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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.
1406 The final component of the current working directory.
1408 The entire path of the current working directory.
1412 for normal users and
1416 A literal backslash.
1419 The secondary prompt string, which defaults to
1422 may include any of the formatting sequences from
1425 The prefix for the trace output (if
1432 This clause describes the various expansions that are
1434 Not all expansions are performed on
1435 every word, as explained later.
1437 Tilde expansions, parameter expansions, command substitutions,
1438 arithmetic expansions, and quote removals that occur within
1439 a single word expand to a single field.
1441 splitting or pathname expansion that can create multiple
1442 fields from a single word.
1443 The single exception to this rule is
1444 the expansion of the special parameter
1446 within double-quotes,
1447 as was described above.
1449 The order of word expansion is:
1452 Tilde Expansion, Parameter Expansion, Command Substitution,
1453 Arithmetic Expansion (these all occur at the same time).
1455 Field Splitting is performed on fields generated by step (1)
1460 Pathname Expansion (unless the
1462 option is in effect).
1469 character is used to introduce parameter expansion, command
1470 substitution, or arithmetic expansion.
1471 .Ss Tilde Expansion (substituting a user's home directory)
1472 A word beginning with an unquoted tilde character
1475 subjected to tilde expansion.
1476 All the characters up to a slash
1478 or the end of the word are treated as a username
1479 and are replaced with the user's home directory.
1481 username is missing (as in
1483 the tilde is replaced with the value of the
1485 variable (the current user's home directory).
1486 .Ss Parameter Expansion
1487 The format for parameter expansion is as follows:
1489 .D1 Li ${ Ns Ar expression Ns Li }
1493 consists of all characters until the matching
1497 escaped by a backslash or within a single-quoted or double-quoted
1498 string, and characters in
1499 embedded arithmetic expansions, command substitutions, and variable
1500 expansions, are not examined in determining the matching
1502 If the variants with
1508 occur within a double-quoted string,
1509 as an extension there may be unquoted parts
1510 (via double-quotes inside the expansion);
1512 within such parts are also not examined in determining the matching
1515 The simplest form for parameter expansion is:
1517 .D1 Li ${ Ns Ar parameter Ns Li }
1519 The value, if any, of
1523 The parameter name or symbol can be enclosed in braces, which are
1524 optional except for positional parameters with more than one digit or
1525 when parameter is followed by a character that could be interpreted as
1527 If a parameter expansion occurs inside double-quotes:
1530 Field splitting is not performed on the results of the
1531 expansion, with the exception of the special parameter
1534 Pathname expansion is not performed on the results of the
1538 In addition, a parameter expansion can be modified by using one of the
1540 .Bl -tag -width indent
1541 .It Li ${ Ns Ar parameter Ns Li :- Ns Ar word Ns Li }
1545 is unset or null, the expansion of
1547 is substituted; otherwise, the value of
1550 .It Li ${ Ns Ar parameter Ns Li := Ns Ar word Ns Li }
1551 Assign Default Values.
1554 is unset or null, the expansion of
1564 does not prevent field splitting or pathname expansion.
1565 Only variables, not positional
1566 parameters or special parameters, can be
1567 assigned in this way.
1568 .It Li ${ Ns Ar parameter Ns Li :? Ns Oo Ar word Oc Ns Li }
1569 Indicate Error if Null or Unset.
1572 is unset or null, the expansion of
1574 (or a message indicating it is unset if
1576 is omitted) is written to standard
1577 error and the shell exits with a nonzero
1579 Otherwise, the value of
1583 interactive shell need not exit.
1584 .It Li ${ Ns Ar parameter Ns Li :+ Ns Ar word Ns Li }
1585 Use Alternate Value.
1588 is unset or null, null is substituted;
1589 otherwise, the expansion of
1594 In the parameter expansions shown previously, use of the colon in the
1595 format results in a test for a parameter that is unset or null; omission
1596 of the colon results in a test for a parameter that is only unset.
1600 inherits the type of quoting
1601 (unquoted, double-quoted or here-document)
1602 from the surroundings,
1603 with the exception that a backslash that quotes a closing brace is removed
1604 during quote removal.
