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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 (they do not affect expansions).
574 Redirection operators and
575 their arguments (as described below) are stripped
576 off and saved for processing.
578 The remaining words are expanded as described in
580 .Sx Word Expansions ,
581 and the first remaining word is considered the command
582 name and the command is located.
584 words are considered the arguments of the command.
585 If no command name resulted, then the
587 variable assignments recognized in 1) affect the
590 Redirections are performed as described in
594 Redirections are used to change where a command reads its input
596 In general, redirections open, close, or
597 duplicate an existing reference to a file.
599 used for redirection is:
601 .D1 Oo Ar n Oc Ar redir-op file
605 is one of the redirection operators mentioned
607 The following gives some examples of how these
608 operators can be used.
609 Note that stdin and stdout are commonly used abbreviations
610 for standard input and standard output respectively.
611 .Bl -tag -width "1234567890XX" -offset indent
612 .It Oo Ar n Oc Ns Li > Ar file
613 redirect stdout (or file descriptor
617 .It Oo Ar n Oc Ns Li >| Ar file
618 same as above, but override the
621 .It Oo Ar n Oc Ns Li >> Ar file
622 append stdout (or file descriptor
626 .It Oo Ar n Oc Ns Li < Ar file
627 redirect stdin (or file descriptor
631 .It Oo Ar n Oc Ns Li <> Ar file
632 redirect stdin (or file descriptor
636 .It Oo Ar n1 Oc Ns Li <& Ns Ar n2
637 duplicate stdin (or file descriptor
641 .It Oo Ar n Oc Ns Li <&-
642 close stdin (or file descriptor
644 .It Oo Ar n1 Oc Ns Li >& Ns Ar n2
645 duplicate stdout (or file descriptor
649 .It Oo Ar n Oc Ns Li >&-
650 close stdout (or file descriptor
654 The following redirection is often called a
656 .Bd -unfilled -offset indent
657 .Oo Ar n Oc Ns Li << Ar delimiter
663 All the text on successive lines up to the delimiter is
664 saved away and made available to the command on standard
665 input, or file descriptor
670 as specified on the initial line is quoted, then the
672 is treated literally, otherwise the text is subjected to
673 parameter expansion, command substitution, and arithmetic
674 expansion (as described in the section on
675 .Sx Word Expansions ) .
684 .Ss Search and Execution
685 There are three types of commands: shell functions,
686 built-in commands, and normal programs.
687 The command is searched for (by name) in that order.
688 The three types of commands are all executed in a different way.
690 When a shell function is executed, all of the shell positional
693 which remains unchanged) are
694 set to the arguments of the shell function.
695 The variables which are explicitly placed in the environment of
696 the command (by placing assignments to them before the
697 function name) are made local to the function and are set
699 Then the command given in the function definition is executed.
700 The positional parameters are restored to their original values
701 when the command completes.
702 This all occurs within the current shell.
704 Shell built-in commands are executed internally to the shell, without
705 spawning a new process.
706 There are two kinds of built-in commands: regular and special.
707 Assignments before special builtins persist after they finish
708 executing and assignment errors, redirection errors and certain
709 operand errors cause a script to be aborted.
710 Special builtins cannot be overridden with a function.
711 Both regular and special builtins can affect the shell in ways
712 normal programs cannot.
714 Otherwise, if the command name does not match a function
715 or built-in command, the command is searched for as a normal
716 program in the file system (as described in the next section).
717 When a normal program is executed, the shell runs the program,
718 passing the arguments and the environment to the program.
719 If the program is not a normal executable file
720 (i.e., if it does not begin with the
730 but appears to be a text file,
731 the shell will run a new instance of
735 Note that previous versions of this document
736 and the source code itself misleadingly and sporadically
737 refer to a shell script without a magic number
739 .Dq "shell procedure" .
741 When locating a command, the shell first looks to see if
742 it has a shell function by that name.
744 built-in command by that name.
745 If a built-in command is not found,
746 one of two things happen:
749 Command names containing a slash are simply executed without
750 performing any searches.
752 The shell searches each entry in the
755 in turn for the command.
758 variable should be a series of
759 entries separated by colons.
760 Each entry consists of a
762 The current directory
763 may be indicated implicitly by an empty directory name,
764 or explicitly by a single period.
766 .Ss Command Exit Status
767 Each command has an exit status that can influence the behavior
768 of other shell commands.
769 The paradigm is that a command exits
770 with zero for normal or success, and non-zero for failure,
771 error, or a false indication.
772 The man page for each command
773 should indicate the various exit codes and what they mean.
774 Additionally, the built-in commands return exit codes, as does
775 an executed shell function.
777 If a command is terminated by a signal, its exit status is 128 plus
779 Signal numbers are defined in the header file
782 Complex commands are combinations of simple commands
783 with control operators or keywords, together creating a larger complex
785 More generally, a command is one of the following:
786 .Bl -item -offset indent
792 list or compound-list
799 Unless otherwise stated, the exit status of a command is
800 that of the last simple command executed by the command.
802 A pipeline is a sequence of one or more commands separated
803 by the control operator
805 The standard output of all but
806 the last command is connected to the standard input
808 The standard output of the last
809 command is inherited from the shell, as usual.
811 The format for a pipeline is:
813 .D1 Oo Li \&! Oc Ar command1 Op Li \&| Ar command2 ...
815 The standard output of
817 is connected to the standard input of
819 The standard input, standard output, or
820 both of a command is considered to be assigned by the
821 pipeline before any redirection specified by redirection
822 operators that are part of the command.
