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32 .\" from: @(#)sh.1 8.6 (Berkeley) 5/4/95
40 .Nd command interpreter (shell)
43 .Op Fl /+abCEefhIimnPpTuVvx
44 .Op Fl /+o Ar longname
50 .Op Fl /+abCEefhIimnPpTuVvx
51 .Op Fl /+o Ar longname
58 .Op Fl /+abCEefhIimnPpTuVvx
59 .Op Fl /+o Ar longname
65 utility is the standard command interpreter for the system.
66 The current version of
70 specification for the shell.
71 It only supports features
74 plus a few Berkeley extensions.
75 This man page is not intended to be a tutorial nor a complete
76 specification of the shell.
78 The shell is a command that reads lines from
79 either a file or the terminal, interprets them, and
80 generally executes other commands.
81 It is the program that is started when a user logs into the system,
82 although a user can select a different shell with the
86 implements a language that has flow control constructs,
87 a macro facility that provides a variety of features in
88 addition to data storage, along with built-in history and line
90 It incorporates many features to
91 aid interactive use and has the advantage that the interpretative
92 language is common to both interactive and non-interactive
94 That is, commands can be typed directly
95 to the running shell or can be put into a file,
96 which can be executed directly by the shell.
99 .\" XXX This next sentence is incredibly confusing.
101 If no arguments are present and if the standard input of the shell
102 is connected to a terminal
106 the shell is considered an interactive shell.
108 generally prompts before each command and handles programming
109 and command errors differently (as described below).
110 When first starting, the shell inspects argument 0, and
111 if it begins with a dash
113 the shell is also considered a login shell.
114 This is normally done automatically by the system
115 when the user first logs in.
116 A login shell first reads commands
121 in a user's home directory,
123 If the environment variable
125 is set on entry to a shell, or is set in the
127 of a login shell, the shell then subjects its value to parameter expansion
128 and arithmetic expansion and reads commands from the named file.
129 Therefore, a user should place commands that are to be executed only
132 file, and commands that are executed for every shell inside the
137 variable to some file by placing the following line in the file
139 in the home directory,
142 the filename desired:
144 .Dl "ENV=$HOME/.shrc; export ENV"
146 The first non-option argument specified on the command line
147 will be treated as the
148 name of a file from which to read commands (a shell script), and
149 the remaining arguments are set as the positional parameters
153 Otherwise, the shell reads commands
154 from its standard input.
156 Unlike older versions of
160 script is only sourced on invocation of interactive shells.
162 closes a well-known, and sometimes easily exploitable security
163 hole related to poorly thought out
166 .Ss Argument List Processing
167 All of the single letter options to
169 have a corresponding long name,
170 with the exception of
174 These long names are provided next to the single letter options
175 in the descriptions below.
176 The long name for an option may be specified as an argument to the
180 Once the shell is running,
181 the long name for an option may be specified as an argument to the
186 (described later in the section called
187 .Sx Built-in Commands ) .
188 Introducing an option with a dash
198 will stop option processing and will force the remaining
199 words on the command line to be treated as arguments.
204 options do not have long names.
205 They take arguments and are described after the single letter options.
206 .Bl -tag -width indent
207 .It Fl a Li allexport
208 Flag variables for export when assignments are made to them.
210 Enable asynchronous notification of background job
213 .It Fl C Li noclobber
214 Do not overwrite existing files with
219 command line editor (disables the
221 option if it has been set;
222 set automatically when interactive on terminals).
224 Exit immediately if any untested command fails in non-interactive mode.
225 The exit status of a command is considered to be
226 explicitly tested if the command is part of the list used to control
228 .Ic if , elif , while ,
231 if the command is the left
236 operator; or if the command is a pipeline preceded by the
239 If a shell function is executed and its exit status is explicitly
240 tested, all commands of the function are considered to be tested as
243 It is recommended to check for failures explicitly
244 instead of relying on
246 because it tends to behave in unexpected ways,
247 particularly in larger scripts.
249 Disable pathname expansion.
251 A do-nothing option for
254 .It Fl I Li ignoreeof
257 from input when in interactive mode.
258 .It Fl i Li interactive
259 Force the shell to behave interactively.
261 Turn on job control (set automatically when interactive).
262 A new process group is created for each pipeline (called a job).
263 It is possible to suspend jobs or to have them run in the foreground or
265 In a non-interactive shell,
266 this option can be set even if no terminal is available
267 and is useful to place processes in separate process groups.
269 If not interactive, read commands but do not
271 This is useful for checking the
272 syntax of shell scripts.
274 Change the default for the
280 (logical directory layout)
283 (physical directory layout).
284 .It Fl p Li privileged
285 Turn on privileged mode.
286 This mode is enabled on startup
287 if either the effective user or group ID is not equal to the
288 real user or group ID.
289 Turning this mode off sets the
290 effective user and group IDs to the real user and group IDs.
291 When this mode is enabled for interactive shells, the file
292 .Pa /etc/suid_profile
293 is sourced instead of
297 is sourced, and the contents of the
299 variable are ignored.
301 Read commands from standard input (set automatically
302 if no file arguments are present).
304 no effect when set after the shell has already started
305 running (i.e., when set with the
308 .It Fl T Li trapsasync
309 When waiting for a child, execute traps immediately.
310 If this option is not set,
311 traps are executed after the child exits,
314 This nonstandard option is useful for putting guarding shells around
315 children that block signals.
316 The surrounding shell may kill the child
317 or it may just return control to the tty and leave the child alone,
319 .Bd -literal -offset indent
320 sh -T -c "trap 'exit 1' 2 ; some-blocking-program"
323 Write a message to standard error when attempting
324 to expand a variable, a positional parameter or
325 the special parameter
327 that is not set, and if the
328 shell is not interactive, exit immediately.
332 command line editor (disables
336 The shell writes its input to standard error
338 Useful for debugging.
341 (preceded by the value of the
343 variable subjected to parameter expansion and arithmetic expansion)
344 to standard error before it is executed.
345 Useful for debugging.
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.
465 The byte whose octal value is
467 (one to three digits)
469 The byte whose hexadecimal value is
471 (one or more digits only the last two of which are used)
473 The Unicode code point
475 (four hexadecimal digits)
476 .It \eU Ns Ar nnnnnnnn
477 The Unicode code point
479 (eight hexadecimal digits)
482 The sequences for Unicode code points are currently only useful with
484 They reject code point 0 and UTF-16 surrogates.
486 If an escape sequence would produce a byte with value 0,
487 that byte and the rest of the string until the matching single-quote
490 Any other string starting with a backslash is an error.
492 Enclosing characters within double quotes preserves the literal
493 meaning of all characters except dollar sign
499 The backslash inside double quotes is historically weird.
500 It remains literal unless it precedes the following characters,
501 which it serves to quote:
503 .Bl -column "XXX" "XXX" "XXX" "XXX" "XXX" -offset center -compact
504 .It Li $ Ta Li ` Ta Li \&" Ta Li \e Ta Li \en
507 A backslash preserves the literal meaning of the following
508 character, with the exception of the newline character
510 A backslash preceding a newline is treated as a line continuation.
513 Keywords or reserved words are words that have special meaning to the
514 shell and are recognized at the beginning of a line and
515 after a control operator.