1605 .Bl -tag -width indent
1606 .It Li ${# Ns Ar parameter Ns Li }
1608 The length in characters of
1613 The following four varieties of parameter expansion provide for substring
1615 In each case, pattern matching notation
1617 .Sx Shell Patterns ) ,
1618 rather than regular expression notation,
1619 is used to evaluate the patterns.
1620 If parameter is one of the special parameters
1624 the result of the expansion is unspecified.
1625 Enclosing the full parameter expansion string in double-quotes does not
1626 cause the following four varieties of pattern characters to be quoted,
1627 whereas quoting characters within the braces has this effect.
1628 .Bl -tag -width indent
1629 .It Li ${ Ns Ar parameter Ns Li % Ns Ar word Ns Li }
1630 Remove Smallest Suffix Pattern.
1633 is expanded to produce a pattern.
1635 parameter expansion then results in
1637 with the smallest portion of the
1638 suffix matched by the pattern deleted.
1639 .It Li ${ Ns Ar parameter Ns Li %% Ns Ar word Ns Li }
1640 Remove Largest Suffix Pattern.
1643 is expanded to produce a pattern.
1645 parameter expansion then results in
1647 with the largest portion of the
1648 suffix matched by the pattern deleted.
1649 .It Li ${ Ns Ar parameter Ns Li # Ns Ar word Ns Li }
1650 Remove Smallest Prefix Pattern.
1653 is expanded to produce a pattern.
1655 parameter expansion then results in
1657 with the smallest portion of the
1658 prefix matched by the pattern deleted.
1659 .It Li ${ Ns Ar parameter Ns Li ## Ns Ar word Ns Li }
1660 Remove Largest Prefix Pattern.
1663 is expanded to produce a pattern.
1665 parameter expansion then results in
1667 with the largest portion of the
1668 prefix matched by the pattern deleted.
1670 .Ss Command Substitution
1671 Command substitution allows the output of a command to be substituted in
1672 place of the command name itself.
1673 Command substitution occurs when
1674 the command is enclosed as follows:
1676 .D1 Li $( Ns Ar command Ns Li )\&
1678 or the backquoted version:
1680 .D1 Li ` Ns Ar command Ns Li `
1682 The shell expands the command substitution by executing command
1683 and replacing the command substitution
1684 with the standard output of the command,
1685 removing sequences of one or more newlines at the end of the substitution.
1686 Embedded newlines before the end of the output are not removed;
1687 however, during field splitting, they may be translated into spaces
1688 depending on the value of
1690 and the quoting that is in effect.
1691 The command is executed in a subshell environment,
1692 except that the built-in commands
1697 return information about the parent shell environment
1700 returns information about the same process
1701 if they are the only command in a command substitution.
1703 If a command substitution of the
1705 form begins with a subshell,
1710 must be separated by whitespace
1711 to avoid ambiguity with arithmetic expansion.
1712 .Ss Arithmetic Expansion
1713 Arithmetic expansion provides a mechanism for evaluating an arithmetic
1714 expression and substituting its value.
1715 The format for arithmetic expansion is as follows:
1717 .D1 Li $(( Ns Ar expression Ns Li ))
1721 is treated as if it were in double-quotes, except
1722 that a double-quote inside the expression is not treated specially.
1724 shell expands all tokens in the
1726 for parameter expansion,
1727 command substitution,
1728 arithmetic expansion
1731 The allowed expressions are a subset of C expressions,
1733 .Bl -tag -width "Variables" -offset indent
1735 All values are of type
1738 Decimal, octal (starting with
1740 and hexadecimal (starting with
1744 Shell variables can be read and written
1745 and contain integer constants.
1748 .It Binary operators
1749 .Li "* / % + - << >> < <= > >= == != & ^ | && ||"\&
1750 .It Assignment operators
1751 .Li "= += -= *= /= %= <<= >>= &= ^= |="
1752 .It Conditional operator
1756 The result of the expression is substituted in decimal.
1757 .Ss White Space Splitting (Field Splitting)
1758 In certain contexts,
1759 after parameter expansion, command substitution, and
1760 arithmetic expansion the shell scans the results of
1761 expansions and substitutions that did not occur in double-quotes for
1762 field splitting and multiple fields can result.
1773 are treated differently from other characters in
1778 at the beginning or end of a word is discarded.
