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32 .\" from: @(#)sh.1 8.6 (Berkeley) 5/4/95
40 .Nd command interpreter (shell)
43 .Op Fl /+abCEefhIimnPpTuVvx
44 .Op Fl /+o Ar longname
50 .Op Fl /+abCEefhIimnPpTuVvx
51 .Op Fl /+o Ar longname
58 .Op Fl /+abCEefhIimnPpTuVvx
59 .Op Fl /+o Ar longname
65 utility is the standard command interpreter for the system.
66 The current version of
70 specification for the shell.
71 It only supports features
74 plus a few Berkeley extensions.
75 This man page is not intended to be a tutorial nor a complete
76 specification of the shell.
78 The shell is a command that reads lines from
79 either a file or the terminal, interprets them, and
80 generally executes other commands.
81 It is the program that is started when a user logs into the system,
82 although a user can select a different shell with the
86 implements a language that has flow control constructs,
87 a macro facility that provides a variety of features in
88 addition to data storage, along with built-in history and line
90 It incorporates many features to
91 aid interactive use and has the advantage that the interpretative
92 language is common to both interactive and non-interactive
94 That is, commands can be typed directly
95 to the running shell or can be put into a file,
96 which can be executed directly by the shell.
99 .\" XXX This next sentence is incredibly confusing.
101 If no arguments are present and if the standard input of the shell
102 is connected to a terminal
106 the shell is considered an interactive shell.
108 generally prompts before each command and handles programming
109 and command errors differently (as described below).
110 When first starting, the shell inspects argument 0, and
111 if it begins with a dash
113 the shell is also considered a login shell.
114 This is normally done automatically by the system
115 when the user first logs in.
116 A login shell first reads commands
121 in a user's home directory,
123 If the environment variable
125 is set on entry to a shell, or is set in the
127 of a login shell, the shell then subjects its value to parameter expansion
128 and arithmetic expansion and reads commands from the named file.
129 Therefore, a user should place commands that are to be executed only
132 file, and commands that are executed for every shell inside the
137 variable to some file by placing the following line in the file
139 in the home directory,
142 the filename desired:
144 .Dl "ENV=$HOME/.shinit; export ENV"
146 The first non-option argument specified on the command line
147 will be treated as the
148 name of a file from which to read commands (a shell script), and
149 the remaining arguments are set as the positional parameters
153 Otherwise, the shell reads commands
154 from its standard input.
156 Unlike older versions of
160 script is only sourced on invocation of interactive shells.
162 closes a well-known, and sometimes easily exploitable security
163 hole related to poorly thought out
166 .Ss Argument List Processing
167 All of the single letter options to
169 have a corresponding long name,
170 with the exception of
174 These long names are provided next to the single letter options
175 in the descriptions below.
176 The long name for an option may be specified as an argument to the
180 Once the shell is running,
181 the long name for an option may be specified as an argument to the
186 (described later in the section called
187 .Sx Built-in Commands ) .
188 Introducing an option with a dash
198 will stop option processing and will force the remaining
199 words on the command line to be treated as arguments.
204 options do not have long names.
205 They take arguments and are described after the single letter options.
206 .Bl -tag -width indent
207 .It Fl a Li allexport
208 Flag variables for export when assignments are made to them.
210 Enable asynchronous notification of background job
213 .It Fl C Li noclobber
214 Do not overwrite existing files with
219 command line editor (disables the
221 option if it has been set;
222 set automatically when interactive on terminals).
224 Exit immediately if any untested command fails in non-interactive mode.
225 The exit status of a command is considered to be
226 explicitly tested if the command is part of the list used to control
228 .Ic if , elif , while ,
231 if the command is the left
236 operator; or if the command is a pipeline preceded by the
239 If a shell function is executed and its exit status is explicitly
240 tested, all commands of the function are considered to be tested as
243 It is recommended to check for failures explicitly
244 instead of relying on
246 because it tends to behave in unexpected ways,
247 particularly in larger scripts.
249 Disable pathname expansion.
251 A do-nothing option for
254 .It Fl I Li ignoreeof
257 from input when in interactive mode.
258 .It Fl i Li interactive
259 Force the shell to behave interactively.
261 Turn on job control (set automatically when interactive).
263 If not interactive, read commands but do not
265 This is useful for checking the
266 syntax of shell scripts.
268 Change the default for the
274 (logical directory layout)
277 (physical directory layout).
278 .It Fl p Li privileged
279 Turn on privileged mode.
280 This mode is enabled on startup
281 if either the effective user or group ID is not equal to the
282 real user or group ID.
283 Turning this mode off sets the
284 effective user and group IDs to the real user and group IDs.
285 When this mode is enabled for interactive shells, the file
286 .Pa /etc/suid_profile
287 is sourced instead of
291 is sourced, and the contents of the
293 variable are ignored.
295 Read commands from standard input (set automatically
296 if no file arguments are present).
298 no effect when set after the shell has already started
299 running (i.e., when set with the
302 .It Fl T Li trapsasync
303 When waiting for a child, execute traps immediately.
304 If this option is not set,
305 traps are executed after the child exits,
308 This nonstandard option is useful for putting guarding shells around
309 children that block signals.
310 The surrounding shell may kill the child
311 or it may just return control to the tty and leave the child alone,
313 .Bd -literal -offset indent
314 sh -T -c "trap 'exit 1' 2 ; some-blocking-program"
317 Write a message to standard error when attempting
318 to expand a variable, a positional parameter or
319 the special parameter
321 that is not set, and if the
322 shell is not interactive, exit immediately.
326 command line editor (disables
330 The shell writes its input to standard error
332 Useful for debugging.
335 (preceded by the value of the
337 variable subjected to parameter expansion and arithmetic expansion)
338 to standard error before it is executed.
339 Useful for debugging.
344 option causes the commands to be read from the
346 operand instead of from the standard input.
347 Keep in mind that this option only accepts a single string as its
348 argument, hence multi-word strings must be quoted.
352 option takes as its only argument the long name of an option
353 to be enabled or disabled.
354 For example, the following two invocations of
356 both enable the built-in
359 .Bd -literal -offset indent
364 If used without an argument, the
366 option displays the current option settings in a human-readable format.
369 is used without an argument, the current option settings are output
370 in a format suitable for re-input into the shell.
371 .Ss Lexical Structure
372 The shell reads input in terms of lines from a file and breaks
373 it up into words at whitespace (blanks and tabs), and at
377 which are special to the shell.
378 There are two types of operators: control operators and
379 redirection operators (their meaning is discussed later).
