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32 .\" from: @(#)sh.1 8.6 (Berkeley) 5/4/95
40 .Nd command interpreter (shell)
43 .Op Fl /+abCEefIimnPpTuVvx
44 .Op Fl /+o Ar longname
50 .Op Fl /+abCEefIimnPpTuVvx
51 .Op Fl /+o Ar longname
58 .Op Fl /+abCEefIimnPpTuVvx
59 .Op Fl /+o Ar longname
65 utility is the standard command interpreter for the system.
66 The current version of
70 specification for the shell.
71 It only supports features
74 plus a few Berkeley extensions.
75 This man page is not intended to be a tutorial nor a complete
76 specification of the shell.
78 The shell is a command that reads lines from
79 either a file or the terminal, interprets them, and
80 generally executes other commands.
81 It is the program that is started when a user logs into the system,
82 although a user can select a different shell with the
86 implements a language that has flow control constructs,
87 a macro facility that provides a variety of features in
88 addition to data storage, along with built-in history and line
90 It incorporates many features to
91 aid interactive use and has the advantage that the interpretative
92 language is common to both interactive and non-interactive
94 That is, commands can be typed directly
95 to the running shell or can be put into a file,
96 which can be executed directly by the shell.
99 .\" XXX This next sentence is incredibly confusing.
101 If no arguments are present and if the standard input of the shell
102 is connected to a terminal
106 the shell is considered an interactive shell.
108 generally prompts before each command and handles programming
109 and command errors differently (as described below).
110 When first starting, the shell inspects argument 0, and
111 if it begins with a dash
113 the shell is also considered a login shell.
114 This is normally done automatically by the system
115 when the user first logs in.
116 A login shell first reads commands
121 in a user's home directory,
123 If the environment variable
125 is set on entry to a shell, or is set in the
127 of a login shell, the shell then subjects its value to parameter expansion
128 and arithmetic expansion and reads commands from the named file.
129 Therefore, a user should place commands that are to be executed only
132 file, and commands that are executed for every shell inside the
137 variable to some file by placing the following line in the file
139 in the home directory,
142 the filename desired:
144 .Dl "ENV=$HOME/.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 Disable pathname expansion.
245 A do-nothing option for
248 .It Fl I Li ignoreeof
251 from input when in interactive mode.
252 .It Fl i Li interactive
253 Force the shell to behave interactively.
255 Turn on job control (set automatically when interactive).
257 If not interactive, read commands but do not
259 This is useful for checking the
260 syntax of shell scripts.
262 Change the default for the
268 (logical directory layout)
271 (physical directory layout).
272 .It Fl p Li privileged
273 Turn on privileged mode.
274 This mode is enabled on startup
275 if either the effective user or group ID is not equal to the
276 real user or group ID.
277 Turning this mode off sets the
278 effective user and group IDs to the real user and group IDs.
279 When this mode is enabled for interactive shells, the file
280 .Pa /etc/suid_profile
281 is sourced instead of
285 is sourced, and the contents of the
287 variable are ignored.
289 Read commands from standard input (set automatically
290 if no file arguments are present).
292 no effect when set after the shell has already started
293 running (i.e., when set with the
296 .It Fl T Li trapsasync
297 When waiting for a child, execute traps immediately.
298 If this option is not set,
299 traps are executed after the child exits,
302 This nonstandard option is useful for putting guarding shells around
303 children that block signals.
304 The surrounding shell may kill the child
305 or it may just return control to the tty and leave the child alone,
307 .Bd -literal -offset indent
308 sh -T -c "trap 'exit 1' 2 ; some-blocking-program"
311 Write a message to standard error when attempting
312 to expand a variable, a positional parameter or
313 the special parameter
315 that is not set, and if the
316 shell is not interactive, exit immediately.
320 command line editor (disables
324 The shell writes its input to standard error
326 Useful for debugging.
329 (preceded by the value of the
331 variable subjected to parameter expansion and arithmetic expansion)
332 to standard error before it is executed.
333 Useful for debugging.
338 option causes the commands to be read from the
340 operand instead of from the standard input.
341 Keep in mind that this option only accepts a single string as its
342 argument, hence multi-word strings must be quoted.
346 option takes as its only argument the long name of an option
347 to be enabled or disabled.
348 For example, the following two invocations of
350 both enable the built-in
353 .Bd -literal -offset indent
358 If used without an argument, the
360 option displays the current option settings in a human-readable format.
363 is used without an argument, the current option settings are output
364 in a format suitable for re-input into the shell.
365 .Ss Lexical Structure
366 The shell reads input in terms of lines from a file and breaks
367 it up into words at whitespace (blanks and tabs), and at
371 which are special to the shell.
372 There are two types of operators: control operators and
373 redirection operators (their meaning is discussed later).
374 The following is a list of valid operators:
375 .Bl -tag -width indent
376 .It Control operators:
377 .Bl -column "XXX" "XXX" "XXX" "XXX" "XXX" -offset center -compact
378 .It Li & Ta Li && Ta Li \&( Ta Li \&) Ta Li \en
379 .It Li ;; Ta Li ;& Ta Li \&; Ta Li \&| Ta Li ||
381 .It Redirection operators:
382 .Bl -column "XXX" "XXX" "XXX" "XXX" "XXX" -offset center -compact
383 .It Li < Ta Li > Ta Li << Ta Li >> Ta Li <>
384 .It Li <& Ta Li >& Ta Li <<- Ta Li >| Ta \&
390 introduces a comment if used at the beginning of a word.
391 The word starting with
393 and the rest of the line are ignored.
397 characters (character code 0) are not allowed in shell input.
399 Quoting is used to remove the special meaning of certain characters
400 or words to the shell, such as operators, whitespace, keywords,
403 There are four types of quoting: matched single quotes,
404 dollar-single quotes,
405 matched double quotes, and backslash.
406 .Bl -tag -width indent
408 Enclosing characters in single quotes preserves the literal
409 meaning of all the characters (except single quotes, making
410 it impossible to put single-quotes in a single-quoted string).
411 .It Dollar-Single Quotes
412 Enclosing characters between
416 preserves the literal meaning of all characters
417 except backslashes and single quotes.
418 A backslash introduces a C-style escape sequence:
419 .Bl -tag -width xUnnnnnnnn
421 Alert (ring the terminal bell)
425 The control character denoted by
431 is a backslash, it must be doubled.