1780 Subsequently, a field is delimited by either
1783 a non-whitespace character in
1785 with any whitespace in
1789 one or more whitespace characters in
1793 If a word ends with a non-whitespace character in
1795 there is no empty field after this character.
1797 If no field is delimited, the word is discarded.
1798 In particular, if a word consists solely of an unquoted substitution
1799 and the result of the substitution is null,
1800 it is removed by field splitting even if
1803 .Ss Pathname Expansion (File Name Generation)
1807 file name generation is performed
1808 after word splitting is complete.
1810 viewed as a series of patterns, separated by slashes.
1812 process of expansion replaces the word with the names of
1813 all existing files whose names can be formed by replacing
1814 each pattern with a string that matches the specified pattern.
1815 There are two restrictions on this: first, a pattern cannot match
1816 a string containing a slash, and second,
1817 a pattern cannot match a string starting with a period
1818 unless the first character of the pattern is a period.
1819 The next section describes the patterns used for
1821 the four varieties of parameter expansion for substring processing and the
1825 A pattern consists of normal characters, which match themselves,
1826 and meta-characters.
1827 The meta-characters are
1832 These characters lose their special meanings if they are quoted.
1833 When command or variable substitution is performed and the dollar sign
1834 or back quotes are not double-quoted, the value of the
1835 variable or the output of the command is scanned for these
1836 characters and they are turned into meta-characters.
1840 matches any string of characters.
1843 matches any single character.
1846 introduces a character class.
1847 The end of the character class is indicated by a
1855 rather than introducing a character class.
1856 A character class matches any of the characters between the square brackets.
1857 A locale-dependent range of characters may be specified using a minus sign.
1858 A named class of characters (see
1860 may be specified by surrounding the name with
1865 .Ql \&[\&[:alpha:\&]\&]
1866 is a shell pattern that matches a single letter.
1867 The character class may be complemented by making an exclamation point
1869 the first character of the character class.
1872 has the same effect but is non-standard.
1876 in a character class, make it the first character listed
1884 make it the first or last character listed.
1885 .Ss Built-in Commands
1886 This section lists the built-in commands.
1887 .Bl -tag -width indent
1889 A null command that returns a 0 (true) exit value.
1891 The commands in the specified file are read and executed by the shell.
1894 command may be used to return to the
1901 characters, it is used as is.
1902 Otherwise, the shell searches the
1905 If it is not found in the
1907 it is sought in the current working directory.
1909 A built-in equivalent of
1911 .It Ic alias Oo Ar name Ns Oo = Ns Ar string Oc ... Oc
1913 .Ar name Ns = Ns Ar string
1914 is specified, the shell defines the alias
1920 is specified, the value of the alias
1923 With no arguments, the
1925 built-in command prints the names and values of all defined aliases
1928 Alias values are written with appropriate quoting so that they are
1929 suitable for re-input to the shell.
1933 .It Ic bg Op Ar job ...
1934 Continue the specified jobs
1935 (or the current job if no jobs are given)
1937 .It Ic bind Oo Fl aeklrsv Oc Oo Ar key Oo Ar command Oc Oc
1938 List or alter key bindings for the line editor.
1939 This command is documented in
1941 .It Ic break Op Ar num
1943 .Sx Flow-Control Constructs
1945 .It Ic builtin Ar cmd Op Ar arg ...
1946 Execute the specified built-in command,
1948 This is useful when the user wishes to override a shell function
1949 with the same name as a built-in command.
1950 .It Ic cd Oo Fl L | P Oc Oo Fl e Oc Op Ar directory
1952 Switch to the specified
1954 to the directory specified in the
1956 environment variable if no
1959 to the directory specified in the
1961 environment variable if
1971 then the directories listed in the
1974 searched for the specified
1978 is unset, the current directory is searched.
1981 is the same as that of
1983 In an interactive shell,
1986 command will print out the name of the directory
1987 that it actually switched to
1990 mechanism was used or if
1997 option is specified,
1999 is handled physically and symbolic links are resolved before
2001 components are processed.
2004 option is specified,
2006 is handled logically.
2007 This is the default.
2013 to return exit status 1 if the full pathname of the new directory
2014 cannot be determined reliably or at all.
2015 Normally this is not considered an error,
2016 although a warning is printed.