516 The following are keywords:
517 .Bl -column "doneXX" "elifXX" "elseXX" "untilXX" "whileX" -offset center
518 .It Li \&! Ta { Ta } Ta Ic case Ta Ic do
519 .It Ic done Ta Ic elif Ta Ic else Ta Ic esac Ta Ic fi
520 .It Ic for Ta Ic if Ta Ic then Ta Ic until Ta Ic while
523 An alias is a name and corresponding value set using the
526 Wherever the command word of a simple command may occur,
527 and after checking for keywords if a keyword may occur, the shell
528 checks the word to see if it matches an alias.
529 If it does, it replaces it in the input stream with its value.
530 For example, if there is an alias called
542 Aliases are also recognized after an alias
543 whose value ends with a space or tab.
544 For example, if there is also an alias called
550 .Dl "nohup lf foobar"
554 .Dl "nohup ls -F foobar"
556 Aliases provide a convenient way for naive users to
557 create shorthands for commands without having to learn how
558 to create functions with arguments.
559 Using aliases in scripts is discouraged
560 because the command that defines them must be executed
561 before the code that uses them is parsed.
562 This is fragile and not portable.
564 An alias name may be escaped in a command line, so that it is not
565 replaced by its alias value, by using quoting characters within or
566 adjacent to the alias name.
567 This is most often done by prefixing
568 an alias name with a backslash to execute a function, built-in, or
569 normal program with the same name.
574 The shell interprets the words it reads according to a
575 language, the specification of which is outside the scope
576 of this man page (refer to the BNF in the
579 Essentially though, a line is read and if
580 the first word of the line (or after a control operator)
581 is not a keyword, then the shell has recognized a
583 Otherwise, a complex command or some
584 other special construct may have been recognized.
586 If a simple command has been recognized, the shell performs
587 the following actions:
590 Leading words of the form
592 are stripped off and assigned to the environment of
594 (they do not affect expansions).
595 Redirection operators and
596 their arguments (as described below) are stripped
597 off and saved for processing.
599 The remaining words are expanded as described in
601 .Sx Word Expansions ,
602 and the first remaining word is considered the command
603 name and the command is located.
605 words are considered the arguments of the command.
606 If no command name resulted, then the
608 variable assignments recognized in 1) affect the
611 Redirections are performed as described in
615 Redirections are used to change where a command reads its input
617 In general, redirections open, close, or
618 duplicate an existing reference to a file.
620 used for redirection is:
622 .D1 Oo Ar n Oc Ar redir-op file
626 is one of the redirection operators mentioned
628 The following gives some examples of how these
629 operators can be used.
630 Note that stdin and stdout are commonly used abbreviations
631 for standard input and standard output respectively.
632 .Bl -tag -width "1234567890XX" -offset indent
633 .It Oo Ar n Oc Ns Li > Ar file
634 redirect stdout (or file descriptor
638 .It Oo Ar n Oc Ns Li >| Ar file
639 same as above, but override the
642 .It Oo Ar n Oc Ns Li >> Ar file
643 append stdout (or file descriptor
647 .It Oo Ar n Oc Ns Li < Ar file
648 redirect stdin (or file descriptor
652 .It Oo Ar n Oc Ns Li <> Ar file
653 redirect stdin (or file descriptor
657 .It Oo Ar n1 Oc Ns Li <& Ns Ar n2
658 duplicate stdin (or file descriptor
662 .It Oo Ar n Oc Ns Li <&-
663 close stdin (or file descriptor
665 .It Oo Ar n1 Oc Ns Li >& Ns Ar n2
666 duplicate stdout (or file descriptor
670 .It Oo Ar n Oc Ns Li >&-
671 close stdout (or file descriptor
675 The following redirection is often called a
677 .Bd -unfilled -offset indent
678 .Oo Ar n Oc Ns Li << Ar delimiter
684 All the text on successive lines up to the delimiter is
685 saved away and made available to the command on standard
686 input, or file descriptor
691 as specified on the initial line is quoted, then the
693 is treated literally, otherwise the text is subjected to
694 parameter expansion, command substitution, and arithmetic
695 expansion (as described in the section on
696 .Sx Word Expansions ) .
705 .Ss Search and Execution
706 There are three types of commands: shell functions,
707 built-in commands, and normal programs.
708 The command is searched for (by name) in that order.
709 The three types of commands are all executed in a different way.
711 When a shell function is executed, all of the shell positional
714 which remains unchanged) are
715 set to the arguments of the shell function.
716 The variables which are explicitly placed in the environment of
717 the command (by placing assignments to them before the
718 function name) are made local to the function and are set
720 Then the command given in the function definition is executed.
721 The positional parameters are restored to their original values
722 when the command completes.
723 This all occurs within the current shell.
725 Shell built-in commands are executed internally to the shell, without
726 spawning a new process.
727 There are two kinds of built-in commands: regular and special.
728 Assignments before special builtins persist after they finish
729 executing and assignment errors, redirection errors and certain
730 operand errors cause a script to be aborted.
731 Special builtins cannot be overridden with a function.
732 Both regular and special builtins can affect the shell in ways
733 normal programs cannot.
735 Otherwise, if the command name does not match a function
736 or built-in command, the command is searched for as a normal
737 program in the file system (as described in the next section).
738 When a normal program is executed, the shell runs the program,
739 passing the arguments and the environment to the program.
740 If the program is not a normal executable file
741 (i.e., if it does not begin with the
751 but appears to be a text file,
752 the shell will run a new instance of
756 Note that previous versions of this document
757 and the source code itself misleadingly and sporadically
758 refer to a shell script without a magic number
760 .Dq "shell procedure" .
762 When locating a command, the shell first looks to see if
763 it has a shell function by that name.
765 built-in command by that name.
766 If a built-in command is not found,
767 one of two things happen:
770 Command names containing a slash are simply executed without
771 performing any searches.
773 The shell searches each entry in the
776 in turn for the command.
779 variable should be a series of
780 entries separated by colons.
781 Each entry consists of a
783 The current directory
784 may be indicated implicitly by an empty directory name,
785 or explicitly by a single period.
787 .Ss Command Exit Status
788 Each command has an exit status that can influence the behavior
789 of other shell commands.