824 Note that unlike some other shells,
826 executes each process in a pipeline with more than one command
827 in a subshell environment and as a child of the
831 If the pipeline is not in the background (discussed later),
832 the shell waits for all commands to complete.
836 does not precede the pipeline, the
837 exit status is the exit status of the last command specified
839 Otherwise, the exit status is the logical
840 NOT of the exit status of the last command.
842 the last command returns zero, the exit status is 1; if
843 the last command returns greater than zero, the exit status
846 Because pipeline assignment of standard input or standard
847 output or both takes place before redirection, it can be
848 modified by redirection.
851 .Dl "command1 2>&1 | command2"
853 sends both the standard output and standard error of
855 to the standard input of
860 or newline terminator causes the preceding
862 (described below in the section called
863 .Sx Short-Circuit List Operators )
864 to be executed sequentially;
867 causes asynchronous execution of the preceding AND-OR-list.
868 .Ss Background Commands (&)
869 If a command is terminated by the control operator ampersand
871 the shell executes the command in a subshell environment (see
872 .Sx Grouping Commands Together
873 below) and asynchronously;
874 the shell does not wait for the command to finish
875 before executing the next command.
877 The format for running a command in background is:
879 .D1 Ar command1 Li & Op Ar command2 Li & Ar ...
881 If the shell is not interactive, the standard input of an
882 asynchronous command is set to
884 .Ss Lists (Generally Speaking)
885 A list is a sequence of zero or more commands separated by
886 newlines, semicolons, or ampersands,
887 and optionally terminated by one of these three characters.
889 list are executed in the order they are written.
890 If command is followed by an ampersand, the shell starts the
891 command and immediately proceeds onto the next command;
892 otherwise it waits for the command to terminate before
893 proceeding to the next one.
894 .Ss Short-Circuit List Operators
898 are AND-OR list operators.
900 executes the first command, and then executes the second command
901 if the exit status of the first command is zero.
903 is similar, but executes the second command if the exit
904 status of the first command is nonzero.
908 both have the same priority.
909 .Ss Flow-Control Constructs (if, while, for, case)
913 .Bd -unfilled -offset indent -compact
917 .Ic then Ar list Oc Ar ...
925 .Bd -unfilled -offset indent -compact
931 The two lists are executed repeatedly while the exit status of the
935 command is similar, but has the word
940 repeat until the exit status of the first list is zero.
945 .Bd -unfilled -offset indent -compact
946 .Ic for Ar variable Op Ic in Ar word ...
953 and the following words are omitted,
956 The words are expanded, and then the list is executed
957 repeatedly with the variable set to each word in turn.
962 commands may be replaced with
972 .D1 Ic break Op Ar num
973 .D1 Ic continue Op Ar num
977 command terminates the
986 command continues with the next iteration of the innermost loop.
987 These are implemented as special built-in commands.
992 .Bd -unfilled -offset indent -compact
993 .Ic case Ar word Ic in
994 .Ar pattern Ns Li ) Ar list Li ;;
999 The pattern can actually be one or more patterns
1006 Tilde expansion, parameter expansion, command substitution,
1007 arithmetic expansion and quote removal are applied to the word.
1008 Then, each pattern is expanded in turn using tilde expansion,
1009 parameter expansion, command substitution and arithmetic expansion and
1010 the expanded form of the word is checked against it.
1011 If a match is found, the corresponding list is executed.
1012 If the selected list is terminated by the control operator
1016 execution continues with the next list,
1017 continuing until a list terminated with
1022 The exit code of the
1024 command is the exit code of the last command executed in the list or
1025 zero if no patterns were matched.
1026 .Ss Grouping Commands Together
1027 Commands may be grouped by writing either
1029 .D1 Li \&( Ns Ar list Ns Li \%)
1033 .D1 Li { Ar list Ns Li \&; }
1035 The first form executes the commands in a subshell environment.
1036 A subshell environment has its own copy of:
1040 The current working directory as set by
1043 The file creation mask as set by
1046 Resource limits as set by
1049 References to open files.
1056 Positional parameters and variables.
1065 These are copied from the parent shell environment,
1066 except that trapped (but not ignored) signals are reset to the default action
1067 and known jobs are cleared.
1068 Any changes do not affect the parent shell environment.
1070 A subshell environment may be implemented as a child process or differently.
1071 If job control is enabled in an interactive shell,
1072 commands grouped in parentheses can be suspended and continued as a unit.
1074 For compatibility with other shells,
1075 two open parentheses in sequence should be separated by whitespace.
1077 The second form never forks another shell,
1078 so it is slightly more efficient.
1079 Grouping commands together this way allows the user to
1080 redirect their output as though they were one program:
1081 .Bd -literal -offset indent
1082 { echo -n "hello"; echo " world"; } > greeting
1085 The syntax of a function definition is
1087 .D1 Ar name Li \&( \&) Ar command
1089 A function definition is an executable statement; when
1090 executed it installs a function named
1093 exit status of zero.
1102 Variables may be declared to be local to a function by
1106 This should appear as the first statement of a function,
1109 .D1 Ic local Oo Ar variable ... Oc Op Fl
1113 command is implemented as a built-in command.
