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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
217 .Xr emacs 1 Pq Pa ports/editors/emacs
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.
347 Change the exit status of a pipeline to the last non-zero exit status of
348 any command in the pipeline, if any.
351 counts as a non-zero exit status,
352 this option may cause non-zero exit status for successful pipelines
355 in the pipeline terminates with status 0 without reading its
357 This option only has a long name.
361 when sourcing files or loading profiles.
363 .\" .Xr mac_veriexec 4 . TODO Does not exist; write it.
368 option causes the commands to be read from the
370 operand instead of from the standard input.
371 Keep in mind that this option only accepts a single string as its
372 argument, hence multi-word strings must be quoted.
376 option takes as its only argument the long name of an option
377 to be enabled or disabled.
378 For example, the following two invocations of
380 both enable the built-in
381 .Xr emacs 1 Pq Pa ports/editors/emacs
383 .Bd -literal -offset indent
388 If used without an argument, the
390 option displays the current option settings in a human-readable format.
393 is used without an argument, the current option settings are output
394 in a format suitable for re-input into the shell.
395 .Ss Lexical Structure
396 The shell reads input in terms of lines from a file and breaks
397 it up into words at whitespace (blanks and tabs), and at
401 which are special to the shell.
402 There are two types of operators: control operators and
403 redirection operators (their meaning is discussed later).
404 The following is a list of valid operators:
405 .Bl -tag -width indent
406 .It Control operators:
407 .Bl -column "XXX" "XXX" "XXX" "XXX" "XXX" -offset center -compact
408 .It Li & Ta Li && Ta Li \&( Ta Li \&) Ta Li \en
409 .It Li ;; Ta Li ;& Ta Li \&; Ta Li \&| Ta Li ||
411 .It Redirection operators:
412 .Bl -column "XXX" "XXX" "XXX" "XXX" "XXX" -offset center -compact
413 .It Li < Ta Li > Ta Li << Ta Li >> Ta Li <>
414 .It Li <& Ta Li >& Ta Li <<- Ta Li >| Ta \&
420 introduces a comment if used at the beginning of a word.
421 The word starting with
423 and the rest of the line are ignored.
427 characters (character code 0) are not allowed in shell input.
429 Quoting is used to remove the special meaning of certain characters
430 or words to the shell, such as operators, whitespace, keywords,
433 There are four types of quoting: matched single quotes,
434 dollar-single quotes,
435 matched double quotes, and backslash.
436 .Bl -tag -width indent
438 Enclosing characters in single quotes preserves the literal
439 meaning of all the characters (except single quotes, making
440 it impossible to put single-quotes in a single-quoted string).
441 .It Dollar-Single Quotes
442 Enclosing characters between
446 preserves the literal meaning of all characters
447 except backslashes and single quotes.
448 A backslash introduces a C-style escape sequence:
449 .Bl -tag -width xUnnnnnnnn
451 Alert (ring the terminal bell)
455 The control character denoted by
461 is a backslash, it must be doubled.
463 The ESC character (ASCII 0x1b)
481 The byte whose octal value is
483 (one to three digits)
485 The byte whose hexadecimal value is
487 (one or more digits only the last two of which are used)
489 The Unicode code point
491 (four hexadecimal digits)
492 .It \eU Ns Ar nnnnnnnn
493 The Unicode code point
495 (eight hexadecimal digits)
498 The sequences for Unicode code points are currently only useful with
500 They reject code point 0 and UTF-16 surrogates.
502 If an escape sequence would produce a byte with value 0,
503 that byte and the rest of the string until the matching single-quote
506 Any other string starting with a backslash is an error.
508 Enclosing characters within double quotes preserves the literal
509 meaning of all characters except dollar sign
515 The backslash inside double quotes is historically weird.
516 It remains literal unless it precedes the following characters,
517 which it serves to quote:
519 .Bl -column "XXX" "XXX" "XXX" "XXX" "XXX" -offset center -compact
520 .It Li $ Ta Li ` Ta Li \&" Ta Li \e Ta Li \en
523 A backslash preserves the literal meaning of the following
524 character, with the exception of the newline character
526 A backslash preceding a newline is treated as a line continuation.
529 Keywords or reserved words are words that have special meaning to the
530 shell and are recognized at the beginning of a line and
531 after a control operator.
