by using one of the
1512 .Bl -tag -width indent
1513 .It Li ${ Ns Ar parameter Ns Li :- Ns Ar word Ns Li }
1517 is unset or null, the expansion of
1519 is substituted; otherwise, the value of
1522 .It Li ${ Ns Ar parameter Ns Li := Ns Ar word Ns Li }
1523 Assign Default Values.
1526 is unset or null, the expansion of
1536 does not prevent field splitting or pathname expansion.
1537 Only variables, not positional
1538 parameters or special parameters, can be
1539 assigned in this way.
1540 .It Li ${ Ns Ar parameter Ns Li :? Ns Oo Ar word Oc Ns Li }
1541 Indicate Error if Null or Unset.
1544 is unset or null, the expansion of
1546 (or a message indicating it is unset if
1548 is omitted) is written to standard
1549 error and the shell exits with a nonzero
1551 Otherwise, the value of
1555 interactive shell need not exit.
1556 .It Li ${ Ns Ar parameter Ns Li :+ Ns Ar word Ns Li }
1557 Use Alternate Value.
1560 is unset or null, null is substituted;
1561 otherwise, the expansion of
1566 In the parameter expansions shown previously, use of the colon in the
1567 format results in a test for a parameter that is unset or null; omission
1568 of the colon results in a test for a parameter that is only unset.
1572 inherits the type of quoting
1573 (unquoted, double-quoted or here-document)
1574 from the surroundings,
1575 with the exception that a backslash that quotes a closing brace is removed
1576 during quote removal.
1577 .Bl -tag -width indent
1578 .It Li ${# Ns Ar parameter Ns Li }
1580 The length in characters of
1585 The following four varieties of parameter expansion provide for substring
1587 In each case, pattern matching notation
1589 .Sx Shell Patterns ) ,
1590 rather than regular expression notation,
1591 is used to evaluate the patterns.
1592 If parameter is one of the special parameters
1596 the result of the expansion is unspecified.
1597 Enclosing the full parameter expansion string in double-quotes does not
1598 cause the following four varieties of pattern characters to be quoted,
1599 whereas quoting characters within the braces has this effect.
1600 .Bl -tag -width indent
1601 .It Li ${ Ns Ar parameter Ns Li % Ns Ar word Ns Li }
1602 Remove Smallest Suffix Pattern.
1605 is expanded to produce a pattern.
1607 parameter expansion then results in
1609 with the smallest portion of the
1610 suffix matched by the pattern deleted.
1611 .It Li ${ Ns Ar parameter Ns Li %% Ns Ar word Ns Li }
1612 Remove Largest Suffix Pattern.
1615 is expanded to produce a pattern.
1617 parameter expansion then results in
1619 with the largest portion of the
1620 suffix matched by the pattern deleted.
1621 .It Li ${ Ns Ar parameter Ns Li # Ns Ar word Ns Li }
1622 Remove Smallest Prefix Pattern.
1625 is expanded to produce a pattern.
1627 parameter expansion then results in
1629 with the smallest portion of the
1630 prefix matched by the pattern deleted.
1631 .It Li ${ Ns Ar parameter Ns Li ## Ns Ar word Ns Li }
1632 Remove Largest Prefix Pattern.
1635 is expanded to produce a pattern.
1637 parameter expansion then results in
1639 with the largest portion of the
1640 prefix matched by the pattern deleted.
1642 .Ss Command Substitution
1643 Command substitution allows the output of a command to be substituted in
1644 place of the command name itself.
1645 Command substitution occurs when
1646 the command is enclosed as follows:
1648 .D1 Li $( Ns Ar command Ns Li )\&
1650 or the backquoted version:
1652 .D1 Li ` Ns Ar command Ns Li `
1654 The shell expands the command substitution by executing command
1655 and replacing the command substitution
1656 with the standard output of the command,
1657 removing sequences of one or more newlines at the end of the substitution.
1658 Embedded newlines before the end of the output are not removed;
1659 however, during field splitting, they may be translated into spaces
1660 depending on the value of
1662 and the quoting that is in effect.
1663 The command is executed in a subshell environment,
1664 except that the built-in commands
1669 return information about the parent shell environment
1672 returns information about the same process
1673 if they are the only command in a command substitution.
1675 If a command substitution of the
1677 form begins with a subshell,
1682 must be separated by whitespace
1683 to avoid ambiguity with arithmetic expansion.