790 The paradigm is that a command exits
791 with zero for normal or success, and non-zero for failure,
792 error, or a false indication.
793 The man page for each command
794 should indicate the various exit codes and what they mean.
795 Additionally, the built-in commands return exit codes, as does
796 an executed shell function.
798 If a command is terminated by a signal, its exit status is greater than 128.
799 The signal name can be found by passing the exit status to
802 If there is no command word,
803 the exit status is the exit status of the last command substitution executed,
804 or zero if the command does not contain any command substitutions.
806 Complex commands are combinations of simple commands
807 with control operators or keywords, together creating a larger complex
809 More generally, a command is one of the following:
810 .Bl -item -offset indent
816 list or compound-list
823 Unless otherwise stated, the exit status of a command is
824 that of the last simple command executed by the command,
825 or zero if no simple command was executed.
827 A pipeline is a sequence of one or more commands separated
828 by the control operator
830 The standard output of all but
831 the last command is connected to the standard input
833 The standard output of the last
834 command is inherited from the shell, as usual.
836 The format for a pipeline is:
838 .D1 Oo Li \&! Oc Ar command1 Op Li \&| Ar command2 ...
840 The standard output of
842 is connected to the standard input of
844 The standard input, standard output, or
845 both of a command is considered to be assigned by the
846 pipeline before any redirection specified by redirection
847 operators that are part of the command.
849 Note that unlike some other shells,
851 executes each process in a pipeline with more than one command
852 in a subshell environment and as a child of the
856 If the pipeline is not in the background (discussed later),
857 the shell waits for all commands to complete.
861 does not precede the pipeline, the
862 exit status is the exit status of the last command specified
864 Otherwise, the exit status is the logical
865 NOT of the exit status of the last command.
867 the last command returns zero, the exit status is 1; if
868 the last command returns greater than zero, the exit status
871 Because pipeline assignment of standard input or standard
872 output or both takes place before redirection, it can be
873 modified by redirection.
876 .Dl "command1 2>&1 | command2"
878 sends both the standard output and standard error of
880 to the standard input of
885 or newline terminator causes the preceding
887 (described below in the section called
888 .Sx Short-Circuit List Operators )
889 to be executed sequentially;
892 causes asynchronous execution of the preceding AND-OR-list.
893 .Ss Background Commands (&)
894 If a command is terminated by the control operator ampersand
896 the shell executes the command in a subshell environment (see
897 .Sx Grouping Commands Together
898 below) and asynchronously;
899 the shell does not wait for the command to finish
900 before executing the next command.
902 The format for running a command in background is:
904 .D1 Ar command1 Li & Op Ar command2 Li & Ar ...
906 If the shell is not interactive, the standard input of an
907 asynchronous command is set to
910 The exit status is zero.
911 .Ss Lists (Generally Speaking)
912 A list is a sequence of zero or more commands separated by
913 newlines, semicolons, or ampersands,
914 and optionally terminated by one of these three characters.
916 list are executed in the order they are written.
917 If command is followed by an ampersand, the shell starts the
918 command and immediately proceeds onto the next command;
919 otherwise it waits for the command to terminate before
920 proceeding to the next one.
921 .Ss Short-Circuit List Operators
925 are AND-OR list operators.
927 executes the first command, and then executes the second command
928 if the exit status of the first command is zero.
930 is similar, but executes the second command if the exit
931 status of the first command is nonzero.
935 both have the same priority.
936 .Ss Flow-Control Constructs (if, while, for, case)
940 .Bd -unfilled -offset indent -compact
944 .Ic then Ar list Oc Ar ...
949 The exit status is that of selected
954 or zero if no list was selected.
959 .Bd -unfilled -offset indent -compact
965 The two lists are executed repeatedly while the exit status of the
969 command is similar, but has the word
974 repeat until the exit status of the first list is zero.
976 The exit status is that of the last execution of the second list,
977 or zero if it was never executed.
982 .Bd -unfilled -offset indent -compact
983 .Ic for Ar variable Op Ic in Ar word ...
990 and the following words are omitted,
993 The words are expanded, and then the list is executed
994 repeatedly with the variable set to each word in turn.
999 commands may be replaced with
1009 .D1 Ic break Op Ar num
1010 .D1 Ic continue Op Ar num
1014 command terminates the
1023 command continues with the next iteration of the innermost loop.
1024 These are implemented as special built-in commands.
1029 .Bd -unfilled -offset indent -compact
1030 .Ic case Ar word Ic in
1031 .Ar pattern Ns Li ) Ar list Li ;;
1036 The pattern can actually be one or more patterns
1043 Tilde expansion, parameter expansion, command substitution,
1044 arithmetic expansion and quote removal are applied to the word.
1045 Then, each pattern is expanded in turn using tilde expansion,
1046 parameter expansion, command substitution and arithmetic expansion and
1047 the expanded form of the word is checked against it.
1048 If a match is found, the corresponding list is executed.
1049 If the selected list is terminated by the control operator
1053 execution continues with the next list,
1054 continuing until a list terminated with
1059 .Ss Grouping Commands Together
1060 Commands may be grouped by writing either
1062 .D1 Li \&( Ns Ar list Ns Li \%)
1066 .D1 Li { Ar list Ns Li \&; }
1068 The first form executes the commands in a subshell environment.
1069 A subshell environment has its own copy of:
1072 The current working directory as set by
1075 The file creation mask as set by
1078 Resource limits as set by
1081 References to open files.
1088 Positional parameters and variables.
1097 These are copied from the parent shell environment,
1098 except that trapped (but not ignored) signals are reset to the default action
1099 and known jobs are cleared.
1100 Any changes do not affect the parent shell environment.
1102 A subshell environment may be implemented as a child process or differently.
1103 If job control is enabled in an interactive shell,
1104 commands grouped in parentheses can be suspended and continued as a unit.
1106 For compatibility with other shells,
1107 two open parentheses in sequence should be separated by whitespace.
1109 The second form never forks another shell,
1110 so it is slightly more efficient.
1111 Grouping commands together this way allows the user to
1112 redirect their output as though they were one program:
1113 .Bd -literal -offset indent
1114 { echo -n "hello"; echo " world"; } > greeting
1117 The syntax of a function definition is
1119 .D1 Ar name Li \&( \&) Ar command
1121 A function definition is an executable statement; when
1122 executed it installs a function named
1125 exit status of zero.
1134 Variables may be declared to be local to a function by
1138 This should appear as the first statement of a function,
1141 .D1 Ic local Oo Ar variable ... Oc Op Fl
1145 command is implemented as a built-in command.
1146 The exit status is zero
1147 unless the command is not in a function or a variable name is invalid.