380 The following is a list of valid operators:
381 .Bl -tag -width indent
382 .It Control operators:
383 .Bl -column "XXX" "XXX" "XXX" "XXX" "XXX" -offset center -compact
384 .It Li & Ta Li && Ta Li ( Ta Li ) Ta Li \en
385 .It Li ;; Ta Li ;& Ta Li ; Ta Li | Ta Li ||
387 .It Redirection operators:
388 .Bl -column "XXX" "XXX" "XXX" "XXX" "XXX" -offset center -compact
389 .It Li < Ta Li > Ta Li << Ta Li >> Ta Li <>
390 .It Li <& Ta Li >& Ta Li <<- Ta Li >|
396 introduces a comment if used at the beginning of a word.
397 The word starting with
399 and the rest of the line are ignored.
403 characters (character code 0) are not allowed in shell input.
405 Quoting is used to remove the special meaning of certain characters
406 or words to the shell, such as operators, whitespace, keywords,
409 There are four types of quoting: matched single quotes,
410 dollar-single quotes,
411 matched double quotes, and backslash.
412 .Bl -tag -width indent
414 Enclosing characters in single quotes preserves the literal
415 meaning of all the characters (except single quotes, making
416 it impossible to put single-quotes in a single-quoted string).
417 .It Dollar-Single Quotes
418 Enclosing characters between
422 preserves the literal meaning of all characters
423 except backslashes and single quotes.
424 A backslash introduces a C-style escape sequence:
425 .Bl -tag -width xUnnnnnnnn
427 Alert (ring the terminal bell)
431 The control character denoted by
437 is a backslash, it must be doubled.
459 The byte whose octal value is
461 (one to three digits)
463 The byte whose hexadecimal value is
465 (one or more digits only the last two of which are used)
467 The Unicode code point
469 (four hexadecimal digits)
470 .It \eU Ns Ar nnnnnnnn
471 The Unicode code point
473 (eight hexadecimal digits)
476 The sequences for Unicode code points are currently only useful with
478 They reject code point 0 and UTF-16 surrogates.
480 If an escape sequence would produce a byte with value 0,
481 that byte and the rest of the string until the matching single-quote
484 Any other string starting with a backslash is an error.
486 Enclosing characters within double quotes preserves the literal
487 meaning of all characters except dollar sign
493 The backslash inside double quotes is historically weird.
494 It remains literal unless it precedes the following characters,
495 which it serves to quote:
496 .Bl -column "XXX" "XXX" "XXX" "XXX" "XXX" -offset center -compact
497 .It Li $ Ta Li ` Ta Li \&" Ta Li \e\ Ta Li \en
500 A backslash preserves the literal meaning of the following
501 character, with the exception of the newline character
503 A backslash preceding a newline is treated as a line continuation.
506 Keywords or reserved words are words that have special meaning to the
507 shell and are recognized at the beginning of a line and
508 after a control operator.
509 The following are keywords:
510 .Bl -column "doneXX" "elifXX" "elseXX" "untilXX" "whileX" -offset center
511 .It Li \&! Ta { Ta } Ta Ic case Ta Ic do
512 .It Ic done Ta Ic elif Ta Ic else Ta Ic esac Ta Ic fi
513 .It Ic for Ta Ic if Ta Ic then Ta Ic until Ta Ic while
516 An alias is a name and corresponding value set using the
519 Wherever the command word of a simple command may occur,
520 and after checking for keywords if a keyword may occur, the shell
521 checks the word to see if it matches an alias.
522 If it does, it replaces it in the input stream with its value.
523 For example, if there is an alias called
535 Aliases provide a convenient way for naive users to
536 create shorthands for commands without having to learn how
537 to create functions with arguments.
538 Using aliases in scripts is discouraged
539 because the command that defines them must be executed
540 before the code that uses them is parsed.
541 This is fragile and not portable.
543 An alias name may be escaped in a command line, so that it is not
544 replaced by its alias value, by using quoting characters within or
545 adjacent to the alias name.
546 This is most often done by prefixing
547 an alias name with a backslash to execute a function, built-in, or
548 normal program with the same name.
553 The shell interprets the words it reads according to a
554 language, the specification of which is outside the scope
555 of this man page (refer to the BNF in the
558 Essentially though, a line is read and if
559 the first word of the line (or after a control operator)
560 is not a keyword, then the shell has recognized a
562 Otherwise, a complex command or some
563 other special construct may have been recognized.
565 If a simple command has been recognized, the shell performs
566 the following actions:
569 Leading words of the form
571 are stripped off and assigned to the environment of
573 Redirection operators and
574 their arguments (as described below) are stripped
575 off and saved for processing.
577 The remaining words are expanded as described in
579 .Sx Word Expansions ,
580 and the first remaining word is considered the command
581 name and the command is located.
583 words are considered the arguments of the command.
584 If no command name resulted, then the
586 variable assignments recognized in 1) affect the
589 Redirections are performed as described in
593 Redirections are used to change where a command reads its input
595 In general, redirections open, close, or
596 duplicate an existing reference to a file.
598 used for redirection is:
600 .D1 Oo Ar n Oc Ar redir-op file
604 is one of the redirection operators mentioned
606 The following gives some examples of how these
607 operators can be used.
608 Note that stdin and stdout are commonly used abbreviations
609 for standard input and standard output respectively.
610 .Bl -tag -width "1234567890XX" -offset indent
611 .It Oo Ar n Oc Ns Li > Ar file
612 redirect stdout (or file descriptor
616 .It Oo Ar n Oc Ns Li >| Ar file
617 same as above, but override the
620 .It Oo Ar n Oc Ns Li >> Ar file
621 append stdout (or file descriptor
625 .It Oo Ar n Oc Ns Li < Ar file
626 redirect stdin (or file descriptor
630 .It Oo Ar n Oc Ns Li <> Ar file
631 redirect stdin (or file descriptor
635 .It Oo Ar n1 Oc Ns Li <& Ns Ar n2
636 duplicate stdin (or file descriptor
640 .It Oo Ar n Oc Ns Li <&-
641 close stdin (or file descriptor
643 .It Oo Ar n1 Oc Ns Li >& Ns Ar n2
644 duplicate stdout (or file descriptor
648 .It Oo Ar n Oc Ns Li >&-
649 close stdout (or file descriptor
653 The following redirection is often called a
655 .Bd -unfilled -offset indent
656 .Oo Ar n Oc Ns Li << Ar delimiter
662 All the text on successive lines up to the delimiter is
663 saved away and made available to the command on standard
664 input, or file descriptor
669 as specified on the initial line is quoted, then the
671 is treated literally, otherwise the text is subjected to
672 parameter expansion, command substitution, and arithmetic
673 expansion (as described in the section on
674 .Sx Word Expansions ) .
683 .Ss Search and Execution
684 There are three types of commands: shell functions,
685 built-in commands, and normal programs.
686 The command is searched for (by name) in that order.
687 The three types of commands are all executed in a different way.
689 When a shell function is executed, all of the shell positional
692 which remains unchanged) are
693 set to the arguments of the shell function.
