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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
73 plus a few Berkeley extensions.
74 This man page is not intended to be a tutorial nor a complete
75 specification of the shell.
77 The shell is a command that reads lines from
78 either a file or the terminal, interprets them, and
79 generally executes other commands.
80 It is the program that is started when a user logs into the system,
81 although a user can select a different shell with the
85 implements a language that has flow control constructs,
86 a macro facility that provides a variety of features in
87 addition to data storage, along with built-in history and line
89 It incorporates many features to
90 aid interactive use and has the advantage that the interpretative
91 language is common to both interactive and non-interactive
93 That is, commands can be typed directly
94 to the running shell or can be put into a file,
95 which can be executed directly by the shell.
98 .\" XXX This next sentence is incredibly confusing.
100 If no arguments are present and if the standard input of the shell
101 is connected to a terminal
105 the shell is considered an interactive shell.
107 generally prompts before each command and handles programming
108 and command errors differently (as described below).
109 When first starting, the shell inspects argument 0, and
110 if it begins with a dash
112 the shell is also considered a login shell.
113 This is normally done automatically by the system
114 when the user first logs in.
115 A login shell first reads commands
120 in a user's home directory,
122 If the environment variable
124 is set on entry to a shell, or is set in the
126 of a login shell, the shell then subjects its value to parameter expansion
127 and arithmetic expansion and reads commands from the named file.
128 Therefore, a user should place commands that are to be executed only
131 file, and commands that are executed for every shell inside the
136 variable to some file by placing the following line in the file
138 in the home directory,
141 the filename desired:
143 .Dl "ENV=$HOME/.shrc; export ENV"
145 The first non-option argument specified on the command line
146 will be treated as the
147 name of a file from which to read commands (a shell script), and
148 the remaining arguments are set as the positional parameters
152 Otherwise, the shell reads commands
153 from its standard input.
155 Unlike older versions of
159 script is only sourced on invocation of interactive shells.
161 closes a well-known, and sometimes easily exploitable security
162 hole related to poorly thought out
165 .Ss Argument List Processing
166 All of the single letter options to
168 have a corresponding long name,
169 with the exception of
173 These long names are provided next to the single letter options
174 in the descriptions below.
175 The long name for an option may be specified as an argument to the
179 Once the shell is running,
180 the long name for an option may be specified as an argument to the
185 (described later in the section called
186 .Sx Built-in Commands ) .
187 Introducing an option with a dash
197 will stop option processing and will force the remaining
198 words on the command line to be treated as arguments.
203 options do not have long names.
204 They take arguments and are described after the single letter options.
205 .Bl -tag -width indent
206 .It Fl a Li allexport
207 Flag variables for export when assignments are made to them.
209 Enable asynchronous notification of background job
212 .It Fl C Li noclobber
213 Do not overwrite existing files with
218 command line editor (disables the
220 option if it has been set;
221 set automatically when interactive on terminals).
223 Exit immediately if any untested command fails in non-interactive mode.
224 The exit status of a command is considered to be
225 explicitly tested if the command is part of the list used to control
227 .Ic if , elif , while ,
230 if the command is the left
235 operator; or if the command is a pipeline preceded by the
238 If a shell function is executed and its exit status is explicitly
239 tested, all commands of the function are considered to be tested as
242 It is recommended to check for failures explicitly
243 instead of relying on
245 because it tends to behave in unexpected ways,
246 particularly in larger scripts.
248 Disable pathname expansion.
250 A do-nothing option for POSIX compliance.
251 .It Fl I Li ignoreeof
254 from input when in interactive mode.
255 .It Fl i Li interactive
256 Force the shell to behave interactively.
258 Turn on job control (set automatically when interactive).
259 A new process group is created for each pipeline (called a job).
260 It is possible to suspend jobs or to have them run in the foreground or
262 In a non-interactive shell,
263 this option can be set even if no terminal is available
264 and is useful to place processes in separate process groups.
266 If not interactive, read commands but do not
268 This is useful for checking the
269 syntax of shell scripts.
271 Change the default for the
277 (logical directory layout)
280 (physical directory layout).
281 .It Fl p Li privileged
282 Turn on privileged mode.
283 This mode is enabled on startup
284 if either the effective user or group ID is not equal to the
285 real user or group ID.
286 Turning this mode off sets the
287 effective user and group IDs to the real user and group IDs.
288 When this mode is enabled for interactive shells, the file
289 .Pa /etc/suid_profile
290 is sourced instead of
294 is sourced, and the contents of the
296 variable are ignored.
298 Read commands from standard input (set automatically
299 if no file arguments are present).
301 no effect when set after the shell has already started
302 running (i.e., when set with the
305 .It Fl T Li trapsasync
306 When waiting for a child, execute traps immediately.
307 If this option is not set,
308 traps are executed after the child exits,
311 This nonstandard option is useful for putting guarding shells around
312 children that block signals.
313 The surrounding shell may kill the child
314 or it may just return control to the tty and leave the child alone,
316 .Bd -literal -offset indent
317 sh -T -c "trap 'exit 1' 2 ; some-blocking-program"
320 Write a message to standard error when attempting
321 to expand a variable, a positional parameter or
322 the special parameter
324 that is not set, and if the
325 shell is not interactive, exit immediately.
329 command line editor (disables
333 The shell writes its input to standard error
335 Useful for debugging.
338 (preceded by the value of the
340 variable subjected to parameter expansion and arithmetic expansion)
341 to standard error before it is executed.
342 Useful for debugging.
344 Another do-nothing option for POSIX compliance.
345 It only has a long name.
350 option causes the commands to be read from the
352 operand instead of from the standard input.
353 Keep in mind that this option only accepts a single string as its
354 argument, hence multi-word strings must be quoted.
358 option takes as its only argument the long name of an option
359 to be enabled or disabled.
360 For example, the following two invocations of
362 both enable the built-in
365 .Bd -literal -offset indent
370 If used without an argument, the
372 option displays the current option settings in a human-readable format.
375 is used without an argument, the current option settings are output
376 in a format suitable for re-input into the shell.
377 .Ss Lexical Structure
378 The shell reads input in terms of lines from a file and breaks
379 it up into words at whitespace (blanks and tabs), and at
383 which are special to the shell.
384 There are two types of operators: control operators and
385 redirection operators (their meaning is discussed later).
386 The following is a list of valid operators:
387 .Bl -tag -width indent
388 .It Control operators:
389 .Bl -column "XXX" "XXX" "XXX" "XXX" "XXX" -offset center -compact
390 .It Li & Ta Li && Ta Li \&( Ta Li \&) Ta Li \en
391 .It Li ;; Ta Li ;& Ta Li \&; Ta Li \&| Ta Li ||
393 .It Redirection operators:
394 .Bl -column "XXX" "XXX" "XXX" "XXX" "XXX" -offset center -compact
395 .It Li < Ta Li > Ta Li << Ta Li >> Ta Li <>
396 .It Li <& Ta Li >& Ta Li <<- Ta Li >| Ta \&
402 introduces a comment if used at the beginning of a word.
