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40 .Nd command interpreter (shell)
43 .Op Fl /+abCEefIimnPpTuVvx
44 .Op Fl /+o Ar longname
50 .Op Fl /+abCEefIimnPpTuVvx
51 .Op Fl /+o Ar longname
58 .Op Fl /+abCEefIimnPpTuVvx
59 .Op Fl /+o Ar longname
65 utility is the standard command interpreter for the system.
66 The current version of
70 specification for the shell.
71 It only supports features
74 plus a few Berkeley extensions.
75 This man page is not intended to be a tutorial nor a complete
76 specification of the shell.
78 The shell is a command that reads lines from
79 either a file or the terminal, interprets them, and
80 generally executes other commands.
81 It is the program that is started when a user logs into the system,
82 although a user can select a different shell with the
86 implements a language that has flow control constructs,
87 a macro facility that provides a variety of features in
88 addition to data storage, along with built-in history and line
90 It incorporates many features to
91 aid interactive use and has the advantage that the interpretative
92 language is common to both interactive and non-interactive
94 That is, commands can be typed directly
95 to the running shell or can be put into a file,
96 which can be executed directly by the shell.
99 .\" XXX This next sentence is incredibly confusing.
101 If no arguments are present and if the standard input of the shell
102 is connected to a terminal
106 the shell is considered an interactive shell.
108 generally prompts before each command and handles programming
109 and command errors differently (as described below).
110 When first starting, the shell inspects argument 0, and
111 if it begins with a dash
113 the shell is also considered a login shell.
114 This is normally done automatically by the system
115 when the user first logs in.
116 A login shell first reads commands
121 in a user's home directory,
123 If the environment variable
125 is set on entry to a shell, or is set in the
127 of a login shell, the shell then subjects its value to parameter expansion
128 and arithmetic expansion and reads commands from the named file.
129 Therefore, a user should place commands that are to be executed only
132 file, and commands that are executed for every shell inside the
137 variable to some file by placing the following line in the file
139 in the home directory,
142 the filename desired:
144 .Dl "ENV=$HOME/.shrc; export ENV"
146 The first non-option argument specified on the command line
147 will be treated as the
148 name of a file from which to read commands (a shell script), and
149 the remaining arguments are set as the positional parameters
153 Otherwise, the shell reads commands
154 from its standard input.
156 Unlike older versions of
160 script is only sourced on invocation of interactive shells.
162 closes a well-known, and sometimes easily exploitable security
163 hole related to poorly thought out
166 .Ss Argument List Processing
167 All of the single letter options to
169 have a corresponding long name,
170 with the exception of
174 These long names are provided next to the single letter options
175 in the descriptions below.
176 The long name for an option may be specified as an argument to the
180 Once the shell is running,
181 the long name for an option may be specified as an argument to the
186 (described later in the section called
187 .Sx Built-in Commands ) .
188 Introducing an option with a dash
198 will stop option processing and will force the remaining
199 words on the command line to be treated as arguments.
204 options do not have long names.
205 They take arguments and are described after the single letter options.
206 .Bl -tag -width indent
207 .It Fl a Li allexport
208 Flag variables for export when assignments are made to them.
210 Enable asynchronous notification of background job
213 .It Fl C Li noclobber
214 Do not overwrite existing files with
219 command line editor (disables the
221 option if it has been set;
222 set automatically when interactive on terminals).
224 Exit immediately if any untested command fails in non-interactive mode.
225 The exit status of a command is considered to be
226 explicitly tested if the command is part of the list used to control
228 .Ic if , elif , while ,
231 if the command is the left
236 operator; or if the command is a pipeline preceded by the
239 If a shell function is executed and its exit status is explicitly
240 tested, all commands of the function are considered to be tested as
243 Disable pathname expansion.
245 A do-nothing option for
248 .It Fl I Li ignoreeof
251 from input when in interactive mode.
252 .It Fl i Li interactive
253 Force the shell to behave interactively.
255 Turn on job control (set automatically when interactive).
257 If not interactive, read commands but do not
259 This is useful for checking the
260 syntax of shell scripts.
262 Change the default for the
268 (logical directory layout)
271 (physical directory layout).
272 .It Fl p Li privileged
273 Turn on privileged mode.
274 This mode is enabled on startup
275 if either the effective user or group ID is not equal to the
276 real user or group ID.
277 Turning this mode off sets the
278 effective user and group IDs to the real user and group IDs.
279 When this mode is enabled for interactive shells, the file
280 .Pa /etc/suid_profile
281 is sourced instead of
285 is sourced, and the contents of the
287 variable are ignored.
289 Read commands from standard input (set automatically
290 if no file arguments are present).
292 no effect when set after the shell has already started
293 running (i.e., when set with the
296 .It Fl T Li trapsasync
297 When waiting for a child, execute traps immediately.
298 If this option is not set,
299 traps are executed after the child exits,
302 This nonstandard option is useful for putting guarding shells around
303 children that block signals.
304 The surrounding shell may kill the child
305 or it may just return control to the tty and leave the child alone,
307 .Bd -literal -offset indent
308 sh -T -c "trap 'exit 1' 2 ; some-blocking-program"
311 Write a message to standard error when attempting
312 to expand a variable, a positional parameter or
313 the special parameter
315 that is not set, and if the
316 shell is not interactive, exit immediately.
320 command line editor (disables
324 The shell writes its input to standard error
326 Useful for debugging.
329 (preceded by the value of the
331 variable subjected to parameter expansion and arithmetic expansion)
332 to standard error before it is executed.
333 Useful for debugging.
334 .It "\ \ " Em tabcomplete
335 Enables filename completion in the command line editor.
336 Typing a tab character will extend the current input word to match a
338 If more than one filename matches it is only extended to be the common prefix.
339 Typing a second tab character will list all the matching names.
340 Turned on by default in an interactive shell.
345 option causes the commands to be read from the
347 operand instead of from the standard input.
348 Keep in mind that this option only accepts a single string as its
349 argument, hence multi-word strings must be quoted.
353 option takes as its only argument the long name of an option
354 to be enabled or disabled.
355 For example, the following two invocations of
357 both enable the built-in
360 .Bd -literal -offset indent
365 If used without an argument, the
367 option displays the current option settings in a human-readable format.
