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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 References to open files.
1046 Positional parameters and variables.
1055 These are copied from the parent shell environment,
1056 except that trapped (but not ignored) signals are reset to the default action
1057 and known jobs are cleared.
1058 Any changes do not affect the parent shell environment.
1060 A subshell environment may be implemented as a child process or differently.
1061 If job control is enabled in an interactive shell,
1062 commands grouped in parentheses can be suspended and continued as a unit.
1064 For compatibility with other shells,
1065 two open parentheses in sequence should be separated by whitespace.
1067 The second form never forks another shell,
1068 so it is slightly more efficient.
1069 Grouping commands together this way allows the user to
1070 redirect their output as though they were one program:
1071 .Bd -literal -offset indent
1072 { echo -n "hello"; echo " world"; } > greeting
1075 The syntax of a function definition is
1077 .D1 Ar name Li \&( \&) Ar command
1079 A function definition is an executable statement; when
1080 executed it installs a function named
1083 exit status of zero.
1092 Variables may be declared to be local to a function by
1096 This should appear as the first statement of a function,
1099 .D1 Ic local Oo Ar variable ... Oc Op Fl
1103 command is implemented as a built-in command.
1105 When a variable is made local, it inherits the initial
1106 value and exported and readonly flags from the variable
1107 with the same name in the surrounding scope, if there is
1109 Otherwise, the variable is initially unset.
1111 uses dynamic scoping, so that if the variable
1113 is made local to function
1115 which then calls function
1117 references to the variable
1121 will refer to the variable
1125 not to the global variable named
1128 The only special parameter that can be made local is
1132 local causes any shell options that are
1135 command inside the function to be
1136 restored to their original values when the function
1143 .D1 Ic return Op Ar exitstatus
1145 It terminates the current executional scope, returning from the previous
1146 nested function, sourced script, or shell instance, in that order.
1149 command is implemented as a special built-in command.
1150 .Ss Variables and Parameters
1151 The shell maintains a set of parameters.
1153 denoted by a name is called a variable.
1155 the shell turns all the environment variables into shell
1157 New variables can be set using the form
1159 .D1 Ar name Ns = Ns Ar value
1161 Variables set by the user must have a name consisting solely
1162 of alphabetics, numerics, and underscores.
1163 The first letter of a variable name must not be numeric.
1164 A parameter can also be denoted by a number
1165 or a special character as explained below.
1167 Assignments are expanded differently from other words:
1168 tilde expansion is also performed after the equals sign and after any colon
1169 and usernames are also terminated by colons,
1170 and field splitting and pathname expansion are not performed.
1172 This special expansion applies not only to assignments that form a simple
1173 command by themselves or precede a command word,
1174 but also to words passed to the
1179 built-in commands that have this form.
1180 For this, the builtin's name must be literal
1181 (not the result of an expansion)
1182 and may optionally be preceded by one or more literal instances of
1185 .Ss Positional Parameters
1186 A positional parameter is a parameter denoted by a number greater than zero.
1187 The shell sets these initially to the values of its command line
1188 arguments that follow the name of the shell script.
1191 built-in command can also be used to set or reset them.
1192 .Ss Special Parameters
1193 Special parameters are parameters denoted by a single special character
1195 They are shown in the following list, exactly as they would appear in input
1196 typed by the user or in the source of a shell script.
1199 Expands to the positional parameters, starting from one.
1201 the expansion occurs within a double-quoted string
1202 it expands to a single field with the value of each parameter
1203 separated by the first character of the
1210 Expands to the positional parameters, starting from one.
1212 the expansion occurs within double-quotes, each positional
1213 parameter expands as a separate argument.
1214 If there are no positional parameters, the
1217 generates zero arguments, even when
1220 What this basically means, for example, is
1233 .Bd -literal -offset indent
1237 Expands to the number of positional parameters.
1239 Expands to the exit status of the most recent pipeline.
1241 (hyphen) Expands to the current option flags (the single-letter
1242 option names concatenated into a string) as specified on
1245 built-in command, or implicitly
1248 Expands to the process ID of the invoked shell.
1250 retains the same value of
1254 Expands to the process ID of the most recent background
1255 command executed from the current shell.
1257 pipeline, the process ID is that of the last command in the
1259 If this parameter is referenced, the shell will remember
1260 the process ID and its exit status until the
1262 built-in command reports completion of the process.