1115 When a variable is made local, it inherits the initial
1116 value and exported and readonly flags from the variable
1117 with the same name in the surrounding scope, if there is
1119 Otherwise, the variable is initially unset.
1121 uses dynamic scoping, so that if the variable
1123 is made local to function
1125 which then calls function
1127 references to the variable
1131 will refer to the variable
1135 not to the global variable named
1138 The only special parameter that can be made local is
1142 local causes any shell options that are
1145 command inside the function to be
1146 restored to their original values when the function
1153 .D1 Ic return Op Ar exitstatus
1155 It terminates the current executional scope, returning from the previous
1156 nested function, sourced script, or shell instance, in that order.
1159 command is implemented as a special built-in command.
1160 .Ss Variables and Parameters
1161 The shell maintains a set of parameters.
1163 denoted by a name is called a variable.
1165 the shell turns all the environment variables into shell
1167 New variables can be set using the form
1169 .D1 Ar name Ns = Ns Ar value
1171 Variables set by the user must have a name consisting solely
1172 of alphabetics, numerics, and underscores.
1173 The first letter of a variable name must not be numeric.
1174 A parameter can also be denoted by a number
1175 or a special character as explained below.
1177 Assignments are expanded differently from other words:
1178 tilde expansion is also performed after the equals sign and after any colon
1179 and usernames are also terminated by colons,
1180 and field splitting and pathname expansion are not performed.
1182 This special expansion applies not only to assignments that form a simple
1183 command by themselves or precede a command word,
1184 but also to words passed to the
1189 built-in commands that have this form.
1190 For this, the builtin's name must be literal
1191 (not the result of an expansion)
1192 and may optionally be preceded by one or more literal instances of
1195 .Ss Positional Parameters
1196 A positional parameter is a parameter denoted by a number greater than zero.
1197 The shell sets these initially to the values of its command line
1198 arguments that follow the name of the shell script.
1201 built-in command can also be used to set or reset them.
1202 .Ss Special Parameters
1203 Special parameters are parameters denoted by a single special character
1205 They are shown in the following list, exactly as they would appear in input
1206 typed by the user or in the source of a shell script.
1209 Expands to the positional parameters, starting from one.
1211 the expansion occurs within a double-quoted string
1212 it expands to a single field with the value of each parameter
1213 separated by the first character of the
1220 Expands to the positional parameters, starting from one.
1222 the expansion occurs within double-quotes, each positional
1223 parameter expands as a separate argument.
1224 If there are no positional parameters, the
1227 generates zero arguments, even when
1230 What this basically means, for example, is
1243 .Bd -literal -offset indent
1247 Expands to the number of positional parameters.
1249 Expands to the exit status of the most recent pipeline.
1251 (hyphen) Expands to the current option flags (the single-letter
1252 option names concatenated into a string) as specified on
1255 built-in command, or implicitly
1258 Expands to the process ID of the invoked shell.
1260 retains the same value of
1264 Expands to the process ID of the most recent background
1265 command executed from the current shell.
1267 pipeline, the process ID is that of the last command in the
1269 If this parameter is referenced, the shell will remember
1270 the process ID and its exit status until the
1272 built-in command reports completion of the process.
1274 (zero) Expands to the name of the shell script if passed on the command line,
1277 operand if given (with
1279 or otherwise argument 0 passed to the shell.
1281 .Ss Special Variables
1282 The following variables are set by the shell or
1283 have special meaning to it:
1284 .Bl -tag -width ".Va HISTSIZE"
1286 The search path used with the
1290 The fallback editor used with the
1293 If not set, the default editor is
1296 The default editor used with the
1300 The number of previous commands that are accessible.
1302 The user's home directory,
1303 used in tilde expansion and as a default directory for the
1307 Input Field Separators.
1308 The default value is
1314 This default also applies if
1316 is unset, but not if it is set to the empty string.
1318 .Sx White Space Splitting
1319 section for more details.
1321 The current line number in the script or function.
1323 The name of a mail file, that will be checked for the arrival of new
1330 separated list of file names, for the shell to check for incoming
1332 This variable overrides the
1335 There is a maximum of 10 mailboxes that can be monitored at once.
1337 The default search path for executables.
1340 section for details.
1342 The parent process ID of the invoked shell.
1343 This is set at startup
1344 unless this variable is in the environment.
1345 A later change of parent process ID is not reflected.
1346 A subshell retains the same value of
1349 The primary prompt string, which defaults to
1351 unless you are the superuser, in which case it defaults to
1354 The secondary prompt string, which defaults to
1357 The prefix for the trace output (if
1364 This clause describes the various expansions that are
1366 Not all expansions are performed on
1367 every word, as explained later.
1369 Tilde expansions, parameter expansions, command substitutions,
1370 arithmetic expansions, and quote removals that occur within
1371 a single word expand to a single field.
1373 splitting or pathname expansion that can create multiple
1374 fields from a single word.
1375 The single exception to this rule is
1376 the expansion of the special parameter
1378 within double-quotes,
1379 as was described above.
1381 The order of word expansion is:
1384 Tilde Expansion, Parameter Expansion, Command Substitution,
1385 Arithmetic Expansion (these all occur at the same time).
1387 Field Splitting is performed on fields generated by step (1)
1392 Pathname Expansion (unless the
1394 option is in effect).
1401 character is used to introduce parameter expansion, command
1402 substitution, or arithmetic expansion.
1403 .Ss Tilde Expansion (substituting a user's home directory)
1404 A word beginning with an unquoted tilde character
1407 subjected to tilde expansion.
1408 All the characters up to a slash
1410 or the end of the word are treated as a username
1411 and are replaced with the user's home directory.