453 The byte whose octal value is
455 (one to three digits)
457 The byte whose hexadecimal value is
459 (one or more digits only the last two of which are used)
461 The Unicode code point
463 (four hexadecimal digits)
464 .It \eU Ns Ar nnnnnnnn
465 The Unicode code point
467 (eight hexadecimal digits)
470 The sequences for Unicode code points are currently only useful with
472 They reject code point 0 and UTF-16 surrogates.
474 If an escape sequence would produce a byte with value 0,
475 that byte and the rest of the string until the matching single-quote
478 Any other string starting with a backslash is an error.
480 Enclosing characters within double quotes preserves the literal
481 meaning of all characters except dollar sign
487 The backslash inside double quotes is historically weird.
488 It remains literal unless it precedes the following characters,
489 which it serves to quote:
491 .Bl -column "XXX" "XXX" "XXX" "XXX" "XXX" -offset center -compact
492 .It Li $ Ta Li ` Ta Li \&" Ta Li \e Ta Li \en
495 A backslash preserves the literal meaning of the following
496 character, with the exception of the newline character
498 A backslash preceding a newline is treated as a line continuation.
501 Keywords or reserved words are words that have special meaning to the
502 shell and are recognized at the beginning of a line and
503 after a control operator.
504 The following are keywords:
505 .Bl -column "doneXX" "elifXX" "elseXX" "untilXX" "whileX" -offset center
506 .It Li \&! Ta { Ta } Ta Ic case Ta Ic do
507 .It Ic done Ta Ic elif Ta Ic else Ta Ic esac Ta Ic fi
508 .It Ic for Ta Ic if Ta Ic then Ta Ic until Ta Ic while
511 An alias is a name and corresponding value set using the
514 Wherever the command word of a simple command may occur,
515 and after checking for keywords if a keyword may occur, the shell
516 checks the word to see if it matches an alias.
517 If it does, it replaces it in the input stream with its value.
518 For example, if there is an alias called
530 Aliases provide a convenient way for naive users to
531 create shorthands for commands without having to learn how
532 to create functions with arguments.
533 Using aliases in scripts is discouraged
534 because the command that defines them must be executed
535 before the code that uses them is parsed.
536 This is fragile and not portable.
538 An alias name may be escaped in a command line, so that it is not
539 replaced by its alias value, by using quoting characters within or
540 adjacent to the alias name.
541 This is most often done by prefixing
542 an alias name with a backslash to execute a function, built-in, or
543 normal program with the same name.
548 The shell interprets the words it reads according to a
549 language, the specification of which is outside the scope
550 of this man page (refer to the BNF in the
553 Essentially though, a line is read and if
554 the first word of the line (or after a control operator)
555 is not a keyword, then the shell has recognized a
557 Otherwise, a complex command or some
558 other special construct may have been recognized.
560 If a simple command has been recognized, the shell performs
561 the following actions:
564 Leading words of the form
566 are stripped off and assigned to the environment of
568 Redirection operators and
569 their arguments (as described below) are stripped
570 off and saved for processing.
572 The remaining words are expanded as described in
574 .Sx Word Expansions ,
575 and the first remaining word is considered the command
576 name and the command is located.
578 words are considered the arguments of the command.
579 If no command name resulted, then the
581 variable assignments recognized in 1) affect the
584 Redirections are performed as described in
588 Redirections are used to change where a command reads its input
590 In general, redirections open, close, or
591 duplicate an existing reference to a file.
593 used for redirection is:
595 .D1 Oo Ar n Oc Ar redir-op file
599 is one of the redirection operators mentioned
601 The following gives some examples of how these
602 operators can be used.
603 Note that stdin and stdout are commonly used abbreviations
604 for standard input and standard output respectively.
605 .Bl -tag -width "1234567890XX" -offset indent
606 .It Oo Ar n Oc Ns Li > Ar file
607 redirect stdout (or file descriptor
611 .It Oo Ar n Oc Ns Li >| Ar file
612 same as above, but override the
615 .It Oo Ar n Oc Ns Li >> Ar file
616 append stdout (or file descriptor
620 .It Oo Ar n Oc Ns Li < Ar file
621 redirect stdin (or file descriptor
625 .It Oo Ar n Oc Ns Li <> Ar file
626 redirect stdin (or file descriptor
630 .It Oo Ar n1 Oc Ns Li <& Ns Ar n2
631 duplicate stdin (or file descriptor
635 .It Oo Ar n Oc Ns Li <&-
636 close stdin (or file descriptor
638 .It Oo Ar n1 Oc Ns Li >& Ns Ar n2
639 duplicate stdout (or file descriptor
643 .It Oo Ar n Oc Ns Li >&-
644 close stdout (or file descriptor
648 The following redirection is often called a
650 .Bd -unfilled -offset indent
651 .Oo Ar n Oc Ns Li << Ar delimiter
657 All the text on successive lines up to the delimiter is
658 saved away and made available to the command on standard
659 input, or file descriptor
664 as specified on the initial line is quoted, then the
666 is treated literally, otherwise the text is subjected to
667 parameter expansion, command substitution, and arithmetic
668 expansion (as described in the section on
669 .Sx Word Expansions ) .
678 .Ss Search and Execution
679 There are three types of commands: shell functions,
680 built-in commands, and normal programs.
681 The command is searched for (by name) in that order.
682 The three types of commands are all executed in a different way.
684 When a shell function is executed, all of the shell positional
687 which remains unchanged) are
688 set to the arguments of the shell function.
689 The variables which are explicitly placed in the environment of
690 the command (by placing assignments to them before the
691 function name) are made local to the function and are set
693 Then the command given in the function definition is executed.
694 The positional parameters are restored to their original values
695 when the command completes.
696 This all occurs within the current shell.
698 Shell built-in commands are executed internally to the shell, without
699 spawning a new process.
700 There are two kinds of built-in commands: regular and special.
701 Assignments before special builtins persist after they finish
702 executing and assignment errors, redirection errors and certain
703 operand errors cause a script to be aborted.
704 Special builtins cannot be overridden with a function.
705 Both regular and special builtins can affect the shell in ways
706 normal programs cannot.
708 Otherwise, if the command name does not match a function
709 or built-in command, the command is searched for as a normal
710 program in the file system (as described in the next section).
711 When a normal program is executed, the shell runs the program,
712 passing the arguments and the environment to the program.
713 If the program is not a normal executable file
714 (i.e., if it does not begin with the
724 but appears to be a text file,
725 the shell will run a new instance of
729 Note that previous versions of this document
730 and the source code itself misleadingly and sporadically
731 refer to a shell script without a magic number
733 .Dq "shell procedure" .
735 When locating a command, the shell first looks to see if
736 it has a shell function by that name.
738 built-in command by that name.
739 If a built-in command is not found,
740 one of two things happen:
743 Command names containing a slash are simply executed without
744 performing any searches.
746 The shell searches each entry in the
749 in turn for the command.
752 variable should be a series of
753 entries separated by colons.