370 is used without an argument, the current option settings are output
371 in a format suitable for re-input into the shell.
372 .Ss Lexical Structure
373 The shell reads input in terms of lines from a file and breaks
374 it up into words at whitespace (blanks and tabs), and at
378 which are special to the shell.
379 There are two types of operators: control operators and
380 redirection operators (their meaning is discussed later).
381 The following is a list of valid operators:
382 .Bl -tag -width indent
383 .It Control operators:
384 .Bl -column "XXX" "XXX" "XXX" "XXX" "XXX" -offset center -compact
385 .It Li & Ta Li && Ta Li \&( Ta Li \&) Ta Li \en
386 .It Li ;; Ta Li ;& Ta Li \&; Ta Li \&| Ta Li ||
388 .It Redirection operators:
389 .Bl -column "XXX" "XXX" "XXX" "XXX" "XXX" -offset center -compact
390 .It Li < Ta Li > Ta Li << Ta Li >> Ta Li <>
391 .It Li <& Ta Li >& Ta Li <<- Ta Li >| Ta \&
397 introduces a comment if used at the beginning of a word.
398 The word starting with
400 and the rest of the line are ignored.
404 characters (character code 0) are not allowed in shell input.
406 Quoting is used to remove the special meaning of certain characters
407 or words to the shell, such as operators, whitespace, keywords,
410 There are four types of quoting: matched single quotes,
411 dollar-single quotes,
412 matched double quotes, and backslash.
413 .Bl -tag -width indent
415 Enclosing characters in single quotes preserves the literal
416 meaning of all the characters (except single quotes, making
417 it impossible to put single-quotes in a single-quoted string).
418 .It Dollar-Single Quotes
419 Enclosing characters between
423 preserves the literal meaning of all characters
424 except backslashes and single quotes.
425 A backslash introduces a C-style escape sequence:
426 .Bl -tag -width xUnnnnnnnn
428 Alert (ring the terminal bell)
432 The control character denoted by
438 is a backslash, it must be doubled.
460 The byte whose octal value is
462 (one to three digits)
464 The byte whose hexadecimal value is
466 (one or more digits only the last two of which are used)
468 The Unicode code point
470 (four hexadecimal digits)
471 .It \eU Ns Ar nnnnnnnn
472 The Unicode code point
474 (eight hexadecimal digits)
477 The sequences for Unicode code points are currently only useful with
479 They reject code point 0 and UTF-16 surrogates.
481 If an escape sequence would produce a byte with value 0,
482 that byte and the rest of the string until the matching single-quote
485 Any other string starting with a backslash is an error.
487 Enclosing characters within double quotes preserves the literal
488 meaning of all characters except dollar sign
494 The backslash inside double quotes is historically weird.
495 It remains literal unless it precedes the following characters,
496 which it serves to quote:
498 .Bl -column "XXX" "XXX" "XXX" "XXX" "XXX" -offset center -compact
499 .It Li $ Ta Li ` Ta Li \&" Ta Li \e Ta Li \en
502 A backslash preserves the literal meaning of the following
503 character, with the exception of the newline character
505 A backslash preceding a newline is treated as a line continuation.
508 Keywords or reserved words are words that have special meaning to the
509 shell and are recognized at the beginning of a line and
510 after a control operator.
511 The following are keywords:
512 .Bl -column "doneXX" "elifXX" "elseXX" "untilXX" "whileX" -offset center
513 .It Li \&! Ta { Ta } Ta Ic case Ta Ic do
514 .It Ic done Ta Ic elif Ta Ic else Ta Ic esac Ta Ic fi
515 .It Ic for Ta Ic if Ta Ic then Ta Ic until Ta Ic while
518 An alias is a name and corresponding value set using the
521 Wherever the command word of a simple command may occur,
522 and after checking for keywords if a keyword may occur, the shell
523 checks the word to see if it matches an alias.
524 If it does, it replaces it in the input stream with its value.
525 For example, if there is an alias called
537 Aliases provide a convenient way for naive users to
538 create shorthands for commands without having to learn how
539 to create functions with arguments.
540 Using aliases in scripts is discouraged
541 because the command that defines them must be executed
542 before the code that uses them is parsed.
543 This is fragile and not portable.
545 An alias name may be escaped in a command line, so that it is not
546 replaced by its alias value, by using quoting characters within or
547 adjacent to the alias name.
548 This is most often done by prefixing
549 an alias name with a backslash to execute a function, built-in, or
550 normal program with the same name.
555 The shell interprets the words it reads according to a
556 language, the specification of which is outside the scope
557 of this man page (refer to the BNF in the
560 Essentially though, a line is read and if
561 the first word of the line (or after a control operator)
562 is not a keyword, then the shell has recognized a
564 Otherwise, a complex command or some
565 other special construct may have been recognized.
567 If a simple command has been recognized, the shell performs
568 the following actions:
571 Leading words of the form
573 are stripped off and assigned to the environment of
575 Redirection operators and
576 their arguments (as described below) are stripped
577 off and saved for processing.
579 The remaining words are expanded as described in
581 .Sx Word Expansions ,
582 and the first remaining word is considered the command
583 name and the command is located.
585 words are considered the arguments of the command.
586 If no command name resulted, then the
588 variable assignments recognized in 1) affect the
591 Redirections are performed as described in
595 Redirections are used to change where a command reads its input
597 In general, redirections open, close, or
598 duplicate an existing reference to a file.
600 used for redirection is:
602 .D1 Oo Ar n Oc Ar redir-op file
606 is one of the redirection operators mentioned
608 The following gives some examples of how these
609 operators can be used.
610 Note that stdin and stdout are commonly used abbreviations
611 for standard input and standard output respectively.