1149 When a variable is made local, it inherits the initial
1150 value and exported and readonly flags from the variable
1151 with the same name in the surrounding scope, if there is
1153 Otherwise, the variable is initially unset.
1155 uses dynamic scoping, so that if the variable
1157 is made local to function
1159 which then calls function
1161 references to the variable
1165 will refer to the variable
1169 not to the global variable named
1172 The only special parameter that can be made local is
1176 local causes any shell options that are
1179 command inside the function to be
1180 restored to their original values when the function
1187 .D1 Ic return Op Ar exitstatus
1189 It terminates the current executional scope, returning from the closest
1190 nested function or sourced script;
1191 if no function or sourced script is being executed,
1192 it exits the shell instance.
1195 command is implemented as a special built-in command.
1196 .Ss Variables and Parameters
1197 The shell maintains a set of parameters.
1199 denoted by a name is called a variable.
1201 the shell turns all the environment variables into shell
1203 New variables can be set using the form
1205 .D1 Ar name Ns = Ns Ar value
1207 Variables set by the user must have a name consisting solely
1208 of alphabetics, numerics, and underscores.
1209 The first letter of a variable name must not be numeric.
1210 A parameter can also be denoted by a number
1211 or a special character as explained below.
1213 Assignments are expanded differently from other words:
1214 tilde expansion is also performed after the equals sign and after any colon
1215 and usernames are also terminated by colons,
1216 and field splitting and pathname expansion are not performed.
1218 This special expansion applies not only to assignments that form a simple
1219 command by themselves or precede a command word,
1220 but also to words passed to the
1225 built-in commands that have this form.
1226 For this, the builtin's name must be literal
1227 (not the result of an expansion)
1228 and may optionally be preceded by one or more literal instances of
1231 .Ss Positional Parameters
1232 A positional parameter is a parameter denoted by a number greater than zero.
1233 The shell sets these initially to the values of its command line
1234 arguments that follow the name of the shell script.
1237 built-in command can also be used to set or reset them.
1238 .Ss Special Parameters
1239 Special parameters are parameters denoted by a single special character
1241 They are shown in the following list, exactly as they would appear in input
1242 typed by the user or in the source of a shell script.
1245 Expands to the positional parameters, starting from one.
1247 the expansion occurs within a double-quoted string
1248 it expands to a single field with the value of each parameter
1249 separated by the first character of the
1256 Expands to the positional parameters, starting from one.
1258 the expansion occurs within double-quotes, each positional
1259 parameter expands as a separate argument.
1260 If there are no positional parameters, the
1263 generates zero arguments, even when
1266 What this basically means, for example, is
1279 .Bd -literal -offset indent
1283 Expands to the number of positional parameters.
1285 Expands to the exit status of the most recent pipeline.
1287 (hyphen) Expands to the current option flags (the single-letter
1288 option names concatenated into a string) as specified on
1291 built-in command, or implicitly
1294 Expands to the process ID of the invoked shell.
1296 retains the same value of
1300 Expands to the process ID of the most recent background
1301 command executed from the current shell.
1303 pipeline, the process ID is that of the last command in the
1305 If this parameter is referenced, the shell will remember
1306 the process ID and its exit status until the
1308 built-in command reports completion of the process.
1310 (zero) Expands to the name of the shell script if passed on the command line,
1313 operand if given (with
1315 or otherwise argument 0 passed to the shell.
1317 .Ss Special Variables
1318 The following variables are set by the shell or
1319 have special meaning to it:
1320 .Bl -tag -width ".Va HISTSIZE"
1322 The search path used with the
1326 The fallback editor used with the
1329 If not set, the default editor is
1332 The default editor used with the
1336 The number of previous commands that are accessible.
1338 The user's home directory,
1339 used in tilde expansion and as a default directory for the
1343 Input Field Separators.
1344 The default value is
1350 This default also applies if
1352 is unset, but not if it is set to the empty string.
1354 .Sx White Space Splitting
1355 section for more details.
1357 The current line number in the script or function.
1359 The name of a mail file, that will be checked for the arrival of new
1366 separated list of file names, for the shell to check for incoming
1368 This variable overrides the
1371 There is a maximum of 10 mailboxes that can be monitored at once.
1373 The default search path for executables.
1376 section for details.
1378 The parent process ID of the invoked shell.
1379 This is set at startup
1380 unless this variable is in the environment.
1381 A later change of parent process ID is not reflected.
1382 A subshell retains the same value of
1385 The primary prompt string, which defaults to
1387 unless you are the superuser, in which case it defaults to
1390 may include any of the following formatting sequences,
1391 which are replaced by the given information:
1392 .Bl -tag -width indent
1396 The fully-qualified hostname.
1398 The final component of the current working directory.
1400 The entire path of the current working directory.
1404 for normal users and
1408 A literal backslash.
1411 The secondary prompt string, which defaults to
1414 may include any of the formatting sequences from
1417 The prefix for the trace output (if
1424 This clause describes the various expansions that are
1426 Not all expansions are performed on
1427 every word, as explained later.
1429 Tilde expansions, parameter expansions, command substitutions,
1430 arithmetic expansions, and quote removals that occur within
1431 a single word expand to a single field.
1433 splitting or pathname expansion that can create multiple
1434 fields from a single word.
1435 The single exception to this rule is
1436 the expansion of the special parameter
1438 within double-quotes,
1439 as was described above.
1441 The order of word expansion is:
1444 Tilde Expansion, Parameter Expansion, Command Substitution,
1445 Arithmetic Expansion (these all occur at the same time).
1447 Field Splitting is performed on fields generated by step (1)
1452 Pathname Expansion (unless the
1454 option is in effect).
1461 character is used to introduce parameter expansion, command
1462 substitution, or arithmetic expansion.
1463 .Ss Tilde Expansion (substituting a user's home directory)
1464 A word beginning with an unquoted tilde character
1467 subjected to tilde expansion.
1468 All the characters up to a slash
1470 or the end of the word are treated as a username
1471 and are replaced with the user's home directory.
1473 username is missing (as in
1475 the tilde is replaced with the value of the
1477 variable (the current user's home directory).