403 The word starting with
405 and the rest of the line are ignored.
409 characters (character code 0) are not allowed in shell input.
411 Quoting is used to remove the special meaning of certain characters
412 or words to the shell, such as operators, whitespace, keywords,
415 There are four types of quoting: matched single quotes,
416 dollar-single quotes,
417 matched double quotes, and backslash.
418 .Bl -tag -width indent
420 Enclosing characters in single quotes preserves the literal
421 meaning of all the characters (except single quotes, making
422 it impossible to put single-quotes in a single-quoted string).
423 .It Dollar-Single Quotes
424 Enclosing characters between
428 preserves the literal meaning of all characters
429 except backslashes and single quotes.
430 A backslash introduces a C-style escape sequence:
431 .Bl -tag -width xUnnnnnnnn
433 Alert (ring the terminal bell)
437 The control character denoted by
443 is a backslash, it must be doubled.
445 The ESC character (ASCII 0x1b)
463 The byte whose octal value is
465 (one to three digits)
467 The byte whose hexadecimal value is
469 (one or more digits only the last two of which are used)
471 The Unicode code point
473 (four hexadecimal digits)
474 .It \eU Ns Ar nnnnnnnn
475 The Unicode code point
477 (eight hexadecimal digits)
480 The sequences for Unicode code points are currently only useful with
482 They reject code point 0 and UTF-16 surrogates.
484 If an escape sequence would produce a byte with value 0,
485 that byte and the rest of the string until the matching single-quote
488 Any other string starting with a backslash is an error.
490 Enclosing characters within double quotes preserves the literal
491 meaning of all characters except dollar sign
497 The backslash inside double quotes is historically weird.
498 It remains literal unless it precedes the following characters,
499 which it serves to quote:
501 .Bl -column "XXX" "XXX" "XXX" "XXX" "XXX" -offset center -compact
502 .It Li $ Ta Li ` Ta Li \&" Ta Li \e Ta Li \en
505 A backslash preserves the literal meaning of the following
506 character, with the exception of the newline character
508 A backslash preceding a newline is treated as a line continuation.
511 Keywords or reserved words are words that have special meaning to the
512 shell and are recognized at the beginning of a line and
513 after a control operator.
514 The following are keywords:
515 .Bl -column "doneXX" "elifXX" "elseXX" "untilXX" "whileX" -offset center
516 .It Li \&! Ta { Ta } Ta Ic case Ta Ic do
517 .It Ic done Ta Ic elif Ta Ic else Ta Ic esac Ta Ic fi
518 .It Ic for Ta Ic if Ta Ic then Ta Ic until Ta Ic while
521 An alias is a name and corresponding value set using the
524 Wherever the command word of a simple command may occur,
525 and after checking for keywords if a keyword may occur, the shell
526 checks the word to see if it matches an alias.
527 If it does, it replaces it in the input stream with its value.
528 For example, if there is an alias called
540 Aliases are also recognized after an alias
541 whose value ends with a space or tab.
542 For example, if there is also an alias called
548 .Dl "nohup lf foobar"
552 .Dl "nohup ls -F foobar"
554 Aliases provide a convenient way for naive users to
555 create shorthands for commands without having to learn how
556 to create functions with arguments.
557 Using aliases in scripts is discouraged
558 because the command that defines them must be executed
559 before the code that uses them is parsed.
560 This is fragile and not portable.
562 An alias name may be escaped in a command line, so that it is not
563 replaced by its alias value, by using quoting characters within or
564 adjacent to the alias name.
565 This is most often done by prefixing
566 an alias name with a backslash to execute a function, built-in, or
567 normal program with the same name.
572 The shell interprets the words it reads according to a
573 language, the specification of which is outside the scope
574 of this man page (refer to the BNF in the
577 Essentially though, a line is read and if
578 the first word of the line (or after a control operator)
579 is not a keyword, then the shell has recognized a
581 Otherwise, a complex command or some
582 other special construct may have been recognized.
584 If a simple command has been recognized, the shell performs
585 the following actions:
588 Leading words of the form
590 are stripped off and assigned to the environment of
592 (they do not affect expansions).
593 Redirection operators and
594 their arguments (as described below) are stripped
595 off and saved for processing.
597 The remaining words are expanded as described in
599 .Sx Word Expansions ,
600 and the first remaining word is considered the command
601 name and the command is located.
603 words are considered the arguments of the command.
604 If no command name resulted, then the
606 variable assignments recognized in 1) affect the
609 Redirections are performed as described in
613 Redirections are used to change where a command reads its input
615 In general, redirections open, close, or
616 duplicate an existing reference to a file.
618 used for redirection is:
620 .D1 Oo Ar n Oc Ar redir-op file
624 is one of the redirection operators mentioned
626 The following gives some examples of how these
627 operators can be used.
628 Note that stdin and stdout are commonly used abbreviations
629 for standard input and standard output respectively.
630 .Bl -tag -width "1234567890XX" -offset indent
631 .It Oo Ar n Oc Ns Li > Ar file
632 redirect stdout (or file descriptor
636 .It Oo Ar n Oc Ns Li >| Ar file
637 same as above, but override the
640 .It Oo Ar n Oc Ns Li >> Ar file
641 append stdout (or file descriptor
645 .It Oo Ar n Oc Ns Li < Ar file
646 redirect stdin (or file descriptor
650 .It Oo Ar n Oc Ns Li <> Ar file
651 redirect stdin (or file descriptor
655 .It Oo Ar n1 Oc Ns Li <& Ns Ar n2
656 duplicate stdin (or file descriptor
660 .It Oo Ar n Oc Ns Li <&-
661 close stdin (or file descriptor
663 .It Oo Ar n1 Oc Ns Li >& Ns Ar n2
664 duplicate stdout (or file descriptor
668 .It Oo Ar n Oc Ns Li >&-
669 close stdout (or file descriptor
673 The following redirection is often called a
675 .Bd -unfilled -offset indent
676 .Oo Ar n Oc Ns Li << Ar delimiter
682 All the text on successive lines up to the delimiter is
683 saved away and made available to the command on standard
684 input, or file descriptor
689 as specified on the initial line is quoted, then the
691 is treated literally, otherwise the text is subjected to
692 parameter expansion, command substitution, and arithmetic
693 expansion (as described in the section on
694 .Sx Word Expansions ) .
703 .Ss Search and Execution
704 There are three types of commands: shell functions,
705 built-in commands, and normal programs.
706 The command is searched for (by name) in that order.
707 The three types of commands are all executed in a different way.
709 When a shell function is executed, all of the shell positional
712 which remains unchanged) are
713 set to the arguments of the shell function.
714 The variables which are explicitly placed in the environment of
715 the command (by placing assignments to them before the
716 function name) are made local to the function and are set
718 Then the command given in the function definition is executed.
719 The positional parameters are restored to their original values
720 when the command completes.
721 This all occurs within the current shell.
723 Shell built-in commands are executed internally to the shell, without
724 spawning a new process.