612 .Bl -tag -width "1234567890XX" -offset indent
613 .It Oo Ar n Oc Ns Li > Ar file
614 redirect stdout (or file descriptor
618 .It Oo Ar n Oc Ns Li >| Ar file
619 same as above, but override the
622 .It Oo Ar n Oc Ns Li >> Ar file
623 append stdout (or file descriptor
627 .It Oo Ar n Oc Ns Li < Ar file
628 redirect stdin (or file descriptor
632 .It Oo Ar n Oc Ns Li <> Ar file
633 redirect stdin (or file descriptor
637 .It Oo Ar n1 Oc Ns Li <& Ns Ar n2
638 duplicate stdin (or file descriptor
642 .It Oo Ar n Oc Ns Li <&-
643 close stdin (or file descriptor
645 .It Oo Ar n1 Oc Ns Li >& Ns Ar n2
646 duplicate stdout (or file descriptor
650 .It Oo Ar n Oc Ns Li >&-
651 close stdout (or file descriptor
655 The following redirection is often called a
657 .Bd -unfilled -offset indent
658 .Oo Ar n Oc Ns Li << Ar delimiter
664 All the text on successive lines up to the delimiter is
665 saved away and made available to the command on standard
666 input, or file descriptor
671 as specified on the initial line is quoted, then the
673 is treated literally, otherwise the text is subjected to
674 parameter expansion, command substitution, and arithmetic
675 expansion (as described in the section on
676 .Sx Word Expansions ) .
685 .Ss Search and Execution
686 There are three types of commands: shell functions,
687 built-in commands, and normal programs.
688 The command is searched for (by name) in that order.
689 The three types of commands are all executed in a different way.
691 When a shell function is executed, all of the shell positional
694 which remains unchanged) are
695 set to the arguments of the shell function.
696 The variables which are explicitly placed in the environment of
697 the command (by placing assignments to them before the
698 function name) are made local to the function and are set
700 Then the command given in the function definition is executed.
701 The positional parameters are restored to their original values
702 when the command completes.
703 This all occurs within the current shell.
705 Shell built-in commands are executed internally to the shell, without
706 spawning a new process.
707 There are two kinds of built-in commands: regular and special.
708 Assignments before special builtins persist after they finish
709 executing and assignment errors, redirection errors and certain
710 operand errors cause a script to be aborted.
711 Special builtins cannot be overridden with a function.
712 Both regular and special builtins can affect the shell in ways
713 normal programs cannot.
715 Otherwise, if the command name does not match a function
716 or built-in command, the command is searched for as a normal
717 program in the file system (as described in the next section).
718 When a normal program is executed, the shell runs the program,
719 passing the arguments and the environment to the program.
720 If the program is not a normal executable file
721 (i.e., if it does not begin with the
731 but appears to be a text file,
732 the shell will run a new instance of
736 Note that previous versions of this document
737 and the source code itself misleadingly and sporadically
738 refer to a shell script without a magic number
740 .Dq "shell procedure" .
742 When locating a command, the shell first looks to see if
743 it has a shell function by that name.
745 built-in command by that name.
746 If a built-in command is not found,
747 one of two things happen:
750 Command names containing a slash are simply executed without
751 performing any searches.
753 The shell searches each entry in the
756 in turn for the command.
759 variable should be a series of
760 entries separated by colons.
761 Each entry consists of a
763 The current directory
764 may be indicated implicitly by an empty directory name,
765 or explicitly by a single period.
767 .Ss Command Exit Status
768 Each command has an exit status that can influence the behavior
769 of other shell commands.
770 The paradigm is that a command exits
771 with zero for normal or success, and non-zero for failure,
772 error, or a false indication.
773 The man page for each command
774 should indicate the various exit codes and what they mean.
775 Additionally, the built-in commands return exit codes, as does
776 an executed shell function.
778 If a command is terminated by a signal, its exit status is 128 plus
780 Signal numbers are defined in the header file
783 Complex commands are combinations of simple commands
784 with control operators or keywords, together creating a larger complex
786 More generally, a command is one of the following:
787 .Bl -item -offset indent
793 list or compound-list
800 Unless otherwise stated, the exit status of a command is
801 that of the last simple command executed by the command.
803 A pipeline is a sequence of one or more commands separated
804 by the control operator
806 The standard output of all but
807 the last command is connected to the standard input
809 The standard output of the last
810 command is inherited from the shell, as usual.
812 The format for a pipeline is:
814 .D1 Oo Li \&! Oc Ar command1 Op Li \&| Ar command2 ...
816 The standard output of
818 is connected to the standard input of
820 The standard input, standard output, or
821 both of a command is considered to be assigned by the
822 pipeline before any redirection specified by redirection
823 operators that are part of the command.
825 Note that unlike some other shells,
827 executes each process in a pipeline with more than one command
828 in a subshell environment and as a child of the
832 If the pipeline is not in the background (discussed later),
833 the shell waits for all commands to complete.
837 does not precede the pipeline, the
838 exit status is the exit status of the last command specified
840 Otherwise, the exit status is the logical
841 NOT of the exit status of the last command.
843 the last command returns zero, the exit status is 1; if
844 the last command returns greater than zero, the exit status
847 Because pipeline assignment of standard input or standard
848 output or both takes place before redirection, it can be
849 modified by redirection.
852 .Dl "command1 2>&1 | command2"
854 sends both the standard output and standard error of
856 to the standard input of
861 or newline terminator causes the preceding
863 (described below in the section called
864 .Sx Short-Circuit List Operators )
865 to be executed sequentially;
868 causes asynchronous execution of the preceding AND-OR-list.
869 .Ss Background Commands (&)
870 If a command is terminated by the control operator ampersand
872 the shell executes the command in a subshell environment (see
873 .Sx Grouping Commands Together
874 below) and asynchronously;
875 the shell does not wait for the command to finish
876 before executing the next command.
878 The format for running a command in background is:
880 .D1 Ar command1 Li & Op Ar command2 Li & Ar ...
882 If the shell is not interactive, the standard input of an
883 asynchronous command is set to
885 .Ss Lists (Generally Speaking)
886 A list is a sequence of zero or more commands separated by
887 newlines, semicolons, or ampersands,
888 and optionally terminated by one of these three characters.
890 list are executed in the order they are written.
891 If command is followed by an ampersand, the shell starts the
892 command and immediately proceeds onto the next command;
893 otherwise it waits for the command to terminate before
894 proceeding to the next one.
895 .Ss Short-Circuit List Operators
899 are AND-OR list operators.
901 executes the first command, and then executes the second command
902 if the exit status of the first command is zero.
904 is similar, but executes the second command if the exit
905 status of the first command is nonzero.
909 both have the same priority.