1478 .Ss Parameter Expansion
1479 The format for parameter expansion is as follows:
1481 .D1 Li ${ Ns Ar expression Ns Li }
1485 consists of all characters until the matching
1489 escaped by a backslash or within a single-quoted or double-quoted
1490 string, and characters in
1491 embedded arithmetic expansions, command substitutions, and variable
1492 expansions, are not examined in determining the matching
1494 If the variants with
1500 occur within a double-quoted string,
1501 as an extension there may be unquoted parts
1502 (via double-quotes inside the expansion);
1504 within such parts are also not examined in determining the matching
1507 The simplest form for parameter expansion is:
1509 .D1 Li ${ Ns Ar parameter Ns Li }
1511 The value, if any, of
1515 The parameter name or symbol can be enclosed in braces, which are
1516 optional except for positional parameters with more than one digit or
1517 when parameter is followed by a character that could be interpreted as
1519 If a parameter expansion occurs inside double-quotes:
1522 Field splitting is not performed on the results of the
1523 expansion, with the exception of the special parameter
1526 Pathname expansion is not performed on the results of the
1530 In addition, a parameter expansion can be modified by using one of the
1532 .Bl -tag -width indent
1533 .It Li ${ Ns Ar parameter Ns Li :- Ns Ar word Ns Li }
1537 is unset or null, the expansion of
1539 is substituted; otherwise, the value of
1542 .It Li ${ Ns Ar parameter Ns Li := Ns Ar word Ns Li }
1543 Assign Default Values.
1546 is unset or null, the expansion of
1556 does not prevent field splitting or pathname expansion.
1557 Only variables, not positional
1558 parameters or special parameters, can be
1559 assigned in this way.
1560 .It Li ${ Ns Ar parameter Ns Li :? Ns Oo Ar word Oc Ns Li }
1561 Indicate Error if Null or Unset.
1564 is unset or null, the expansion of
1566 (or a message indicating it is unset if
1568 is omitted) is written to standard
1569 error and the shell exits with a nonzero
1571 Otherwise, the value of
1575 interactive shell need not exit.
1576 .It Li ${ Ns Ar parameter Ns Li :+ Ns Ar word Ns Li }
1577 Use Alternate Value.
1580 is unset or null, null is substituted;
1581 otherwise, the expansion of
1586 In the parameter expansions shown previously, use of the colon in the
1587 format results in a test for a parameter that is unset or null; omission
1588 of the colon results in a test for a parameter that is only unset.
1592 inherits the type of quoting
1593 (unquoted, double-quoted or here-document)
1594 from the surroundings,
1595 with the exception that a backslash that quotes a closing brace is removed
1596 during quote removal.
1597 .Bl -tag -width indent
1598 .It Li ${# Ns Ar parameter Ns Li }
1600 The length in characters of
1605 The following four varieties of parameter expansion provide for substring
1607 In each case, pattern matching notation
1609 .Sx Shell Patterns ) ,
1610 rather than regular expression notation,
1611 is used to evaluate the patterns.
1612 If parameter is one of the special parameters
1616 the result of the expansion is unspecified.
1617 Enclosing the full parameter expansion string in double-quotes does not
1618 cause the following four varieties of pattern characters to be quoted,
1619 whereas quoting characters within the braces has this effect.
1620 .Bl -tag -width indent
1621 .It Li ${ Ns Ar parameter Ns Li % Ns Ar word Ns Li }
1622 Remove Smallest Suffix Pattern.
1625 is expanded to produce a pattern.
1627 parameter expansion then results in
1629 with the smallest portion of the
1630 suffix matched by the pattern deleted.
1631 .It Li ${ Ns Ar parameter Ns Li %% Ns Ar word Ns Li }
1632 Remove Largest Suffix Pattern.
1635 is expanded to produce a pattern.
1637 parameter expansion then results in
1639 with the largest 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 Smallest Prefix Pattern.
1645 is expanded to produce a pattern.
1647 parameter expansion then results in
1649 with the smallest portion of the
1650 prefix matched by the pattern deleted.
1651 .It Li ${ Ns Ar parameter Ns Li ## Ns Ar word Ns Li }
1652 Remove Largest Prefix Pattern.
1655 is expanded to produce a pattern.
1657 parameter expansion then results in
1659 with the largest portion of the
1660 prefix matched by the pattern deleted.
1662 .Ss Command Substitution
1663 Command substitution allows the output of a command to be substituted in
1664 place of the command name itself.
1665 Command substitution occurs when
1666 the command is enclosed as follows:
1668 .D1 Li $( Ns Ar command Ns Li )\&
1670 or the backquoted version:
1672 .D1 Li ` Ns Ar command Ns Li `
1674 The shell expands the command substitution by executing command
1675 and replacing the command substitution
1676 with the standard output of the command,
1677 removing sequences of one or more newlines at the end of the substitution.
1678 Embedded newlines before the end of the output are not removed;
1679 however, during field splitting, they may be translated into spaces
1680 depending on the value of
1682 and the quoting that is in effect.
1683 The command is executed in a subshell environment,
1684 except that the built-in commands
1689 return information about the parent shell environment
1692 returns information about the same process
1693 if they are the only command in a command substitution.
1695 If a command substitution of the
1697 form begins with a subshell,
1702 must be separated by whitespace
1703 to avoid ambiguity with arithmetic expansion.
1704 .Ss Arithmetic Expansion
1705 Arithmetic expansion provides a mechanism for evaluating an arithmetic
1706 expression and substituting its value.
1707 The format for arithmetic expansion is as follows:
1709 .D1 Li $(( Ns Ar expression Ns Li ))
1713 is treated as if it were in double-quotes, except
1714 that a double-quote inside the expression is not treated specially.
1716 shell expands all tokens in the
1718 for parameter expansion,
1719 command substitution,
1720 arithmetic expansion
1723 The allowed expressions are a subset of C expressions,
1725 .Bl -tag -width "Variables" -offset indent
1727 All values are of type
1730 Decimal, octal (starting with
1732 and hexadecimal (starting with
1736 Shell variables can be read and written
1737 and contain integer constants.
1740 .It Binary operators
1741 .Li "* / % + - << >> < <= > >= == != & ^ | && ||"
1742 .It Assignment operators
1743 .Li "= += -= *= /= %= <<= >>= &= ^= |="
1744 .It Conditional operator
1748 The result of the expression is substituted in decimal.
1749 .Ss White Space Splitting (Field Splitting)
1750 In certain contexts,
1751 after parameter expansion, command substitution, and
1752 arithmetic expansion the shell scans the results of
1753 expansions and substitutions that did not occur in double-quotes for
1754 field splitting and multiple fields can result.
1765 are treated differently from other characters in
1770 at the beginning or end of a word is discarded.
1772 Subsequently, a field is delimited by either
1775 a non-whitespace character in
1777 with any whitespace in
1781 one or more whitespace characters in
1785 If a word ends with a non-whitespace character in
1787 there is no empty field after this character.
1789 If no field is delimited, the word is discarded.
1790 In particular, if a word consists solely of an unquoted substitution
1791 and the result of the substitution is null,
1792 it is removed by field splitting even if
1795 .Ss Pathname Expansion (File Name Generation)
1799 file name generation is performed
1800 after word splitting is complete.
1802 viewed as a series of patterns, separated by slashes.