2018 If changing the directory fails, the exit status is greater than 1.
2019 If the directory is changed, the exit status is 0, or also 1 if
2026 .It Ic command Oo Fl p Oc Op Ar utility Op Ar argument ...
2027 .It Ic command Oo Fl p Oc Fl v Ar utility
2028 .It Ic command Oo Fl p Oc Fl V Ar utility
2029 The first form of invocation executes the specified
2031 ignoring shell functions in the search.
2034 is a special builtin,
2035 it is executed as if it were a regular builtin.
2039 option is specified, the command search is performed using a
2042 that is guaranteed to find all of the standard utilities.
2046 option is specified,
2048 is not executed but a description of its interpretation by the shell is
2050 For ordinary commands the output is the path name; for shell built-in
2051 commands, shell functions and keywords only the name is written.
2052 Aliases are printed as
2053 .Dq Ic alias Ar name Ns = Ns Ar value .
2057 option is identical to
2059 except for the output.
2061 .Dq Ar utility Ic is Ar description
2067 a special shell builtin,
2074 .It Ic continue Op Ar num
2076 .Sx Flow-Control Constructs
2078 .It Ic echo Oo Fl e | n Oc Op Ar string ...
2079 Print a space-separated list of the arguments to the standard output
2080 and append a newline character.
2081 .Bl -tag -width indent
2083 Suppress the output of the trailing newline.
2085 Process C-style backslash escape sequences.
2088 command understands the following character escapes:
2089 .Bl -tag -width indent
2091 Alert (ring the terminal bell)
2095 Suppress the trailing newline (this has the side-effect of truncating the
2096 line if it is not the last character)
2098 The ESC character (ASCII 0x1b)
2112 (Zero) The character whose octal value is
2118 is not enclosed in quotes then the backslash itself must be escaped
2119 with a backslash to protect it from the shell.
2121 .Bd -literal -offset indent
2130 $ echo -e a\e\e\e\eb
2139 options may be specified.
2140 .It Ic eval Ar string ...
2141 Concatenate all the arguments with spaces.
2142 Then re-parse and execute the command.
2143 .It Ic exec Op Ar command Op arg ...
2147 the shell process is replaced with the specified program
2148 (which must be a real program, not a shell built-in command or function).
2149 Any redirections on the
2151 command are marked as permanent,
2152 so that they are not undone when the
2155 .It Ic exit Op Ar exitstatus
2156 Terminate the shell process.
2160 it is used as the exit status of the shell.
2161 Otherwise, if the shell is executing an
2163 trap, the exit status of the last command before the trap is used;
2164 if the shell is executing a trap for a signal,
2165 the shell exits by resending the signal to itself.
2166 Otherwise, the exit status of the preceding command is used.
2167 The exit status should be an integer between 0 and 255.
2168 .It Ic export Ar name ...
2169 .It Ic export Op Fl p
2170 The specified names are exported so that they will
2171 appear in the environment of subsequent commands.
2172 The only way to un-export a variable is to
2175 The shell allows the value of a variable to be set
2176 at the same time as it is exported by writing
2178 .D1 Ic export Ar name Ns = Ns Ar value
2180 With no arguments the
2182 command lists the names
2183 of all exported variables.
2186 option is specified, the exported variables are printed as
2187 .Dq Ic export Ar name Ns = Ns Ar value
2188 lines, suitable for re-input to the shell.
2190 A null command that returns a non-zero (false) exit value.
2191 .It Ic fc Oo Fl e Ar editor Oc Op Ar first Op Ar last
2192 .It Ic fc Fl l Oo Fl nr Oc Op Ar first Op Ar last
2193 .It Ic fc Fl s Oo Ar old Ns = Ns Ar new Oc Op Ar first
2196 built-in command lists, or edits and re-executes,
2197 commands previously entered to an interactive shell.
2198 .Bl -tag -width indent
2200 Use the editor named by
2202 to edit the commands.
2205 string is a command name,
2206 subject to search via the
2211 variable is used as a default when
2216 is null or unset, the value of the
2223 is used as the editor.
2225 List the commands rather than invoking
2227 The commands are written in the
2228 sequence indicated by the
2232 operands, as affected by
2234 with each command preceded by the command number.