910 .Ss Flow-Control Constructs (if, while, for, case)
914 .Bd -unfilled -offset indent -compact
918 .Ic then Ar list Oc Ar ...
926 .Bd -unfilled -offset indent -compact
932 The two lists are executed repeatedly while the exit status of the
936 command is similar, but has the word
941 repeat until the exit status of the first list is zero.
946 .Bd -unfilled -offset indent -compact
947 .Ic for Ar variable Op Ic in Ar word ...
954 and the following words are omitted,
957 The words are expanded, and then the list is executed
958 repeatedly with the variable set to each word in turn.
963 commands may be replaced with
973 .D1 Ic break Op Ar num
974 .D1 Ic continue Op Ar num
978 command terminates the
987 command continues with the next iteration of the innermost loop.
988 These are implemented as special built-in commands.
993 .Bd -unfilled -offset indent -compact
994 .Ic case Ar word Ic in
995 .Ar pattern Ns Li ) Ar list Li ;;
1000 The pattern can actually be one or more patterns
1007 Tilde expansion, parameter expansion, command substitution,
1008 arithmetic expansion and quote removal are applied to the word.
1009 Then, each pattern is expanded in turn using tilde expansion,
1010 parameter expansion, command substitution and arithmetic expansion and
1011 the expanded form of the word is checked against it.
1012 If a match is found, the corresponding list is executed.
1013 If the selected list is terminated by the control operator
1017 execution continues with the next list,
1018 continuing until a list terminated with
1023 The exit code of the
1025 command is the exit code of the last command executed in the list or
1026 zero if no patterns were matched.
1027 .Ss Grouping Commands Together
1028 Commands may be grouped by writing either
1030 .D1 Li \&( Ns Ar list Ns Li \%)
1034 .D1 Li { Ar list Ns Li \&; }
1036 The first form executes the commands in a subshell environment.
1037 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 may include any of the following formatting sequences,
1355 which are replaced by the given information:
1356 .Bl -tag -width indent
1360 The fully-qualified hostname.
1362 The final component of the current working directory.
1364 The entire path of the current working directory.
1368 for normal users and
1372 A literal backslash.
1375 The secondary prompt string, which defaults to
1378 may include any of the formatting sequences from
1381 The prefix for the trace output (if
1388 This clause describes the various expansions that are
1390 Not all expansions are performed on
1391 every word, as explained later.
1393 Tilde expansions, parameter expansions, command substitutions,
1394 arithmetic expansions, and quote removals that occur within
1395 a single word expand to a single field.
1397 splitting or pathname expansion that can create multiple
1398 fields from a single word.
1399 The single exception to this rule is
1400 the expansion of the special parameter
1402 within double-quotes,
1403 as was described above.
1405 The order of word expansion is:
1408 Tilde Expansion, Parameter Expansion, Command Substitution,
1409 Arithmetic Expansion (these all occur at the same time).
1411 Field Splitting is performed on fields generated by step (1)
1416 Pathname Expansion (unless the
1418 option is in effect).
1425 character is used to introduce parameter expansion, command
1426 substitution, or arithmetic expansion.
1427 .Ss Tilde Expansion (substituting a user's home directory)
1428 A word beginning with an unquoted tilde character
1431 subjected to tilde expansion.
1432 All the characters up to a slash
1434 or the end of the word are treated as a username
1435 and are replaced with the user's home directory.
1437 username is missing (as in
1439 the tilde is replaced with the value of the
1441 variable (the current user's home directory).
1442 .Ss Parameter Expansion
1443 The format for parameter expansion is as follows:
1445 .D1 Li ${ Ns Ar expression Ns Li }
1449 consists of all characters until the matching
1453 escaped by a backslash or within a single-quoted or double-quoted
1454 string, and characters in
1455 embedded arithmetic expansions, command substitutions, and variable
1456 expansions, are not examined in determining the matching
1458 If the variants with
1464 occur within a double-quoted string,
1465 as an extension there may be unquoted parts
1466 (via double-quotes inside the expansion);
1468 within such parts are also not examined in determining the matching
1471 The simplest form for parameter expansion is:
1473 .D1 Li ${ Ns Ar parameter Ns Li }
1475 The value, if any, of
1479 The parameter name or symbol can be enclosed in braces, which are
1480 optional except for positional parameters with more than one digit or
1481 when parameter is followed by a character that could be interpreted as
1483 If a parameter expansion occurs inside double-quotes:
1486 Field splitting is not performed on the results of the
1487 expansion, with the exception of the special parameter
1490 Pathname expansion is not performed on the results of the
1494 In addition, a parameter expansion can be modified by using one of the
1496 .Bl -tag -width indent
1497 .It Li ${ Ns Ar parameter Ns Li :- Ns Ar word Ns Li }
1501 is unset or null, the expansion of
1503 is substituted; otherwise, the value of
1506 .It Li ${ Ns Ar parameter Ns Li := Ns Ar word Ns Li }
1507 Assign Default Values.
1510 is unset or null, the expansion of
1520 does not prevent field splitting or pathname expansion.
1521 Only variables, not positional
1522 parameters or special parameters, can be
1523 assigned in this way.
1524 .It Li ${ Ns Ar parameter Ns Li :? Ns Oo Ar word Oc Ns Li }
1525 Indicate Error if Null or Unset.
1528 is unset or null, the expansion of
1530 (or a message indicating it is unset if
1532 is omitted) is written to standard
1533 error and the shell exits with a nonzero
1535 Otherwise, the value of
1539 interactive shell need not exit.
1540 .It Li ${ Ns Ar parameter Ns Li :+ Ns Ar word Ns Li }
1541 Use Alternate Value.
1544 is unset or null, null is substituted;
1545 otherwise, the expansion of
1550 In the parameter expansions shown previously, use of the colon in the
1551 format results in a test for a parameter that is unset or null; omission
1552 of the colon results in a test for a parameter that is only unset.
1556 inherits the type of quoting
1557 (unquoted, double-quoted or here-document)
1558 from the surroundings,
1559 with the exception that a backslash that quotes a closing brace is removed
1560 during quote removal.