694 The variables which are explicitly placed in the environment of
695 the command (by placing assignments to them before the
696 function name) are made local to the function and are set
698 Then the command given in the function definition is executed.
699 The positional parameters are restored to their original values
700 when the command completes.
701 This all occurs within the current shell.
703 Shell built-in commands are executed internally to the shell, without
704 spawning a new process.
705 There are two kinds of built-in commands: regular and special.
706 Assignments before special builtins persist after they finish
707 executing and assignment errors, redirection errors and certain
708 operand errors cause a script to be aborted.
709 Special builtins cannot be overridden with a function.
710 Both regular and special builtins can affect the shell in ways
711 normal programs cannot.
713 Otherwise, if the command name does not match a function
714 or built-in command, the command is searched for as a normal
715 program in the file system (as described in the next section).
716 When a normal program is executed, the shell runs the program,
717 passing the arguments and the environment to the program.
718 If the program is not a normal executable file
719 (i.e., if it does not begin with the
729 but appears to be a text file,
730 the shell will run a new instance of
734 Note that previous versions of this document
735 and the source code itself misleadingly and sporadically
736 refer to a shell script without a magic number
738 .Dq "shell procedure" .
740 When locating a command, the shell first looks to see if
741 it has a shell function by that name.
743 built-in command by that name.
744 If a built-in command is not found,
745 one of two things happen:
748 Command names containing a slash are simply executed without
749 performing any searches.
751 The shell searches each entry in the
754 in turn for the command.
757 variable should be a series of
758 entries separated by colons.
759 Each entry consists of a
761 The current directory
762 may be indicated implicitly by an empty directory name,
763 or explicitly by a single period.
765 .Ss Command Exit Status
766 Each command has an exit status that can influence the behavior
767 of other shell commands.
768 The paradigm is that a command exits
769 with zero for normal or success, and non-zero for failure,
770 error, or a false indication.
771 The man page for each command
772 should indicate the various exit codes and what they mean.
773 Additionally, the built-in commands return exit codes, as does
774 an executed shell function.
776 If a command is terminated by a signal, its exit status is 128 plus
778 Signal numbers are defined in the header file
781 Complex commands are combinations of simple commands
782 with control operators or keywords, together creating a larger complex
784 More generally, a command is one of the following:
785 .Bl -item -offset indent
791 list or compound-list
798 Unless otherwise stated, the exit status of a command is
799 that of the last simple command executed by the command.
801 A pipeline is a sequence of one or more commands separated
802 by the control operator
804 The standard output of all but
805 the last command is connected to the standard input
807 The standard output of the last
808 command is inherited from the shell, as usual.
810 The format for a pipeline is:
812 .D1 Oo Li \&! Oc Ar command1 Op Li \&| Ar command2 ...
814 The standard output of
816 is connected to the standard input of
818 The standard input, standard output, or
819 both of a command is considered to be assigned by the
820 pipeline before any redirection specified by redirection
821 operators that are part of the command.
823 Note that unlike some other shells,
825 executes each process in a pipeline with more than one command
826 in a subshell environment and as a child of the
830 If the pipeline is not in the background (discussed later),
831 the shell waits for all commands to complete.
835 does not precede the pipeline, the
836 exit status is the exit status of the last command specified
838 Otherwise, the exit status is the logical
839 NOT of the exit status of the last command.
841 the last command returns zero, the exit status is 1; if
842 the last command returns greater than zero, the exit status
845 Because pipeline assignment of standard input or standard
846 output or both takes place before redirection, it can be
847 modified by redirection.
850 .Dl "command1 2>&1 | command2"
852 sends both the standard output and standard error of
854 to the standard input of
859 or newline terminator causes the preceding
861 (described below in the section called
862 .Sx Short-Circuit List Operators )
863 to be executed sequentially;
866 causes asynchronous execution of the preceding AND-OR-list.
867 .Ss Background Commands (&)
868 If a command is terminated by the control operator ampersand
870 the shell executes the command in a subshell environment (see
871 .Sx Grouping Commands Together
872 below) and asynchronously;
873 the shell does not wait for the command to finish
874 before executing the next command.
876 The format for running a command in background is:
878 .D1 Ar command1 Li & Op Ar command2 Li & Ar ...
880 If the shell is not interactive, the standard input of an
881 asynchronous command is set to
883 .Ss Lists (Generally Speaking)
884 A list is a sequence of zero or more commands separated by
885 newlines, semicolons, or ampersands,
886 and optionally terminated by one of these three characters.
888 list are executed in the order they are written.
889 If command is followed by an ampersand, the shell starts the
890 command and immediately proceeds onto the next command;
891 otherwise it waits for the command to terminate before
892 proceeding to the next one.
893 .Ss Short-Circuit List Operators
897 are AND-OR list operators.
899 executes the first command, and then executes the second command
900 if the exit status of the first command is zero.
902 is similar, but executes the second command if the exit
903 status of the first command is nonzero.
907 both have the same priority.
908 .Ss Flow-Control Constructs (if, while, for, case)
912 .Bd -unfilled -offset indent -compact
916 .Ic then Ar list Oc Ar ...
924 .Bd -unfilled -offset indent -compact
930 The two lists are executed repeatedly while the exit status of the
934 command is similar, but has the word
939 repeat until the exit status of the first list is zero.
944 .Bd -unfilled -offset indent -compact
945 .Ic for Ar variable Op Ic in Ar word ...
952 and the following words are omitted,
955 The words are expanded, and then the list is executed
956 repeatedly with the variable set to each word in turn.
961 commands may be replaced with
971 .D1 Ic break Op Ar num
972 .D1 Ic continue Op Ar num
976 command terminates the
985 command continues with the next iteration of the innermost loop.
986 These are implemented as special built-in commands.
991 .Bd -unfilled -offset indent -compact
992 .Ic case Ar word Ic in
993 .Ar pattern Ns Li ) Ar list Li ;;
998 The pattern can actually be one or more patterns
1005 Tilde expansion, parameter expansion, command substitution,
1006 arithmetic expansion and quote removal are applied to the word.
1007 Then, each pattern is expanded in turn using tilde expansion,
1008 parameter expansion, command substitution and arithmetic expansion and
1009 the expanded form of the word is checked against it.
1010 If a match is found, the corresponding list is executed.
1011 If the selected list is terminated by the control operator
1015 execution continues with the next list,
1016 continuing until a list terminated with
1021 The exit code of the
1023 command is the exit code of the last command executed in the list or
1024 zero if no patterns were matched.
1025 .Ss Grouping Commands Together
1026 Commands may be grouped by writing either
1028 .D1 Li \&( Ns Ar list Ns Li \%)
1032 .D1 Li { Ar list Ns Li \&; }
1034 The first form executes the commands in a subshell environment.
1035 A subshell environment has its own copy of:
1039 The current working directory as set by
1042 The file creation mask as set by
1045 Resource limits as set by
1048 References to open files.
1055 Positional parameters and variables.
1064 These are copied from the parent shell environment,
1065 except that trapped (but not ignored) signals are reset to the default action
1066 and known jobs are cleared.