1684 .Ss Arithmetic Expansion
1685 Arithmetic expansion provides a mechanism for evaluating an arithmetic
1686 expression and substituting its value.
1687 The format for arithmetic expansion is as follows:
1689 .D1 Li $(( Ns Ar expression Ns Li ))
1693 is treated as if it were in double-quotes, except
1694 that a double-quote inside the expression is not treated specially.
1696 shell expands all tokens in the
1698 for parameter expansion,
1699 command substitution,
1700 arithmetic expansion
1703 The allowed expressions are a subset of C expressions,
1705 .Bl -tag -width "Variables" -offset indent
1707 All values are of type
1710 Decimal, octal (starting with
1712 and hexadecimal (starting with
1716 Shell variables can be read and written
1717 and contain integer constants.
1720 .It Binary operators
1721 .Li "* / % + - << >> < <= > >= == != & ^ | && ||"
1722 .It Assignment operators
1723 .Li "= += -= *= /= %= <<= >>= &= ^= |="
1724 .It Conditional operator
1728 The result of the expression is substituted in decimal.
1729 .Ss White Space Splitting (Field Splitting)
1730 In certain contexts,
1731 after parameter expansion, command substitution, and
1732 arithmetic expansion the shell scans the results of
1733 expansions and substitutions that did not occur in double-quotes for
1734 field splitting and multiple fields can result.
1745 are treated differently from other characters in
1750 at the beginning or end of a word is discarded.
1752 Subsequently, a field is delimited by either
1755 a non-whitespace character in
1757 with any whitespace in
1761 one or more whitespace characters in
1765 If a word ends with a non-whitespace character in
1767 there is no empty field after this character.
1769 If no field is delimited, the word is discarded.
1770 In particular, if a word consists solely of an unquoted substitution
1771 and the result of the substitution is null,
1772 it is removed by field splitting even if
1775 .Ss Pathname Expansion (File Name Generation)
1779 file name generation is performed
1780 after word splitting is complete.
1782 viewed as a series of patterns, separated by slashes.
1784 process of expansion replaces the word with the names of
1785 all existing files whose names can be formed by replacing
1786 each pattern with a string that matches the specified pattern.
1787 There are two restrictions on this: first, a pattern cannot match
1788 a string containing a slash, and second,
1789 a pattern cannot match a string starting with a period
1790 unless the first character of the pattern is a period.
1791 The next section describes the patterns used for
1793 the four varieties of parameter expansion for substring processing and the
1797 A pattern consists of normal characters, which match themselves,
1798 and meta-characters.
1799 The meta-characters are
1804 These characters lose their special meanings if they are quoted.
1805 When command or variable substitution is performed and the dollar sign
1806 or back quotes are not double-quoted, the value of the
1807 variable or the output of the command is scanned for these
1808 characters and they are turned into meta-characters.
1812 matches any string of characters.
1815 matches any single character.
1818 introduces a character class.
1819 The end of the character class is indicated by a
1827 rather than introducing a character class.
1828 A character class matches any of the characters between the square brackets.
1829 A locale-dependent range of characters may be specified using a minus sign.
1830 A named class of characters (see
1832 may be specified by surrounding the name with
1837 .Ql \&[\&[:alpha:\&]\&]
1838 is a shell pattern that matches a single letter.
1839 The character class may be complemented by making an exclamation point
1841 the first character of the character class.
1844 has the same effect but is non-standard.
1848 in a character class, make it the first character listed
1856 make it the first or last character listed.
1857 .Ss Built-in Commands
1858 This section lists the built-in commands.
1859 .Bl -tag -width indent
1861 A null command that returns a 0 (true) exit value.
1863 The commands in the specified file are read and executed by the shell.
1866 command may be used to return to the
1873 characters, it is used as is.
1874 Otherwise, the shell searches the
1877 If it is not found in the
1879 it is sought in the current working directory.
1881 A built-in equivalent of
1883 .It Ic alias Oo Ar name Ns Oo = Ns Ar string Oc ... Oc
1885 .Ar name Ns = Ns Ar string
1886 is specified, the shell defines the alias
1892 is specified, the value of the alias
1895 With no arguments, the
1897 built-in command prints the names and values of all defined aliases
1900 Alias values are written with appropriate quoting so that they are
1901 suitable for re-input to the shell.
1905 .It Ic bg Op Ar job ...