725 There are two kinds of built-in commands: regular and special.
726 Assignments before special builtins persist after they finish
727 executing and assignment errors, redirection errors and certain
728 operand errors cause a script to be aborted.
729 Special builtins cannot be overridden with a function.
730 Both regular and special builtins can affect the shell in ways
731 normal programs cannot.
733 Otherwise, if the command name does not match a function
734 or built-in command, the command is searched for as a normal
735 program in the file system (as described in the next section).
736 When a normal program is executed, the shell runs the program,
737 passing the arguments and the environment to the program.
738 If the program is not a normal executable file
739 (i.e., if it does not begin with the
741 whose ASCII representation is
747 but appears to be a text file,
748 the shell will run a new instance of
752 Note that previous versions of this document
753 and the source code itself misleadingly and sporadically
754 refer to a shell script without a magic number
756 .Dq "shell procedure" .
758 When locating a command, the shell first looks to see if
759 it has a shell function by that name.
761 built-in command by that name.
762 If a built-in command is not found,
763 one of two things happen:
766 Command names containing a slash are simply executed without
767 performing any searches.
769 The shell searches each entry in the
772 in turn for the command.
775 variable should be a series of
776 entries separated by colons.
777 Each entry consists of a
779 The current directory
780 may be indicated implicitly by an empty directory name,
781 or explicitly by a single period.
783 .Ss Command Exit Status
784 Each command has an exit status that can influence the behavior
785 of other shell commands.
786 The paradigm is that a command exits
787 with zero for normal or success, and non-zero for failure,
788 error, or a false indication.
789 The man page for each command
790 should indicate the various exit codes and what they mean.
791 Additionally, the built-in commands return exit codes, as does
792 an executed shell function.
794 If a command is terminated by a signal, its exit status is greater than 128.
795 The signal name can be found by passing the exit status to
798 If there is no command word,
799 the exit status is the exit status of the last command substitution executed,
800 or zero if the command does not contain any command substitutions.
802 Complex commands are combinations of simple commands
803 with control operators or keywords, together creating a larger complex
805 More generally, a command is one of the following:
806 .Bl -item -offset indent
812 list or compound-list
819 Unless otherwise stated, the exit status of a command is
820 that of the last simple command executed by the command,
821 or zero if no simple command was executed.
823 A pipeline is a sequence of one or more commands separated
824 by the control operator
826 The standard output of all but
827 the last command is connected to the standard input
829 The standard output of the last
830 command is inherited from the shell, as usual.
832 The format for a pipeline is:
834 .D1 Oo Li \&! Oc Ar command1 Op Li \&| Ar command2 ...
836 The standard output of
838 is connected to the standard input of
840 The standard input, standard output, or
841 both of a command is considered to be assigned by the
842 pipeline before any redirection specified by redirection
843 operators that are part of the command.
845 Note that unlike some other shells,
847 executes each process in a pipeline with more than one command
848 in a subshell environment and as a child of the
852 If the pipeline is not in the background (discussed later),
853 the shell waits for all commands to complete.
857 does not precede the pipeline, the
858 exit status is the exit status of the last command specified
860 Otherwise, the exit status is the logical
861 NOT of the exit status of the last command.
863 the last command returns zero, the exit status is 1; if
864 the last command returns greater than zero, the exit status
867 Because pipeline assignment of standard input or standard
868 output or both takes place before redirection, it can be
869 modified by redirection.
872 .Dl "command1 2>&1 | command2"
874 sends both the standard output and standard error of
876 to the standard input of
881 or newline terminator causes the preceding
883 (described below in the section called
884 .Sx Short-Circuit List Operators )
885 to be executed sequentially;
888 causes asynchronous execution of the preceding AND-OR-list.
889 .Ss Background Commands (&)
890 If a command is terminated by the control operator ampersand
892 the shell executes the command in a subshell environment (see
893 .Sx Grouping Commands Together
894 below) and asynchronously;
895 the shell does not wait for the command to finish
896 before executing the next command.
898 The format for running a command in background is:
900 .D1 Ar command1 Li & Op Ar command2 Li & Ar ...
902 If the shell is not interactive, the standard input of an
903 asynchronous command is set to
906 The exit status is zero.
907 .Ss Lists (Generally Speaking)
908 A list is a sequence of zero or more commands separated by
909 newlines, semicolons, or ampersands,
910 and optionally terminated by one of these three characters.
912 list are executed in the order they are written.
913 If command is followed by an ampersand, the shell starts the
914 command and immediately proceeds onto the next command;
915 otherwise it waits for the command to terminate before
916 proceeding to the next one.
917 .Ss Short-Circuit List Operators
921 are AND-OR list operators.
923 executes the first command, and then executes the second command
924 if the exit status of the first command is zero.
926 is similar, but executes the second command if the exit
927 status of the first command is nonzero.
931 both have the same priority.
932 .Ss Flow-Control Constructs (if, while, for, case)
936 .Bd -unfilled -offset indent -compact
940 .Ic then Ar list Oc Ar ...
945 The exit status is that of selected
950 or zero if no list was selected.
955 .Bd -unfilled -offset indent -compact
961 The two lists are executed repeatedly while the exit status of the
965 command is similar, but has the word
970 repeat until the exit status of the first list is zero.
972 The exit status is that of the last execution of the second list,
973 or zero if it was never executed.
978 .Bd -unfilled -offset indent -compact
979 .Ic for Ar variable Op Ic in Ar word ...
986 and the following words are omitted,
989 The words are expanded, and then the list is executed
990 repeatedly with the variable set to each word in turn.
995 commands may be replaced with
1005 .D1 Ic break Op Ar num
1006 .D1 Ic continue Op Ar num
1010 command terminates the
1019 command continues with the next iteration of the innermost loop.
1020 These are implemented as special built-in commands.
1025 .Bd -unfilled -offset indent -compact
1026 .Ic case Ar word Ic in
1027 .Ar pattern ) Ar list Li ;;
1032 The pattern can actually be one or more patterns
1039 Tilde expansion, parameter expansion, command substitution,
1040 arithmetic expansion and quote removal are applied to the word.
1041 Then, each pattern is expanded in turn using tilde expansion,
1042 parameter expansion, command substitution and arithmetic expansion and
1043 the expanded form of the word is checked against it.
1044 If a match is found, the corresponding list is executed.
1045 If the selected list is terminated by the control operator
1049 execution continues with the next list,
1050 continuing until a list terminated with
1055 .Ss Grouping Commands Together
1056 Commands may be grouped by writing either
1059 .Bd -literal -offset -ident
1065 .Bd -literal -offset -ident
1069 The first form executes the commands in a subshell environment.
1070 A subshell environment has its own copy of:
1073 The current working directory as set by
1076 The file creation mask as set by
1079 Resource limits as set by
1082 References to open files.
1089 Positional parameters and variables.
1098 These are copied from the parent shell environment,
1099 except that trapped (but not ignored) signals are reset to the default action
1100 and known jobs are cleared.