754 Each entry consists of a
756 The current directory
757 may be indicated implicitly by an empty directory name,
758 or explicitly by a single period.
760 .Ss Command Exit Status
761 Each command has an exit status that can influence the behavior
762 of other shell commands.
763 The paradigm is that a command exits
764 with zero for normal or success, and non-zero for failure,
765 error, or a false indication.
766 The man page for each command
767 should indicate the various exit codes and what they mean.
768 Additionally, the built-in commands return exit codes, as does
769 an executed shell function.
771 If a command is terminated by a signal, its exit status is 128 plus
773 Signal numbers are defined in the header file
776 Complex commands are combinations of simple commands
777 with control operators or keywords, together creating a larger complex
779 More generally, a command is one of the following:
780 .Bl -item -offset indent
786 list or compound-list
793 Unless otherwise stated, the exit status of a command is
794 that of the last simple command executed by the command.
796 A pipeline is a sequence of one or more commands separated
797 by the control operator
799 The standard output of all but
800 the last command is connected to the standard input
802 The standard output of the last
803 command is inherited from the shell, as usual.
805 The format for a pipeline is:
807 .D1 Oo Li \&! Oc Ar command1 Op Li \&| Ar command2 ...
809 The standard output of
811 is connected to the standard input of
813 The standard input, standard output, or
814 both of a command is considered to be assigned by the
815 pipeline before any redirection specified by redirection
816 operators that are part of the command.
818 Note that unlike some other shells,
820 executes each process in a pipeline with more than one command
821 in a subshell environment and as a child of the
825 If the pipeline is not in the background (discussed later),
826 the shell waits for all commands to complete.
830 does not precede the pipeline, the
831 exit status is the exit status of the last command specified
833 Otherwise, the exit status is the logical
834 NOT of the exit status of the last command.
836 the last command returns zero, the exit status is 1; if
837 the last command returns greater than zero, the exit status
840 Because pipeline assignment of standard input or standard
841 output or both takes place before redirection, it can be
842 modified by redirection.
845 .Dl "command1 2>&1 | command2"
847 sends both the standard output and standard error of
849 to the standard input of
854 or newline terminator causes the preceding
856 (described below in the section called
857 .Sx Short-Circuit List Operators )
858 to be executed sequentially;
861 causes asynchronous execution of the preceding AND-OR-list.
862 .Ss Background Commands (&)
863 If a command is terminated by the control operator ampersand
865 the shell executes the command in a subshell environment (see
866 .Sx Grouping Commands Together
867 below) and asynchronously;
868 the shell does not wait for the command to finish
869 before executing the next command.
871 The format for running a command in background is:
873 .D1 Ar command1 Li & Op Ar command2 Li & Ar ...
875 If the shell is not interactive, the standard input of an
876 asynchronous command is set to
878 .Ss Lists (Generally Speaking)
879 A list is a sequence of zero or more commands separated by
880 newlines, semicolons, or ampersands,
881 and optionally terminated by one of these three characters.
883 list are executed in the order they are written.
884 If command is followed by an ampersand, the shell starts the
885 command and immediately proceeds onto the next command;
886 otherwise it waits for the command to terminate before
887 proceeding to the next one.
888 .Ss Short-Circuit List Operators
892 are AND-OR list operators.
894 executes the first command, and then executes the second command
895 if the exit status of the first command is zero.
897 is similar, but executes the second command if the exit
898 status of the first command is nonzero.
902 both have the same priority.
903 .Ss Flow-Control Constructs (if, while, for, case)
907 .Bd -unfilled -offset indent -compact
911 .Ic then Ar list Oc Ar ...
919 .Bd -unfilled -offset indent -compact
925 The two lists are executed repeatedly while the exit status of the
929 command is similar, but has the word
934 repeat until the exit status of the first list is zero.
939 .Bd -unfilled -offset indent -compact
940 .Ic for Ar variable Op Ic in Ar word ...
947 and the following words are omitted,
950 The words are expanded, and then the list is executed
951 repeatedly with the variable set to each word in turn.
956 commands may be replaced with
966 .D1 Ic break Op Ar num
967 .D1 Ic continue Op Ar num
971 command terminates the
980 command continues with the next iteration of the innermost loop.
981 These are implemented as special built-in commands.
986 .Bd -unfilled -offset indent -compact
987 .Ic case Ar word Ic in
988 .Ar pattern Ns Li ) Ar list Li ;;
993 The pattern can actually be one or more patterns
1000 Tilde expansion, parameter expansion, command substitution,
1001 arithmetic expansion and quote removal are applied to the word.
1002 Then, each pattern is expanded in turn using tilde expansion,
1003 parameter expansion, command substitution and arithmetic expansion and
1004 the expanded form of the word is checked against it.
1005 If a match is found, the corresponding list is executed.
1006 If the selected list is terminated by the control operator
1010 execution continues with the next list,
1011 continuing until a list terminated with
1016 The exit code of the
1018 command is the exit code of the last command executed in the list or
1019 zero if no patterns were matched.
1020 .Ss Grouping Commands Together
1021 Commands may be grouped by writing either
1023 .D1 Li \&( Ns Ar list Ns Li \%)
1027 .D1 Li { Ar list Ns Li \&; }
1029 The first form executes the commands in a subshell environment.
1030 A subshell environment has its own copy of:
1033 The current working directory as set by
1036 The file creation mask as set by
1039 Resource limits as set by
1042 References to open files.
1049 Positional parameters and variables.
1058 These are copied from the parent shell environment,
1059 except that trapped (but not ignored) signals are reset to the default action
1060 and known jobs are cleared.
1061 Any changes do not affect the parent shell environment.
1063 A subshell environment may be implemented as a child process or differently.
1064 If job control is enabled in an interactive shell,
1065 commands grouped in parentheses can be suspended and continued as a unit.
1067 For compatibility with other shells,
1068 two open parentheses in sequence should be separated by whitespace.
1070 The second form never forks another shell,
1071 so it is slightly more efficient.
1072 Grouping commands together this way allows the user to
1073 redirect their output as though they were one program:
1074 .Bd -literal -offset indent
1075 { echo -n "hello"; echo " world"; } > greeting
1078 The syntax of a function definition is
1080 .D1 Ar name Li \&( \&) Ar command
1082 A function definition is an executable statement; when
1083 executed it installs a function named
1086 exit status of zero.
1095 Variables may be declared to be local to a function by
1099 This should appear as the first statement of a function,
1102 .D1 Ic local Oo Ar variable ... Oc Op Fl
1106 command is implemented as a built-in command.