1561 .Bl -tag -width indent
1562 .It Li ${# Ns Ar parameter Ns Li }
1564 The length in characters of
1569 The following four varieties of parameter expansion provide for substring
1571 In each case, pattern matching notation
1573 .Sx Shell Patterns ) ,
1574 rather than regular expression notation,
1575 is used to evaluate the patterns.
1576 If parameter is one of the special parameters
1580 the result of the expansion is unspecified.
1581 Enclosing the full parameter expansion string in double-quotes does not
1582 cause the following four varieties of pattern characters to be quoted,
1583 whereas quoting characters within the braces has this effect.
1584 .Bl -tag -width indent
1585 .It Li ${ Ns Ar parameter Ns Li % Ns Ar word Ns Li }
1586 Remove Smallest Suffix Pattern.
1589 is expanded to produce a pattern.
1591 parameter expansion then results in
1593 with the smallest portion of the
1594 suffix matched by the pattern deleted.
1595 .It Li ${ Ns Ar parameter Ns Li %% Ns Ar word Ns Li }
1596 Remove Largest Suffix Pattern.
1599 is expanded to produce a pattern.
1601 parameter expansion then results in
1603 with the largest portion of the
1604 suffix matched by the pattern deleted.
1605 .It Li ${ Ns Ar parameter Ns Li # Ns Ar word Ns Li }
1606 Remove Smallest Prefix Pattern.
1609 is expanded to produce a pattern.
1611 parameter expansion then results in
1613 with the smallest portion of the
1614 prefix matched by the pattern deleted.
1615 .It Li ${ Ns Ar parameter Ns Li ## Ns Ar word Ns Li }
1616 Remove Largest Prefix Pattern.
1619 is expanded to produce a pattern.
1621 parameter expansion then results in
1623 with the largest portion of the
1624 prefix matched by the pattern deleted.
1626 .Ss Command Substitution
1627 Command substitution allows the output of a command to be substituted in
1628 place of the command name itself.
1629 Command substitution occurs when
1630 the command is enclosed as follows:
1632 .D1 Li $( Ns Ar command Ns Li )\&
1634 or the backquoted version:
1636 .D1 Li ` Ns Ar command Ns Li `
1638 The shell expands the command substitution by executing command
1639 and replacing the command substitution
1640 with the standard output of the command,
1641 removing sequences of one or more newlines at the end of the substitution.
1642 Embedded newlines before the end of the output are not removed;
1643 however, during field splitting, they may be translated into spaces
1644 depending on the value of
1646 and the quoting that is in effect.
1647 The command is executed in a subshell environment,
1648 except that the built-in commands
1653 return information about the parent shell environment
1656 returns information about the same process
1657 if they are the only command in a command substitution.
1659 If a command substitution of the
1661 form begins with a subshell,
1666 must be separated by whitespace
1667 to avoid ambiguity with arithmetic expansion.
1668 .Ss Arithmetic Expansion
1669 Arithmetic expansion provides a mechanism for evaluating an arithmetic
1670 expression and substituting its value.
1671 The format for arithmetic expansion is as follows:
1673 .D1 Li $(( Ns Ar expression Ns Li ))
1677 is treated as if it were in double-quotes, except
1678 that a double-quote inside the expression is not treated specially.
1680 shell expands all tokens in the
1682 for parameter expansion,
1683 command substitution,
1684 arithmetic expansion
1687 The allowed expressions are a subset of C expressions,
1689 .Bl -tag -width "Variables" -offset indent
1691 All values are of type
1694 Decimal, octal (starting with
1696 and hexadecimal (starting with
1700 Shell variables can be read and written
1701 and contain integer constants.
1704 .It Binary operators
1705 .Li "* / % + - << >> < <= > >= == != & ^ | && ||"
1706 .It Assignment operators
1707 .Li "= += -= *= /= %= <<= >>= &= ^= |="
1708 .It Conditional operator
1712 The result of the expression is substituted in decimal.
1713 .Ss White Space Splitting (Field Splitting)
1714 In certain contexts,
1715 after parameter expansion, command substitution, and
1716 arithmetic expansion the shell scans the results of
1717 expansions and substitutions that did not occur in double-quotes for
1718 field splitting and multiple fields can result.
1729 are treated differently from other characters in
1734 at the beginning or end of a word is discarded.
1736 Subsequently, a field is delimited by either
1739 a non-whitespace character in
1741 with any whitespace in
1745 one or more whitespace characters in
1749 If a word ends with a non-whitespace character in
1751 there is no empty field after this character.
1753 If no field is delimited, the word is discarded.
1754 In particular, if a word consists solely of an unquoted substitution
1755 and the result of the substitution is null,
1756 it is removed by field splitting even if
1759 .Ss Pathname Expansion (File Name Generation)
1763 file name generation is performed
1764 after word splitting is complete.
1766 viewed as a series of patterns, separated by slashes.
1768 process of expansion replaces the word with the names of
1769 all existing files whose names can be formed by replacing
1770 each pattern with a string that matches the specified pattern.
1771 There are two restrictions on this: first, a pattern cannot match
1772 a string containing a slash, and second,
1773 a pattern cannot match a string starting with a period
1774 unless the first character of the pattern is a period.
1775 The next section describes the patterns used for
1777 the four varieties of parameter expansion for substring processing and the
1781 A pattern consists of normal characters, which match themselves,
1782 and meta-characters.
1783 The meta-characters are
1788 These characters lose their special meanings if they are quoted.
1789 When command or variable substitution is performed and the dollar sign
1790 or back quotes are not double-quoted, the value of the
1791 variable or the output of the command is scanned for these
1792 characters and they are turned into meta-characters.
1796 matches any string of characters.
1799 matches any single character.
1802 introduces a character class.
1803 The end of the character class is indicated by a
1811 rather than introducing a character class.
1812 A character class matches any of the characters between the square brackets.
1813 A locale-dependent range of characters may be specified using a minus sign.
1814 A named class of characters (see
1816 may be specified by surrounding the name with
1821 .Ql \&[\&[:alpha:\&]\&]
1822 is a shell pattern that matches a single letter.
1823 The character class may be complemented by making an exclamation point
1825 the first character of the character class.
1828 has the same effect but is non-standard.
1832 in a character class, make it the first character listed
1840 make it the first or last character listed.