1804 process of expansion replaces the word with the names of
1805 all existing files whose names can be formed by replacing
1806 each pattern with a string that matches the specified pattern.
1807 There are two restrictions on this: first, a pattern cannot match
1808 a string containing a slash, and second,
1809 a pattern cannot match a string starting with a period
1810 unless the first character of the pattern is a period.
1811 The next section describes the patterns used for
1813 the four varieties of parameter expansion for substring processing and the
1817 A pattern consists of normal characters, which match themselves,
1818 and meta-characters.
1819 The meta-characters are
1824 These characters lose their special meanings if they are quoted.
1825 When command or variable substitution is performed and the dollar sign
1826 or back quotes are not double-quoted, the value of the
1827 variable or the output of the command is scanned for these
1828 characters and they are turned into meta-characters.
1832 matches any string of characters.
1835 matches any single character.
1838 introduces a character class.
1839 The end of the character class is indicated by a
1847 rather than introducing a character class.
1848 A character class matches any of the characters between the square brackets.
1849 A locale-dependent range of characters may be specified using a minus sign.
1850 A named class of characters (see
1852 may be specified by surrounding the name with
1857 .Ql \&[\&[:alpha:\&]\&]
1858 is a shell pattern that matches a single letter.
1859 The character class may be complemented by making an exclamation point
1861 the first character of the character class.
1864 has the same effect but is non-standard.
1868 in a character class, make it the first character listed
1876 make it the first or last character listed.
1877 .Ss Built-in Commands
1878 This section lists the built-in commands.
1879 .Bl -tag -width indent
1881 A null command that returns a 0 (true) exit value.
1883 The commands in the specified file are read and executed by the shell.
1886 command may be used to return to the
1893 characters, it is used as is.
1894 Otherwise, the shell searches the
1897 If it is not found in the
1899 it is sought in the current working directory.
1901 A built-in equivalent of
1903 .It Ic alias Oo Ar name Ns Oo = Ns Ar string Oc ... Oc
1905 .Ar name Ns = Ns Ar string
1906 is specified, the shell defines the alias
1912 is specified, the value of the alias
1915 With no arguments, the
1917 built-in command prints the names and values of all defined aliases
1920 Alias values are written with appropriate quoting so that they are
1921 suitable for re-input to the shell.
1925 .It Ic bg Op Ar job ...
1926 Continue the specified jobs
1927 (or the current job if no jobs are given)
1929 .It Ic bind Oo Fl aeklrsv Oc Oo Ar key Oo Ar command Oc Oc
1930 List or alter key bindings for the line editor.
1931 This command is documented in
1933 .It Ic break Op Ar num
1935 .Sx Flow-Control Constructs
1937 .It Ic builtin Ar cmd Op Ar arg ...
1938 Execute the specified built-in command,
1940 This is useful when the user wishes to override a shell function
1941 with the same name as a built-in command.
1942 .It Ic cd Oo Fl L | P Oc Oo Fl e Oc Op Ar directory
1943 Switch to the specified
1945 or to the directory specified in the
1947 environment variable if no
1956 then the directories listed in the
1959 searched for the specified
1963 is unset, the current directory is searched.
1966 is the same as that of
1968 In an interactive shell,
1971 command will print out the name of the directory
1972 that it actually switched to
1973 if this is different from the name that the user gave.
1974 These may be different either because the
1976 mechanism was used or because a symbolic link was crossed.
1980 option is specified,
1982 is handled physically and symbolic links are resolved before
1984 components are processed.
1987 option is specified,
1989 is handled logically.
1990 This is the default.
1996 to return exit status 1 if the full pathname of the new directory
1997 cannot be determined reliably or at all.
1998 Normally this is not considered an error,
1999 although a warning is printed.
2004 .It Ic command Oo Fl p Oc Op Ar utility Op Ar argument ...
2005 .It Ic command Oo Fl p Oc Fl v Ar utility
2006 .It Ic command Oo Fl p Oc Fl V Ar utility
2007 The first form of invocation executes the specified
2009 ignoring shell functions in the search.
2012 is a special builtin,
2013 it is executed as if it were a regular builtin.
2017 option is specified, the command search is performed using a
2020 that is guaranteed to find all of the standard utilities.
2024 option is specified,
2026 is not executed but a description of its interpretation by the shell is
2028 For ordinary commands the output is the path name; for shell built-in
2029 commands, shell functions and keywords only the name is written.
2030 Aliases are printed as
2031 .Dq Ic alias Ar name Ns = Ns Ar value .
2035 option is identical to
2037 except for the output.
2039 .Dq Ar utility Ic is Ar description
2045 a special shell builtin,
2052 .It Ic continue Op Ar num
2054 .Sx Flow-Control Constructs
2056 .It Ic echo Oo Fl e | n Oc Op Ar string ...
2057 Print a space-separated list of the arguments to the standard output
2058 and append a newline character.
2059 .Bl -tag -width indent
2061 Suppress the output of the trailing newline.
2063 Process C-style backslash escape sequences.
2066 command understands the following character escapes:
2067 .Bl -tag -width indent
2069 Alert (ring the terminal bell)
2073 Suppress the trailing newline (this has the side-effect of truncating the
2074 line if it is not the last character)
2092 (Zero) The character whose octal value is
2098 is not enclosed in quotes then the backslash itself must be escaped
2099 with a backslash to protect it from the shell.
2101 .Bd -literal -offset indent
2110 $ echo -e a\e\e\e\eb
2119 options may be specified.
2120 .It Ic eval Ar string ...
2121 Concatenate all the arguments with spaces.
2122 Then re-parse and execute the command.
2123 .It Ic exec Op Ar command Op arg ...
2127 the shell process is replaced with the specified program
2128 (which must be a real program, not a shell built-in command or function).
2129 Any redirections on the
2131 command are marked as permanent,
2132 so that they are not undone when the
2135 .It Ic exit Op Ar exitstatus
2136 Terminate the shell process.
2140 it is used as the exit status of the shell.
2141 Otherwise, if the shell is executing an
2143 trap, the exit status of the last command before the trap is used;
2144 if the shell is executing a trap for a signal,
2145 the shell exits by resending the signal to itself.
2146 Otherwise, the exit status of the preceding command is used.
2147 The exit status should be an integer between 0 and 255.
2148 .It Ic export Ar name ...
2149 .It Ic export Op Fl p
2150 The specified names are exported so that they will
2151 appear in the environment of subsequent commands.
2152 The only way to un-export a variable is to
2155 The shell allows the value of a variable to be set
2156 at the same time as it is exported by writing
2158 .D1 Ic export Ar name Ns = Ns Ar value
2160 With no arguments the
2162 command lists the names
2163 of all exported variables.