1108 When a variable is made local, it inherits the initial
1109 value and exported and readonly flags from the variable
1110 with the same name in the surrounding scope, if there is
1112 Otherwise, the variable is initially unset.
1114 uses dynamic scoping, so that if the variable
1116 is made local to function
1118 which then calls function
1120 references to the variable
1124 will refer to the variable
1128 not to the global variable named
1131 The only special parameter that can be made local is
1135 local causes any shell options that are
1138 command inside the function to be
1139 restored to their original values when the function
1146 .D1 Ic return Op Ar exitstatus
1148 It terminates the current executional scope, returning from the previous
1149 nested function, sourced script, or shell instance, in that order.
1152 command is implemented as a special built-in command.
1153 .Ss Variables and Parameters
1154 The shell maintains a set of parameters.
1156 denoted by a name is called a variable.
1158 the shell turns all the environment variables into shell
1160 New variables can be set using the form
1162 .D1 Ar name Ns = Ns Ar value
1164 Variables set by the user must have a name consisting solely
1165 of alphabetics, numerics, and underscores.
1166 The first letter of a variable name must not be numeric.
1167 A parameter can also be denoted by a number
1168 or a special character as explained below.
1170 Assignments are expanded differently from other words:
1171 tilde expansion is also performed after the equals sign and after any colon
1172 and usernames are also terminated by colons,
1173 and field splitting and pathname expansion are not performed.
1175 This special expansion applies not only to assignments that form a simple
1176 command by themselves or precede a command word,
1177 but also to words passed to the
1182 built-in commands that have this form.
1183 For this, the builtin's name must be literal
1184 (not the result of an expansion)
1185 and may optionally be preceded by one or more literal instances of
1188 .Ss Positional Parameters
1189 A positional parameter is a parameter denoted by a number greater than zero.
1190 The shell sets these initially to the values of its command line
1191 arguments that follow the name of the shell script.
1194 built-in command can also be used to set or reset them.
1195 .Ss Special Parameters
1196 Special parameters are parameters denoted by a single special character
1198 They are shown in the following list, exactly as they would appear in input
1199 typed by the user or in the source of a shell script.
1202 Expands to the positional parameters, starting from one.
1204 the expansion occurs within a double-quoted string
1205 it expands to a single field with the value of each parameter
1206 separated by the first character of the
1213 Expands to the positional parameters, starting from one.
1215 the expansion occurs within double-quotes, each positional
1216 parameter expands as a separate argument.
1217 If there are no positional parameters, the
1220 generates zero arguments, even when
1223 What this basically means, for example, is
1236 .Bd -literal -offset indent
1240 Expands to the number of positional parameters.
1242 Expands to the exit status of the most recent pipeline.
1244 (hyphen) Expands to the current option flags (the single-letter
1245 option names concatenated into a string) as specified on
1248 built-in command, or implicitly
1251 Expands to the process ID of the invoked shell.
1253 retains the same value of
1257 Expands to the process ID of the most recent background
1258 command executed from the current shell.
1260 pipeline, the process ID is that of the last command in the
1262 If this parameter is referenced, the shell will remember
1263 the process ID and its exit status until the
1265 built-in command reports completion of the process.
1267 (zero) Expands to the name of the shell script if passed on the command line,
1270 operand if given (with
1272 or otherwise argument 0 passed to the shell.
1274 .Ss Special Variables
1275 The following variables are set by the shell or
1276 have special meaning to it:
1277 .Bl -tag -width ".Va HISTSIZE"
1279 The search path used with the
1283 The fallback editor used with the
1286 If not set, the default editor is
1289 The default editor used with the
1293 The number of previous commands that are accessible.
1295 The user's home directory,
1296 used in tilde expansion and as a default directory for the
1300 Input Field Separators.
1301 The default value is
1307 This default also applies if
1309 is unset, but not if it is set to the empty string.
1311 .Sx White Space Splitting
1312 section for more details.
1314 The current line number in the script or function.
1316 The name of a mail file, that will be checked for the arrival of new
1323 separated list of file names, for the shell to check for incoming
1325 This variable overrides the
1328 There is a maximum of 10 mailboxes that can be monitored at once.
1330 The default search path for executables.
1333 section for details.
1335 The parent process ID of the invoked shell.
1336 This is set at startup
1337 unless this variable is in the environment.
1338 A later change of parent process ID is not reflected.
1339 A subshell retains the same value of
1342 The primary prompt string, which defaults to
1344 unless you are the superuser, in which case it defaults to
1347 may include any of the following formatting sequences,
1348 which are replaced by the given information:
1349 .Bl -tag -width indent
1353 The fully-qualified hostname.
1355 The final component of the current working directory.
1357 The entire path of the current working directory.
1361 for normal users and
1365 A literal backslash.
1368 The secondary prompt string, which defaults to
1371 may include any of the formatting sequences from
1374 The prefix for the trace output (if
1381 This clause describes the various expansions that are
1383 Not all expansions are performed on
1384 every word, as explained later.
1386 Tilde expansions, parameter expansions, command substitutions,
1387 arithmetic expansions, and quote removals that occur within
1388 a single word expand to a single field.
1390 splitting or pathname expansion that can create multiple
1391 fields from a single word.
1392 The single exception to this rule is
1393 the expansion of the special parameter
1395 within double-quotes,
1396 as was described above.
1398 The order of word expansion is:
1401 Tilde Expansion, Parameter Expansion, Command Substitution,
1402 Arithmetic Expansion (these all occur at the same time).
1404 Field Splitting is performed on fields generated by step (1)
1409 Pathname Expansion (unless the
1411 option is in effect).
1418 character is used to introduce parameter expansion, command
1419 substitution, or arithmetic expansion.
1420 .Ss Tilde Expansion (substituting a user's home directory)
1421 A word beginning with an unquoted tilde character
1424 subjected to tilde expansion.
1425 All the characters up to a slash
1427 or the end of the word are treated as a username
1428 and are replaced with the user's home directory.
1430 username is missing (as in
1432 the tilde is replaced with the value of the
1434 variable (the current user's home directory).
1435 .Ss Parameter Expansion
1436 The format for parameter expansion is as follows:
1438 .D1 Li ${ Ns Ar expression Ns Li }
1442 consists of all characters until the matching
1446 escaped by a backslash or within a single-quoted or double-quoted
1447 string, and characters in
1448 embedded arithmetic expansions, command substitutions, and variable
1449 expansions, are not examined in determining the matching
1451 If the variants with
1457 occur within a double-quoted string,
1458 as an extension there may be unquoted parts
1459 (via double-quotes inside the expansion);
1461 within such parts are also not examined in determining the matching
1464 The simplest form for parameter expansion is:
1466 .D1 Li ${ Ns Ar parameter Ns Li }
1468 The value, if any, of
1472 The parameter name or symbol can be enclosed in braces, which are
1473 optional except for positional parameters with more than one digit or
1474 when parameter is followed by a character that could be interpreted as
1476 If a parameter expansion occurs inside double-quotes:
1479 Field splitting is not performed on the results of the
1480 expansion, with the exception of the special parameter
1483 Pathname expansion is not performed on the results of the
1487 In addition, a parameter expansion can be modified by using one of the
1489 .Bl -tag -width indent
1490 .It Li ${ Ns Ar parameter Ns Li :- Ns Ar word Ns Li }
1494 is unset or null, the expansion of
1496 is substituted; otherwise, the value of
1499 .It Li ${ Ns Ar parameter Ns Li := Ns Ar word Ns Li }
1500 Assign Default Values.
1503 is unset or null, the expansion of
1513 does not prevent field splitting or pathname expansion.