1101 Any changes do not affect the parent shell environment.
1103 A subshell environment may be implemented as a child process or differently.
1104 If job control is enabled in an interactive shell,
1105 commands grouped in parentheses can be suspended and continued as a unit.
1107 For compatibility with other shells,
1108 two open parentheses in sequence should be separated by whitespace.
1110 The second form never forks another shell,
1111 so it is slightly more efficient.
1112 Grouping commands together this way allows the user to
1113 redirect their output as though they were one program:
1114 .Bd -literal -offset indent
1115 { echo -n "hello"; echo " world"; } > greeting
1118 The syntax of a function definition is
1120 .D1 Ar name Li \&( \&) Ar command
1122 A function definition is an executable statement; when
1123 executed it installs a function named
1126 exit status of zero.
1135 Variables may be declared to be local to a function by
1139 This should appear as the first statement of a function,
1142 .D1 Ic local Oo Ar variable ... Oc Op Fl
1146 command is implemented as a built-in command.
1147 The exit status is zero
1148 unless the command is not in a function or a variable name is invalid.
1150 When a variable is made local, it inherits the initial
1151 value and exported and readonly flags from the variable
1152 with the same name in the surrounding scope, if there is
1154 Otherwise, the variable is initially unset.
1156 uses dynamic scoping, so that if the variable
1158 is made local to function
1160 which then calls function
1162 references to the variable
1166 will refer to the variable
1170 not to the global variable named
1173 The only special parameter that can be made local is
1177 local causes any shell options
1178 (including those that only have long names)
1182 command inside the function to be
1183 restored to their original values when the function
1190 .D1 Ic return Op Ar exitstatus
1192 It terminates the current executional scope, returning from the closest
1193 nested function or sourced script;
1194 if no function or sourced script is being executed,
1195 it exits the shell instance.
1198 command is implemented as a special built-in command.
1199 .Ss Variables and Parameters
1200 The shell maintains a set of parameters.
1204 of alphabetics, numerics, and underscores,
1205 and starting with an alphabetic or an underscore)
1206 is called a variable.
1208 the shell turns all environment variables with valid names into shell
1210 New variables can be set using the form
1212 .D1 Ar name Ns = Ns Ar value
1214 A parameter can also be denoted by a number
1215 or a special character as explained below.
1217 Assignments are expanded differently from other words:
1218 tilde expansion is also performed after the equals sign and after any colon
1219 and usernames are also terminated by colons,
1220 and field splitting and pathname expansion are not performed.
1222 This special expansion applies not only to assignments that form a simple
1223 command by themselves or precede a command word,
1224 but also to words passed to the
1229 built-in commands that have this form.
1230 For this, the builtin's name must be literal
1231 (not the result of an expansion)
1232 and may optionally be preceded by one or more literal instances of
1235 .Ss Positional Parameters
1236 A positional parameter is a parameter denoted by a number greater than zero.
1237 The shell sets these initially to the values of its command line
1238 arguments that follow the name of the shell script.
1241 built-in command can also be used to set or reset them.
1242 .Ss Special Parameters
1243 Special parameters are parameters denoted by a single special character
1245 They are shown in the following list, exactly as they would appear in input
1246 typed by the user or in the source of a shell script.
1249 Expands to the positional parameters, starting from one.
1251 the expansion occurs within a double-quoted string
1252 it expands to a single field with the value of each parameter
1253 separated by the first character of the
1260 Expands to the positional parameters, starting from one.
1262 the expansion occurs within double-quotes, each positional
1263 parameter expands as a separate argument.
1264 If there are no positional parameters, the
1267 generates zero arguments, even when
1270 What this basically means, for example, is
1283 .Bd -literal -offset indent
1287 Expands to the number of positional parameters.
1289 Expands to the exit status of the most recent pipeline.
1291 (hyphen) Expands to the current option flags (the single-letter
1292 option names concatenated into a string) as specified on
1295 built-in command, or implicitly
1298 Expands to the process ID of the invoked shell.
1300 retains the same value of
1304 Expands to the process ID of the most recent background
1305 command executed from the current shell.
1307 pipeline, the process ID is that of the last command in the
1309 If this parameter is referenced, the shell will remember
1310 the process ID and its exit status until the
1312 built-in command reports completion of the process.
1314 (zero) Expands to the name of the shell script if passed on the command line,
1317 operand if given (with
1319 or otherwise argument 0 passed to the shell.
1321 .Ss Special Variables
1322 The following variables are set by the shell or
1323 have special meaning to it:
1324 .Bl -tag -width ".Va HISTSIZE"
1326 The search path used with the
1330 The fallback editor used with the
1333 If not set, the default editor is
1336 The default editor used with the
1340 The number of previous commands that are accessible.
1342 The user's home directory,
1343 used in tilde expansion and as a default directory for the
1347 Input Field Separators.
1348 This is initialized at startup to
1354 This value also applies if
1356 is unset, but not if it is set to the empty string.
1358 .Sx White Space Splitting
1359 section for more details.
1361 The current line number in the script or function.
1363 The name of a mail file, that will be checked for the arrival of new
1370 separated list of file names, for the shell to check for incoming
1372 This variable overrides the
1375 There is a maximum of 10 mailboxes that can be monitored at once.
1377 The index of the next argument to be processed by
1379 This is initialized to 1 at startup.
1381 The default search path for executables.
1384 section for details.
1386 The parent process ID of the invoked shell.
1387 This is set at startup
1388 unless this variable is in the environment.
1389 A later change of parent process ID is not reflected.
1390 A subshell retains the same value of
1393 The primary prompt string, which defaults to
1395 unless you are the superuser, in which case it defaults to
1398 may include any of the following formatting sequences,
1399 which are replaced by the given information:
1400 .Bl -tag -width indent
1402 This system's fully-qualified hostname (FQDN).
1404 This system's hostname.
1408 The final component of the current working directory.
1410 The entire path of the current working directory.
1414 for normal users and
1418 A literal backslash.
1421 The secondary prompt string, which defaults to
1424 may include any of the formatting sequences from
1427 The prefix for the trace output (if
1434 This clause describes the various expansions that are
1436 Not all expansions are performed on
1437 every word, as explained later.
1439 Tilde expansions, parameter expansions, command substitutions,
1440 arithmetic expansions, and quote removals that occur within
1441 a single word expand to a single field.
1443 splitting or pathname expansion that can create multiple
1444 fields from a single word.
1445 The single exception to this rule is
1446 the expansion of the special parameter
1448 within double-quotes,
1449 as was described above.
1451 The order of word expansion is:
1454 Tilde Expansion, Parameter Expansion, Command Substitution,
1455 Arithmetic Expansion (these all occur at the same time).
1457 Field Splitting is performed on fields generated by step (1)
1462 Pathname Expansion (unless the
1464 option is in effect).
1471 character is used to introduce parameter expansion, command
1472 substitution, or arithmetic expansion.
1473 .Ss Tilde Expansion (substituting a user's home directory)
1474 A word beginning with an unquoted tilde character
1477 subjected to tilde expansion.
1478 All the characters up to a slash
1480 or the end of the word are treated as a username
1481 and are replaced with the user's home directory.