2166 option is specified, the exported variables are printed as
2167 .Dq Ic export Ar name Ns = Ns Ar value
2168 lines, suitable for re-input to the shell.
2170 A null command that returns a non-zero (false) exit value.
2171 .It Ic fc Oo Fl e Ar editor Oc Op Ar first Op Ar last
2172 .It Ic fc Fl l Oo Fl nr Oc Op Ar first Op Ar last
2173 .It Ic fc Fl s Oo Ar old Ns = Ns Ar new Oc Op Ar first
2176 built-in command lists, or edits and re-executes,
2177 commands previously entered to an interactive shell.
2178 .Bl -tag -width indent
2180 Use the editor named by
2182 to edit the commands.
2185 string is a command name,
2186 subject to search via the
2191 variable is used as a default when
2196 is null or unset, the value of the
2203 is used as the editor.
2205 List the commands rather than invoking
2207 The commands are written in the
2208 sequence indicated by the
2212 operands, as affected by
2214 with each command preceded by the command number.
2216 Suppress command numbers when listing with
2219 Reverse the order of the commands listed
2228 Re-execute the command without invoking an editor.
2231 Select the commands to list or edit.
2232 The number of previous commands that can be accessed
2233 are determined by the value of the
2240 or both are one of the following:
2241 .Bl -tag -width indent
2242 .It Oo Cm + Oc Ns Ar num
2243 A positive number representing a command number;
2244 command numbers can be displayed with the
2248 A negative decimal number representing the
2249 command that was executed
2252 commands previously.
2253 For example, \-1 is the immediately previous command.
2255 A string indicating the most recently entered command
2256 that begins with that string.
2258 .Ar old Ns = Ns Ar new
2259 operand is not also specified with
2261 the string form of the first operand cannot contain an embedded equal sign.
2265 The following variables affect the execution of
2267 .Bl -tag -width ".Va HISTSIZE"
2269 Name of the editor to use for history editing.
2271 The number of previous commands that are accessible.
2276 or the current job to the foreground.
2277 .It Ic getopts Ar optstring var
2284 command deprecates the older
2287 The first argument should be a series of letters, each possibly
2288 followed by a colon which indicates that the option takes an argument.
2289 The specified variable is set to the parsed option.
2291 the next argument is placed into the shell variable
2293 If an option takes an argument, it is placed into the shell variable
2295 If an invalid option is encountered,
2299 It returns a false value (1) when it encounters the end of the options.
2300 .It Ic hash Oo Fl rv Oc Op Ar command ...
2301 The shell maintains a hash table which remembers the locations of commands.
2302 With no arguments whatsoever, the
2304 command prints out the contents of this table.
2308 command removes each specified
2310 from the hash table (unless they are functions) and then locates it.
2315 prints the locations of the commands as it finds them.
2320 command to delete all the entries in the hash table except for functions.
2321 .It Ic jobid Op Ar job
2322 Print the process IDs of the processes in the specified
2326 argument is omitted, use the current job.
2327 .It Ic jobs Oo Fl lps Oc Op Ar job ...
2328 Print information about the specified jobs, or all jobs if no
2331 The information printed includes job ID, status and command name.
2335 option is specified, the PID of each job is also printed.
2338 option is specified, only the process IDs for the process group leaders
2339 are printed, one per line.
2342 option is specified, only the PIDs of the job commands are printed, one per
2345 A built-in equivalent of
2347 that additionally supports sending signals to jobs.
2348 .It Ic local Oo Ar variable ... Oc Op Fl
2353 A built-in equivalent of
2355 .It Ic pwd Op Fl L | P
2356 Print the path of the current directory.
2357 The built-in command may
2358 differ from the program of the same name because the
2359 built-in command remembers what the current directory
2360 is rather than recomputing it each time.
2363 However, if the current directory is
2365 the built-in version of
2367 will continue to print the old name for the directory.
2371 option is specified, symbolic links are resolved.
2374 option is specified, the shell's notion of the current directory
2375 is printed (symbolic links are not resolved).
2376 This is the default.
2377 .It Ic read Oo Fl p Ar prompt Oc Oo
2378 .Fl t Ar timeout Oc Oo Fl er Oc Ar variable ...
2384 and the standard input is a terminal.
2386 read from the standard input.
2387 The trailing newline
2388 is deleted from the line and the line is split as
2389 described in the section on
2390 .Sx White Space Splitting (Field Splitting)
2392 the pieces are assigned to the variables in order.
2393 If there are more pieces than variables, the remaining
2394 pieces (along with the characters in
2396 that separated them)
2397 are assigned to the last variable.
2398 If there are more variables than pieces, the remaining
2399 variables are assigned the null string.
2401 Backslashes are treated specially, unless the
2405 If a backslash is followed by
2406 a newline, the backslash and the newline will be
2408 If a backslash is followed by any other
2409 character, the backslash will be deleted and the following
2410 character will be treated as though it were not in
2416 option is specified and the
2418 elapses before a complete line of input is supplied,
2421 command will return an exit status as if terminated by
2423 without assigning any values.
2426 value may optionally be followed by one of
2431 to explicitly specify seconds, minutes or hours.
2432 If none is supplied,
2438 option exists only for backward compatibility with older scripts.
2440 The exit status is 0 on success, 1 on end of file,
2441 between 2 and 128 if an error occurs
2442 and greater than 128 if a trapped signal interrupts
2444 .It Ic readonly Oo Fl p Oc Op Ar name ...
2447 is marked as read only,
2448 so that it cannot be subsequently modified or unset.
2449 The shell allows the value of a variable to be set
2450 at the same time as it is marked read only
2451 by using the following form:
2453 .D1 Ic readonly Ar name Ns = Ns Ar value
2455 With no arguments the
2457 command lists the names of all read only variables.
2460 option is specified, the read-only variables are printed as
2461 .Dq Ic readonly Ar name Ns = Ns Ar value
2462 lines, suitable for re-input to the shell.
2463 .It Ic return Op Ar exitstatus
2467 .It Ic set Oo Fl /+abCEefIimnpTuVvx Oc Oo Fl /+o Ar longname Oc Oo
2468 .Fl c Ar string Oc Op Fl - Ar arg ...
2471 command performs three different functions:
2474 With no arguments, it lists the values of all shell variables.
2476 If options are given,
2477 either in short form or using the long
2478 .Dq Fl /+o Ar longname
2480 it sets or clears the specified options as described in the section called
2481 .Sx Argument List Processing .
2485 option is specified,
2487 will replace the shell's positional parameters with the subsequent
2489 If no arguments follow the
2492 all the positional parameters will be cleared,
2493 which is equivalent to executing the command
2497 flag may be omitted when specifying arguments to be used
2498 as positional replacement parameters.