1514 Only variables, not positional
1515 parameters or special parameters, can be
1516 assigned in this way.
1517 .It Li ${ Ns Ar parameter Ns Li :? Ns Oo Ar word Oc Ns Li }
1518 Indicate Error if Null or Unset.
1521 is unset or null, the expansion of
1523 (or a message indicating it is unset if
1525 is omitted) is written to standard
1526 error and the shell exits with a nonzero
1528 Otherwise, the value of
1532 interactive shell need not exit.
1533 .It Li ${ Ns Ar parameter Ns Li :+ Ns Ar word Ns Li }
1534 Use Alternate Value.
1537 is unset or null, null is substituted;
1538 otherwise, the expansion of
1543 In the parameter expansions shown previously, use of the colon in the
1544 format results in a test for a parameter that is unset or null; omission
1545 of the colon results in a test for a parameter that is only unset.
1549 inherits the type of quoting
1550 (unquoted, double-quoted or here-document)
1551 from the surroundings,
1552 with the exception that a backslash that quotes a closing brace is removed
1553 during quote removal.
1554 .Bl -tag -width indent
1555 .It Li ${# Ns Ar parameter Ns Li }
1557 The length in characters of
1562 The following four varieties of parameter expansion provide for substring
1564 In each case, pattern matching notation
1566 .Sx Shell Patterns ) ,
1567 rather than regular expression notation,
1568 is used to evaluate the patterns.
1569 If parameter is one of the special parameters
1573 the result of the expansion is unspecified.
1574 Enclosing the full parameter expansion string in double-quotes does not
1575 cause the following four varieties of pattern characters to be quoted,
1576 whereas quoting characters within the braces has this effect.
1577 .Bl -tag -width indent
1578 .It Li ${ Ns Ar parameter Ns Li % Ns Ar word Ns Li }
1579 Remove Smallest Suffix Pattern.
1582 is expanded to produce a pattern.
1584 parameter expansion then results in
1586 with the smallest portion of the
1587 suffix matched by the pattern deleted.
1588 .It Li ${ Ns Ar parameter Ns Li %% Ns Ar word Ns Li }
1589 Remove Largest Suffix Pattern.
1592 is expanded to produce a pattern.
1594 parameter expansion then results in
1596 with the largest portion of the
1597 suffix matched by the pattern deleted.
1598 .It Li ${ Ns Ar parameter Ns Li # Ns Ar word Ns Li }
1599 Remove Smallest Prefix Pattern.
1602 is expanded to produce a pattern.
1604 parameter expansion then results in
1606 with the smallest portion of the
1607 prefix matched by the pattern deleted.
1608 .It Li ${ Ns Ar parameter Ns Li ## Ns Ar word Ns Li }
1609 Remove Largest Prefix Pattern.
1612 is expanded to produce a pattern.
1614 parameter expansion then results in
1616 with the largest portion of the
1617 prefix matched by the pattern deleted.
1619 .Ss Command Substitution
1620 Command substitution allows the output of a command to be substituted in
1621 place of the command name itself.
1622 Command substitution occurs when
1623 the command is enclosed as follows:
1625 .D1 Li $( Ns Ar command Ns Li )\&
1627 or the backquoted version:
1629 .D1 Li ` Ns Ar command Ns Li `
1631 The shell expands the command substitution by executing command
1632 and replacing the command substitution
1633 with the standard output of the command,
1634 removing sequences of one or more newlines at the end of the substitution.
1635 Embedded newlines before the end of the output are not removed;
1636 however, during field splitting, they may be translated into spaces
1637 depending on the value of
1639 and the quoting that is in effect.
1640 The command is executed in a subshell environment,
1641 except that the built-in commands
1646 return information about the parent shell environment
1649 returns information about the same process
1650 if they are the only command in a command substitution.
1652 If a command substitution of the
1654 form begins with a subshell,
1659 must be separated by whitespace
1660 to avoid ambiguity with arithmetic expansion.
1661 .Ss Arithmetic Expansion
1662 Arithmetic expansion provides a mechanism for evaluating an arithmetic
1663 expression and substituting its value.
1664 The format for arithmetic expansion is as follows:
1666 .D1 Li $(( Ns Ar expression Ns Li ))
1670 is treated as if it were in double-quotes, except
1671 that a double-quote inside the expression is not treated specially.
1673 shell expands all tokens in the
1675 for parameter expansion,
1676 command substitution,
1677 arithmetic expansion
1680 The allowed expressions are a subset of C expressions,
1682 .Bl -tag -width "Variables" -offset indent
1684 All values are of type
1687 Decimal, octal (starting with
1689 and hexadecimal (starting with
1693 Shell variables can be read and written
1694 and contain integer constants.
1697 .It Binary operators
1698 .Li "* / % + - << >> < <= > >= == != & ^ | && ||"
1699 .It Assignment operators
1700 .Li "= += -= *= /= %= <<= >>= &= ^= |="
1701 .It Conditional operator
1705 The result of the expression is substituted in decimal.
1706 .Ss White Space Splitting (Field Splitting)
1707 In certain contexts,
1708 after parameter expansion, command substitution, and
1709 arithmetic expansion the shell scans the results of
1710 expansions and substitutions that did not occur in double-quotes for
1711 field splitting and multiple fields can result.
1722 are treated differently from other characters in
1727 at the beginning or end of a word is discarded.
1729 Subsequently, a field is delimited by either
1732 a non-whitespace character in
1734 with any whitespace in
1738 one or more whitespace characters in
1742 If a word ends with a non-whitespace character in
1744 there is no empty field after this character.
1746 If no field is delimited, the word is discarded.
1747 In particular, if a word consists solely of an unquoted substitution
1748 and the result of the substitution is null,
1749 it is removed by field splitting even if
1752 .Ss Pathname Expansion (File Name Generation)
1756 file name generation is performed
1757 after word splitting is complete.
1759 viewed as a series of patterns, separated by slashes.