1264 (zero) Expands to the name of the shell script if passed on the command line,
1267 operand if given (with
1269 or otherwise argument 0 passed to the shell.
1271 .Ss Special Variables
1272 The following variables are set by the shell or
1273 have special meaning to it:
1274 .Bl -tag -width ".Va HISTSIZE"
1276 The search path used with the
1280 The fallback editor used with the
1283 If not set, the default editor is
1286 The default editor used with the
1290 The number of previous commands that are accessible.
1292 The user's home directory,
1293 used in tilde expansion and as a default directory for the
1297 Input Field Separators.
1298 The default value is
1304 This default also applies if
1306 is unset, but not if it is set to the empty string.
1308 .Sx White Space Splitting
1309 section for more details.
1311 The current line number in the script or function.
1313 The name of a mail file, that will be checked for the arrival of new
1320 separated list of file names, for the shell to check for incoming
1322 This variable overrides the
1325 There is a maximum of 10 mailboxes that can be monitored at once.
1327 The default search path for executables.
1330 section for details.
1332 The parent process ID of the invoked shell.
1333 This is set at startup
1334 unless this variable is in the environment.
1335 A later change of parent process ID is not reflected.
1336 A subshell retains the same value of
1339 The primary prompt string, which defaults to
1341 unless you are the superuser, in which case it defaults to
1344 The secondary prompt string, which defaults to
1347 The prefix for the trace output (if
1354 This clause describes the various expansions that are
1356 Not all expansions are performed on
1357 every word, as explained later.
1359 Tilde expansions, parameter expansions, command substitutions,
1360 arithmetic expansions, and quote removals that occur within
1361 a single word expand to a single field.
1363 splitting or pathname expansion that can create multiple
1364 fields from a single word.
1365 The single exception to this rule is
1366 the expansion of the special parameter
1368 within double-quotes,
1369 as was described above.
1371 The order of word expansion is:
1374 Tilde Expansion, Parameter Expansion, Command Substitution,
1375 Arithmetic Expansion (these all occur at the same time).
1377 Field Splitting is performed on fields generated by step (1)
1382 Pathname Expansion (unless the
1384 option is in effect).
1391 character is used to introduce parameter expansion, command
1392 substitution, or arithmetic expansion.
1393 .Ss Tilde Expansion (substituting a user's home directory)
1394 A word beginning with an unquoted tilde character
1397 subjected to tilde expansion.
1398 All the characters up to a slash
1400 or the end of the word are treated as a username
1401 and are replaced with the user's home directory.
1403 username is missing (as in
1405 the tilde is replaced with the value of the
1407 variable (the current user's home directory).
1408 .Ss Parameter Expansion
1409 The format for parameter expansion is as follows:
1411 .D1 Li ${ Ns Ar expression Ns Li }
1415 consists of all characters until the matching
1419 escaped by a backslash or within a single-quoted or double-quoted
1420 string, and characters in
1421 embedded arithmetic expansions, command substitutions, and variable
1422 expansions, are not examined in determining the matching
1424 If the variants with
1430 occur within a double-quoted string,
1431 as an extension there may be unquoted parts
1432 (via double-quotes inside the expansion);
1434 within such parts are also not examined in determining the matching
1437 The simplest form for parameter expansion is:
1439 .D1 Li ${ Ns Ar parameter Ns Li }
1441 The value, if any, of
1445 The parameter name or symbol can be enclosed in braces, which are
1446 optional except for positional parameters with more than one digit or
1447 when parameter is followed by a character that could be interpreted as
1449 If a parameter expansion occurs inside double-quotes:
1452 Field splitting is not performed on the results of the
1453 expansion, with the exception of the special parameter
1456 Pathname expansion is not performed on the results of the
1460 In addition, a parameter expansion can be modified by using one of the
1462 .Bl -tag -width indent
1463 .It Li ${ Ns Ar parameter Ns Li :- Ns Ar word Ns Li }
1467 is unset or null, the expansion of
1469 is substituted; otherwise, the value of
1472 .It Li ${ Ns Ar parameter Ns Li := Ns Ar word Ns Li }
1473 Assign Default Values.
1476 is unset or null, the expansion of
1486 does not prevent field splitting or pathname expansion.
1487 Only variables, not positional
1488 parameters or special parameters, can be
1489 assigned in this way.