1906 Continue the specified jobs
1907 (or the current job if no jobs are given)
1909 .It Ic bind Oo Fl aeklrsv Oc Oo Ar key Oo Ar command Oc Oc
1910 List or alter key bindings for the line editor.
1911 This command is documented in
1913 .It Ic break Op Ar num
1915 .Sx Flow-Control Constructs
1917 .It Ic builtin Ar cmd Op Ar arg ...
1918 Execute the specified built-in command,
1920 This is useful when the user wishes to override a shell function
1921 with the same name as a built-in command.
1922 .It Ic cd Oo Fl L | P Oc Oo Fl e Oc Op Ar directory
1923 Switch to the specified
1925 or to the directory specified in the
1927 environment variable if no
1936 then the directories listed in the
1939 searched for the specified
1943 is unset, the current directory is searched.
1946 is the same as that of
1948 In an interactive shell,
1951 command will print out the name of the directory
1952 that it actually switched to
1953 if this is different from the name that the user gave.
1954 These may be different either because the
1956 mechanism was used or because a symbolic link was crossed.
1960 option is specified,
1962 is handled physically and symbolic links are resolved before
1964 components are processed.
1967 option is specified,
1969 is handled logically.
1970 This is the default.
1976 to return exit status 1 if the full pathname of the new directory
1977 cannot be determined reliably or at all.
1978 Normally this is not considered an error,
1979 although a warning is printed.
1984 .It Ic command Oo Fl p Oc Op Ar utility Op Ar argument ...
1985 .It Ic command Oo Fl p Oc Fl v Ar utility
1986 .It Ic command Oo Fl p Oc Fl V Ar utility
1987 The first form of invocation executes the specified
1989 ignoring shell functions in the search.
1992 is a special builtin,
1993 it is executed as if it were a regular builtin.
1997 option is specified, the command search is performed using a
2000 that is guaranteed to find all of the standard utilities.
2004 option is specified,
2006 is not executed but a description of its interpretation by the shell is
2008 For ordinary commands the output is the path name; for shell built-in
2009 commands, shell functions and keywords only the name is written.
2010 Aliases are printed as
2011 .Dq Ic alias Ar name Ns = Ns Ar value .
2015 option is identical to
2017 except for the output.
2019 .Dq Ar utility Ic is Ar description
2025 a special shell builtin,
2032 .It Ic continue Op Ar num
2034 .Sx Flow-Control Constructs
2036 .It Ic echo Oo Fl e | n Oc Op Ar string ...
2037 Print a space-separated list of the arguments to the standard output
2038 and append a newline character.
2039 .Bl -tag -width indent
2041 Suppress the output of the trailing newline.
2043 Process C-style backslash escape sequences.
2046 command understands the following character escapes:
2047 .Bl -tag -width indent
2049 Alert (ring the terminal bell)
2053 Suppress the trailing newline (this has the side-effect of truncating the
2054 line if it is not the last character)
2072 (Zero) The character whose octal value is
2078 is not enclosed in quotes then the backslash itself must be escaped
2079 with a backslash to protect it from the shell.
2081 .Bd -literal -offset indent
2090 $ echo -e a\e\e\e\eb
2099 options may be specified.
2100 .It Ic eval Ar string ...
2101 Concatenate all the arguments with spaces.
2102 Then re-parse and execute the command.
2103 .It Ic exec Op Ar command Op arg ...
2107 the shell process is replaced with the specified program
2108 (which must be a real program, not a shell built-in command or function).
2109 Any redirections on the
2111 command are marked as permanent,
2112 so that they are not undone when the
2115 .It Ic exit Op Ar exitstatus
2116 Terminate the shell process.
2120 it is used as the exit status of the shell.
2121 Otherwise, if the shell is executing an
2123 trap, the exit status of the last command before the trap is used;
2124 if the shell is executing a trap for a signal,
2125 the shell exits by resending the signal to itself.
2126 Otherwise, the exit status of the preceding command is used.
2127 The exit status should be an integer between 0 and 255.
2128 .It Ic export Ar name ...
2129 .It Ic export Op Fl p
2130 The specified names are exported so that they will
2131 appear in the environment of subsequent commands.
2132 The only way to un-export a variable is to
2135 The shell allows the value of a variable to be set
2136 at the same time as it is exported by writing
2138 .D1 Ic export Ar name Ns = Ns Ar value
2140 With no arguments the
2142 command lists the names
2143 of all exported variables.
2146 option is specified, the exported variables are printed as
2147 .Dq Ic export Ar name Ns = Ns Ar value
2148 lines, suitable for re-input to the shell.