2236 Suppress command numbers when listing with
2239 Reverse the order of the commands listed
2248 Re-execute the command without invoking an editor.
2251 Select the commands to list or edit.
2252 The number of previous commands that can be accessed
2253 are determined by the value of the
2260 or both are one of the following:
2261 .Bl -tag -width indent
2262 .It Oo Cm + Oc Ns Ar num
2263 A positive number representing a command number;
2264 command numbers can be displayed with the
2268 A negative decimal number representing the
2269 command that was executed
2272 commands previously.
2273 For example, \-1 is the immediately previous command.
2275 A string indicating the most recently entered command
2276 that begins with that string.
2278 .Ar old Ns = Ns Ar new
2279 operand is not also specified with
2281 the string form of the first operand cannot contain an embedded equal sign.
2285 The following variables affect the execution of
2287 .Bl -tag -width ".Va HISTSIZE"
2289 Name of the editor to use for history editing.
2291 The number of previous commands that are accessible.
2296 or the current job to the foreground.
2297 .It Ic getopts Ar optstring var
2303 command deprecates the older
2306 The first argument should be a series of letters, each possibly
2307 followed by a colon which indicates that the option takes an argument.
2308 The specified variable is set to the parsed option.
2310 the next argument is placed into the shell variable
2312 If an option takes an argument, it is placed into the shell variable
2314 If an invalid option is encountered,
2318 It returns a false value (1) when it encounters the end of the options.
2319 A new set of arguments may be parsed by assigning
2321 .It Ic hash Oo Fl rv Oc Op Ar command ...
2322 The shell maintains a hash table which remembers the locations of commands.
2323 With no arguments whatsoever, the
2325 command prints out the contents of this table.
2329 command removes each specified
2331 from the hash table (unless they are functions) and then locates it.
2336 prints the locations of the commands as it finds them.
2341 command to delete all the entries in the hash table except for functions.
2342 .It Ic jobid Op Ar job
2343 Print the process IDs of the processes in the specified
2347 argument is omitted, use the current job.
2348 .It Ic jobs Oo Fl lps Oc Op Ar job ...
2349 Print information about the specified jobs, or all jobs if no
2352 The information printed includes job ID, status and command name.
2356 option is specified, the PID of each job is also printed.
2359 option is specified, only the process IDs for the process group leaders
2360 are printed, one per line.
2363 option is specified, only the PIDs of the job commands are printed, one per
2366 A built-in equivalent of
2368 that additionally supports sending signals to jobs.
2369 .It Ic local Oo Ar variable ... Oc Op Fl
2374 A built-in equivalent of
2376 .It Ic pwd Op Fl L | P
2377 Print the path of the current directory.
2378 The built-in command may
2379 differ from the program of the same name because the
2380 built-in command remembers what the current directory
2381 is rather than recomputing it each time.
2384 However, if the current directory is
2386 the built-in version of
2388 will continue to print the old name for the directory.
2392 option is specified, symbolic links are resolved.
2395 option is specified, the shell's notion of the current directory
2396 is printed (symbolic links are not resolved).
2397 This is the default.
2398 .It Ic read Oo Fl p Ar prompt Oc Oo
2399 .Fl t Ar timeout Oc Oo Fl er Oc Ar variable ...
2405 and the standard input is a terminal.
2407 read from the standard input.
2408 The trailing newline
2409 is deleted from the line and the line is split as
2410 described in the section on
2411 .Sx White Space Splitting (Field Splitting)\&
2413 the pieces are assigned to the variables in order.
2414 If there are more pieces than variables, the remaining
2415 pieces (along with the characters in
2417 that separated them)
2418 are assigned to the last variable.
2419 If there are more variables than pieces, the remaining
2420 variables are assigned the null string.
2422 Backslashes are treated specially, unless the
2426 If a backslash is followed by
2427 a newline, the backslash and the newline will be
2429 If a backslash is followed by any other
2430 character, the backslash will be deleted and the following
2431 character will be treated as though it were not in
2437 option is specified and the
2439 elapses before a complete line of input is supplied,
2442 command will return an exit status as if terminated by
2444 without assigning any values.
2447 value may optionally be followed by one of
2452 to explicitly specify seconds, minutes or hours.
2453 If none is supplied,
2459 option exists only for backward compatibility with older scripts.