1413 username is missing (as in
1415 the tilde is replaced with the value of the
1417 variable (the current user's home directory).
1418 .Ss Parameter Expansion
1419 The format for parameter expansion is as follows:
1421 .D1 Li ${ Ns Ar expression Ns Li }
1425 consists of all characters until the matching
1429 escaped by a backslash or within a single-quoted or double-quoted
1430 string, and characters in
1431 embedded arithmetic expansions, command substitutions, and variable
1432 expansions, are not examined in determining the matching
1434 If the variants with
1440 occur within a double-quoted string,
1441 as an extension there may be unquoted parts
1442 (via double-quotes inside the expansion);
1444 within such parts are also not examined in determining the matching
1447 The simplest form for parameter expansion is:
1449 .D1 Li ${ Ns Ar parameter Ns Li }
1451 The value, if any, of
1455 The parameter name or symbol can be enclosed in braces, which are
1456 optional except for positional parameters with more than one digit or
1457 when parameter is followed by a character that could be interpreted as
1459 If a parameter expansion occurs inside double-quotes:
1462 Field splitting is not performed on the results of the
1463 expansion, with the exception of the special parameter
1466 Pathname expansion is not performed on the results of the
1470 In addition, a parameter expansion can be modified by using one of the
1472 .Bl -tag -width indent
1473 .It Li ${ Ns Ar parameter Ns Li :- Ns Ar word Ns Li }
1477 is unset or null, the expansion of
1479 is substituted; otherwise, the value of
1482 .It Li ${ Ns Ar parameter Ns Li := Ns Ar word Ns Li }
1483 Assign Default Values.
1486 is unset or null, the expansion of
1496 does not prevent field splitting or pathname expansion.
1497 Only variables, not positional
1498 parameters or special parameters, can be
1499 assigned in this way.
1500 .It Li ${ Ns Ar parameter Ns Li :? Ns Oo Ar word Oc Ns Li }
1501 Indicate Error if Null or Unset.
1504 is unset or null, the expansion of
1506 (or a message indicating it is unset if
1508 is omitted) is written to standard
1509 error and the shell exits with a nonzero
1511 Otherwise, the value of
1515 interactive shell need not exit.
1516 .It Li ${ Ns Ar parameter Ns Li :+ Ns Ar word Ns Li }
1517 Use Alternate Value.
1520 is unset or null, null is substituted;
1521 otherwise, the expansion of
1526 In the parameter expansions shown previously, use of the colon in the
1527 format results in a test for a parameter that is unset or null; omission
1528 of the colon results in a test for a parameter that is only unset.
1532 inherits the type of quoting
1533 (unquoted, double-quoted or here-document)
1534 from the surroundings,
1535 with the exception that a backslash that quotes a closing brace is removed
1536 during quote removal.
1537 .Bl -tag -width indent
1538 .It Li ${# Ns Ar parameter Ns Li }
1540 The length in characters of
1545 The following four varieties of parameter expansion provide for substring
1547 In each case, pattern matching notation
1549 .Sx Shell Patterns ) ,
1550 rather than regular expression notation,
1551 is used to evaluate the patterns.
1552 If parameter is one of the special parameters
1556 the result of the expansion is unspecified.
1557 Enclosing the full parameter expansion string in double-quotes does not
1558 cause the following four varieties of pattern characters to be quoted,
1559 whereas quoting characters within the braces has this effect.
1560 .Bl -tag -width indent
1561 .It Li ${ Ns Ar parameter Ns Li % Ns Ar word Ns Li }
1562 Remove Smallest Suffix Pattern.
1565 is expanded to produce a pattern.
1567 parameter expansion then results in
1569 with the smallest 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 Largest Suffix Pattern.
1575 is expanded to produce a pattern.
1577 parameter expansion then results in
1579 with the largest portion of the
1580 suffix matched by the pattern deleted.
1581 .It Li ${ Ns Ar parameter Ns Li # Ns Ar word Ns Li }
1582 Remove Smallest Prefix Pattern.
1585 is expanded to produce a pattern.
1587 parameter expansion then results in
1589 with the smallest portion of the
1590 prefix matched by the pattern deleted.
1591 .It Li ${ Ns Ar parameter Ns Li ## Ns Ar word Ns Li }
1592 Remove Largest Prefix Pattern.
1595 is expanded to produce a pattern.
1597 parameter expansion then results in
1599 with the largest portion of the
1600 prefix matched by the pattern deleted.
1602 .Ss Command Substitution
1603 Command substitution allows the output of a command to be substituted in
1604 place of the command name itself.
1605 Command substitution occurs when
1606 the command is enclosed as follows:
1608 .D1 Li $( Ns Ar command Ns Li )\&
1610 or the backquoted version:
1612 .D1 Li ` Ns Ar command Ns Li `
1614 The shell expands the command substitution by executing command
1615 and replacing the command substitution
1616 with the standard output of the command,
1617 removing sequences of one or more newlines at the end of the substitution.
1618 Embedded newlines before the end of the output are not removed;
1619 however, during field splitting, they may be translated into spaces
1620 depending on the value of
1622 and the quoting that is in effect.
1623 The command is executed in a subshell environment,
1624 except that the built-in commands
1629 return information about the parent shell environment
1632 returns information about the same process
1633 if they are the only command in a command substitution.
1635 If a command substitution of the
1637 form begins with a subshell,
1642 must be separated by whitespace
1643 to avoid ambiguity with arithmetic expansion.