1483 username is missing (as in
1485 the tilde is replaced with the value of the
1487 variable (the current user's home directory).
1488 .Ss Parameter Expansion
1489 The format for parameter expansion is as follows:
1491 .D1 Li ${ Ns Ar expression Ns Li }
1495 consists of all characters until the matching
1499 escaped by a backslash or within a single-quoted or double-quoted
1500 string, and characters in
1501 embedded arithmetic expansions, command substitutions, and variable
1502 expansions, are not examined in determining the matching
1504 If the variants with
1510 occur within a double-quoted string,
1511 as an extension there may be unquoted parts
1512 (via double-quotes inside the expansion);
1514 within such parts are also not examined in determining the matching
1517 The simplest form for parameter expansion is:
1519 .D1 Li ${ Ns Ar parameter Ns Li }
1521 The value, if any, of
1525 The parameter name or symbol can be enclosed in braces, which are
1526 optional except for positional parameters with more than one digit or
1527 when parameter is followed by a character that could be interpreted as
1529 If a parameter expansion occurs inside double-quotes:
1532 Field splitting is not performed on the results of the
1533 expansion, with the exception of the special parameter
1536 Pathname expansion is not performed on the results of the
1540 In addition, a parameter expansion can be modified by using one of the
1542 .Bl -tag -width indent
1543 .It Li ${ Ns Ar parameter Ns Li :- Ns Ar word Ns Li }
1547 is unset or null, the expansion of
1549 is substituted; otherwise, the value of
1552 .It Li ${ Ns Ar parameter Ns Li := Ns Ar word Ns Li }
1553 Assign Default Values.
1556 is unset or null, the expansion of
1566 does not prevent field splitting or pathname expansion.
1567 Only variables, not positional
1568 parameters or special parameters, can be
1569 assigned in this way.
1570 .It Li ${ Ns Ar parameter Ns Li :? Ns Oo Ar word Oc Ns Li }
1571 Indicate Error if Null or Unset.
1574 is unset or null, the expansion of
1576 (or a message indicating it is unset if
1578 is omitted) is written to standard
1579 error and the shell exits with a nonzero
1581 Otherwise, the value of
1585 interactive shell need not exit.
1586 .It Li ${ Ns Ar parameter Ns Li :+ Ns Ar word Ns Li }
1587 Use Alternate Value.
1590 is unset or null, null is substituted;
1591 otherwise, the expansion of
1596 In the parameter expansions shown previously, use of the colon in the
1597 format results in a test for a parameter that is unset or null; omission
1598 of the colon results in a test for a parameter that is only unset.
1602 inherits the type of quoting
1603 (unquoted, double-quoted or here-document)
1604 from the surroundings,
1605 with the exception that a backslash that quotes a closing brace is removed
1606 during quote removal.
1607 .Bl -tag -width indent
1608 .It Li ${# Ns Ar parameter Ns Li }
1610 The length in characters of
1615 The following four varieties of parameter expansion provide for substring
1617 In each case, pattern matching notation
1619 .Sx Shell Patterns ) ,
1620 rather than regular expression notation,
1621 is used to evaluate the patterns.
1622 If parameter is one of the special parameters
1626 the result of the expansion is unspecified.
1627 Enclosing the full parameter expansion string in double-quotes does not
1628 cause the following four varieties of pattern characters to be quoted,
1629 whereas quoting characters within the braces has this effect.
1630 .Bl -tag -width indent
1631 .It Li ${ Ns Ar parameter Ns Li % Ns Ar word Ns Li }
1632 Remove Smallest Suffix Pattern.
1635 is expanded to produce a pattern.
1637 parameter expansion then results in
1639 with the smallest portion of the
1640 suffix matched by the pattern deleted.
1641 .It Li ${ Ns Ar parameter Ns Li %% Ns Ar word Ns Li }
1642 Remove Largest Suffix Pattern.
1645 is expanded to produce a pattern.
1647 parameter expansion then results in
1649 with the largest portion of the
1650 suffix matched by the pattern deleted.
1651 .It Li ${ Ns Ar parameter Ns Li # Ns Ar word Ns Li }
1652 Remove Smallest Prefix Pattern.
1655 is expanded to produce a pattern.
1657 parameter expansion then results in
1659 with the smallest portion of the
1660 prefix matched by the pattern deleted.
1661 .It Li ${ Ns Ar parameter Ns Li ## Ns Ar word Ns Li }
1662 Remove Largest Prefix Pattern.
1665 is expanded to produce a pattern.
1667 parameter expansion then results in
1669 with the largest portion of the
1670 prefix matched by the pattern deleted.
1672 .Ss Command Substitution
1673 Command substitution allows the output of a command to be substituted in
1674 place of the command name itself.
1675 Command substitution occurs when
1676 the command is enclosed as follows:
1678 .D1 Li $( Ns Ar command Ns Li )\&
1680 or the backquoted version:
1682 .D1 Li ` Ns Ar command Ns Li `
1684 The shell expands the command substitution by executing command
1685 and replacing the command substitution
1686 with the standard output of the command,
1687 removing sequences of one or more newlines at the end of the substitution.
1688 Embedded newlines before the end of the output are not removed;
1689 however, during field splitting, they may be translated into spaces
1690 depending on the value of
1692 and the quoting that is in effect.
1693 The command is executed in a subshell environment,
1694 except that the built-in commands
1699 return information about the parent shell environment
1702 returns information about the same process
1703 if they are the only command in a command substitution.
1705 If a command substitution of the
1707 form begins with a subshell,
1712 must be separated by whitespace
1713 to avoid ambiguity with arithmetic expansion.
1714 .Ss Arithmetic Expansion
1715 Arithmetic expansion provides a mechanism for evaluating an arithmetic
1716 expression and substituting its value.
1717 The format for arithmetic expansion is as follows:
1719 .D1 Li $(( Ns Ar expression Ns Li ))
1723 is treated as if it were in double-quotes, except
1724 that a double-quote inside the expression is not treated specially.
1726 shell expands all tokens in the
1728 for parameter expansion,
1729 command substitution,
1730 arithmetic expansion
1733 The allowed expressions are a subset of C expressions,
1735 .Bl -tag -width "Variables" -offset indent
1737 All values are of type
1740 Decimal, octal (starting with
1742 and hexadecimal (starting with
1746 Shell variables can be read and written
1747 and contain integer constants.
1750 .It Binary operators
1751 .Li "* / % + - << >> < <= > >= == != & ^ | && ||"\&
1752 .It Assignment operators
1753 .Li "= += -= *= /= %= <<= >>= &= ^= |="
1754 .It Conditional operator
1758 The result of the expression is substituted in decimal.
1759 .Ss White Space Splitting (Field Splitting)
1760 In certain contexts,
1761 after parameter expansion, command substitution, and
1762 arithmetic expansion the shell scans the results of
1763 expansions and substitutions that did not occur in double-quotes for
1764 field splitting and multiple fields can result.