2461 The exit status is 0 on success, 1 on end of file,
2462 between 2 and 128 if an error occurs
2463 and greater than 128 if a trapped signal interrupts
2465 .It Ic readonly Oo Fl p Oc Op Ar name ...
2468 is marked as read only,
2469 so that it cannot be subsequently modified or unset.
2470 The shell allows the value of a variable to be set
2471 at the same time as it is marked read only
2472 by using the following form:
2474 .D1 Ic readonly Ar name Ns = Ns Ar value
2476 With no arguments the
2478 command lists the names of all read only variables.
2481 option is specified, the read-only variables are printed as
2482 .Dq Ic readonly Ar name Ns = Ns Ar value
2483 lines, suitable for re-input to the shell.
2484 .It Ic return Op Ar exitstatus
2488 .It Ic set Oo Fl /+abCEefIimnpTuVvx Oc Oo Fl /+o Ar longname
2489 .Oc Op Fl - Ar arg ...
2492 command performs three different functions:
2495 With no arguments, it lists the values of all shell variables.
2497 If options are given,
2498 either in short form or using the long
2499 .Dq Fl /+o Ar longname
2501 it sets or clears the specified options as described in the section called
2502 .Sx Argument List Processing .
2506 option is specified,
2508 will replace the shell's positional parameters with the subsequent
2510 If no arguments follow the
2513 all the positional parameters will be cleared,
2514 which is equivalent to executing the command
2518 flag may be omitted when specifying arguments to be used
2519 as positional replacement parameters.
2520 This is not recommended,
2521 because the first argument may begin with a dash
2527 command will interpret as a request to enable or disable options.
2529 .It Ic setvar Ar variable value
2530 Assigns the specified
2536 command is intended to be used in functions that
2537 assign values to variables whose names are passed as parameters.
2538 In general it is better to write
2539 .Dq Ar variable Ns = Ns Ar value
2542 .It Ic shift Op Ar n
2543 Shift the positional parameters
2548 A shift sets the value of
2557 decreasing the value of
2560 For portability, shifting if there are zero positional parameters
2561 should be avoided, since the shell may abort.
2563 A built-in equivalent of
2566 Print the amount of time spent executing the shell process and its children.
2567 The first output line shows the user and system times for the shell process
2568 itself, the second one contains the user and system times for the
2570 .It Ic trap Oo Ar action Oc Ar signal ...
2572 Cause the shell to parse and execute
2577 The signals are specified by name or number.
2578 In addition, the pseudo-signal
2580 may be used to specify an
2582 that is performed when the shell terminates.
2585 may be an empty string or a dash
2587 the former causes the specified signal to be ignored
2588 and the latter causes the default action to be taken.
2591 and using only signal numbers is another way to request the default action.
2592 In a subshell or utility environment,
2593 the shell resets trapped (but not ignored) signals to the default action.
2596 command has no effect on signals that were ignored on entry to the shell.
2602 command to display a list of valid signal names.
2604 A null command that returns a 0 (true) exit value.
2605 .It Ic type Op Ar name ...
2608 as a command and print the resolution of the command search.
2609 Possible resolutions are:
2610 shell keyword, alias, special shell builtin, shell builtin, command,
2613 For aliases the alias expansion is printed;
2614 for commands and tracked aliases
2615 the complete pathname of the command is printed.
2616 .It Ic ulimit Oo Fl HSabcdfklmnopstuvw Oc Op Ar limit
2617 Set or display resource limits (see
2621 is specified, the named resource will be set;
2622 otherwise the current resource value will be displayed.
2626 is specified, the hard limits will be set or displayed.
2627 While everybody is allowed to reduce a hard limit,
2628 only the superuser can increase it.
2632 specifies the soft limits instead.
2633 When displaying limits,
2639 The default is to display the soft limits,
2640 and to set both the hard and the soft limits.
2646 command to display all resources.
2649 is not acceptable in this mode.
2651 The remaining options specify which resource value is to be
2652 displayed or modified.
2653 They are mutually exclusive.
2654 .Bl -tag -width indent
2656 The maximum size of socket buffer usage, in bytes.
2657 .It Fl c Ar coredumpsize
2658 The maximal size of core dump files, in 512-byte blocks.
2661 to 0 prevents core dump files from being created.