1644 .Ss Arithmetic Expansion
1645 Arithmetic expansion provides a mechanism for evaluating an arithmetic
1646 expression and substituting its value.
1647 The format for arithmetic expansion is as follows:
1649 .D1 Li $(( Ns Ar expression Ns Li ))
1653 is treated as if it were in double-quotes, except
1654 that a double-quote inside the expression is not treated specially.
1656 shell expands all tokens in the
1658 for parameter expansion,
1659 command substitution,
1660 arithmetic expansion
1663 The allowed expressions are a subset of C expressions,
1665 .Bl -tag -width "Variables" -offset indent
1667 All values are of type
1670 Decimal, octal (starting with
1672 and hexadecimal (starting with
1676 Shell variables can be read and written
1677 and contain integer constants.
1680 .It Binary operators
1681 .Li "* / % + - << >> < <= > >= == != & ^ | && ||"
1682 .It Assignment operators
1683 .Li "= += -= *= /= %= <<= >>= &= ^= |="
1684 .It Conditional operator
1688 The result of the expression is substituted in decimal.
1689 .Ss White Space Splitting (Field Splitting)
1690 In certain contexts,
1691 after parameter expansion, command substitution, and
1692 arithmetic expansion the shell scans the results of
1693 expansions and substitutions that did not occur in double-quotes for
1694 field splitting and multiple fields can result.
1705 are treated differently from other characters in
1710 at the beginning or end of a word is discarded.
1712 Subsequently, a field is delimited by either
1715 a non-whitespace character in
1717 with any whitespace in
1721 one or more whitespace characters in
1725 If a word ends with a non-whitespace character in
1727 there is no empty field after this character.
1729 If no field is delimited, the word is discarded.
1730 In particular, if a word consists solely of an unquoted substitution
1731 and the result of the substitution is null,
1732 it is removed by field splitting even if
1735 .Ss Pathname Expansion (File Name Generation)
1739 file name generation is performed
1740 after word splitting is complete.
1742 viewed as a series of patterns, separated by slashes.
1744 process of expansion replaces the word with the names of
1745 all existing files whose names can be formed by replacing
1746 each pattern with a string that matches the specified pattern.
1747 There are two restrictions on this: first, a pattern cannot match
1748 a string containing a slash, and second,
1749 a pattern cannot match a string starting with a period
1750 unless the first character of the pattern is a period.
1751 The next section describes the patterns used for
1753 the four varieties of parameter expansion for substring processing and the
1757 A pattern consists of normal characters, which match themselves,
1758 and meta-characters.
1759 The meta-characters are
1764 These characters lose their special meanings if they are quoted.
1765 When command or variable substitution is performed and the dollar sign
1766 or back quotes are not double-quoted, the value of the
1767 variable or the output of the command is scanned for these
1768 characters and they are turned into meta-characters.
1772 matches any string of characters.
1775 matches any single character.
1778 introduces a character class.
1779 The end of the character class is indicated by a
1787 rather than introducing a character class.
1788 A character class matches any of the characters between the square brackets.
1789 A locale-dependent range of characters may be specified using a minus sign.
1790 A named class of characters (see
1792 may be specified by surrounding the name with
1797 .Ql \&[\&[:alpha:\&]\&]
1798 is a shell pattern that matches a single letter.
1799 The character class may be complemented by making an exclamation point
1801 the first character of the character class.
1804 has the same effect but is non-standard.
1808 in a character class, make it the first character listed
1816 make it the first or last character listed.
1817 .Ss Built-in Commands
1818 This section lists the built-in commands.
1819 .Bl -tag -width indent
1821 A null command that returns a 0 (true) exit value.
1823 The commands in the specified file are read and executed by the shell.
1826 command may be used to return to the
1833 characters, it is used as is.
1834 Otherwise, the shell searches the
1837 If it is not found in the
1839 it is sought in the current working directory.
1841 A built-in equivalent of
1843 .It Ic alias Oo Ar name Ns Oo = Ns Ar string Oc ... Oc
1845 .Ar name Ns = Ns Ar string
1846 is specified, the shell defines the alias
1852 is specified, the value of the alias
1855 With no arguments, the
1857 built-in command prints the names and values of all defined aliases
1860 Alias values are written with appropriate quoting so that they are
1861 suitable for re-input to the shell.
1865 .It Ic bg Op Ar job ...
1866 Continue the specified jobs
1867 (or the current job if no jobs are given)
1869 .It Ic bind Oo Fl aeklrsv Oc Oo Ar key Oo Ar command Oc Oc
1870 List or alter key bindings for the line editor.
1871 This command is documented in
1873 .It Ic break Op Ar num
1875 .Sx Flow-Control Constructs
1877 .It Ic builtin Ar cmd Op Ar arg ...
1878 Execute the specified built-in command,
1880 This is useful when the user wishes to override a shell function
1881 with the same name as a built-in command.
1882 .It Ic cd Oo Fl L | P Oc Oo Fl e Oc Op Ar directory
1883 Switch to the specified
1885 or to the directory specified in the
1887 environment variable if no
1896 then the directories listed in the
1899 searched for the specified
1903 is unset, the current directory is searched.
1906 is the same as that of
1908 In an interactive shell,
1911 command will print out the name of the directory
1912 that it actually switched to
1913 if this is different from the name that the user gave.
1914 These may be different either because the
1916 mechanism was used or because a symbolic link was crossed.
1920 option is specified,
1922 is handled physically and symbolic links are resolved before
1924 components are processed.