532 The following are keywords:
533 .Bl -column "doneXX" "elifXX" "elseXX" "untilXX" "whileX" -offset center
534 .It Li \&! Ta { Ta } Ta Ic case Ta Ic do
535 .It Ic done Ta Ic elif Ta Ic else Ta Ic esac Ta Ic fi
536 .It Ic for Ta Ic if Ta Ic then Ta Ic until Ta Ic while
539 An alias is a name and corresponding value set using the
542 Wherever the command word of a simple command may occur,
543 and after checking for keywords if a keyword may occur, the shell
544 checks the word to see if it matches an alias.
545 If it does, it replaces it in the input stream with its value.
546 For example, if there is an alias called
558 Aliases are also recognized after an alias
559 whose value ends with a space or tab.
560 For example, if there is also an alias called
566 .Dl "nohup lf foobar"
570 .Dl "nohup ls -F foobar"
572 Aliases provide a convenient way for naive users to
573 create shorthands for commands without having to learn how
574 to create functions with arguments.
575 Using aliases in scripts is discouraged
576 because the command that defines them must be executed
577 before the code that uses them is parsed.
578 This is fragile and not portable.
580 An alias name may be escaped in a command line, so that it is not
581 replaced by its alias value, by using quoting characters within or
582 adjacent to the alias name.
583 This is most often done by prefixing
584 an alias name with a backslash to execute a function, built-in, or
585 normal program with the same name.
590 The shell interprets the words it reads according to a
591 language, the specification of which is outside the scope
592 of this man page (refer to the BNF in the
595 Essentially though, a line is read and if
596 the first word of the line (or after a control operator)
597 is not a keyword, then the shell has recognized a
599 Otherwise, a complex command or some
600 other special construct may have been recognized.
602 If a simple command has been recognized, the shell performs
603 the following actions:
606 Leading words of the form
608 are stripped off and assigned to the environment of
610 (they do not affect expansions).
611 Redirection operators and
612 their arguments (as described below) are stripped
613 off and saved for processing.
615 The remaining words are expanded as described in
617 .Sx Word Expansions ,
618 and the first remaining word is considered the command
619 name and the command is located.
621 words are considered the arguments of the command.
622 If no command name resulted, then the
624 variable assignments recognized in 1) affect the
627 Redirections are performed as described in
631 Redirections are used to change where a command reads its input
633 In general, redirections open, close, or
634 duplicate an existing reference to a file.
636 used for redirection is:
638 .D1 Oo Ar n Oc Ar redir-op file
642 is one of the redirection operators mentioned
644 The following gives some examples of how these
645 operators can be used.
646 Note that stdin and stdout are commonly used abbreviations
647 for standard input and standard output respectively.
648 .Bl -tag -width "1234567890XX" -offset indent
649 .It Oo Ar n Oc Ns Li > Ar file
650 redirect stdout (or file descriptor
654 .It Oo Ar n Oc Ns Li >| Ar file
655 same as above, but override the
658 .It Oo Ar n Oc Ns Li >> Ar file
659 append stdout (or file descriptor
663 .It Oo Ar n Oc Ns Li < Ar file
664 redirect stdin (or file descriptor
668 .It Oo Ar n Oc Ns Li <> Ar file
669 redirect stdin (or file descriptor
673 .It Oo Ar n1 Oc Ns Li <& Ns Ar n2
674 duplicate stdin (or file descriptor
678 .It Oo Ar n Oc Ns Li <&-
679 close stdin (or file descriptor
681 .It Oo Ar n1 Oc Ns Li >& Ns Ar n2
682 duplicate stdout (or file descriptor
686 .It Oo Ar n Oc Ns Li >&-
687 close stdout (or file descriptor
691 The following redirection is often called a
693 .Bd -unfilled -offset indent
694 .Oo Ar n Oc Ns Li << Ar delimiter
700 All the text on successive lines up to the delimiter is
701 saved away and made available to the command on standard
702 input, or file descriptor
707 as specified on the initial line is quoted, then the
709 is treated literally, otherwise the text is subjected to
710 parameter expansion, command substitution, and arithmetic
711 expansion (as described in the section on
712 .Sx Word Expansions ) .