1490 .It Li ${ Ns Ar parameter Ns Li :? Ns Oo Ar word Oc Ns Li }
1491 Indicate Error if Null or Unset.
1494 is unset or null, the expansion of
1496 (or a message indicating it is unset if
1498 is omitted) is written to standard
1499 error and the shell exits with a nonzero
1501 Otherwise, the value of
1505 interactive shell need not exit.
1506 .It Li ${ Ns Ar parameter Ns Li :+ Ns Ar word Ns Li }
1507 Use Alternate Value.
1510 is unset or null, null is substituted;
1511 otherwise, the expansion of
1516 In the parameter expansions shown previously, use of the colon in the
1517 format results in a test for a parameter that is unset or null; omission
1518 of the colon results in a test for a parameter that is only unset.
1522 inherits the type of quoting
1523 (unquoted, double-quoted or here-document)
1524 from the surroundings,
1525 with the exception that a backslash that quotes a closing brace is removed
1526 during quote removal.
1527 .Bl -tag -width indent
1528 .It Li ${# Ns Ar parameter Ns Li }
1530 The length in characters of
1535 The following four varieties of parameter expansion provide for substring
1537 In each case, pattern matching notation
1539 .Sx Shell Patterns ) ,
1540 rather than regular expression notation,
1541 is used to evaluate the patterns.
1542 If parameter is one of the special parameters
1546 the result of the expansion is unspecified.
1547 Enclosing the full parameter expansion string in double-quotes does not
1548 cause the following four varieties of pattern characters to be quoted,
1549 whereas quoting characters within the braces has this effect.
1550 .Bl -tag -width indent
1551 .It Li ${ Ns Ar parameter Ns Li % Ns Ar word Ns Li }
1552 Remove Smallest Suffix Pattern.
1555 is expanded to produce a pattern.
1557 parameter expansion then results in
1559 with the smallest portion of the
1560 suffix matched by the pattern deleted.
1561 .It Li ${ Ns Ar parameter Ns Li %% Ns Ar word Ns Li }
1562 Remove Largest Suffix Pattern.
1565 is expanded to produce a pattern.
1567 parameter expansion then results in
1569 with the largest portion of the
1570 suffix matched by the pattern deleted.
1571 .It Li ${ Ns Ar parameter Ns Li # Ns Ar word Ns Li }
1572 Remove Smallest Prefix Pattern.
1575 is expanded to produce a pattern.
1577 parameter expansion then results in
1579 with the smallest portion of the
1580 prefix matched by the pattern deleted.
1581 .It Li ${ Ns Ar parameter Ns Li ## Ns Ar word Ns Li }
1582 Remove Largest Prefix Pattern.
1585 is expanded to produce a pattern.
1587 parameter expansion then results in
1589 with the largest portion of the
1590 prefix matched by the pattern deleted.
1592 .Ss Command Substitution
1593 Command substitution allows the output of a command to be substituted in
1594 place of the command name itself.
1595 Command substitution occurs when
1596 the command is enclosed as follows:
1598 .D1 Li $( Ns Ar command Ns Li )\&
1600 or the backquoted version:
1602 .D1 Li ` Ns Ar command Ns Li `
1604 The shell expands the command substitution by executing command
1605 and replacing the command substitution
1606 with the standard output of the command,
1607 removing sequences of one or more newlines at the end of the substitution.
1608 Embedded newlines before the end of the output are not removed;
1609 however, during field splitting, they may be translated into spaces
1610 depending on the value of
1612 and the quoting that is in effect.
1613 The command is executed in a subshell environment,
1614 except that the built-in commands
1619 return information about the parent shell environment
1622 returns information about the same process
1623 if they are the only command in a command substitution.
1625 If a command substitution of the
1627 form begins with a subshell,
1632 must be separated by whitespace
1633 to avoid ambiguity with arithmetic expansion.
1634 .Ss Arithmetic Expansion
1635 Arithmetic expansion provides a mechanism for evaluating an arithmetic
1636 expression and substituting its value.
1637 The format for arithmetic expansion is as follows:
1639 .D1 Li $(( Ns Ar expression Ns Li ))
1643 is treated as if it were in double-quotes, except
1644 that a double-quote inside the expression is not treated specially.