1927 option is specified,
1929 is handled logically.
1930 This is the default.
1936 to return exit status 1 if the full pathname of the new directory
1937 cannot be determined reliably or at all.
1938 Normally this is not considered an error,
1939 although a warning is printed.
1944 .It Ic command Oo Fl p Oc Op Ar utility Op Ar argument ...
1945 .It Ic command Oo Fl p Oc Fl v Ar utility
1946 .It Ic command Oo Fl p Oc Fl V Ar utility
1947 The first form of invocation executes the specified
1949 ignoring shell functions in the search.
1952 is a special builtin,
1953 it is executed as if it were a regular builtin.
1957 option is specified, the command search is performed using a
1960 that is guaranteed to find all of the standard utilities.
1964 option is specified,
1966 is not executed but a description of its interpretation by the shell is
1968 For ordinary commands the output is the path name; for shell built-in
1969 commands, shell functions and keywords only the name is written.
1970 Aliases are printed as
1971 .Dq Ic alias Ar name Ns = Ns Ar value .
1975 option is identical to
1977 except for the output.
1979 .Dq Ar utility Ic is Ar description
1985 a special shell builtin,
1992 .It Ic continue Op Ar num
1994 .Sx Flow-Control Constructs
1996 .It Ic echo Oo Fl e | n Oc Op Ar string ...
1997 Print a space-separated list of the arguments to the standard output
1998 and append a newline character.
1999 .Bl -tag -width indent
2001 Suppress the output of the trailing newline.
2003 Process C-style backslash escape sequences.
2006 command understands the following character escapes:
2007 .Bl -tag -width indent
2009 Alert (ring the terminal bell)
2013 Suppress the trailing newline (this has the side-effect of truncating the
2014 line if it is not the last character)
2032 (Zero) The character whose octal value is
2038 is not enclosed in quotes then the backslash itself must be escaped
2039 with a backslash to protect it from the shell.
2041 .Bd -literal -offset indent
2050 $ echo -e a\e\e\e\eb
2059 options may be specified.
2060 .It Ic eval Ar string ...
2061 Concatenate all the arguments with spaces.
2062 Then re-parse and execute the command.
2063 .It Ic exec Op Ar command Op arg ...
2067 the shell process is replaced with the specified program
2068 (which must be a real program, not a shell built-in command or function).
2069 Any redirections on the
2071 command are marked as permanent,
2072 so that they are not undone when the
2075 .It Ic exit Op Ar exitstatus
2076 Terminate the shell process.
2080 it is used as the exit status of the shell.
2081 Otherwise, if the shell is executing an
2083 trap, the exit status of the last command before the trap is used;
2084 if the shell is executing a trap for a signal,
2085 the shell exits by resending the signal to itself.
2086 Otherwise, the exit status of the preceding command is used.
2087 The exit status should be an integer between 0 and 255.
2088 .It Ic export Ar name ...
2089 .It Ic export Op Fl p
2090 The specified names are exported so that they will
2091 appear in the environment of subsequent commands.
2092 The only way to un-export a variable is to
2095 The shell allows the value of a variable to be set
2096 at the same time as it is exported by writing
2098 .D1 Ic export Ar name Ns = Ns Ar value
2100 With no arguments the
2102 command lists the names
2103 of all exported variables.
2106 option is specified, the exported variables are printed as
2107 .Dq Ic export Ar name Ns = Ns Ar value
2108 lines, suitable for re-input to the shell.
2110 A null command that returns a non-zero (false) exit value.
2111 .It Ic fc Oo Fl e Ar editor Oc Op Ar first Op Ar last
2112 .It Ic fc Fl l Oo Fl nr Oc Op Ar first Op Ar last
2113 .It Ic fc Fl s Oo Ar old Ns = Ns Ar new Oc Op Ar first
2116 built-in command lists, or edits and re-executes,
2117 commands previously entered to an interactive shell.
2118 .Bl -tag -width indent
2120 Use the editor named by
2122 to edit the commands.
2125 string is a command name,
2126 subject to search via the
2131 variable is used as a default when
2136 is null or unset, the value of the
2143 is used as the editor.
2145 List the commands rather than invoking
2147 The commands are written in the
2148 sequence indicated by the
2152 operands, as affected by
2154 with each command preceded by the command number.
2156 Suppress command numbers when listing with
2159 Reverse the order of the commands listed
2168 Re-execute the command without invoking an editor.
2171 Select the commands to list or edit.
2172 The number of previous commands that can be accessed
2173 are determined by the value of the
2180 or both are one of the following:
2181 .Bl -tag -width indent
2182 .It Oo Cm + Oc Ns Ar num
2183 A positive number representing a command number;
2184 command numbers can be displayed with the
2188 A negative decimal number representing the
2189 command that was executed
2192 commands previously.
2193 For example, \-1 is the immediately previous command.
2195 A string indicating the most recently entered command
2196 that begins with that string.
2198 .Ar old Ns = Ns Ar new
2199 operand is not also specified with
2201 the string form of the first operand cannot contain an embedded equal sign.
2205 The following variables affect the execution of
2207 .Bl -tag -width ".Va HISTSIZE"
2209 Name of the editor to use for history editing.
2211 The number of previous commands that are accessible.
2216 or the current job to the foreground.
2217 .It Ic getopts Ar optstring var
2224 command deprecates the older
2227 The first argument should be a series of letters, each possibly
2228 followed by a colon which indicates that the option takes an argument.