1775 are treated differently from other characters in
1780 at the beginning or end of a word is discarded.
1782 Subsequently, a field is delimited by either
1785 a non-whitespace character in
1787 with any whitespace in
1791 one or more whitespace characters in
1795 If a word ends with a non-whitespace character in
1797 there is no empty field after this character.
1799 If no field is delimited, the word is discarded.
1800 In particular, if a word consists solely of an unquoted substitution
1801 and the result of the substitution is null,
1802 it is removed by field splitting even if
1805 .Ss Pathname Expansion (File Name Generation)
1809 file name generation is performed
1810 after word splitting is complete.
1812 viewed as a series of patterns, separated by slashes.
1814 process of expansion replaces the word with the names of
1815 all existing files whose names can be formed by replacing
1816 each pattern with a string that matches the specified pattern.
1817 There are two restrictions on this: first, a pattern cannot match
1818 a string containing a slash, and second,
1819 a pattern cannot match a string starting with a period
1820 unless the first character of the pattern is a period.
1821 The next section describes the patterns used for
1823 the four varieties of parameter expansion for substring processing and the
1827 A pattern consists of normal characters, which match themselves,
1828 and meta-characters.
1829 The meta-characters are
1834 These characters lose their special meanings if they are quoted.
1835 When command or variable substitution is performed and the dollar sign
1836 or back quotes are not double-quoted, the value of the
1837 variable or the output of the command is scanned for these
1838 characters and they are turned into meta-characters.
1842 matches any string of characters.
1845 matches any single character.
1848 introduces a character class.
1849 The end of the character class is indicated by a
1857 rather than introducing a character class.
1858 A character class matches any of the characters between the square brackets.
1859 A locale-dependent range of characters may be specified using a minus sign.
1860 A named class of characters (see
1862 may be specified by surrounding the name with
1867 .Ql \&[\&[:alpha:\&]\&]
1868 is a shell pattern that matches a single letter.
1869 The character class may be complemented by making an exclamation point
1871 the first character of the character class.
1874 has the same effect but is non-standard.
1878 in a character class, make it the first character listed
1886 make it the first or last character listed.
1887 .Ss Built-in Commands
1888 This section lists the built-in commands.
1889 .Bl -tag -width indent
1891 A null command that returns a 0 (true) exit value.
1893 The commands in the specified file are read and executed by the shell.
1896 command may be used to return to the
1903 characters, it is used as is.
1904 Otherwise, the shell searches the
1907 If it is not found in the
1909 it is sought in the current working directory.
1911 A built-in equivalent of
1913 .It Ic alias Oo Ar name Ns Oo = Ns Ar string Oc ... Oc
1915 .Ar name Ns = Ns Ar string
1916 is specified, the shell defines the alias
1922 is specified, the value of the alias
1925 With no arguments, the
1927 built-in command prints the names and values of all defined aliases
1930 Alias values are written with appropriate quoting so that they are
1931 suitable for re-input to the shell.
1935 .It Ic bg Op Ar job ...
1936 Continue the specified jobs
1937 (or the current job if no jobs are given)
1939 .It Ic bind Oo Fl aeklrsv Oc Oo Ar key Oo Ar command Oc Oc
1940 List or alter key bindings for the line editor.
1941 This command is documented in
1943 .It Ic break Op Ar num
1945 .Sx Flow-Control Constructs
1947 .It Ic builtin Ar cmd Op Ar arg ...
1948 Execute the specified built-in command,
1950 This is useful when the user wishes to override a shell function
1951 with the same name as a built-in command.
1952 .It Ic cd Oo Fl L | P Oc Oo Fl e Oc Op Ar directory
1954 Switch to the specified
1956 to the directory specified in the
1958 environment variable if no
1961 to the directory specified in the
1963 environment variable if
1973 then the directories listed in the
1976 searched for the specified
1980 is unset, the current directory is searched.
1983 is the same as that of
1985 In an interactive shell,
1988 command will print out the name of the directory
1989 that it actually switched to
1992 mechanism was used or if
1999 option is specified,
2001 is handled physically and symbolic links are resolved before
2003 components are processed.
2006 option is specified,
2008 is handled logically.
2009 This is the default.
2015 to return exit status 1 if the full pathname of the new directory
2016 cannot be determined reliably or at all.
2017 Normally this is not considered an error,
2018 although a warning is printed.
2020 If changing the directory fails, the exit status is greater than 1.
2021 If the directory is changed, the exit status is 0, or also 1 if
2028 .It Ic command Oo Fl p Oc Op Ar utility Op Ar argument ...
2029 .It Ic command Oo Fl p Oc Fl v Ar utility
2030 .It Ic command Oo Fl p Oc Fl V Ar utility
2031 The first form of invocation executes the specified
2033 ignoring shell functions in the search.
2036 is a special builtin,
2037 it is executed as if it were a regular builtin.
2041 option is specified, the command search is performed using a
2044 that is guaranteed to find all of the standard utilities.
2048 option is specified,
2050 is not executed but a description of its interpretation by the shell is
2052 For ordinary commands the output is the path name; for shell built-in
2053 commands, shell functions and keywords only the name is written.
2054 Aliases are printed as
2055 .Dq Ic alias Ar name Ns = Ns Ar value .
2059 option is identical to
2061 except for the output.
2063 .Dq Ar utility Ic is Ar description
2069 a special shell builtin,
2076 .It Ic continue Op Ar num
2078 .Sx Flow-Control Constructs
2080 .It Ic echo Oo Fl e | n Oc Op Ar string ...
2081 Print a space-separated list of the arguments to the standard output
2082 and append a newline character.
2083 .Bl -tag -width indent
2085 Suppress the output of the trailing newline.
2087 Process C-style backslash escape sequences.
2090 command understands the following character escapes:
2091 .Bl -tag -width indent
2093 Alert (ring the terminal bell)
2097 Suppress the trailing newline (this has the side-effect of truncating the
2098 line if it is not the last character)
2100 The ESC character (ASCII 0x1b)
2114 (Zero) The character whose octal value is
2120 is not enclosed in quotes then the backslash itself must be escaped
2121 with a backslash to protect it from the shell.
2123 .Bd -literal -offset indent
2132 $ echo -e a\e\e\e\eb
2141 options may be specified.
2142 .It Ic eval Ar string ...
2143 Concatenate all the arguments with spaces.
2144 Then re-parse and execute the command.
2145 .It Ic exec Op Ar command Op arg ...
2149 the shell process is replaced with the specified program
2150 (which must be a real program, not a shell built-in command or function).
2151 Any redirections on the
2153 command are marked as permanent,
2154 so that they are not undone when the
2157 .It Ic exit Op Ar exitstatus
2158 Terminate the shell process.
2162 it is used as the exit status of the shell.
2163 Otherwise, if the shell is executing an
2165 trap, the exit status of the last command before the trap is used;
2166 if the shell is executing a trap for a signal,
2167 the shell exits by resending the signal to itself.
2168 Otherwise, the exit status of the preceding command is used.
2169 The exit status should be an integer between 0 and 255.
2170 .It Ic export Ar name ...