1841 .Ss Built-in Commands
1842 This section lists the built-in commands.
1843 .Bl -tag -width indent
1845 A null command that returns a 0 (true) exit value.
1847 The commands in the specified file are read and executed by the shell.
1850 command may be used to return to the
1857 characters, it is used as is.
1858 Otherwise, the shell searches the
1861 If it is not found in the
1863 it is sought in the current working directory.
1865 A built-in equivalent of
1867 .It Ic alias Oo Ar name Ns Oo = Ns Ar string Oc Ar ... Oc
1869 .Ar name Ns = Ns Ar string
1870 is specified, the shell defines the alias
1876 is specified, the value of the alias
1879 With no arguments, the
1881 built-in command prints the names and values of all defined aliases
1884 Alias values are written with appropriate quoting so that they are
1885 suitable for re-input to the shell.
1889 .It Ic bg Op Ar job ...
1890 Continue the specified jobs
1891 (or the current job if no jobs are given)
1893 .It Ic bind Oo Fl aeklrsv Oc Oo Ar key Oo Ar command Oc Oc
1894 List or alter key bindings for the line editor.
1895 This command is documented in
1897 .It Ic break Op Ar num
1899 .Sx Flow-Control Constructs
1901 .It Ic builtin Ar cmd Op Ar arg ...
1902 Execute the specified built-in command,
1904 This is useful when the user wishes to override a shell function
1905 with the same name as a built-in command.
1906 .It Ic cd Oo Fl L | P Oc Oo Fl e Oc Op Ar directory
1907 Switch to the specified
1909 or to the directory specified in the
1911 environment variable if no
1920 then the directories listed in the
1923 searched for the specified
1927 is unset, the current directory is searched.
1930 is the same as that of
1932 In an interactive shell,
1935 command will print out the name of the directory
1936 that it actually switched to
1937 if this is different from the name that the user gave.
1938 These may be different either because the
1940 mechanism was used or because a symbolic link was crossed.
1944 option is specified,
1946 is handled physically and symbolic links are resolved before
1948 components are processed.
1951 option is specified,
1953 is handled logically.
1954 This is the default.
1960 to return exit status 1 if the full pathname of the new directory
1961 cannot be determined reliably or at all.
1962 Normally this is not considered an error,
1963 although a warning is printed.
1968 .It Ic command Oo Fl p Oc Op Ar utility Op Ar argument ...
1969 .It Ic command Oo Fl p Oc Fl v Ar utility
1970 .It Ic command Oo Fl p Oc Fl V Ar utility
1971 The first form of invocation executes the specified
1973 ignoring shell functions in the search.
1976 is a special builtin,
1977 it is executed as if it were a regular builtin.
1981 option is specified, the command search is performed using a
1984 that is guaranteed to find all of the standard utilities.
1988 option is specified,
1990 is not executed but a description of its interpretation by the shell is
1992 For ordinary commands the output is the path name; for shell built-in
1993 commands, shell functions and keywords only the name is written.
1994 Aliases are printed as
1995 .Dq Ic alias Ar name Ns = Ns Ar value .
1999 option is identical to
2001 except for the output.
2003 .Dq Ar utility Ic is Ar description
2009 a special shell builtin,
2016 .It Ic continue Op Ar num
2018 .Sx Flow-Control Constructs
2020 .It Ic echo Oo Fl e | n Oc Op Ar string ...
2021 Print a space-separated list of the arguments to the standard output
2022 and append a newline character.
2023 .Bl -tag -width indent
2025 Suppress the output of the trailing newline.
2027 Process C-style backslash escape sequences.
2030 command understands the following character escapes:
2031 .Bl -tag -width indent
2033 Alert (ring the terminal bell)
2037 Suppress the trailing newline (this has the side-effect of truncating the
2038 line if it is not the last character)
2056 (Zero) The character whose octal value is
2062 is not enclosed in quotes then the backslash itself must be escaped
2063 with a backslash to protect it from the shell.
2065 .Bd -literal -offset indent
2074 $ echo -e a\e\e\e\eb
2083 options may be specified.
2084 .It Ic eval Ar string ...
2085 Concatenate all the arguments with spaces.
2086 Then re-parse and execute the command.
2087 .It Ic exec Op Ar command Op Ar arg ...
2091 the shell process is replaced with the specified program
2092 (which must be a real program, not a shell built-in command or function).
2093 Any redirections on the
2095 command are marked as permanent,
2096 so that they are not undone when the
2099 .It Ic exit Op Ar exitstatus
2100 Terminate the shell process.
2104 it is used as the exit status of the shell.
2105 Otherwise, if the shell is executing an
2107 trap, the exit status of the last command before the trap is used;
2108 if the shell is executing a trap for a signal,
2109 the shell exits by resending the signal to itself.
2110 Otherwise, the exit status of the preceding command is used.
2111 The exit status should be an integer between 0 and 255.
2112 .It Ic export Ar name ...
2113 .It Ic export Op Fl p
2114 The specified names are exported so that they will
2115 appear in the environment of subsequent commands.
2116 The only way to un-export a variable is to
2119 The shell allows the value of a variable to be set
2120 at the same time as it is exported by writing
2122 .D1 Ic export Ar name Ns = Ns Ar value
2124 With no arguments the
2126 command lists the names
2127 of all exported variables.
2130 option is specified, the exported variables are printed as
2131 .Dq Ic export Ar name Ns = Ns Ar value
2132 lines, suitable for re-input to the shell.
2134 A null command that returns a non-zero (false) exit value.
2135 .It Ic fc Oo Fl e Ar editor Oc Op Ar first Op Ar last
2136 .It Ic fc Fl l Oo Fl nr Oc Op Ar first Op Ar last
2137 .It Ic fc Fl s Oo Ar old Ns = Ns Ar new Oc Op Ar first
2140 built-in command lists, or edits and re-executes,
2141 commands previously entered to an interactive shell.
2142 .Bl -tag -width indent
2144 Use the editor named by
2146 to edit the commands.
2149 string is a command name,
2150 subject to search via the
2155 variable is used as a default when
2160 is null or unset, the value of the
2167 is used as the editor.
2169 List the commands rather than invoking
2171 The commands are written in the
2172 sequence indicated by the
2176 operands, as affected by
2178 with each command preceded by the command number.