2229 The specified variable is set to the parsed option.
2231 the next argument is placed into the shell variable
2233 If an option takes an argument, it is placed into the shell variable
2235 If an invalid option is encountered,
2239 It returns a false value (1) when it encounters the end of the options.
2240 .It Ic hash Oo Fl rv Oc Op Ar command ...
2241 The shell maintains a hash table which remembers the locations of commands.
2242 With no arguments whatsoever, the
2244 command prints out the contents of this table.
2245 Entries which have not been looked at since the last
2247 command are marked with an asterisk;
2248 it is possible for these entries to be invalid.
2252 command removes each specified
2254 from the hash table (unless they are functions) and then locates it.
2259 prints the locations of the commands as it finds them.
2264 command to delete all the entries in the hash table except for functions.
2265 .It Ic jobid Op Ar job
2266 Print the process IDs of the processes in the specified
2270 argument is omitted, use the current job.
2271 .It Ic jobs Oo Fl lps Oc Op Ar job ...
2272 Print information about the specified jobs, or all jobs if no
2275 The information printed includes job ID, status and command name.
2279 option is specified, the PID of each job is also printed.
2282 option is specified, only the process IDs for the process group leaders
2283 are printed, one per line.
2286 option is specified, only the PIDs of the job commands are printed, one per
2289 A built-in equivalent of
2291 that additionally supports sending signals to jobs.
2292 .It Ic local Oo Ar variable ... Oc Op Fl
2297 A built-in equivalent of
2299 .It Ic pwd Op Fl L | P
2300 Print the path of the current directory.
2301 The built-in command may
2302 differ from the program of the same name because the
2303 built-in command remembers what the current directory
2304 is rather than recomputing it each time.
2307 However, if the current directory is
2309 the built-in version of
2311 will continue to print the old name for the directory.
2315 option is specified, symbolic links are resolved.
2318 option is specified, the shell's notion of the current directory
2319 is printed (symbolic links are not resolved).
2320 This is the default.
2321 .It Ic read Oo Fl p Ar prompt Oc Oo
2322 .Fl t Ar timeout Oc Oo Fl er Oc Ar variable ...
2328 and the standard input is a terminal.
2330 read from the standard input.
2331 The trailing newline
2332 is deleted from the line and the line is split as
2333 described in the section on
2334 .Sx White Space Splitting (Field Splitting)
2336 the pieces are assigned to the variables in order.
2337 If there are more pieces than variables, the remaining
2338 pieces (along with the characters in
2340 that separated them)
2341 are assigned to the last variable.
2342 If there are more variables than pieces, the remaining
2343 variables are assigned the null string.
2345 Backslashes are treated specially, unless the
2349 If a backslash is followed by
2350 a newline, the backslash and the newline will be
2352 If a backslash is followed by any other
2353 character, the backslash will be deleted and the following
2354 character will be treated as though it were not in
2360 option is specified and the
2362 elapses before a complete line of input is supplied,
2365 command will return an exit status of 1 without assigning any values.
2368 value may optionally be followed by one of
2373 to explicitly specify seconds, minutes or hours.
2374 If none is supplied,
2380 option exists only for backward compatibility with older scripts.
2381 .It Ic readonly Oo Fl p Oc Op Ar name ...
2384 is marked as read only,
2385 so that it cannot be subsequently modified or unset.
2386 The shell allows the value of a variable to be set
2387 at the same time as it is marked read only
2388 by using the following form:
2390 .D1 Ic readonly Ar name Ns = Ns Ar value
2392 With no arguments the
2394 command lists the names of all read only variables.
2397 option is specified, the read-only variables are printed as
2398 .Dq Ic readonly Ar name Ns = Ns Ar value
2399 lines, suitable for re-input to the shell.
2400 .It Ic return Op Ar exitstatus
2404 .It Ic set Oo Fl /+abCEefIimnpTuVvx Oc Oo Fl /+o Ar longname Oc Oo
2405 .Fl c Ar string Oc Op Fl - Ar arg ...
2408 command performs three different functions:
2411 With no arguments, it lists the values of all shell variables.
2413 If options are given,
2414 either in short form or using the long
2415 .Dq Fl /+o Ar longname
2417 it sets or clears the specified options as described in the section called
2418 .Sx Argument List Processing .
2422 option is specified,
2424 will replace the shell's positional parameters with the subsequent
2426 If no arguments follow the
2429 all the positional parameters will be cleared,
2430 which is equivalent to executing the command
2434 flag may be omitted when specifying arguments to be used
2435 as positional replacement parameters.
2436 This is not recommended,
2437 because the first argument may begin with a dash
2443 command will interpret as a request to enable or disable options.
2445 .It Ic setvar Ar variable value
2446 Assigns the specified
2452 command is intended to be used in functions that
2453 assign values to variables whose names are passed as parameters.
2454 In general it is better to write
2455 .Dq Ar variable Ns = Ns Ar value
2458 .It Ic shift Op Ar n
2459 Shift the positional parameters
2464 A shift sets the value of
2473 decreasing the value of
2476 For portability, shifting if there are zero positional parameters
2477 should be avoided, since the shell may abort.
2479 A built-in equivalent of
2482 Print the amount of time spent executing the shell process and its children.
2483 The first output line shows the user and system times for the shell process
2484 itself, the second one contains the user and system times for the
2486 .It Ic trap Oo Ar action Oc Ar signal ...