2150 A null command that returns a non-zero (false) exit value.
2151 .It Ic fc Oo Fl e Ar editor Oc Op Ar first Op Ar last
2152 .It Ic fc Fl l Oo Fl nr Oc Op Ar first Op Ar last
2153 .It Ic fc Fl s Oo Ar old Ns = Ns Ar new Oc Op Ar first
2156 built-in command lists, or edits and re-executes,
2157 commands previously entered to an interactive shell.
2158 .Bl -tag -width indent
2160 Use the editor named by
2162 to edit the commands.
2165 string is a command name,
2166 subject to search via the
2171 variable is used as a default when
2176 is null or unset, the value of the
2183 is used as the editor.
2185 List the commands rather than invoking
2187 The commands are written in the
2188 sequence indicated by the
2192 operands, as affected by
2194 with each command preceded by the command number.
2196 Suppress command numbers when listing with
2199 Reverse the order of the commands listed
2208 Re-execute the command without invoking an editor.
2211 Select the commands to list or edit.
2212 The number of previous commands that can be accessed
2213 are determined by the value of the
2220 or both are one of the following:
2221 .Bl -tag -width indent
2222 .It Oo Cm + Oc Ns Ar num
2223 A positive number representing a command number;
2224 command numbers can be displayed with the
2228 A negative decimal number representing the
2229 command that was executed
2232 commands previously.
2233 For example, \-1 is the immediately previous command.
2235 A string indicating the most recently entered command
2236 that begins with that string.
2238 .Ar old Ns = Ns Ar new
2239 operand is not also specified with
2241 the string form of the first operand cannot contain an embedded equal sign.
2245 The following variables affect the execution of
2247 .Bl -tag -width ".Va HISTSIZE"
2249 Name of the editor to use for history editing.
2251 The number of previous commands that are accessible.
2256 or the current job to the foreground.
2257 .It Ic getopts Ar optstring var
2264 command deprecates the older
2267 The first argument should be a series of letters, each possibly
2268 followed by a colon which indicates that the option takes an argument.
2269 The specified variable is set to the parsed option.
2271 the next argument is placed into the shell variable
2273 If an option takes an argument, it is placed into the shell variable
2275 If an invalid option is encountered,
2279 It returns a false value (1) when it encounters the end of the options.
2280 .It Ic hash Oo Fl rv Oc Op Ar command ...
2281 The shell maintains a hash table which remembers the locations of commands.
2282 With no arguments whatsoever, the
2284 command prints out the contents of this table.
2288 command removes each specified
2290 from the hash table (unless they are functions) and then locates it.
2295 prints the locations of the commands as it finds them.
2300 command to delete all the entries in the hash table except for functions.
2301 .It Ic jobid Op Ar job
2302 Print the process IDs of the processes in the specified
2306 argument is omitted, use the current job.
2307 .It Ic jobs Oo Fl lps Oc Op Ar job ...
2308 Print information about the specified jobs, or all jobs if no
2311 The information printed includes job ID, status and command name.
2315 option is specified, the PID of each job is also printed.
2318 option is specified, only the process IDs for the process group leaders
2319 are printed, one per line.
2322 option is specified, only the PIDs of the job commands are printed, one per
2325 A built-in equivalent of
2327 that additionally supports sending signals to jobs.
2328 .It Ic local Oo Ar variable ... Oc Op Fl
2333 A built-in equivalent of
2335 .It Ic pwd Op Fl L | P
2336 Print the path of the current directory.
2337 The built-in command may
2338 differ from the program of the same name because the
2339 built-in command remembers what the current directory
2340 is rather than recomputing it each time.
2343 However, if the current directory is
2345 the built-in version of
2347 will continue to print the old name for the directory.
2351 option is specified, symbolic links are resolved.
2354 option is specified, the shell's notion of the current directory
2355 is printed (symbolic links are not resolved).
2356 This is the default.
2357 .It Ic read Oo Fl p Ar prompt Oc Oo
2358 .Fl t Ar timeout Oc Oo Fl er Oc Ar variable ...
2364 and the standard input is a terminal.
2366 read from the standard input.
2367 The trailing newline
2368 is deleted from the line and the line is split as
2369 described in the section on
2370 .Sx White Space Splitting (Field Splitting)
2372 the pieces are assigned to the variables in order.
2373 If there are more pieces than variables, the remaining
2374 pieces (along with the characters in
2376 that separated them)
2377 are assigned to the last variable.