1761 process of expansion replaces the word with the names of
1762 all existing files whose names can be formed by replacing
1763 each pattern with a string that matches the specified pattern.
1764 There are two restrictions on this: first, a pattern cannot match
1765 a string containing a slash, and second,
1766 a pattern cannot match a string starting with a period
1767 unless the first character of the pattern is a period.
1768 The next section describes the patterns used for
1770 the four varieties of parameter expansion for substring processing and the
1774 A pattern consists of normal characters, which match themselves,
1775 and meta-characters.
1776 The meta-characters are
1781 These characters lose their special meanings if they are quoted.
1782 When command or variable substitution is performed and the dollar sign
1783 or back quotes are not double-quoted, the value of the
1784 variable or the output of the command is scanned for these
1785 characters and they are turned into meta-characters.
1789 matches any string of characters.
1792 matches any single character.
1795 introduces a character class.
1796 The end of the character class is indicated by a
1804 rather than introducing a character class.
1805 A character class matches any of the characters between the square brackets.
1806 A locale-dependent range of characters may be specified using a minus sign.
1807 A named class of characters (see
1809 may be specified by surrounding the name with
1814 .Ql \&[\&[:alpha:\&]\&]
1815 is a shell pattern that matches a single letter.
1816 The character class may be complemented by making an exclamation point
1818 the first character of the character class.
1821 has the same effect but is non-standard.
1825 in a character class, make it the first character listed
1833 make it the first or last character listed.
1834 .Ss Built-in Commands
1835 This section lists the built-in commands.
1836 .Bl -tag -width indent
1838 A null command that returns a 0 (true) exit value.
1840 The commands in the specified file are read and executed by the shell.
1843 command may be used to return to the
1850 characters, it is used as is.
1851 Otherwise, the shell searches the
1854 If it is not found in the
1856 it is sought in the current working directory.
1858 A built-in equivalent of
1860 .It Ic alias Oo Ar name Ns Oo = Ns Ar string Oc ... Oc
1862 .Ar name Ns = Ns Ar string
1863 is specified, the shell defines the alias
1869 is specified, the value of the alias
1872 With no arguments, the
1874 built-in command prints the names and values of all defined aliases
1877 Alias values are written with appropriate quoting so that they are
1878 suitable for re-input to the shell.
1882 .It Ic bg Op Ar job ...
1883 Continue the specified jobs
1884 (or the current job if no jobs are given)
1886 .It Ic bind Oo Fl aeklrsv Oc Oo Ar key Oo Ar command Oc Oc
1887 List or alter key bindings for the line editor.
1888 This command is documented in
1890 .It Ic break Op Ar num
1892 .Sx Flow-Control Constructs
1894 .It Ic builtin Ar cmd Op Ar arg ...
1895 Execute the specified built-in command,
1897 This is useful when the user wishes to override a shell function
1898 with the same name as a built-in command.
1899 .It Ic cd Oo Fl L | P Oc Oo Fl e Oc Op Ar directory
1900 Switch to the specified
1902 or to the directory specified in the
1904 environment variable if no
1913 then the directories listed in the
1916 searched for the specified
1920 is unset, the current directory is searched.
1923 is the same as that of
1925 In an interactive shell,
1928 command will print out the name of the directory
1929 that it actually switched to
1930 if this is different from the name that the user gave.
1931 These may be different either because the
1933 mechanism was used or because a symbolic link was crossed.
1937 option is specified,
1939 is handled physically and symbolic links are resolved before
1941 components are processed.
1944 option is specified,
1946 is handled logically.
1947 This is the default.
1953 to return exit status 1 if the full pathname of the new directory
1954 cannot be determined reliably or at all.
1955 Normally this is not considered an error,
1956 although a warning is printed.
1961 .It Ic command Oo Fl p Oc Op Ar utility Op Ar argument ...
1962 .It Ic command Oo Fl p Oc Fl v Ar utility
1963 .It Ic command Oo Fl p Oc Fl V Ar utility
1964 The first form of invocation executes the specified
1966 ignoring shell functions in the search.
1969 is a special builtin,
1970 it is executed as if it were a regular builtin.
1974 option is specified, the command search is performed using a
1977 that is guaranteed to find all of the standard utilities.
1981 option is specified,
1983 is not executed but a description of its interpretation by the shell is
1985 For ordinary commands the output is the path name; for shell built-in
1986 commands, shell functions and keywords only the name is written.
1987 Aliases are printed as
1988 .Dq Ic alias Ar name Ns = Ns Ar value .
1992 option is identical to
1994 except for the output.
1996 .Dq Ar utility Ic is Ar description
2002 a special shell builtin,
2009 .It Ic continue Op Ar num
2011 .Sx Flow-Control Constructs
2013 .It Ic echo Oo Fl e | n Oc Op Ar string ...
2014 Print a space-separated list of the arguments to the standard output
2015 and append a newline character.
2016 .Bl -tag -width indent
2018 Suppress the output of the trailing newline.
2020 Process C-style backslash escape sequences.
2023 command understands the following character escapes:
2024 .Bl -tag -width indent
2026 Alert (ring the terminal bell)
2030 Suppress the trailing newline (this has the side-effect of truncating the
2031 line if it is not the last character)
2049 (Zero) The character whose octal value is
2055 is not enclosed in quotes then the backslash itself must be escaped
2056 with a backslash to protect it from the shell.
2058 .Bd -literal -offset indent
2067 $ echo -e a\e\e\e\eb
2076 options may be specified.
2077 .It Ic eval Ar string ...
2078 Concatenate all the arguments with spaces.
2079 Then re-parse and execute the command.
2080 .It Ic exec Op Ar command Op arg ...
2084 the shell process is replaced with the specified program
2085 (which must be a real program, not a shell built-in command or function).
2086 Any redirections on the
2088 command are marked as permanent,
2089 so that they are not undone when the
2092 .It Ic exit Op Ar exitstatus
2093 Terminate the shell process.
2097 it is used as the exit status of the shell.
2098 Otherwise, if the shell is executing an
2100 trap, the exit status of the last command before the trap is used;
2101 if the shell is executing a trap for a signal,
2102 the shell exits by resending the signal to itself.
2103 Otherwise, the exit status of the preceding command is used.
2104 The exit status should be an integer between 0 and 255.
2105 .It Ic export Ar name ...
2106 .It Ic export Op Fl p
2107 The specified names are exported so that they will
2108 appear in the environment of subsequent commands.
2109 The only way to un-export a variable is to
2112 The shell allows the value of a variable to be set
2113 at the same time as it is exported by writing
2115 .D1 Ic export Ar name Ns = Ns Ar value
2117 With no arguments the
2119 command lists the names
2120 of all exported variables.