1646 shell expands all tokens in the
1648 for parameter expansion,
1649 command substitution,
1650 arithmetic expansion
1653 The allowed expressions are a subset of C expressions,
1655 .Bl -tag -width "Variables" -offset indent
1657 All values are of type
1660 Decimal, octal (starting with
1662 and hexadecimal (starting with
1666 Shell variables can be read and written
1667 and contain integer constants.
1670 .It Binary operators
1671 .Li "* / % + - << >> < <= > >= == != & ^ | && ||"
1672 .It Assignment operators
1673 .Li "= += -= *= /= %= <<= >>= &= ^= |="
1674 .It Conditional operator
1678 The result of the expression is substituted in decimal.
1679 .Ss White Space Splitting (Field Splitting)
1680 In certain contexts,
1681 after parameter expansion, command substitution, and
1682 arithmetic expansion the shell scans the results of
1683 expansions and substitutions that did not occur in double-quotes for
1684 field splitting and multiple fields can result.
1695 are treated differently from other characters in
1700 at the beginning or end of a word is discarded.
1702 Subsequently, a field is delimited by either
1705 a non-whitespace character in
1707 with any whitespace in
1711 one or more whitespace characters in
1715 If a word ends with a non-whitespace character in
1717 there is no empty field after this character.
1719 If no field is delimited, the word is discarded.
1720 In particular, if a word consists solely of an unquoted substitution
1721 and the result of the substitution is null,
1722 it is removed by field splitting even if
1725 .Ss Pathname Expansion (File Name Generation)
1729 file name generation is performed
1730 after word splitting is complete.
1732 viewed as a series of patterns, separated by slashes.
1734 process of expansion replaces the word with the names of
1735 all existing files whose names can be formed by replacing
1736 each pattern with a string that matches the specified pattern.
1737 There are two restrictions on this: first, a pattern cannot match
1738 a string containing a slash, and second,
1739 a pattern cannot match a string starting with a period
1740 unless the first character of the pattern is a period.
1741 The next section describes the patterns used for
1743 the four varieties of parameter expansion for substring processing and the
1747 A pattern consists of normal characters, which match themselves,
1748 and meta-characters.
1749 The meta-characters are
1754 These characters lose their special meanings if they are quoted.
1755 When command or variable substitution is performed and the dollar sign
1756 or back quotes are not double-quoted, the value of the
1757 variable or the output of the command is scanned for these
1758 characters and they are turned into meta-characters.
1762 matches any string of characters.
1765 matches any single character.
1768 introduces a character class.
1769 The end of the character class is indicated by a
1777 rather than introducing a character class.
1778 A character class matches any of the characters between the square brackets.
1779 A locale-dependent range of characters may be specified using a minus sign.
1780 A named class of characters (see
1782 may be specified by surrounding the name with
1787 .Ql \&[\&[:alpha:\&]\&]
1788 is a shell pattern that matches a single letter.
1789 The character class may be complemented by making an exclamation point
1791 the first character of the character class.
1794 has the same effect but is non-standard.
1798 in a character class, make it the first character listed
1806 make it the first or last character listed.
1807 .Ss Built-in Commands
1808 This section lists the built-in commands.
1809 .Bl -tag -width indent
1811 A null command that returns a 0 (true) exit value.
1813 The commands in the specified file are read and executed by the shell.
1816 command may be used to return to the
1823 characters, it is used as is.
1824 Otherwise, the shell searches the
1827 If it is not found in the
1829 it is sought in the current working directory.
1831 A built-in equivalent of
1833 .It Ic alias Oo Ar name Ns Oo = Ns Ar string Oc ... Oc
1835 .Ar name Ns = Ns Ar string
1836 is specified, the shell defines the alias
1842 is specified, the value of the alias
1845 With no arguments, the
1847 built-in command prints the names and values of all defined aliases
1850 Alias values are written with appropriate quoting so that they are
1851 suitable for re-input to the shell.
1855 .It Ic bg Op Ar job ...
1856 Continue the specified jobs
1857 (or the current job if no jobs are given)
1859 .It Ic bind Oo Fl aeklrsv Oc Oo Ar key Oo Ar command Oc Oc
1860 List or alter key bindings for the line editor.
1861 This command is documented in
1863 .It Ic break Op Ar num
1865 .Sx Flow-Control Constructs
1867 .It Ic builtin Ar cmd Op Ar arg ...