2662 .It Fl d Ar datasize
2663 The maximal size of the data segment of a process, in kilobytes.
2664 .It Fl f Ar filesize
2665 The maximal size of a file, in 512-byte blocks.
2667 The maximal number of kqueues
2671 .It Fl l Ar lockedmem
2672 The maximal size of memory that can be locked by a process, in
2674 .It Fl m Ar memoryuse
2675 The maximal resident set size of a process, in kilobytes.
2677 The maximal number of descriptors that could be opened by a process.
2679 The maximal number of process-shared locks
2683 .It Fl p Ar pseudoterminals
2684 The maximal number of pseudo-terminals for this user ID.
2685 .It Fl s Ar stacksize
2686 The maximal size of the stack segment, in kilobytes.
2688 The maximal amount of CPU time to be used by each process, in seconds.
2689 .It Fl u Ar userproc
2690 The maximal number of simultaneous processes for this user ID.
2691 .It Fl v Ar virtualmem
2692 The maximal virtual size of a process, in kilobytes.
2694 The maximum amount of swap space reserved or used for this user ID,
2697 .It Ic umask Oo Fl S Oc Op Ar mask
2698 Set the file creation mask (see
2700 to the octal or symbolic (see
2704 If the argument is omitted, the current mask value is printed.
2707 option is specified, the output is symbolic, otherwise the output is octal.
2708 .It Ic unalias Oo Fl a Oc Op Ar name ...
2709 The specified alias names are removed.
2712 is specified, all aliases are removed.
2713 .It Ic unset Oo Fl fv Oc Ar name ...
2714 The specified variables or functions are unset and unexported.
2717 option is specified or no options are given, the
2719 arguments are treated as variable names.
2722 option is specified, the
2724 arguments are treated as function names.
2725 .It Ic wait Op Ar job ...
2726 Wait for each specified
2728 to complete and return the exit status of the last process in the
2733 specified is unknown to the shell, it is treated as if it
2734 were a known job that exited with exit status 127.
2735 If no operands are given, wait for all jobs to complete
2736 and return an exit status of zero.
2738 .Ss Command Line Editing
2741 is being used interactively from a terminal, the current command
2742 and the command history
2746 .Sx Built-in Commands )
2749 command line editing.
2750 This mode uses commands similar
2751 to a subset of those described in the
2769 can be switched between insert mode and command mode by typing
2773 while in command mode will pass the line to the shell.
2776 .Dq Li "set -o emacs"
2779 command can be used to enable a subset of
2781 command line editing features.
2783 The following environment variables affect the execution of
2785 .Bl -tag -width ".Ev LANGXXXXXX"
2787 Initialization file for interactive shells.
2788 .It Ev LANG , Ev LC_*
2790 These are inherited by children of the shell,
2791 and is used in a limited manner by the shell itself.
2793 The previous current directory.
2794 This is used and updated by
2797 An absolute pathname for the current directory,
2798 possibly containing symbolic links.
2799 This is used and updated by the shell.
2801 The default terminal setting for the shell.
2802 This is inherited by children of the shell, and is used in the history
2806 Additionally, environment variables are turned into shell variables
2808 which may affect the shell as described under
2809 .Sx Special Variables .
2811 .Bl -tag -width "/etc/suid_profileXX" -compact
2813 User's login profile.
2815 System login profile.
2818 .It Pa /etc/suid_profile
2819 Privileged shell profile.
2824 cannot be found, the exit status will be 127;
2825 if it cannot be opened for another reason, the exit status will be 126.
2826 Other errors that are detected by the shell, such as a syntax error, will
2827 cause the shell to exit with a non-zero exit status.
2828 If the shell is not an interactive shell, the execution of the shell
2829 file will be aborted.
2830 Otherwise the shell will return the exit status of the last command
2833 builtin is used with a numeric argument, it
2834 will return the argument.
2855 command, the Thompson shell, appeared in
2857 It was superseded in
2859 by the Bourne shell, which inherited the name
2864 was rewritten in 1989 under the
2866 license after the Bourne shell from
2871 was originally written by
2872 .An Kenneth Almquist .
2876 utility does not recognize multibyte characters other than UTF-8.
2879 does not recognize multibyte characters.