1067 Any changes do not affect the parent shell environment.
1069 A subshell environment may be implemented as a child process or differently.
1070 If job control is enabled in an interactive shell,
1071 commands grouped in parentheses can be suspended and continued as a unit.
1073 For compatibility with other shells,
1074 two open parentheses in sequence should be separated by whitespace.
1076 The second form never forks another shell,
1077 so it is slightly more efficient.
1078 Grouping commands together this way allows the user to
1079 redirect their output as though they were one program:
1080 .Bd -literal -offset indent
1081 { echo -n "hello"; echo " world"; } > greeting
1084 The syntax of a function definition is
1086 .D1 Ar name Li \&( \&) Ar command
1088 A function definition is an executable statement; when
1089 executed it installs a function named
1092 exit status of zero.
1101 Variables may be declared to be local to a function by
1105 This should appear as the first statement of a function,
1108 .D1 Ic local Oo Ar variable ... Oc Op Fl
1112 command is implemented as a built-in command.
1114 When a variable is made local, it inherits the initial
1115 value and exported and readonly flags from the variable
1116 with the same name in the surrounding scope, if there is
1118 Otherwise, the variable is initially unset.
1120 uses dynamic scoping, so that if the variable
1122 is made local to function
1124 which then calls function
1126 references to the variable
1130 will refer to the variable
1134 not to the global variable named
1137 The only special parameter that can be made local is
1141 local causes any shell options that are
1144 command inside the function to be
1145 restored to their original values when the function
1152 .D1 Ic return Op Ar exitstatus
1154 It terminates the current executional scope, returning from the previous
1155 nested function, sourced script, or shell instance, in that order.
1158 command is implemented as a special built-in command.
1159 .Ss Variables and Parameters
1160 The shell maintains a set of parameters.
1162 denoted by a name is called a variable.
1164 the shell turns all the environment variables into shell
1166 New variables can be set using the form
1168 .D1 Ar name Ns = Ns Ar value
1170 Variables set by the user must have a name consisting solely
1171 of alphabetics, numerics, and underscores.
1172 The first letter of a variable name must not be numeric.
1173 A parameter can also be denoted by a number
1174 or a special character as explained below.
1176 Assignments are expanded differently from other words:
1177 tilde expansion is also performed after the equals sign and after any colon
1178 and usernames are also terminated by colons,
1179 and field splitting and pathname expansion are not performed.
1181 This special expansion applies not only to assignments that form a simple
1182 command by themselves or precede a command word,
1183 but also to words passed to the
1188 built-in commands that have this form.
1189 For this, the builtin's name must be literal
1190 (not the result of an expansion)
1191 and may optionally be preceded by one or more literal instances of
1194 .Ss Positional Parameters
1195 A positional parameter is a parameter denoted by a number greater than zero.
1196 The shell sets these initially to the values of its command line
1197 arguments that follow the name of the shell script.
1200 built-in command can also be used to set or reset them.
1201 .Ss Special Parameters
1202 Special parameters are parameters denoted by a single special character
1204 They are shown in the following list, exactly as they would appear in input
1205 typed by the user or in the source of a shell script.
1208 Expands to the positional parameters, starting from one.
1210 the expansion occurs within a double-quoted string
1211 it expands to a single field with the value of each parameter
1212 separated by the first character of the
1219 Expands to the positional parameters, starting from one.
1221 the expansion occurs within double-quotes, each positional
1222 parameter expands as a separate argument.
1223 If there are no positional parameters, the
1226 generates zero arguments, even when
1229 What this basically means, for example, is
1242 .Bd -literal -offset indent
1246 Expands to the number of positional parameters.
1248 Expands to the exit status of the most recent pipeline.
1250 (hyphen) Expands to the current option flags (the single-letter
1251 option names concatenated into a string) as specified on
1254 built-in command, or implicitly
1257 Expands to the process ID of the invoked shell.
1259 retains the same value of
1263 Expands to the process ID of the most recent background
1264 command executed from the current shell.
1266 pipeline, the process ID is that of the last command in the
1268 If this parameter is referenced, the shell will remember
1269 the process ID and its exit status until the
1271 built-in command reports completion of the process.
1273 (zero) Expands to the name of the shell script if passed on the command line,
1276 operand if given (with
1278 or otherwise argument 0 passed to the shell.
1280 .Ss Special Variables
1281 The following variables are set by the shell or
1282 have special meaning to it:
1283 .Bl -tag -width ".Va HISTSIZE"
1285 The search path used with the
1289 The fallback editor used with the
1292 If not set, the default editor is
1295 The default editor used with the
1299 The number of previous commands that are accessible.
1301 The user's home directory,
1302 used in tilde expansion and as a default directory for the
1306 Input Field Separators.
1307 The default value is
1313 This default also applies if
1315 is unset, but not if it is set to the empty string.
1317 .Sx White Space Splitting
1318 section for more details.
1320 The current line number in the script or function.
1322 The name of a mail file, that will be checked for the arrival of new
1329 separated list of file names, for the shell to check for incoming
1331 This variable overrides the
1334 There is a maximum of 10 mailboxes that can be monitored at once.
1336 The default search path for executables.
1339 section for details.
1341 The parent process ID of the invoked shell.
1342 This is set at startup
1343 unless this variable is in the environment.
1344 A later change of parent process ID is not reflected.
1345 A subshell retains the same value of
1348 The primary prompt string, which defaults to
1350 unless you are the superuser, in which case it defaults to
1353 The secondary prompt string, which defaults to
1356 The prefix for the trace output (if
1363 This clause describes the various expansions that are
1365 Not all expansions are performed on
1366 every word, as explained later.
1368 Tilde expansions, parameter expansions, command substitutions,
1369 arithmetic expansions, and quote removals that occur within
1370 a single word expand to a single field.
1372 splitting or pathname expansion that can create multiple
1373 fields from a single word.
1374 The single exception to this rule is
1375 the expansion of the special parameter
1377 within double-quotes,
1378 as was described above.
1380 The order of word expansion is:
1383 Tilde Expansion, Parameter Expansion, Command Substitution,
1384 Arithmetic Expansion (these all occur at the same time).
1386 Field Splitting is performed on fields generated by step (1)
1391 Pathname Expansion (unless the
1393 option is in effect).
1400 character is used to introduce parameter expansion, command
1401 substitution, or arithmetic expansion.
1402 .Ss Tilde Expansion (substituting a user's home directory)
1403 A word beginning with an unquoted tilde character
1406 subjected to tilde expansion.
1407 All the characters up to a slash
1409 or the end of the word are treated as a username
1410 and are replaced with the user's home directory.