2123 option is specified, the exported variables are printed as
2124 .Dq Ic export Ar name Ns = Ns Ar value
2125 lines, suitable for re-input to the shell.
2127 A null command that returns a non-zero (false) exit value.
2128 .It Ic fc Oo Fl e Ar editor Oc Op Ar first Op Ar last
2129 .It Ic fc Fl l Oo Fl nr Oc Op Ar first Op Ar last
2130 .It Ic fc Fl s Oo Ar old Ns = Ns Ar new Oc Op Ar first
2133 built-in command lists, or edits and re-executes,
2134 commands previously entered to an interactive shell.
2135 .Bl -tag -width indent
2137 Use the editor named by
2139 to edit the commands.
2142 string is a command name,
2143 subject to search via the
2148 variable is used as a default when
2153 is null or unset, the value of the
2160 is used as the editor.
2162 List the commands rather than invoking
2164 The commands are written in the
2165 sequence indicated by the
2169 operands, as affected by
2171 with each command preceded by the command number.
2173 Suppress command numbers when listing with
2176 Reverse the order of the commands listed
2185 Re-execute the command without invoking an editor.
2188 Select the commands to list or edit.
2189 The number of previous commands that can be accessed
2190 are determined by the value of the
2197 or both are one of the following:
2198 .Bl -tag -width indent
2199 .It Oo Cm + Oc Ns Ar num
2200 A positive number representing a command number;
2201 command numbers can be displayed with the
2205 A negative decimal number representing the
2206 command that was executed
2209 commands previously.
2210 For example, \-1 is the immediately previous command.
2212 A string indicating the most recently entered command
2213 that begins with that string.
2215 .Ar old Ns = Ns Ar new
2216 operand is not also specified with
2218 the string form of the first operand cannot contain an embedded equal sign.
2222 The following variables affect the execution of
2224 .Bl -tag -width ".Va HISTSIZE"
2226 Name of the editor to use for history editing.
2228 The number of previous commands that are accessible.
2233 or the current job to the foreground.
2234 .It Ic getopts Ar optstring var
2241 command deprecates the older
2244 The first argument should be a series of letters, each possibly
2245 followed by a colon which indicates that the option takes an argument.
2246 The specified variable is set to the parsed option.
2248 the next argument is placed into the shell variable
2250 If an option takes an argument, it is placed into the shell variable
2252 If an invalid option is encountered,
2256 It returns a false value (1) when it encounters the end of the options.
2257 .It Ic hash Oo Fl rv Oc Op Ar command ...
2258 The shell maintains a hash table which remembers the locations of commands.
2259 With no arguments whatsoever, the
2261 command prints out the contents of this table.
2265 command removes each specified
2267 from the hash table (unless they are functions) and then locates it.
2272 prints the locations of the commands as it finds them.
2277 command to delete all the entries in the hash table except for functions.
2278 .It Ic jobid Op Ar job
2279 Print the process IDs of the processes in the specified
2283 argument is omitted, use the current job.
2284 .It Ic jobs Oo Fl lps Oc Op Ar job ...
2285 Print information about the specified jobs, or all jobs if no
2288 The information printed includes job ID, status and command name.
2292 option is specified, the PID of each job is also printed.
2295 option is specified, only the process IDs for the process group leaders
2296 are printed, one per line.
2299 option is specified, only the PIDs of the job commands are printed, one per
2302 A built-in equivalent of
2304 that additionally supports sending signals to jobs.
2305 .It Ic local Oo Ar variable ... Oc Op Fl
2310 A built-in equivalent of
2312 .It Ic pwd Op Fl L | P
2313 Print the path of the current directory.
2314 The built-in command may
2315 differ from the program of the same name because the
2316 built-in command remembers what the current directory
2317 is rather than recomputing it each time.
2320 However, if the current directory is
2322 the built-in version of
2324 will continue to print the old name for the directory.
2328 option is specified, symbolic links are resolved.
2331 option is specified, the shell's notion of the current directory
2332 is printed (symbolic links are not resolved).
2333 This is the default.
2334 .It Ic read Oo Fl p Ar prompt Oc Oo
2335 .Fl t Ar timeout Oc Oo Fl er Oc Ar variable ...
2341 and the standard input is a terminal.
2343 read from the standard input.
2344 The trailing newline
2345 is deleted from the line and the line is split as
2346 described in the section on
2347 .Sx White Space Splitting (Field Splitting)
2349 the pieces are assigned to the variables in order.
2350 If there are more pieces than variables, the remaining
2351 pieces (along with the characters in
2353 that separated them)
2354 are assigned to the last variable.
2355 If there are more variables than pieces, the remaining
2356 variables are assigned the null string.
2358 Backslashes are treated specially, unless the
2362 If a backslash is followed by
2363 a newline, the backslash and the newline will be
2365 If a backslash is followed by any other
2366 character, the backslash will be deleted and the following
2367 character will be treated as though it were not in
2373 option is specified and the
2375 elapses before a complete line of input is supplied,
2378 command will return an exit status as if terminated by
2380 without assigning any values.
2383 value may optionally be followed by one of
2388 to explicitly specify seconds, minutes or hours.
2389 If none is supplied,
2395 option exists only for backward compatibility with older scripts.
2397 The exit status is 0 on success, 1 on end of file,
2398 between 2 and 128 if an error occurs
2399 and greater than 128 if a trapped signal interrupts
2401 .It Ic readonly Oo Fl p Oc Op Ar name ...
2404 is marked as read only,
2405 so that it cannot be subsequently modified or unset.
2406 The shell allows the value of a variable to be set
2407 at the same time as it is marked read only
2408 by using the following form:
2410 .D1 Ic readonly Ar name Ns = Ns Ar value
2412 With no arguments the
2414 command lists the names of all read only variables.
2417 option is specified, the read-only variables are printed as
2418 .Dq Ic readonly Ar name Ns = Ns Ar value
2419 lines, suitable for re-input to the shell.
2420 .It Ic return Op Ar exitstatus
2424 .It Ic set Oo Fl /+abCEefIimnpTuVvx Oc Oo Fl /+o Ar longname Oc Oo
2425 .Fl c Ar string Oc Op Fl - Ar arg ...
2428 command performs three different functions:
2431 With no arguments, it lists the values of all shell variables.
2433 If options are given,
2434 either in short form or using the long
2435 .Dq Fl /+o Ar longname
2437 it sets or clears the specified options as described in the section called
2438 .Sx Argument List Processing .
2442 option is specified,
2444 will replace the shell's positional parameters with the subsequent
2446 If no arguments follow the
2449 all the positional parameters will be cleared,
2450 which is equivalent to executing the command
2454 flag may be omitted when specifying arguments to be used
2455 as positional replacement parameters.