2378 If there are more variables than pieces, the remaining
2379 variables are assigned the null string.
2381 Backslashes are treated specially, unless the
2385 If a backslash is followed by
2386 a newline, the backslash and the newline will be
2388 If a backslash is followed by any other
2389 character, the backslash will be deleted and the following
2390 character will be treated as though it were not in
2396 option is specified and the
2398 elapses before a complete line of input is supplied,
2401 command will return an exit status as if terminated by
2403 without assigning any values.
2406 value may optionally be followed by one of
2411 to explicitly specify seconds, minutes or hours.
2412 If none is supplied,
2418 option exists only for backward compatibility with older scripts.
2420 The exit status is 0 on success, 1 on end of file,
2421 between 2 and 128 if an error occurs
2422 and greater than 128 if a trapped signal interrupts
2424 .It Ic readonly Oo Fl p Oc Op Ar name ...
2427 is marked as read only,
2428 so that it cannot be subsequently modified or unset.
2429 The shell allows the value of a variable to be set
2430 at the same time as it is marked read only
2431 by using the following form:
2433 .D1 Ic readonly Ar name Ns = Ns Ar value
2435 With no arguments the
2437 command lists the names of all read only variables.
2440 option is specified, the read-only variables are printed as
2441 .Dq Ic readonly Ar name Ns = Ns Ar value
2442 lines, suitable for re-input to the shell.
2443 .It Ic return Op Ar exitstatus
2447 .It Ic set Oo Fl /+abCEefIimnpTuVvx Oc Oo Fl /+o Ar longname Oc Oo
2448 .Fl c Ar string Oc Op Fl - Ar arg ...
2451 command performs three different functions:
2454 With no arguments, it lists the values of all shell variables.
2456 If options are given,
2457 either in short form or using the long
2458 .Dq Fl /+o Ar longname
2460 it sets or clears the specified options as described in the section called
2461 .Sx Argument List Processing .
2465 option is specified,
2467 will replace the shell's positional parameters with the subsequent
2469 If no arguments follow the
2472 all the positional parameters will be cleared,
2473 which is equivalent to executing the command
2477 flag may be omitted when specifying arguments to be used
2478 as positional replacement parameters.
2479 This is not recommended,
2480 because the first argument may begin with a dash
2486 command will interpret as a request to enable or disable options.
2488 .It Ic setvar Ar variable value
2489 Assigns the specified
2495 command is intended to be used in functions that
2496 assign values to variables whose names are passed as parameters.
2497 In general it is better to write
2498 .Dq Ar variable Ns = Ns Ar value
2501 .It Ic shift Op Ar n
2502 Shift the positional parameters
2507 A shift sets the value of
2516 decreasing the value of
2519 For portability, shifting if there are zero positional parameters
2520 should be avoided, since the shell may abort.
2522 A built-in equivalent of
2525 Print the amount of time spent executing the shell process and its children.
2526 The first output line shows the user and system times for the shell process
2527 itself, the second one contains the user and system times for the
2529 .It Ic trap Oo Ar action Oc Ar signal ...
2531 Cause the shell to parse and execute
2536 The signals are specified by name or number.
2537 In addition, the pseudo-signal
2539 may be used to specify an
2541 that is performed when the shell terminates.
2544 may be an empty string or a dash
2546 the former causes the specified signal to be ignored
2547 and the latter causes the default action to be taken.
2550 is another way to request the default action, for compatibility reasons this
2551 usage is not recommended though.
2552 In a subshell or utility environment,
2553 the shell resets trapped (but not ignored) signals to the default action.
2556 command has no effect on signals that were ignored on entry to the shell.
2562 command to display a list of valid signal names.
2564 A null command that returns a 0 (true) exit value.
2565 .It Ic type Op Ar name ...
2568 as a command and print the resolution of the command search.
2569 Possible resolutions are:
2570 shell keyword, alias, special shell builtin, shell builtin, command,
2573 For aliases the alias expansion is printed;
2574 for commands and tracked aliases
2575 the complete pathname of the command is printed.
2576 .It Ic ulimit Oo Fl HSabcdflmnpstuvw Oc Op Ar limit
2577 Set or display resource limits (see
2581 is specified, the named resource will be set;
2582 otherwise the current resource value will be displayed.
2586 is specified, the hard limits will be set or displayed.
2587 While everybody is allowed to reduce a hard limit,
2588 only the superuser can increase it.
2592 specifies the soft limits instead.