1868 Execute the specified built-in command,
1870 This is useful when the user wishes to override a shell function
1871 with the same name as a built-in command.
1872 .It Ic cd Oo Fl L | P Oc Oo Fl e Oc Op Ar directory
1873 Switch to the specified
1875 or to the directory specified in the
1877 environment variable if no
1886 then the directories listed in the
1889 searched for the specified
1893 is unset, the current directory is searched.
1896 is the same as that of
1898 In an interactive shell,
1901 command will print out the name of the directory
1902 that it actually switched to
1903 if this is different from the name that the user gave.
1904 These may be different either because the
1906 mechanism was used or because a symbolic link was crossed.
1910 option is specified,
1912 is handled physically and symbolic links are resolved before
1914 components are processed.
1917 option is specified,
1919 is handled logically.
1920 This is the default.
1926 to return exit status 1 if the full pathname of the new directory
1927 cannot be determined reliably or at all.
1928 Normally this is not considered an error,
1929 although a warning is printed.
1934 .It Ic command Oo Fl p Oc Op Ar utility Op Ar argument ...
1935 .It Ic command Oo Fl p Oc Fl v Ar utility
1936 .It Ic command Oo Fl p Oc Fl V Ar utility
1937 The first form of invocation executes the specified
1939 ignoring shell functions in the search.
1942 is a special builtin,
1943 it is executed as if it were a regular builtin.
1947 option is specified, the command search is performed using a
1950 that is guaranteed to find all of the standard utilities.
1954 option is specified,
1956 is not executed but a description of its interpretation by the shell is
1958 For ordinary commands the output is the path name; for shell built-in
1959 commands, shell functions and keywords only the name is written.
1960 Aliases are printed as
1961 .Dq Ic alias Ar name Ns = Ns Ar value .
1965 option is identical to
1967 except for the output.
1969 .Dq Ar utility Ic is Ar description
1975 a special shell builtin,
1982 .It Ic continue Op Ar num
1984 .Sx Flow-Control Constructs
1986 .It Ic echo Oo Fl e | n Oc Op Ar string ...
1987 Print a space-separated list of the arguments to the standard output
1988 and append a newline character.
1989 .Bl -tag -width indent
1991 Suppress the output of the trailing newline.
1993 Process C-style backslash escape sequences.
1996 command understands the following character escapes:
1997 .Bl -tag -width indent
1999 Alert (ring the terminal bell)
2003 Suppress the trailing newline (this has the side-effect of truncating the
2004 line if it is not the last character)
2022 (Zero) The character whose octal value is
2028 is not enclosed in quotes then the backslash itself must be escaped
2029 with a backslash to protect it from the shell.
2031 .Bd -literal -offset indent
2040 $ echo -e a\e\e\e\eb
2049 options may be specified.
2050 .It Ic eval Ar string ...
2051 Concatenate all the arguments with spaces.
2052 Then re-parse and execute the command.
2053 .It Ic exec Op Ar command Op arg ...
2057 the shell process is replaced with the specified program
2058 (which must be a real program, not a shell built-in command or function).
2059 Any redirections on the
2061 command are marked as permanent,
2062 so that they are not undone when the
2065 .It Ic exit Op Ar exitstatus
2066 Terminate the shell process.
2070 it is used as the exit status of the shell.
2071 Otherwise, if the shell is executing an
2073 trap, the exit status of the last command before the trap is used;
2074 if the shell is executing a trap for a signal,
2075 the shell exits by resending the signal to itself.
2076 Otherwise, the exit status of the preceding command is used.
2077 The exit status should be an integer between 0 and 255.
2078 .It Ic export Ar name ...
2079 .It Ic export Op Fl p
2080 The specified names are exported so that they will
2081 appear in the environment of subsequent commands.
2082 The only way to un-export a variable is to
2085 The shell allows the value of a variable to be set
2086 at the same time as it is exported by writing
2088 .D1 Ic export Ar name Ns = Ns Ar value
2090 With no arguments the
2092 command lists the names
2093 of all exported variables.
2096 option is specified, the exported variables are printed as
2097 .Dq Ic export Ar name Ns = Ns Ar value
2098 lines, suitable for re-input to the shell.