1412 username is missing (as in
1414 the tilde is replaced with the value of the
1416 variable (the current user's home directory).
1417 .Ss Parameter Expansion
1418 The format for parameter expansion is as follows:
1420 .D1 Li ${ Ns Ar expression Ns Li }
1424 consists of all characters until the matching
1428 escaped by a backslash or within a single-quoted or double-quoted
1429 string, and characters in
1430 embedded arithmetic expansions, command substitutions, and variable
1431 expansions, are not examined in determining the matching
1433 If the variants with
1439 occur within a double-quoted string,
1440 as an extension there may be unquoted parts
1441 (via double-quotes inside the expansion);
1443 within such parts are also not examined in determining the matching
1446 The simplest form for parameter expansion is:
1448 .D1 Li ${ Ns Ar parameter Ns Li }
1450 The value, if any, of
1454 The parameter name or symbol can be enclosed in braces, which are
1455 optional except for positional parameters with more than one digit or
1456 when parameter is followed by a character that could be interpreted as
1458 If a parameter expansion occurs inside double-quotes:
1461 Field splitting is not performed on the results of the
1462 expansion, with the exception of the special parameter
1465 Pathname expansion is not performed on the results of the
1469 In addition, a parameter expansion can be modified by using one of the
1471 .Bl -tag -width indent
1472 .It Li ${ Ns Ar parameter Ns Li :- Ns Ar word Ns Li }
1476 is unset or null, the expansion of
1478 is substituted; otherwise, the value of
1481 .It Li ${ Ns Ar parameter Ns Li := Ns Ar word Ns Li }
1482 Assign Default Values.
1485 is unset or null, the expansion of
1495 does not prevent field splitting or pathname expansion.
1496 Only variables, not positional
1497 parameters or special parameters, can be
1498 assigned in this way.
1499 .It Li ${ Ns Ar parameter Ns Li :? Ns Oo Ar word Oc Ns Li }
1500 Indicate Error if Null or Unset.
1503 is unset or null, the expansion of
1505 (or a message indicating it is unset if
1507 is omitted) is written to standard
1508 error and the shell exits with a nonzero
1510 Otherwise, the value of
1514 interactive shell need not exit.
1515 .It Li ${ Ns Ar parameter Ns Li :+ Ns Ar word Ns Li }
1516 Use Alternate Value.
1519 is unset or null, null is substituted;
1520 otherwise, the expansion of
1525 In the parameter expansions shown previously, use of the colon in the
1526 format results in a test for a parameter that is unset or null; omission
1527 of the colon results in a test for a parameter that is only unset.
1531 inherits the type of quoting
1532 (unquoted, double-quoted or here-document)
1533 from the surroundings,
1534 with the exception that a backslash that quotes a closing brace is removed
1535 during quote removal.
1536 .Bl -tag -width indent
1537 .It Li ${# Ns Ar parameter Ns Li }
1539 The length in characters of
1544 The following four varieties of parameter expansion provide for substring
1546 In each case, pattern matching notation
1548 .Sx Shell Patterns ) ,
1549 rather than regular expression notation,
1550 is used to evaluate the patterns.
1551 If parameter is one of the special parameters
1555 the result of the expansion is unspecified.
1556 Enclosing the full parameter expansion string in double-quotes does not
1557 cause the following four varieties of pattern characters to be quoted,
1558 whereas quoting characters within the braces has this effect.
1559 .Bl -tag -width indent
1560 .It Li ${ Ns Ar parameter Ns Li % Ns Ar word Ns Li }
1561 Remove Smallest Suffix Pattern.
1564 is expanded to produce a pattern.
1566 parameter expansion then results in
1568 with the smallest portion of the
1569 suffix matched by the pattern deleted.
1570 .It Li ${ Ns Ar parameter Ns Li %% Ns Ar word Ns Li }
1571 Remove Largest Suffix Pattern.
1574 is expanded to produce a pattern.
1576 parameter expansion then results in
1578 with the largest portion of the
1579 suffix matched by the pattern deleted.
1580 .It Li ${ Ns Ar parameter Ns Li # Ns Ar word Ns Li }
1581 Remove Smallest Prefix Pattern.
1584 is expanded to produce a pattern.
1586 parameter expansion then results in
1588 with the smallest portion of the
1589 prefix matched by the pattern deleted.
1590 .It Li ${ Ns Ar parameter Ns Li ## Ns Ar word Ns Li }
1591 Remove Largest Prefix Pattern.
1594 is expanded to produce a pattern.
1596 parameter expansion then results in
1598 with the largest portion of the
1599 prefix matched by the pattern deleted.
1601 .Ss Command Substitution
1602 Command substitution allows the output of a command to be substituted in
1603 place of the command name itself.
1604 Command substitution occurs when
1605 the command is enclosed as follows:
1607 .D1 Li $( Ns Ar command Ns Li )\&
1609 or the backquoted version:
1611 .D1 Li ` Ns Ar command Ns Li `
1613 The shell expands the command substitution by executing command
1614 and replacing the command substitution
1615 with the standard output of the command,
1616 removing sequences of one or more newlines at the end of the substitution.
1617 Embedded newlines before the end of the output are not removed;
1618 however, during field splitting, they may be translated into spaces
1619 depending on the value of
1621 and the quoting that is in effect.
1622 The command is executed in a subshell environment,
1623 except that the built-in commands
1628 return information about the parent shell environment
1631 returns information about the same process
1632 if they are the only command in a command substitution.
1634 If a command substitution of the
1636 form begins with a subshell,
1641 must be separated by whitespace
1642 to avoid ambiguity with arithmetic expansion.
1643 .Ss Arithmetic Expansion
1644 Arithmetic expansion provides a mechanism for evaluating an arithmetic
1645 expression and substituting its value.
1646 The format for arithmetic expansion is as follows:
1648 .D1 Li $(( Ns Ar expression Ns Li ))
1652 is treated as if it were in double-quotes, except
1653 that a double-quote inside the expression is not treated specially.
1655 shell expands all tokens in the
1657 for parameter expansion,
1658 command substitution,
1659 arithmetic expansion
1662 The allowed expressions are a subset of C expressions,
1664 .Bl -tag -width "Variables" -offset indent
1666 All values are of type
1669 Decimal, octal (starting with
1671 and hexadecimal (starting with
1675 Shell variables can be read and written
1676 and contain integer constants.
1679 .It Binary operators
1680 .Li "* / % + - << >> < <= > >= == != & ^ | && ||"
1681 .It Assignment operators
1682 .Li "= += -= *= /= %= <<= >>= &= ^= |="
1683 .It Conditional operator
1687 The result of the expression is substituted in decimal.
1688 .Ss White Space Splitting (Field Splitting)
1689 In certain contexts,
1690 after parameter expansion, command substitution, and
1691 arithmetic expansion the shell scans the results of
1692 expansions and substitutions that did not occur in double-quotes for
1693 field splitting and multiple fields can result.