2488 Cause the shell to parse and execute
2493 The signals are specified by name or number.
2494 In addition, the pseudo-signal
2496 may be used to specify an
2498 that is performed when the shell terminates.
2501 may be an empty string or a dash
2503 the former causes the specified signal to be ignored
2504 and the latter causes the default action to be taken.
2507 is another way to request the default action, for compatibility reasons this
2508 usage is not recommended though.
2509 In a subshell or utility environment,
2510 the shell resets trapped (but not ignored) signals to the default action.
2513 command has no effect on signals that were ignored on entry to the shell.
2519 command to display a list of valid signal names.
2521 A null command that returns a 0 (true) exit value.
2522 .It Ic type Op Ar name ...
2525 as a command and print the resolution of the command search.
2526 Possible resolutions are:
2527 shell keyword, alias, special shell builtin, shell builtin, command,
2530 For aliases the alias expansion is printed;
2531 for commands and tracked aliases
2532 the complete pathname of the command is printed.
2533 .It Ic ulimit Oo Fl HSabcdflmnpstuvw Oc Op Ar limit
2534 Set or display resource limits (see
2538 is specified, the named resource will be set;
2539 otherwise the current resource value will be displayed.
2543 is specified, the hard limits will be set or displayed.
2544 While everybody is allowed to reduce a hard limit,
2545 only the superuser can increase it.
2549 specifies the soft limits instead.
2550 When displaying limits,
2556 The default is to display the soft limits,
2557 and to set both the hard and the soft limits.
2563 command to display all resources.
2566 is not acceptable in this mode.
2568 The remaining options specify which resource value is to be
2569 displayed or modified.
2570 They are mutually exclusive.
2571 .Bl -tag -width indent
2573 The maximum size of socket buffer usage, in bytes.
2574 .It Fl c Ar coredumpsize
2575 The maximal size of core dump files, in 512-byte blocks.
2576 .It Fl d Ar datasize
2577 The maximal size of the data segment of a process, in kilobytes.
2578 .It Fl f Ar filesize
2579 The maximal size of a file, in 512-byte blocks.
2580 .It Fl l Ar lockedmem
2581 The maximal size of memory that can be locked by a process, in
2583 .It Fl m Ar memoryuse
2584 The maximal resident set size of a process, in kilobytes.
2586 The maximal number of descriptors that could be opened by a process.
2587 .It Fl p Ar pseudoterminals
2588 The maximal number of pseudo-terminals for this user ID.
2589 .It Fl s Ar stacksize
2590 The maximal size of the stack segment, in kilobytes.
2592 The maximal amount of CPU time to be used by each process, in seconds.
2593 .It Fl u Ar userproc
2594 The maximal number of simultaneous processes for this user ID.
2595 .It Fl v Ar virtualmem
2596 The maximal virtual size of a process, in kilobytes.
2598 The maximum amount of swap space reserved or used for this user ID,
2601 .It Ic umask Oo Fl S Oc Op Ar mask
2602 Set the file creation mask (see
2604 to the octal or symbolic (see
2608 If the argument is omitted, the current mask value is printed.
2611 option is specified, the output is symbolic, otherwise the output is octal.
2612 .It Ic unalias Oo Fl a Oc Op Ar name ...
2613 The specified alias names are removed.
2616 is specified, all aliases are removed.
2617 .It Ic unset Oo Fl fv Oc Ar name ...
2618 The specified variables or functions are unset and unexported.
2621 option is specified or no options are given, the
2623 arguments are treated as variable names.
2626 option is specified, the
2628 arguments are treated as function names.
2629 .It Ic wait Op Ar job
2630 Wait for the specified
2632 to complete and return the exit status of the last process in the
2634 If the argument is omitted, wait for all jobs to complete
2635 and return an exit status of zero.
2637 .Ss Commandline Editing
2640 is being used interactively from a terminal, the current command
2641 and the command history
2645 .Sx Built-in Commands )
2648 command line editing.
2649 This mode uses commands similar
2650 to a subset of those described in the
2668 can be switched between insert mode and command mode by typing
2672 while in command mode will pass the line to the shell.
2675 .Dq Li "set -o emacs"
2678 command can be used to enable a subset of
2680 command line editing features.
2682 The following environment variables affect the execution of
2684 .Bl -tag -width ".Ev LANGXXXXXX"
2686 Initialization file for interactive shells.
2687 .It Ev LANG , Ev LC_*
2689 These are inherited by children of the shell,
2690 and is used in a limited manner by the shell itself.
2692 An absolute pathname for the current directory,
2693 possibly containing symbolic links.
2694 This is used and updated by the shell.
2696 The default terminal setting for the shell.
2697 This is inherited by children of the shell, and is used in the history
2701 Additionally, all environment variables are turned into shell variables
2703 which may affect the shell as described under
2704 .Sx Special Variables .
2706 Errors that are detected by the shell, such as a syntax error, will
2707 cause the shell to exit with a non-zero exit status.
2708 If the shell is not an interactive shell, the execution of the shell
2709 file will be aborted.
2710 Otherwise the shell will return the exit status of the last command
2713 builtin is used with a numeric argument, it
2714 will return the argument.
2734 command, the Thompson shell, appeared in
2736 It was superseded in
2738 by the Bourne shell, which inherited the name
2743 was rewritten in 1989 under the
2745 license after the Bourne shell from
2750 was originally written by
2751 .An Kenneth Almquist .
2755 utility does not recognize multibyte characters other than UTF-8.
2758 and the line editing library
2760 do not recognize multibyte characters.
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