2100 A null command that returns a non-zero (false) exit value.
2101 .It Ic fc Oo Fl e Ar editor Oc Op Ar first Op Ar last
2102 .It Ic fc Fl l Oo Fl nr Oc Op Ar first Op Ar last
2103 .It Ic fc Fl s Oo Ar old Ns = Ns Ar new Oc Op Ar first
2106 built-in command lists, or edits and re-executes,
2107 commands previously entered to an interactive shell.
2108 .Bl -tag -width indent
2110 Use the editor named by
2112 to edit the commands.
2115 string is a command name,
2116 subject to search via the
2121 variable is used as a default when
2126 is null or unset, the value of the
2133 is used as the editor.
2135 List the commands rather than invoking
2137 The commands are written in the
2138 sequence indicated by the
2142 operands, as affected by
2144 with each command preceded by the command number.
2146 Suppress command numbers when listing with
2149 Reverse the order of the commands listed
2158 Re-execute the command without invoking an editor.
2161 Select the commands to list or edit.
2162 The number of previous commands that can be accessed
2163 are determined by the value of the
2170 or both are one of the following:
2171 .Bl -tag -width indent
2172 .It Oo Cm + Oc Ns Ar num
2173 A positive number representing a command number;
2174 command numbers can be displayed with the
2178 A negative decimal number representing the
2179 command that was executed
2182 commands previously.
2183 For example, \-1 is the immediately previous command.
2185 A string indicating the most recently entered command
2186 that begins with that string.
2188 .Ar old Ns = Ns Ar new
2189 operand is not also specified with
2191 the string form of the first operand cannot contain an embedded equal sign.
2195 The following variables affect the execution of
2197 .Bl -tag -width ".Va HISTSIZE"
2199 Name of the editor to use for history editing.
2201 The number of previous commands that are accessible.
2206 or the current job to the foreground.
2207 .It Ic getopts Ar optstring var
2214 command deprecates the older
2217 The first argument should be a series of letters, each possibly
2218 followed by a colon which indicates that the option takes an argument.
2219 The specified variable is set to the parsed option.
2221 the next argument is placed into the shell variable
2223 If an option takes an argument, it is placed into the shell variable
2225 If an invalid option is encountered,
2229 It returns a false value (1) when it encounters the end of the options.
2230 .It Ic hash Oo Fl rv Oc Op Ar command ...
2231 The shell maintains a hash table which remembers the locations of commands.
2232 With no arguments whatsoever, the
2234 command prints out the contents of this table.
2238 command removes each specified
2240 from the hash table (unless they are functions) and then locates it.
2245 prints the locations of the commands as it finds them.
2250 command to delete all the entries in the hash table except for functions.
2251 .It Ic jobid Op Ar job
2252 Print the process IDs of the processes in the specified
2256 argument is omitted, use the current job.
2257 .It Ic jobs Oo Fl lps Oc Op Ar job ...
2258 Print information about the specified jobs, or all jobs if no
2261 The information printed includes job ID, status and command name.
2265 option is specified, the PID of each job is also printed.
2268 option is specified, only the process IDs for the process group leaders
2269 are printed, one per line.
2272 option is specified, only the PIDs of the job commands are printed, one per
2275 A built-in equivalent of
2277 that additionally supports sending signals to jobs.
2278 .It Ic local Oo Ar variable ... Oc Op Fl
2283 A built-in equivalent of
2285 .It Ic pwd Op Fl L | P
2286 Print the path of the current directory.
2287 The built-in command may
2288 differ from the program of the same name because the
2289 built-in command remembers what the current directory
2290 is rather than recomputing it each time.
2293 However, if the current directory is
2295 the built-in version of
2297 will continue to print the old name for the directory.
2301 option is specified, symbolic links are resolved.
2304 option is specified, the shell's notion of the current directory
2305 is printed (symbolic links are not resolved).
2306 This is the default.
2307 .It Ic read Oo Fl p Ar prompt Oc Oo
2308 .Fl t Ar timeout Oc Oo Fl er Oc Ar variable ...
2314 and the standard input is a terminal.
2316 read from the standard input.
2317 The trailing newline
2318 is deleted from the line and the line is split as
2319 described in the section on
2320 .Sx White Space Splitting (Field Splitting)
2322 the pieces are assigned to the variables in order.
2323 If there are more pieces than variables, the remaining
2324 pieces (along with the characters in
2326 that separated them)
2327 are assigned to the last variable.