1704 are treated differently from other characters in
1709 at the beginning or end of a word is discarded.
1711 Subsequently, a field is delimited by either
1714 a non-whitespace character in
1716 with any whitespace in
1720 one or more whitespace characters in
1724 If a word ends with a non-whitespace character in
1726 there is no empty field after this character.
1728 If no field is delimited, the word is discarded.
1729 In particular, if a word consists solely of an unquoted substitution
1730 and the result of the substitution is null,
1731 it is removed by field splitting even if
1734 .Ss Pathname Expansion (File Name Generation)
1738 file name generation is performed
1739 after word splitting is complete.
1741 viewed as a series of patterns, separated by slashes.
1743 process of expansion replaces the word with the names of
1744 all existing files whose names can be formed by replacing
1745 each pattern with a string that matches the specified pattern.
1746 There are two restrictions on this: first, a pattern cannot match
1747 a string containing a slash, and second,
1748 a pattern cannot match a string starting with a period
1749 unless the first character of the pattern is a period.
1750 The next section describes the patterns used for
1752 the four varieties of parameter expansion for substring processing and the
1756 A pattern consists of normal characters, which match themselves,
1757 and meta-characters.
1758 The meta-characters are
1763 These characters lose their special meanings if they are quoted.
1764 When command or variable substitution is performed and the dollar sign
1765 or back quotes are not double-quoted, the value of the
1766 variable or the output of the command is scanned for these
1767 characters and they are turned into meta-characters.
1771 matches any string of characters.
1774 matches any single character.
1777 introduces a character class.
1778 The end of the character class is indicated by a
1786 rather than introducing a character class.
1787 A character class matches any of the characters between the square brackets.
1788 A locale-dependent range of characters may be specified using a minus sign.
1789 A named class of characters (see
1791 may be specified by surrounding the name with
1796 .Ql \&[\&[:alpha:\&]\&]
1797 is a shell pattern that matches a single letter.
1798 The character class may be complemented by making an exclamation point
1800 the first character of the character class.
1803 has the same effect but is non-standard.
1807 in a character class, make it the first character listed
1815 make it the first or last character listed.
1816 .Ss Built-in Commands
1817 This section lists the built-in commands.
1818 .Bl -tag -width indent
1820 A null command that returns a 0 (true) exit value.
1822 The commands in the specified file are read and executed by the shell.
1825 command may be used to return to the
1832 characters, it is used as is.
1833 Otherwise, the shell searches the
1836 If it is not found in the
1838 it is sought in the current working directory.
1840 A built-in equivalent of
1842 .It Ic alias Oo Ar name Ns Oo = Ns Ar string Oc ... Oc
1844 .Ar name Ns = Ns Ar string
1845 is specified, the shell defines the alias
1851 is specified, the value of the alias
1854 With no arguments, the
1856 built-in command prints the names and values of all defined aliases
1859 Alias values are written with appropriate quoting so that they are
1860 suitable for re-input to the shell.
1864 .It Ic bg Op Ar job ...
1865 Continue the specified jobs
1866 (or the current job if no jobs are given)
1868 .It Ic bind Oo Fl aeklrsv Oc Oo Ar key Oo Ar command Oc Oc
1869 List or alter key bindings for the line editor.
1870 This command is documented in
1872 .It Ic break Op Ar num
1874 .Sx Flow-Control Constructs
1876 .It Ic builtin Ar cmd Op Ar arg ...
1877 Execute the specified built-in command,
1879 This is useful when the user wishes to override a shell function
1880 with the same name as a built-in command.
1881 .It Ic cd Oo Fl L | P Oc Oo Fl e Oc Op Ar directory
1882 Switch to the specified
1884 or to the directory specified in the
1886 environment variable if no
1895 then the directories listed in the
1898 searched for the specified
1902 is unset, the current directory is searched.
1905 is the same as that of
1907 In an interactive shell,
1910 command will print out the name of the directory
1911 that it actually switched to
1912 if this is different from the name that the user gave.
1913 These may be different either because the
1915 mechanism was used or because a symbolic link was crossed.
1919 option is specified,
1921 is handled physically and symbolic links are resolved before
1923 components are processed.
1926 option is specified,
1928 is handled logically.
1929 This is the default.
1935 to return exit status 1 if the full pathname of the new directory
1936 cannot be determined reliably or at all.
1937 Normally this is not considered an error,
1938 although a warning is printed.
1943 .It Ic command Oo Fl p Oc Op Ar utility Op Ar argument ...
1944 .It Ic command Oo Fl p Oc Fl v Ar utility
1945 .It Ic command Oo Fl p Oc Fl V Ar utility
1946 The first form of invocation executes the specified
1948 ignoring shell functions in the search.
1951 is a special builtin,
1952 it is executed as if it were a regular builtin.
1956 option is specified, the command search is performed using a
1959 that is guaranteed to find all of the standard utilities.
1963 option is specified,
1965 is not executed but a description of its interpretation by the shell is
1967 For ordinary commands the output is the path name; for shell built-in
1968 commands, shell functions and keywords only the name is written.
1969 Aliases are printed as
1970 .Dq Ic alias Ar name Ns = Ns Ar value .
1974 option is identical to
1976 except for the output.
1978 .Dq Ar utility Ic is Ar description
1984 a special shell builtin,
1991 .It Ic continue Op Ar num
1993 .Sx Flow-Control Constructs
1995 .It Ic echo Oo Fl e | n Oc Op Ar string ...
1996 Print a space-separated list of the arguments to the standard output
1997 and append a newline character.
1998 .Bl -tag -width indent
2000 Suppress the output of the trailing newline.
2002 Process C-style backslash escape sequences.
2005 command understands the following character escapes:
2006 .Bl -tag -width indent
2008 Alert (ring the terminal bell)
2012 Suppress the trailing newline (this has the side-effect of truncating the
2013 line if it is not the last character)
2031 (Zero) The character whose octal value is
2037 is not enclosed in quotes then the backslash itself must be escaped
2038 with a backslash to protect it from the shell.
2040 .Bd -literal -offset indent
2049 $ echo -e a\e\e\e\eb
2058 options may be specified.
2059 .It Ic eval Ar string ...
2060 Concatenate all the arguments with spaces.
2061 Then re-parse and execute the command.
2062 .It Ic exec Op Ar command Op arg ...
2066 the shell process is replaced with the specified program
2067 (which must be a real program, not a shell built-in command or function).
2068 Any redirections on the
2070 command are marked as permanent,
2071 so that they are not undone when the
2074 .It Ic exit Op Ar exitstatus
2075 Terminate the shell process.
2079 it is used as the exit status of the shell.