2456 This is not recommended,
2457 because the first argument may begin with a dash
2463 command will interpret as a request to enable or disable options.
2465 .It Ic setvar Ar variable value
2466 Assigns the specified
2472 command is intended to be used in functions that
2473 assign values to variables whose names are passed as parameters.
2474 In general it is better to write
2475 .Dq Ar variable Ns = Ns Ar value
2478 .It Ic shift Op Ar n
2479 Shift the positional parameters
2484 A shift sets the value of
2493 decreasing the value of
2496 If there are zero positional parameters, shifting does not do anything.
2498 A built-in equivalent of
2501 Print the amount of time spent executing the shell process and its children.
2502 The first output line shows the user and system times for the shell process
2503 itself, the second one contains the user and system times for the
2505 .It Ic trap Oo Ar action Oc Ar signal ...
2507 Cause the shell to parse and execute
2512 The signals are specified by name or number.
2513 In addition, the pseudo-signal
2515 may be used to specify an
2517 that is performed when the shell terminates.
2520 may be an empty string or a dash
2522 the former causes the specified signal to be ignored
2523 and the latter causes the default action to be taken.
2526 is another way to request the default action, for compatibility reasons this
2527 usage is not recommended though.
2528 In a subshell or utility environment,
2529 the shell resets trapped (but not ignored) signals to the default action.
2532 command has no effect on signals that were ignored on entry to the shell.
2538 command to display a list of valid signal names.
2540 A null command that returns a 0 (true) exit value.
2541 .It Ic type Op Ar name ...
2544 as a command and print the resolution of the command search.
2545 Possible resolutions are:
2546 shell keyword, alias, special shell builtin, shell builtin, command,
2549 For aliases the alias expansion is printed;
2550 for commands and tracked aliases
2551 the complete pathname of the command is printed.
2552 .It Ic ulimit Oo Fl HSabcdflmnpstuvw Oc Op Ar limit
2553 Set or display resource limits (see
2557 is specified, the named resource will be set;
2558 otherwise the current resource value will be displayed.
2562 is specified, the hard limits will be set or displayed.
2563 While everybody is allowed to reduce a hard limit,
2564 only the superuser can increase it.
2568 specifies the soft limits instead.
2569 When displaying limits,
2575 The default is to display the soft limits,
2576 and to set both the hard and the soft limits.
2582 command to display all resources.
2585 is not acceptable in this mode.
2587 The remaining options specify which resource value is to be
2588 displayed or modified.
2589 They are mutually exclusive.
2590 .Bl -tag -width indent
2592 The maximum size of socket buffer usage, in bytes.
2593 .It Fl c Ar coredumpsize
2594 The maximal size of core dump files, in 512-byte blocks.
2595 .It Fl d Ar datasize
2596 The maximal size of the data segment of a process, in kilobytes.
2597 .It Fl f Ar filesize
2598 The maximal size of a file, in 512-byte blocks.
2599 .It Fl l Ar lockedmem
2600 The maximal size of memory that can be locked by a process, in
2602 .It Fl m Ar memoryuse
2603 The maximal resident set size of a process, in kilobytes.
2605 The maximal number of descriptors that could be opened by a process.
2606 .It Fl p Ar pseudoterminals
2607 The maximal number of pseudo-terminals for this user ID.
2608 .It Fl s Ar stacksize
2609 The maximal size of the stack segment, in kilobytes.
2611 The maximal amount of CPU time to be used by each process, in seconds.
2612 .It Fl u Ar userproc
2613 The maximal number of simultaneous processes for this user ID.
2614 .It Fl v Ar virtualmem
2615 The maximal virtual size of a process, in kilobytes.
2617 The maximum amount of swap space reserved or used for this user ID,
2620 .It Ic umask Oo Fl S Oc Op Ar mask
2621 Set the file creation mask (see
2623 to the octal or symbolic (see
2627 If the argument is omitted, the current mask value is printed.
2630 option is specified, the output is symbolic, otherwise the output is octal.
2631 .It Ic unalias Oo Fl a Oc Op Ar name ...
2632 The specified alias names are removed.
2635 is specified, all aliases are removed.
2636 .It Ic unset Oo Fl fv Oc Ar name ...
2637 The specified variables or functions are unset and unexported.
2640 option is specified or no options are given, the
2642 arguments are treated as variable names.
2645 option is specified, the
2647 arguments are treated as function names.
2648 .It Ic wait Op Ar job ...
2649 Wait for each specified
2651 to complete and return the exit status of the last process in the
2656 specified is unknown to the shell, it is treated as if it
2657 were a known job that exited with exit status 127.
2658 If no operands are given, wait for all jobs to complete
2659 and return an exit status of zero.
2661 .Ss Commandline Editing
2664 is being used interactively from a terminal, the current command
2665 and the command history
2669 .Sx Built-in Commands )
2672 command line editing.
2673 This mode uses commands similar
2674 to a subset of those described in the
2692 can be switched between insert mode and command mode by typing
2696 while in command mode will pass the line to the shell.
2699 .Dq Li "set -o emacs"
2702 command can be used to enable a subset of
2704 command line editing features.
2706 The following environment variables affect the execution of
2708 .Bl -tag -width ".Ev LANGXXXXXX"
2710 Initialization file for interactive shells.
2711 .It Ev LANG , Ev LC_*
2713 These are inherited by children of the shell,
2714 and is used in a limited manner by the shell itself.
2716 An absolute pathname for the current directory,
2717 possibly containing symbolic links.
2718 This is used and updated by the shell.
2720 The default terminal setting for the shell.
2721 This is inherited by children of the shell, and is used in the history
2725 Additionally, all environment variables are turned into shell variables
2727 which may affect the shell as described under
2728 .Sx Special Variables .
2730 .Bl -tag -width "/etc/suid_profileXX" -compact
2732 User's login profile.
2734 System login profile.
2737 .It Pa /etc/suid_profile
2738 Privileged shell profile.
2741 Errors that are detected by the shell, such as a syntax error, will
2742 cause the shell to exit with a non-zero exit status.
2743 If the shell is not an interactive shell, the execution of the shell
2744 file will be aborted.
2745 Otherwise the shell will return the exit status of the last command
2748 builtin is used with a numeric argument, it
2749 will return the argument.
2770 command, the Thompson shell, appeared in
2772 It was superseded in
2774 by the Bourne shell, which inherited the name
2779 was rewritten in 1989 under the
2781 license after the Bourne shell from
2786 was originally written by
2787 .An Kenneth Almquist .
2791 utility does not recognize multibyte characters other than UTF-8.
2794 and the line editing library
2796 do not recognize multibyte characters.
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