2593 When displaying limits,
2599 The default is to display the soft limits,
2600 and to set both the hard and the soft limits.
2606 command to display all resources.
2609 is not acceptable in this mode.
2611 The remaining options specify which resource value is to be
2612 displayed or modified.
2613 They are mutually exclusive.
2614 .Bl -tag -width indent
2616 The maximum size of socket buffer usage, in bytes.
2617 .It Fl c Ar coredumpsize
2618 The maximal size of core dump files, in 512-byte blocks.
2619 .It Fl d Ar datasize
2620 The maximal size of the data segment of a process, in kilobytes.
2621 .It Fl f Ar filesize
2622 The maximal size of a file, in 512-byte blocks.
2623 .It Fl l Ar lockedmem
2624 The maximal size of memory that can be locked by a process, in
2626 .It Fl m Ar memoryuse
2627 The maximal resident set size of a process, in kilobytes.
2629 The maximal number of descriptors that could be opened by a process.
2630 .It Fl p Ar pseudoterminals
2631 The maximal number of pseudo-terminals for this user ID.
2632 .It Fl s Ar stacksize
2633 The maximal size of the stack segment, in kilobytes.
2635 The maximal amount of CPU time to be used by each process, in seconds.
2636 .It Fl u Ar userproc
2637 The maximal number of simultaneous processes for this user ID.
2638 .It Fl v Ar virtualmem
2639 The maximal virtual size of a process, in kilobytes.
2641 The maximum amount of swap space reserved or used for this user ID,
2644 .It Ic umask Oo Fl S Oc Op Ar mask
2645 Set the file creation mask (see
2647 to the octal or symbolic (see
2651 If the argument is omitted, the current mask value is printed.
2654 option is specified, the output is symbolic, otherwise the output is octal.
2655 .It Ic unalias Oo Fl a Oc Op Ar name ...
2656 The specified alias names are removed.
2659 is specified, all aliases are removed.
2660 .It Ic unset Oo Fl fv Oc Ar name ...
2661 The specified variables or functions are unset and unexported.
2664 option is specified or no options are given, the
2666 arguments are treated as variable names.
2669 option is specified, the
2671 arguments are treated as function names.
2672 .It Ic wait Op Ar job ...
2673 Wait for each specified
2675 to complete and return the exit status of the last process in the
2680 specified is unknown to the shell, it is treated as if it
2681 were a known job that exited with exit status 127.
2682 If no operands are given, wait for all jobs to complete
2683 and return an exit status of zero.
2685 .Ss Commandline Editing
2688 is being used interactively from a terminal, the current command
2689 and the command history
2693 .Sx Built-in Commands )
2696 command line editing.
2697 This mode uses commands similar
2698 to a subset of those described in the
2716 can be switched between insert mode and command mode by typing
2720 while in command mode will pass the line to the shell.
2723 .Dq Li "set -o emacs"
2726 command can be used to enable a subset of
2728 command line editing features.
2730 The following environment variables affect the execution of
2732 .Bl -tag -width ".Ev LANGXXXXXX"
2734 Initialization file for interactive shells.
2735 .It Ev LANG , Ev LC_*
2737 These are inherited by children of the shell,
2738 and is used in a limited manner by the shell itself.
2740 An absolute pathname for the current directory,
2741 possibly containing symbolic links.
2742 This is used and updated by the shell.
2744 The default terminal setting for the shell.
2745 This is inherited by children of the shell, and is used in the history
2749 Additionally, all environment variables are turned into shell variables
2751 which may affect the shell as described under
2752 .Sx Special Variables .
2754 .Bl -tag -width "/etc/suid_profileXX" -compact
2756 User's login profile.
2758 System login profile.
2761 .It Pa /etc/suid_profile
2762 Privileged shell profile.
2765 Errors that are detected by the shell, such as a syntax error, will
2766 cause the shell to exit with a non-zero exit status.
2767 If the shell is not an interactive shell, the execution of the shell
2768 file will be aborted.
2769 Otherwise the shell will return the exit status of the last command
2772 builtin is used with a numeric argument, it
2773 will return the argument.
2794 command, the Thompson shell, appeared in
2796 It was superseded in
2798 by the Bourne shell, which inherited the name
2803 was rewritten in 1989 under the
2805 license after the Bourne shell from
2810 was originally written by
2811 .An Kenneth Almquist .
2815 utility does not recognize multibyte characters other than UTF-8.
2818 and the line editing library
2820 do not recognize multibyte characters.
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