2080 Otherwise, if the shell is executing an
2082 trap, the exit status of the last command before the trap is used;
2083 if the shell is executing a trap for a signal,
2084 the shell exits by resending the signal to itself.
2085 Otherwise, the exit status of the preceding command is used.
2086 The exit status should be an integer between 0 and 255.
2087 .It Ic export Ar name ...
2088 .It Ic export Op Fl p
2089 The specified names are exported so that they will
2090 appear in the environment of subsequent commands.
2091 The only way to un-export a variable is to
2094 The shell allows the value of a variable to be set
2095 at the same time as it is exported by writing
2097 .D1 Ic export Ar name Ns = Ns Ar value
2099 With no arguments the
2101 command lists the names
2102 of all exported variables.
2105 option is specified, the exported variables are printed as
2106 .Dq Ic export Ar name Ns = Ns Ar value
2107 lines, suitable for re-input to the shell.
2109 A null command that returns a non-zero (false) exit value.
2110 .It Ic fc Oo Fl e Ar editor Oc Op Ar first Op Ar last
2111 .It Ic fc Fl l Oo Fl nr Oc Op Ar first Op Ar last
2112 .It Ic fc Fl s Oo Ar old Ns = Ns Ar new Oc Op Ar first
2115 built-in command lists, or edits and re-executes,
2116 commands previously entered to an interactive shell.
2117 .Bl -tag -width indent
2119 Use the editor named by
2121 to edit the commands.
2124 string is a command name,
2125 subject to search via the
2130 variable is used as a default when
2135 is null or unset, the value of the
2142 is used as the editor.
2144 List the commands rather than invoking
2146 The commands are written in the
2147 sequence indicated by the
2151 operands, as affected by
2153 with each command preceded by the command number.
2155 Suppress command numbers when listing with
2158 Reverse the order of the commands listed
2167 Re-execute the command without invoking an editor.
2170 Select the commands to list or edit.
2171 The number of previous commands that can be accessed
2172 are determined by the value of the
2179 or both are one of the following:
2180 .Bl -tag -width indent
2181 .It Oo Cm + Oc Ns Ar num
2182 A positive number representing a command number;
2183 command numbers can be displayed with the
2187 A negative decimal number representing the
2188 command that was executed
2191 commands previously.
2192 For example, \-1 is the immediately previous command.
2194 A string indicating the most recently entered command
2195 that begins with that string.
2197 .Ar old Ns = Ns Ar new
2198 operand is not also specified with
2200 the string form of the first operand cannot contain an embedded equal sign.
2204 The following variables affect the execution of
2206 .Bl -tag -width ".Va HISTSIZE"
2208 Name of the editor to use for history editing.
2210 The number of previous commands that are accessible.
2215 or the current job to the foreground.
2216 .It Ic getopts Ar optstring var
2223 command deprecates the older
2226 The first argument should be a series of letters, each possibly
2227 followed by a colon which indicates that the option takes an argument.
2228 The specified variable is set to the parsed option.
2230 the next argument is placed into the shell variable
2232 If an option takes an argument, it is placed into the shell variable
2234 If an invalid option is encountered,
2238 It returns a false value (1) when it encounters the end of the options.
2239 .It Ic hash Oo Fl rv Oc Op Ar command ...
2240 The shell maintains a hash table which remembers the locations of commands.
2241 With no arguments whatsoever, the
2243 command prints out the contents of this table.
2244 Entries which have not been looked at since the last
2246 command are marked with an asterisk;
2247 it is possible for these entries to be invalid.
2251 command removes each specified
2253 from the hash table (unless they are functions) and then locates it.
2258 prints the locations of the commands as it finds them.
2263 command to delete all the entries in the hash table except for functions.
2264 .It Ic jobid Op Ar job
2265 Print the process IDs of the processes in the specified
2269 argument is omitted, use the current job.
2270 .It Ic jobs Oo Fl lps Oc Op Ar job ...
2271 Print information about the specified jobs, or all jobs if no
2274 The information printed includes job ID, status and command name.
2278 option is specified, the PID of each job is also printed.
2281 option is specified, only the process IDs for the process group leaders
2282 are printed, one per line.
2285 option is specified, only the PIDs of the job commands are printed, one per
2288 A built-in equivalent of
2290 that additionally supports sending signals to jobs.
2291 .It Ic local Oo Ar variable ... Oc Op Fl
2296 A built-in equivalent of
2298 .It Ic pwd Op Fl L | P
2299 Print the path of the current directory.
2300 The built-in command may
2301 differ from the program of the same name because the
2302 built-in command remembers what the current directory
2303 is rather than recomputing it each time.
2306 However, if the current directory is
2308 the built-in version of
2310 will continue to print the old name for the directory.
2314 option is specified, symbolic links are resolved.
2317 option is specified, the shell's notion of the current directory
2318 is printed (symbolic links are not resolved).
2319 This is the default.
2320 .It Ic read Oo Fl p Ar prompt Oc Oo
2321 .Fl t Ar timeout Oc Oo Fl er Oc Ar variable ...
2327 and the standard input is a terminal.
2329 read from the standard input.
2330 The trailing newline
2331 is deleted from the line and the line is split as
2332 described in the section on
2333 .Sx White Space Splitting (Field Splitting)
2335 the pieces are assigned to the variables in order.
2336 If there are more pieces than variables, the remaining
2337 pieces (along with the characters in
2339 that separated them)
2340 are assigned to the last variable.
2341 If there are more variables than pieces, the remaining
2342 variables are assigned the null string.
2344 Backslashes are treated specially, unless the
2348 If a backslash is followed by
2349 a newline, the backslash and the newline will be
2351 If a backslash is followed by any other
2352 character, the backslash will be deleted and the following
2353 character will be treated as though it were not in
2359 option is specified and the
2361 elapses before a complete line of input is supplied,
2364 command will return an exit status of 1 without assigning any values.
2367 value may optionally be followed by one of
2372 to explicitly specify seconds, minutes or hours.
2373 If none is supplied,
2379 option exists only for backward compatibility with older scripts.
2380 .It Ic readonly Oo Fl p Oc Op Ar name ...
2383 is marked as read only,
2384 so that it cannot be subsequently modified or unset.
2385 The shell allows the value of a variable to be set
2386 at the same time as it is marked read only
2387 by using the following form:
2389 .D1 Ic readonly Ar name Ns = Ns Ar value
2391 With no arguments the
2393 command lists the names of all read only variables.
2396 option is specified, the read-only variables are printed as
2397 .Dq Ic readonly Ar name Ns = Ns Ar value
2398 lines, suitable for re-input to the shell.
2399 .It Ic return Op Ar exitstatus
2403 .It Ic set Oo Fl /+abCEefIimnpTuVvx Oc Oo Fl /+o Ar longname Oc Oo
2404 .Fl c Ar string Oc Op Fl - Ar arg ...