2180 Suppress command numbers when listing with
2183 Reverse the order of the commands listed
2192 Re-execute the command without invoking an editor.
2195 Select the commands to list or edit.
2196 The number of previous commands that can be accessed
2197 are determined by the value of the
2204 or both are one of the following:
2205 .Bl -tag -width indent
2206 .It Oo Cm + Oc Ns Ar num
2207 A positive number representing a command number;
2208 command numbers can be displayed with the
2212 A negative decimal number representing the
2213 command that was executed
2216 commands previously.
2217 For example, \-1 is the immediately previous command.
2219 A string indicating the most recently entered command
2220 that begins with that string.
2222 .Ar old Ns = Ns Ar new
2223 operand is not also specified with
2225 the string form of the first operand cannot contain an embedded equal sign.
2229 The following variables affect the execution of
2231 .Bl -tag -width ".Va HISTSIZE"
2233 Name of the editor to use for history editing.
2235 The number of previous commands that are accessible.
2240 or the current job to the foreground.
2241 .It Ic getopts Ar optstring var
2248 command deprecates the older
2251 The first argument should be a series of letters, each possibly
2252 followed by a colon which indicates that the option takes an argument.
2253 The specified variable is set to the parsed option.
2255 the next argument is placed into the shell variable
2257 If an option takes an argument, it is placed into the shell variable
2259 If an invalid option is encountered,
2263 It returns a false value (1) when it encounters the end of the options.
2264 .It Ic hash Oo Fl rv Oc Op Ar command ...
2265 The shell maintains a hash table which remembers the locations of commands.
2266 With no arguments whatsoever, the
2268 command prints out the contents of this table.
2272 command removes each specified
2274 from the hash table (unless they are functions) and then locates it.
2279 prints the locations of the commands as it finds them.
2284 command to delete all the entries in the hash table except for functions.
2285 .It Ic jobid Op Ar job
2286 Print the process IDs of the processes in the specified
2290 argument is omitted, use the current job.
2291 .It Ic jobs Oo Fl lps Oc Op Ar job ...
2292 Print information about the specified jobs, or all jobs if no
2295 The information printed includes job ID, status and command name.
2299 option is specified, the PID of each job is also printed.
2302 option is specified, only the process IDs for the process group leaders
2303 are printed, one per line.
2306 option is specified, only the PIDs of the job commands are printed, one per
2309 A built-in equivalent of
2311 that additionally supports sending signals to jobs.
2312 .It Ic local Oo Ar variable ... Oc Op Fl
2317 A built-in equivalent of
2319 .It Ic pwd Op Fl L | P
2320 Print the path of the current directory.
2321 The built-in command may
2322 differ from the program of the same name because the
2323 built-in command remembers what the current directory
2324 is rather than recomputing it each time.
2327 However, if the current directory is
2329 the built-in version of
2331 will continue to print the old name for the directory.
2335 option is specified, symbolic links are resolved.
2338 option is specified, the shell's notion of the current directory
2339 is printed (symbolic links are not resolved).
2340 This is the default.
2341 .It Ic read Oo Fl p Ar prompt Oc Oo
2342 .Fl t Ar timeout Oc Oo Fl er Oc Ar variable ...
2348 and the standard input is a terminal.
2350 read from the standard input.
2351 The trailing newline
2352 is deleted from the line and the line is split as
2353 described in the section on
2354 .Sx White Space Splitting (Field Splitting)
2356 the pieces are assigned to the variables in order.
2357 If there are more pieces than variables, the remaining
2358 pieces (along with the characters in
2360 that separated them)
2361 are assigned to the last variable.
2362 If there are more variables than pieces, the remaining
2363 variables are assigned the null string.
2365 Backslashes are treated specially, unless the
2369 If a backslash is followed by
2370 a newline, the backslash and the newline will be
2372 If a backslash is followed by any other
2373 character, the backslash will be deleted and the following
2374 character will be treated as though it were not in
2380 option is specified and the
2382 elapses before a complete line of input is supplied,
2385 command will return an exit status as if terminated by
2387 without assigning any values.
2390 value may optionally be followed by one of
2395 to explicitly specify seconds, minutes or hours.
2396 If none is supplied,
2402 option exists only for backward compatibility with older scripts.
2404 The exit status is 0 on success, 1 on end of file,
2405 between 2 and 128 if an error occurs
2406 and greater than 128 if a trapped signal interrupts
2408 .It Ic readonly Oo Fl p Oc Op Ar name ...
2411 is marked as read only,
2412 so that it cannot be subsequently modified or unset.
2413 The shell allows the value of a variable to be set
2414 at the same time as it is marked read only
2415 by using the following form:
2417 .D1 Ic readonly Ar name Ns = Ns Ar value
2419 With no arguments the
2421 command lists the names of all read only variables.
2424 option is specified, the read-only variables are printed as
2425 .Dq Ic readonly Ar name Ns = Ns Ar value
2426 lines, suitable for re-input to the shell.
2427 .It Ic return Op Ar exitstatus
2431 .It Ic set Oo Fl /+abCEefIimnpTuVvx Oc Oo Fl /+o Ar longname Oc Oo
2432 .Fl c Ar string Oc Op Fl - Ar arg ...
2435 command performs three different functions:
2438 With no arguments, it lists the values of all shell variables.
2440 If options are given,
2441 either in short form or using the long
2442 .Dq Fl /+o Ar longname
2444 it sets or clears the specified options as described in the section called
2445 .Sx Argument List Processing .
2449 option is specified,
2451 will replace the shell's positional parameters with the subsequent
2453 If no arguments follow the
2456 all the positional parameters will be cleared,
2457 which is equivalent to executing the command
2461 flag may be omitted when specifying arguments to be used
2462 as positional replacement parameters.
2463 This is not recommended,
2464 because the first argument may begin with a dash
2470 command will interpret as a request to enable or disable options.
2472 .It Ic setvar Ar variable value
2473 Assigns the specified
2479 command is intended to be used in functions that
2480 assign values to variables whose names are passed as parameters.