2171 .It Ic export Op Fl p
2172 The specified names are exported so that they will
2173 appear in the environment of subsequent commands.
2174 The only way to un-export a variable is to
2177 The shell allows the value of a variable to be set
2178 at the same time as it is exported by writing
2180 .D1 Ic export Ar name Ns = Ns Ar value
2182 With no arguments the
2184 command lists the names
2185 of all exported variables.
2188 option is specified, the exported variables are printed as
2189 .Dq Ic export Ar name Ns = Ns Ar value
2190 lines, suitable for re-input to the shell.
2192 A null command that returns a non-zero (false) exit value.
2193 .It Ic fc Oo Fl e Ar editor Oc Op Ar first Op Ar last
2194 .It Ic fc Fl l Oo Fl nr Oc Op Ar first Op Ar last
2195 .It Ic fc Fl s Oo Ar old Ns = Ns Ar new Oc Op Ar first
2198 built-in command lists, or edits and re-executes,
2199 commands previously entered to an interactive shell.
2200 .Bl -tag -width indent
2202 Use the editor named by
2204 to edit the commands.
2207 string is a command name,
2208 subject to search via the
2213 variable is used as a default when
2218 is null or unset, the value of the
2225 is used as the editor.
2227 List the commands rather than invoking
2229 The commands are written in the
2230 sequence indicated by the
2234 operands, as affected by
2236 with each command preceded by the command number.
2238 Suppress command numbers when listing with
2241 Reverse the order of the commands listed
2250 Re-execute the command without invoking an editor.
2253 Select the commands to list or edit.
2254 The number of previous commands that can be accessed
2255 are determined by the value of the
2262 or both are one of the following:
2263 .Bl -tag -width indent
2264 .It Oo Cm + Oc Ns Ar num
2265 A positive number representing a command number;
2266 command numbers can be displayed with the
2270 A negative decimal number representing the
2271 command that was executed
2274 commands previously.
2275 For example, \-1 is the immediately previous command.
2277 A string indicating the most recently entered command
2278 that begins with that string.
2280 .Ar old Ns = Ns Ar new
2281 operand is not also specified with
2283 the string form of the first operand cannot contain an embedded equal sign.
2287 The following variables affect the execution of
2289 .Bl -tag -width ".Va HISTSIZE"
2291 Name of the editor to use for history editing.
2293 The number of previous commands that are accessible.
2298 or the current job to the foreground.
2299 .It Ic getopts Ar optstring var
2305 command deprecates the older
2308 The first argument should be a series of letters, each possibly
2309 followed by a colon which indicates that the option takes an argument.
2310 The specified variable is set to the parsed option.
2312 the next argument is placed into the shell variable
2314 If an option takes an argument, it is placed into the shell variable
2316 If an invalid option is encountered,
2320 It returns a false value (1) when it encounters the end of the options.
2321 A new set of arguments may be parsed by assigning
2323 .It Ic hash Oo Fl rv Oc Op Ar command ...
2324 The shell maintains a hash table which remembers the locations of commands.
2325 With no arguments whatsoever, the
2327 command prints out the contents of this table.
2331 command removes each specified
2333 from the hash table (unless they are functions) and then locates it.
2338 prints the locations of the commands as it finds them.
2343 command to delete all the entries in the hash table except for functions.
2344 .It Ic jobid Op Ar job
2345 Print the process IDs of the processes in the specified
2349 argument is omitted, use the current job.
2350 .It Ic jobs Oo Fl lps Oc Op Ar job ...
2351 Print information about the specified jobs, or all jobs if no
2354 The information printed includes job ID, status and command name.
2358 option is specified, the PID of each job is also printed.
2361 option is specified, only the process IDs for the process group leaders
2362 are printed, one per line.
2365 option is specified, only the PIDs of the job commands are printed, one per
2368 A built-in equivalent of
2370 that additionally supports sending signals to jobs.
2371 .It Ic local Oo Ar variable ... Oc Op Fl
2376 A built-in equivalent of
2378 .It Ic pwd Op Fl L | P
2379 Print the path of the current directory.
2380 The built-in command may
2381 differ from the program of the same name because the
2382 built-in command remembers what the current directory
2383 is rather than recomputing it each time.
2386 However, if the current directory is
2388 the built-in version of
2390 will continue to print the old name for the directory.
2394 option is specified, symbolic links are resolved.
2397 option is specified, the shell's notion of the current directory
2398 is printed (symbolic links are not resolved).
2399 This is the default.
2400 .It Ic read Oo Fl p Ar prompt Oc Oo
2401 .Fl t Ar timeout Oc Oo Fl er Oc Ar variable ...
2407 and the standard input is a terminal.
2409 read from the standard input.
2410 The trailing newline
2411 is deleted from the line and the line is split as
2412 described in the section on
2413 .Sx White Space Splitting (Field Splitting)\&
2415 the pieces are assigned to the variables in order.
2416 If there are more pieces than variables, the remaining
2417 pieces (along with the characters in
2419 that separated them)
2420 are assigned to the last variable.
2421 If there are more variables than pieces, the remaining
2422 variables are assigned the null string.
2424 Backslashes are treated specially, unless the
2428 If a backslash is followed by
2429 a newline, the backslash and the newline will be
2431 If a backslash is followed by any other
2432 character, the backslash will be deleted and the following
2433 character will be treated as though it were not in
2439 option is specified and the
2441 elapses before a complete line of input is supplied,
2444 command will return an exit status as if terminated by
2446 without assigning any values.
2449 value may optionally be followed by one of
2454 to explicitly specify seconds, minutes or hours.
2455 If none is supplied,
2461 option exists only for backward compatibility with older scripts.
2463 The exit status is 0 on success, 1 on end of file,
2464 between 2 and 128 if an error occurs
2465 and greater than 128 if a trapped signal interrupts
2467 .It Ic readonly Oo Fl p Oc Op Ar name ...
2470 is marked as read only,
2471 so that it cannot be subsequently modified or unset.
2472 The shell allows the value of a variable to be set
2473 at the same time as it is marked read only
2474 by using the following form:
2476 .D1 Ic readonly Ar name Ns = Ns Ar value
2478 With no arguments the
2480 command lists the names of all read only variables.
2483 option is specified, the read-only variables are printed as
2484 .Dq Ic readonly Ar name Ns = Ns Ar value
2485 lines, suitable for re-input to the shell.
2486 .It Ic return Op Ar exitstatus
2490 .It Ic set Oo Fl /+abCEefIimnpTuVvx Oc Oo Fl /+o Ar longname
2491 .Oc Op Fl - Ar arg ...
2494 command performs three different functions:
2497 With no arguments, it lists the values of all shell variables.
2499 If options are given,
2500 either in short form or using the long
2501 .Dq Fl /+o Ar longname
2503 it sets or clears the specified options as described in the section called
2504 .Sx Argument List Processing .
2508 option is specified,
2510 will replace the shell's positional parameters with the subsequent
2512 If no arguments follow the
2515 all the positional parameters will be cleared,
2516 which is equivalent to executing the command
2520 flag may be omitted when specifying arguments to be used
2521 as positional replacement parameters.