2407 command performs three different functions:
2410 With no arguments, it lists the values of all shell variables.
2412 If options are given,
2413 either in short form or using the long
2414 .Dq Fl /+o Ar longname
2416 it sets or clears the specified options as described in the section called
2417 .Sx Argument List Processing .
2421 option is specified,
2423 will replace the shell's positional parameters with the subsequent
2425 If no arguments follow the
2428 all the positional parameters will be cleared,
2429 which is equivalent to executing the command
2433 flag may be omitted when specifying arguments to be used
2434 as positional replacement parameters.
2435 This is not recommended,
2436 because the first argument may begin with a dash
2442 command will interpret as a request to enable or disable options.
2444 .It Ic setvar Ar variable value
2445 Assigns the specified
2451 command is intended to be used in functions that
2452 assign values to variables whose names are passed as parameters.
2453 In general it is better to write
2454 .Dq Ar variable Ns = Ns Ar value
2457 .It Ic shift Op Ar n
2458 Shift the positional parameters
2463 A shift sets the value of
2472 decreasing the value of
2475 If there are zero positional parameters, shifting does not do anything.
2477 A built-in equivalent of
2480 Print the amount of time spent executing the shell process and its children.
2481 The first output line shows the user and system times for the shell process
2482 itself, the second one contains the user and system times for the
2484 .It Ic trap Oo Ar action Oc Ar signal ...
2486 Cause the shell to parse and execute
2491 The signals are specified by name or number.
2492 In addition, the pseudo-signal
2494 may be used to specify an
2496 that is performed when the shell terminates.
2499 may be an empty string or a dash
2501 the former causes the specified signal to be ignored
2502 and the latter causes the default action to be taken.
2505 is another way to request the default action, for compatibility reasons this
2506 usage is not recommended though.
2507 In a subshell or utility environment,
2508 the shell resets trapped (but not ignored) signals to the default action.
2511 command has no effect on signals that were ignored on entry to the shell.
2517 command to display a list of valid signal names.
2519 A null command that returns a 0 (true) exit value.
2520 .It Ic type Op Ar name ...
2523 as a command and print the resolution of the command search.
2524 Possible resolutions are:
2525 shell keyword, alias, special shell builtin, shell builtin, command,
2528 For aliases the alias expansion is printed;
2529 for commands and tracked aliases
2530 the complete pathname of the command is printed.
2531 .It Ic ulimit Oo Fl HSabcdflmnpstuvw Oc Op Ar limit
2532 Set or display resource limits (see
2536 is specified, the named resource will be set;
2537 otherwise the current resource value will be displayed.
2541 is specified, the hard limits will be set or displayed.
2542 While everybody is allowed to reduce a hard limit,
2543 only the superuser can increase it.
2547 specifies the soft limits instead.
2548 When displaying limits,
2554 The default is to display the soft limits,
2555 and to set both the hard and the soft limits.
2561 command to display all resources.
2564 is not acceptable in this mode.
2566 The remaining options specify which resource value is to be
2567 displayed or modified.
2568 They are mutually exclusive.
2569 .Bl -tag -width indent
2571 The maximum size of socket buffer usage, in bytes.
2572 .It Fl c Ar coredumpsize
2573 The maximal size of core dump files, in 512-byte blocks.
2574 .It Fl d Ar datasize
2575 The maximal size of the data segment of a process, in kilobytes.
2576 .It Fl f Ar filesize
2577 The maximal size of a file, in 512-byte blocks.
2578 .It Fl l Ar lockedmem
2579 The maximal size of memory that can be locked by a process, in
2581 .It Fl m Ar memoryuse
2582 The maximal resident set size of a process, in kilobytes.
2584 The maximal number of descriptors that could be opened by a process.
2585 .It Fl p Ar pseudoterminals
2586 The maximal number of pseudo-terminals for this user ID.
2587 .It Fl s Ar stacksize
2588 The maximal size of the stack segment, in kilobytes.
2590 The maximal amount of CPU time to be used by each process, in seconds.
2591 .It Fl u Ar userproc
2592 The maximal number of simultaneous processes for this user ID.
2593 .It Fl v Ar virtualmem
2594 The maximal virtual size of a process, in kilobytes.
2596 The maximum amount of swap space reserved or used for this user ID,
2599 .It Ic umask Oo Fl S Oc Op Ar mask
2600 Set the file creation mask (see
2602 to the octal or symbolic (see
2606 If the argument is omitted, the current mask value is printed.
2609 option is specified, the output is symbolic, otherwise the output is octal.
2610 .It Ic unalias Oo Fl a Oc Op Ar name ...
2611 The specified alias names are removed.
2614 is specified, all aliases are removed.
2615 .It Ic unset Oo Fl fv Oc Ar name ...
2616 The specified variables or functions are unset and unexported.
2619 option is specified or no options are given, the
2621 arguments are treated as variable names.
2624 option is specified, the
2626 arguments are treated as function names.
2627 .It Ic wait Op Ar job
2628 Wait for the specified
2630 to complete and return the exit status of the last process in the
2632 If the argument is omitted, wait for all jobs to complete
2633 and return an exit status of zero.
2635 .Ss Commandline Editing
2638 is being used interactively from a terminal, the current command
2639 and the command history
2643 .Sx Built-in Commands )
2646 command line editing.
2647 This mode uses commands similar
2648 to a subset of those described in the
2666 can be switched between insert mode and command mode by typing
2670 while in command mode will pass the line to the shell.
2673 .Dq Li "set -o emacs"
2676 command can be used to enable a subset of
2678 command line editing features.
2680 The following environment variables affect the execution of
2682 .Bl -tag -width ".Ev LANGXXXXXX"
2684 Initialization file for interactive shells.
2685 .It Ev LANG , Ev LC_*
2687 These are inherited by children of the shell,
2688 and is used in a limited manner by the shell itself.
2690 An absolute pathname for the current directory,
2691 possibly containing symbolic links.
2692 This is used and updated by the shell.
2694 The default terminal setting for the shell.
2695 This is inherited by children of the shell, and is used in the history
2699 Additionally, all environment variables are turned into shell variables
2701 which may affect the shell as described under
2702 .Sx Special Variables .
2704 Errors that are detected by the shell, such as a syntax error, will
2705 cause the shell to exit with a non-zero exit status.
2706 If the shell is not an interactive shell, the execution of the shell
2707 file will be aborted.
2708 Otherwise the shell will return the exit status of the last command
2711 builtin is used with a numeric argument, it
2712 will return the argument.
2732 command, the Thompson shell, appeared in
2734 It was superseded in
2736 by the Bourne shell, which inherited the name
2741 was rewritten in 1989 under the
2743 license after the Bourne shell from
2748 was originally written by
2749 .An Kenneth Almquist .
2753 utility does not recognize multibyte characters other than UTF-8.
2756 and the line editing library
2758 do not recognize multibyte characters.
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