2481 In general it is better to write
2482 .Dq Ar variable Ns = Ns Ar value
2485 .It Ic shift Op Ar n
2486 Shift the positional parameters
2491 A shift sets the value of
2500 decreasing the value of
2503 If there are zero positional parameters, shifting does not do anything.
2505 A built-in equivalent of
2508 Print the amount of time spent executing the shell process and its children.
2509 The first output line shows the user and system times for the shell process
2510 itself, the second one contains the user and system times for the
2512 .It Ic trap Oo Ar action Oc Ar signal ...
2514 Cause the shell to parse and execute
2519 The signals are specified by name or number.
2520 In addition, the pseudo-signal
2522 may be used to specify an
2524 that is performed when the shell terminates.
2527 may be an empty string or a dash
2529 the former causes the specified signal to be ignored
2530 and the latter causes the default action to be taken.
2533 is another way to request the default action, for compatibility reasons this
2534 usage is not recommended though.
2535 In a subshell or utility environment,
2536 the shell resets trapped (but not ignored) signals to the default action.
2539 command has no effect on signals that were ignored on entry to the shell.
2545 command to display a list of valid signal names.
2547 A null command that returns a 0 (true) exit value.
2548 .It Ic type Op Ar name ...
2551 as a command and print the resolution of the command search.
2552 Possible resolutions are:
2553 shell keyword, alias, special shell builtin, shell builtin, command,
2556 For aliases the alias expansion is printed;
2557 for commands and tracked aliases
2558 the complete pathname of the command is printed.
2559 .It Ic ulimit Oo Fl HSabcdflmnstuv Oc Op Ar limit
2560 Set or display resource limits (see
2564 is specified, the named resource will be set;
2565 otherwise the current resource value will be displayed.
2569 is specified, the hard limits will be set or displayed.
2570 While everybody is allowed to reduce a hard limit,
2571 only the superuser can increase it.
2575 specifies the soft limits instead.
2576 When displaying limits,
2582 The default is to display the soft limits,
2583 and to set both the hard and the soft limits.
2589 command to display all resources.
2592 is not acceptable in this mode.
2594 The remaining options specify which resource value is to be
2595 displayed or modified.
2596 They are mutually exclusive.
2597 .Bl -tag -width indent
2599 The maximum size of socket buffer usage, in bytes.
2600 .It Fl c Ar coredumpsize
2601 The maximal size of core dump files, in 512-byte blocks.
2602 .It Fl d Ar datasize
2603 The maximal size of the data segment of a process, in kilobytes.
2604 .It Fl f Ar filesize
2605 The maximal size of a file, in 512-byte blocks.
2606 .It Fl l Ar lockedmem
2607 The maximal size of memory that can be locked by a process, in
2609 .It Fl m Ar memoryuse
2610 The maximal resident set size of a process, in kilobytes.
2612 The maximal number of descriptors that could be opened by a process.
2613 .It Fl s Ar stacksize
2614 The maximal size of the stack segment, in kilobytes.
2616 The maximal amount of CPU time to be used by each process, in seconds.
2617 .It Fl u Ar userproc
2618 The maximal number of simultaneous processes for this user ID.
2619 .It Fl v Ar virtualmem
2620 The maximal virtual size of a process, in kilobytes.
2622 .It Ic umask Oo Fl S Oc Op Ar mask
2623 Set the file creation mask (see
2625 to the octal or symbolic (see
2629 If the argument is omitted, the current mask value is printed.
2632 option is specified, the output is symbolic, otherwise the output is octal.
2633 .It Ic unalias Oo Fl a Oc Op Ar name ...
2634 The specified alias names are removed.
2637 is specified, all aliases are removed.
2638 .It Ic unset Oo Fl fv Oc Ar name ...
2639 The specified variables or functions are unset and unexported.
2642 option is specified or no options are given, the
2644 arguments are treated as variable names.
2647 option is specified, the
2649 arguments are treated as function names.
2650 .It Ic wait Op Ar job ...
2651 Wait for each specified
2653 to complete and return the exit status of the last process in the
2658 specified is unknown to the shell, it is treated as if it
2659 were a known job that exited with exit status 127.
2660 If no operands are given, wait for all jobs to complete
2661 and return an exit status of zero.
2663 .Ss Commandline Editing
2666 is being used interactively from a terminal, the current command
2667 and the command history
2671 .Sx Built-in Commands )
2674 command line editing.
2675 This mode uses commands similar
2676 to a subset of those described in the
2694 can be switched between insert mode and command mode by typing
2698 while in command mode will pass the line to the shell.
2701 .Dq Li "set -o emacs"
2704 command can be used to enable a subset of
2706 command line editing features.
2708 The following environment variables affect the execution of
2710 .Bl -tag -width ".Ev LANGXXXXXX"
2712 Initialization file for interactive shells.
2713 .It Ev LANG , Ev LC_*
2715 These are inherited by children of the shell,
2716 and is used in a limited manner by the shell itself.
2718 An absolute pathname for the current directory,
2719 possibly containing symbolic links.
2720 This is used and updated by the shell.
2722 The default terminal setting for the shell.
2723 This is inherited by children of the shell, and is used in the history
2727 Additionally, all environment variables are turned into shell variables
2729 which may affect the shell as described under
2730 .Sx Special Variables .
2732 .Bl -tag -width "/etc/suid_profileXX" -compact
2734 User's login profile.
2736 System login profile.
2739 .It Pa /etc/suid_profile
2740 Privileged shell profile.
2743 Errors that are detected by the shell, such as a syntax error, will
2744 cause the shell to exit with a non-zero exit status.
2745 If the shell is not an interactive shell, the execution of the shell
2746 file will be aborted.
2747 Otherwise the shell will return the exit status of the last command
2750 builtin is used with a numeric argument, it
2751 will return the argument.
2757 .Xr emacs 1 Pq Pa editors/emacs ,
2773 command, the Thompson shell, appeared in
2775 It was superseded in
2777 by the Bourne shell, which inherited the name
2782 was rewritten in 1989 under the
2784 license after the Bourne shell from
2789 was originally written by
2790 .An Kenneth Almquist .
2794 utility does not recognize multibyte characters other than UTF-8.
2797 and the line editing library
2799 do not recognize multibyte characters.
2801 The characters generated by filename completion should probably be quoted
2802 to ensure that the filename is still valid after the input line has been
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