2522 This is not recommended,
2523 because the first argument may begin with a dash
2529 command will interpret as a request to enable or disable options.
2531 .It Ic setvar Ar variable value
2532 Assigns the specified
2538 command is intended to be used in functions that
2539 assign values to variables whose names are passed as parameters.
2540 In general it is better to write
2541 .Dq Ar variable Ns = Ns Ar value
2544 .It Ic shift Op Ar n
2545 Shift the positional parameters
2550 A shift sets the value of
2559 decreasing the value of
2562 For portability, shifting if there are zero positional parameters
2563 should be avoided, since the shell may abort.
2565 A built-in equivalent of
2568 Print the amount of time spent executing the shell process and its children.
2569 The first output line shows the user and system times for the shell process
2570 itself, the second one contains the user and system times for the
2572 .It Ic trap Oo Ar action Oc Ar signal ...
2574 Cause the shell to parse and execute
2579 The signals are specified by name or number.
2580 In addition, the pseudo-signal
2582 may be used to specify an
2584 that is performed when the shell terminates.
2587 may be an empty string or a dash
2589 the former causes the specified signal to be ignored
2590 and the latter causes the default action to be taken.
2593 and using only signal numbers is another way to request the default action.
2594 In a subshell or utility environment,
2595 the shell resets trapped (but not ignored) signals to the default action.
2598 command has no effect on signals that were ignored on entry to the shell.
2604 command to display a list of valid signal names.
2606 A null command that returns a 0 (true) exit value.
2607 .It Ic type Op Ar name ...
2610 as a command and print the resolution of the command search.
2611 Possible resolutions are:
2612 shell keyword, alias, special shell builtin, shell builtin, command,
2615 For aliases the alias expansion is printed;
2616 for commands and tracked aliases
2617 the complete pathname of the command is printed.
2618 .It Ic ulimit Oo Fl HSabcdfklmnopstuvw Oc Op Ar limit
2619 Set or display resource limits (see
2623 is specified, the named resource will be set;
2624 otherwise the current resource value will be displayed.
2628 is specified, the hard limits will be set or displayed.
2629 While everybody is allowed to reduce a hard limit,
2630 only the superuser can increase it.
2634 specifies the soft limits instead.
2635 When displaying limits,
2641 The default is to display the soft limits,
2642 and to set both the hard and the soft limits.
2648 command to display all resources.
2651 is not acceptable in this mode.
2653 The remaining options specify which resource value is to be
2654 displayed or modified.
2655 They are mutually exclusive.
2656 .Bl -tag -width indent
2658 The maximum size of socket buffer usage, in bytes.
2659 .It Fl c Ar coredumpsize
2660 The maximal size of core dump files, in 512-byte blocks.
2663 to 0 prevents core dump files from being created.
2664 .It Fl d Ar datasize
2665 The maximal size of the data segment of a process, in kilobytes.
2666 .It Fl f Ar filesize
2667 The maximal size of a file, in 512-byte blocks.
2669 The maximal number of kqueues
2673 .It Fl l Ar lockedmem
2674 The maximal size of memory that can be locked by a process, in
2676 .It Fl m Ar memoryuse
2677 The maximal resident set size of a process, in kilobytes.
2679 The maximal number of descriptors that could be opened by a process.
2681 The maximal number of process-shared locks
2685 .It Fl p Ar pseudoterminals
2686 The maximal number of pseudo-terminals for this user ID.
2687 .It Fl s Ar stacksize
2688 The maximal size of the stack segment, in kilobytes.
2690 The maximal amount of CPU time to be used by each process, in seconds.
2691 .It Fl u Ar userproc
2692 The maximal number of simultaneous processes for this user ID.
2693 .It Fl v Ar virtualmem
2694 The maximal virtual size of a process, in kilobytes.
2696 The maximum amount of swap space reserved or used for this user ID,
2699 .It Ic umask Oo Fl S Oc Op Ar mask
2700 Set the file creation mask (see
2702 to the octal or symbolic (see
2706 If the argument is omitted, the current mask value is printed.
2709 option is specified, the output is symbolic, otherwise the output is octal.
2710 .It Ic unalias Oo Fl a Oc Op Ar name ...
2711 The specified alias names are removed.
2714 is specified, all aliases are removed.
2715 .It Ic unset Oo Fl fv Oc Ar name ...
2716 The specified variables or functions are unset and unexported.
2719 option is specified or no options are given, the
2721 arguments are treated as variable names.
2724 option is specified, the
2726 arguments are treated as function names.
2727 .It Ic wait Op Ar job ...
2728 Wait for each specified
2730 to complete and return the exit status of the last process in the
2735 specified is unknown to the shell, it is treated as if it
2736 were a known job that exited with exit status 127.
2737 If no operands are given, wait for all jobs to complete
2738 and return an exit status of zero.
2740 .Ss Command Line Editing
2743 is being used interactively from a terminal, the current command
2744 and the command history
2748 .Sx Built-in Commands )
2751 command line editing.
2752 This mode uses commands similar
2753 to a subset of those described in the
2771 can be switched between insert mode and command mode by typing
2775 while in command mode will pass the line to the shell.
2778 .Dq Li "set -o emacs"
2781 command can be used to enable a subset of
2783 command line editing features.
2785 The following environment variables affect the execution of
2787 .Bl -tag -width ".Ev LANGXXXXXX"
2789 Initialization file for interactive shells.
2790 .It Ev LANG , Ev LC_*
2792 These are inherited by children of the shell,
2793 and is used in a limited manner by the shell itself.
2795 The previous current directory.
2796 This is used and updated by
2799 An absolute pathname for the current directory,
2800 possibly containing symbolic links.
2801 This is used and updated by the shell.
2803 The default terminal setting for the shell.
2804 This is inherited by children of the shell, and is used in the history
2808 Additionally, environment variables are turned into shell variables
2810 which may affect the shell as described under
2811 .Sx Special Variables .
2813 .Bl -tag -width "/etc/suid_profileXX" -compact
2815 User's login profile.
2817 System login profile.
2820 .It Pa /etc/suid_profile
2821 Privileged shell profile.
2826 cannot be found, the exit status will be 127;
2827 if it cannot be opened for another reason, the exit status will be 126.
2828 Other errors that are detected by the shell, such as a syntax error, will
2829 cause the shell to exit with a non-zero exit status.
2830 If the shell is not an interactive shell, the execution of the shell
2831 file will be aborted.
2832 Otherwise the shell will return the exit status of the last command
2835 builtin is used with a numeric argument, it
2836 will return the argument.
2857 command, the Thompson shell, appeared in
2859 It was superseded in
2861 by the Bourne shell, which inherited the name
2866 was rewritten in 1989 under the
2868 license after the Bourne shell from
2873 was originally written by
2874 .An Kenneth Almquist .
2878 utility does not recognize multibyte characters other than UTF-8.
2881 does not recognize multibyte characters.