2328 If there are more variables than pieces, the remaining
2329 variables are assigned the null string.
2331 Backslashes are treated specially, unless the
2335 If a backslash is followed by
2336 a newline, the backslash and the newline will be
2338 If a backslash is followed by any other
2339 character, the backslash will be deleted and the following
2340 character will be treated as though it were not in
2346 option is specified and the
2348 elapses before a complete line of input is supplied,
2351 command will return an exit status of 1 without assigning any values.
2354 value may optionally be followed by one of
2359 to explicitly specify seconds, minutes or hours.
2360 If none is supplied,
2366 option exists only for backward compatibility with older scripts.
2367 .It Ic readonly Oo Fl p Oc Op Ar name ...
2370 is marked as read only,
2371 so that it cannot be subsequently modified or unset.
2372 The shell allows the value of a variable to be set
2373 at the same time as it is marked read only
2374 by using the following form:
2376 .D1 Ic readonly Ar name Ns = Ns Ar value
2378 With no arguments the
2380 command lists the names of all read only variables.
2383 option is specified, the read-only variables are printed as
2384 .Dq Ic readonly Ar name Ns = Ns Ar value
2385 lines, suitable for re-input to the shell.
2386 .It Ic return Op Ar exitstatus
2390 .It Ic set Oo Fl /+abCEefIimnpTuVvx Oc Oo Fl /+o Ar longname Oc Oo
2391 .Fl c Ar string Oc Op Fl - Ar arg ...
2394 command performs three different functions:
2397 With no arguments, it lists the values of all shell variables.
2399 If options are given,
2400 either in short form or using the long
2401 .Dq Fl /+o Ar longname
2403 it sets or clears the specified options as described in the section called
2404 .Sx Argument List Processing .
2408 option is specified,
2410 will replace the shell's positional parameters with the subsequent
2412 If no arguments follow the
2415 all the positional parameters will be cleared,
2416 which is equivalent to executing the command
2420 flag may be omitted when specifying arguments to be used
2421 as positional replacement parameters.
2422 This is not recommended,
2423 because the first argument may begin with a dash
2429 command will interpret as a request to enable or disable options.
2431 .It Ic setvar Ar variable value
2432 Assigns the specified
2438 command is intended to be used in functions that
2439 assign values to variables whose names are passed as parameters.
2440 In general it is better to write
2441 .Dq Ar variable Ns = Ns Ar value
2444 .It Ic shift Op Ar n
2445 Shift the positional parameters
2450 A shift sets the value of
2459 decreasing the value of
2462 If there are zero positional parameters, shifting does not do anything.
2464 A built-in equivalent of
2467 Print the amount of time spent executing the shell process and its children.
2468 The first output line shows the user and system times for the shell process
2469 itself, the second one contains the user and system times for the
2471 .It Ic trap Oo Ar action Oc Ar signal ...
2473 Cause the shell to parse and execute
2478 The signals are specified by name or number.
2479 In addition, the pseudo-signal
2481 may be used to specify an
2483 that is performed when the shell terminates.
2486 may be an empty string or a dash
2488 the former causes the specified signal to be ignored
2489 and the latter causes the default action to be taken.
2492 is another way to request the default action, for compatibility reasons this
2493 usage is not recommended though.
2494 In a subshell or utility environment,
2495 the shell resets trapped (but not ignored) signals to the default action.
2498 command has no effect on signals that were ignored on entry to the shell.
2504 command to display a list of valid signal names.
2506 A null command that returns a 0 (true) exit value.
2507 .It Ic type Op Ar name ...
2510 as a command and print the resolution of the command search.
2511 Possible resolutions are:
2512 shell keyword, alias, special shell builtin, shell builtin, command,
2515 For aliases the alias expansion is printed;
2516 for commands and tracked aliases
2517 the complete pathname of the command is printed.
2518 .It Ic ulimit Oo Fl HSabcdflmnpstuvw Oc Op Ar limit
2519 Set or display resource limits (see
2523 is specified, the named resource will be set;
2524 otherwise the current resource value will be displayed.
2528 is specified, the hard limits will be set or displayed.
2529 While everybody is allowed to reduce a hard limit,
2530 only the superuser can increase it.
2534 specifies the soft limits instead.
2535 When displaying limits,
2541 The default is to display the soft limits,
2542 and to set both the hard and the soft limits.