2499 This is not recommended,
2500 because the first argument may begin with a dash
2506 command will interpret as a request to enable or disable options.
2508 .It Ic setvar Ar variable value
2509 Assigns the specified
2515 command is intended to be used in functions that
2516 assign values to variables whose names are passed as parameters.
2517 In general it is better to write
2518 .Dq Ar variable Ns = Ns Ar value
2521 .It Ic shift Op Ar n
2522 Shift the positional parameters
2527 A shift sets the value of
2536 decreasing the value of
2539 For portability, shifting if there are zero positional parameters
2540 should be avoided, since the shell may abort.
2542 A built-in equivalent of
2545 Print the amount of time spent executing the shell process and its children.
2546 The first output line shows the user and system times for the shell process
2547 itself, the second one contains the user and system times for the
2549 .It Ic trap Oo Ar action Oc Ar signal ...
2551 Cause the shell to parse and execute
2556 The signals are specified by name or number.
2557 In addition, the pseudo-signal
2559 may be used to specify an
2561 that is performed when the shell terminates.
2564 may be an empty string or a dash
2566 the former causes the specified signal to be ignored
2567 and the latter causes the default action to be taken.
2570 is another way to request the default action, for compatibility reasons this
2571 usage is not recommended though.
2572 In a subshell or utility environment,
2573 the shell resets trapped (but not ignored) signals to the default action.
2576 command has no effect on signals that were ignored on entry to the shell.
2582 command to display a list of valid signal names.
2584 A null command that returns a 0 (true) exit value.
2585 .It Ic type Op Ar name ...
2588 as a command and print the resolution of the command search.
2589 Possible resolutions are:
2590 shell keyword, alias, special shell builtin, shell builtin, command,
2593 For aliases the alias expansion is printed;
2594 for commands and tracked aliases
2595 the complete pathname of the command is printed.
2596 .It Ic ulimit Oo Fl HSabcdfklmnpstuvw Oc Op Ar limit
2597 Set or display resource limits (see
2601 is specified, the named resource will be set;
2602 otherwise the current resource value will be displayed.
2606 is specified, the hard limits will be set or displayed.
2607 While everybody is allowed to reduce a hard limit,
2608 only the superuser can increase it.
2612 specifies the soft limits instead.
2613 When displaying limits,
2619 The default is to display the soft limits,
2620 and to set both the hard and the soft limits.
2626 command to display all resources.
2629 is not acceptable in this mode.
2631 The remaining options specify which resource value is to be
2632 displayed or modified.
2633 They are mutually exclusive.
2634 .Bl -tag -width indent
2636 The maximum size of socket buffer usage, in bytes.
2637 .It Fl c Ar coredumpsize
2638 The maximal size of core dump files, in 512-byte blocks.
2639 .It Fl d Ar datasize
2640 The maximal size of the data segment of a process, in kilobytes.
2641 .It Fl f Ar filesize
2642 The maximal size of a file, in 512-byte blocks.
2644 The maximal number of kqueues
2648 .It Fl l Ar lockedmem
2649 The maximal size of memory that can be locked by a process, in
2651 .It Fl m Ar memoryuse
2652 The maximal resident set size of a process, in kilobytes.
2654 The maximal number of descriptors that could be opened by a process.
2655 .It Fl p Ar pseudoterminals
2656 The maximal number of pseudo-terminals for this user ID.
2657 .It Fl s Ar stacksize
2658 The maximal size of the stack segment, in kilobytes.
2660 The maximal amount of CPU time to be used by each process, in seconds.
2661 .It Fl u Ar userproc
2662 The maximal number of simultaneous processes for this user ID.
2663 .It Fl v Ar virtualmem
2664 The maximal virtual size of a process, in kilobytes.
2666 The maximum amount of swap space reserved or used for this user ID,
2669 .It Ic umask Oo Fl S Oc Op Ar mask
2670 Set the file creation mask (see
2672 to the octal or symbolic (see
2676 If the argument is omitted, the current mask value is printed.
2679 option is specified, the output is symbolic, otherwise the output is octal.
2680 .It Ic unalias Oo Fl a Oc Op Ar name ...
2681 The specified alias names are removed.
2684 is specified, all aliases are removed.
2685 .It Ic unset Oo Fl fv Oc Ar name ...
2686 The specified variables or functions are unset and unexported.
2689 option is specified or no options are given, the
2691 arguments are treated as variable names.
2694 option is specified, the
2696 arguments are treated as function names.
2697 .It Ic wait Op Ar job ...
2698 Wait for each specified
2700 to complete and return the exit status of the last process in the
2705 specified is unknown to the shell, it is treated as if it
2706 were a known job that exited with exit status 127.
2707 If no operands are given, wait for all jobs to complete
2708 and return an exit status of zero.
2710 .Ss Commandline Editing
2713 is being used interactively from a terminal, the current command
2714 and the command history
2718 .Sx Built-in Commands )
2721 command line editing.
2722 This mode uses commands similar
2723 to a subset of those described in the
2741 can be switched between insert mode and command mode by typing
2745 while in command mode will pass the line to the shell.
2748 .Dq Li "set -o emacs"
2751 command can be used to enable a subset of
2753 command line editing features.
2755 The following environment variables affect the execution of
2757 .Bl -tag -width ".Ev LANGXXXXXX"
2759 Initialization file for interactive shells.
2760 .It Ev LANG , Ev LC_*
2762 These are inherited by children of the shell,
2763 and is used in a limited manner by the shell itself.
2765 An absolute pathname for the current directory,
2766 possibly containing symbolic links.
2767 This is used and updated by the shell.
2769 The default terminal setting for the shell.
2770 This is inherited by children of the shell, and is used in the history
2774 Additionally, all environment variables are turned into shell variables
2776 which may affect the shell as described under
2777 .Sx Special Variables .
2779 .Bl -tag -width "/etc/suid_profileXX" -compact
2781 User's login profile.
2783 System login profile.
2786 .It Pa /etc/suid_profile
2787 Privileged shell profile.
2790 Errors that are detected by the shell, such as a syntax error, will
2791 cause the shell to exit with a non-zero exit status.
2792 If the shell is not an interactive shell, the execution of the shell
2793 file will be aborted.
2794 Otherwise the shell will return the exit status of the last command
2797 builtin is used with a numeric argument, it
2798 will return the argument.
2819 command, the Thompson shell, appeared in
2821 It was superseded in
2823 by the Bourne shell, which inherited the name
2828 was rewritten in 1989 under the
2830 license after the Bourne shell from
2835 was originally written by
2836 .An Kenneth Almquist .
2840 utility does not recognize multibyte characters other than UTF-8.
2843 and the line editing library
2845 do not recognize multibyte characters.
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