2548 command to display all resources.
2551 is not acceptable in this mode.
2553 The remaining options specify which resource value is to be
2554 displayed or modified.
2555 They are mutually exclusive.
2556 .Bl -tag -width indent
2558 The maximum size of socket buffer usage, in bytes.
2559 .It Fl c Ar coredumpsize
2560 The maximal size of core dump files, in 512-byte blocks.
2561 .It Fl d Ar datasize
2562 The maximal size of the data segment of a process, in kilobytes.
2563 .It Fl f Ar filesize
2564 The maximal size of a file, in 512-byte blocks.
2565 .It Fl l Ar lockedmem
2566 The maximal size of memory that can be locked by a process, in
2568 .It Fl m Ar memoryuse
2569 The maximal resident set size of a process, in kilobytes.
2571 The maximal number of descriptors that could be opened by a process.
2572 .It Fl p Ar pseudoterminals
2573 The maximal number of pseudo-terminals for this user ID.
2574 .It Fl s Ar stacksize
2575 The maximal size of the stack segment, in kilobytes.
2577 The maximal amount of CPU time to be used by each process, in seconds.
2578 .It Fl u Ar userproc
2579 The maximal number of simultaneous processes for this user ID.
2580 .It Fl v Ar virtualmem
2581 The maximal virtual size of a process, in kilobytes.
2583 The maximum amount of swap space reserved or used for this user ID,
2586 .It Ic umask Oo Fl S Oc Op Ar mask
2587 Set the file creation mask (see
2589 to the octal or symbolic (see
2593 If the argument is omitted, the current mask value is printed.
2596 option is specified, the output is symbolic, otherwise the output is octal.
2597 .It Ic unalias Oo Fl a Oc Op Ar name ...
2598 The specified alias names are removed.
2601 is specified, all aliases are removed.
2602 .It Ic unset Oo Fl fv Oc Ar name ...
2603 The specified variables or functions are unset and unexported.
2606 option is specified or no options are given, the
2608 arguments are treated as variable names.
2611 option is specified, the
2613 arguments are treated as function names.
2614 .It Ic wait Op Ar job
2615 Wait for the specified
2617 to complete and return the exit status of the last process in the
2619 If the argument is omitted, wait for all jobs to complete
2620 and return an exit status of zero.
2622 .Ss Commandline Editing
2625 is being used interactively from a terminal, the current command
2626 and the command history
2630 .Sx Built-in Commands )
2633 command line editing.
2634 This mode uses commands similar
2635 to a subset of those described in the
2653 can be switched between insert mode and command mode by typing
2657 while in command mode will pass the line to the shell.
2660 .Dq Li "set -o emacs"
2663 command can be used to enable a subset of
2665 command line editing features.
2667 The following environment variables affect the execution of
2669 .Bl -tag -width ".Ev LANGXXXXXX"
2671 Initialization file for interactive shells.
2672 .It Ev LANG , Ev LC_*
2674 These are inherited by children of the shell,
2675 and is used in a limited manner by the shell itself.
2677 An absolute pathname for the current directory,
2678 possibly containing symbolic links.
2679 This is used and updated by the shell.
2681 The default terminal setting for the shell.
2682 This is inherited by children of the shell, and is used in the history
2686 Additionally, all environment variables are turned into shell variables
2688 which may affect the shell as described under
2689 .Sx Special Variables .
2691 .Bl -tag -width "/etc/suid_profileXX" -compact
2693 User's login profile.
2695 System login profile.
2698 .It Pa /etc/suid_profile
2699 Privileged shell profile.
2702 Errors that are detected by the shell, such as a syntax error, will
2703 cause the shell to exit with a non-zero exit status.
2704 If the shell is not an interactive shell, the execution of the shell
2705 file will be aborted.
2706 Otherwise the shell will return the exit status of the last command
2709 builtin is used with a numeric argument, it
2710 will return the argument.
2731 command, the Thompson shell, appeared in
2733 It was superseded in
2735 by the Bourne shell, which inherited the name
2740 was rewritten in 1989 under the
2742 license after the Bourne shell from
2747 was originally written by
2748 .An Kenneth Almquist .
2752 utility does not recognize multibyte characters other than UTF-8.
2755 and the line editing library
2757 do not recognize multibyte characters.
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