721 .Ss Search and Execution
722 There are three types of commands: shell functions,
723 built-in commands, and normal programs.
724 The command is searched for (by name) in that order.
725 The three types of commands are all executed in a different way.
727 When a shell function is executed, all of the shell positional
730 which remains unchanged) are
731 set to the arguments of the shell function.
732 The variables which are explicitly placed in the environment of
733 the command (by placing assignments to them before the
734 function name) are made local to the function and are set
736 Then the command given in the function definition is executed.
737 The positional parameters are restored to their original values
738 when the command completes.
739 This all occurs within the current shell.
741 Shell built-in commands are executed internally to the shell, without
742 spawning a new process.
743 There are two kinds of built-in commands: regular and special.
744 Assignments before special builtins persist after they finish
745 executing and assignment errors, redirection errors and certain
746 operand errors cause a script to be aborted.
747 Special builtins cannot be overridden with a function.
748 Both regular and special builtins can affect the shell in ways
749 normal programs cannot.
751 Otherwise, if the command name does not match a function
752 or built-in command, the command is searched for as a normal
753 program in the file system (as described in the next section).
754 When a normal program is executed, the shell runs the program,
755 passing the arguments and the environment to the program.
756 If the program is not a normal executable file
757 (i.e., if it does not begin with the
759 whose ASCII representation is
765 but appears to be a text file,
766 the shell will run a new instance of
770 Note that previous versions of this document
771 and the source code itself misleadingly and sporadically
772 refer to a shell script without a magic number
774 .Dq "shell procedure" .
776 When locating a command, the shell first looks to see if
777 it has a shell function by that name.
779 built-in command by that name.
780 If a built-in command is not found,
781 one of two things happen:
784 Command names containing a slash are simply executed without
785 performing any searches.
787 The shell searches each entry in the
790 in turn for the command.
793 variable should be a series of
794 entries separated by colons.
795 Each entry consists of a
797 The current directory
798 may be indicated implicitly by an empty directory name,
799 or explicitly by a single period.
801 .Ss Command Exit Status
802 Each command has an exit status that can influence the behavior
803 of other shell commands.
804 The paradigm is that a command exits
805 with zero for normal or success, and non-zero for failure,
806 error, or a false indication.
807 The man page for each command
808 should indicate the various exit codes and what they mean.
809 Additionally, the built-in commands return exit codes, as does
810 an executed shell function.
812 If a command is terminated by a signal, its exit status is greater than 128.
813 The signal name can be found by passing the exit status to
816 If there is no command word,
817 the exit status is the exit status of the last command substitution executed,
818 or zero if the command does not contain any command substitutions.
820 Complex commands are combinations of simple commands
821 with control operators or keywords, together creating a larger complex
823 More generally, a command is one of the following:
824 .Bl -item -offset indent
830 list or compound-list
837 Unless otherwise stated, the exit status of a command is
838 that of the last simple command executed by the command,
839 or zero if no simple command was executed.
841 A pipeline is a sequence of one or more commands separated
842 by the control operator
844 The standard output of all but
845 the last command is connected to the standard input
847 The standard output of the last
848 command is inherited from the shell, as usual.
850 The format for a pipeline is:
852 .D1 Oo Li \&! Oc Ar command1 Op Li \&| Ar command2 ...
854 The standard output of
856 is connected to the standard input of
858 The standard input, standard output, or
859 both of a command is considered to be assigned by the
860 pipeline before any redirection specified by redirection
861 operators that are part of the command.
863 Note that unlike some other shells,
865 executes each process in a pipeline with more than one command
866 in a subshell environment and as a child of the
870 If the pipeline is not in the background (discussed later),
871 the shell waits for all commands to complete.
875 does not precede the pipeline, the
876 exit status is the exit status of the last command specified
877 in the pipeline if the
879 option is not set or all commands returned zero,
880 or the last non-zero exit status of any command in the pipeline otherwise.
881 Otherwise, the exit status is the logical
882 NOT of that exit status.
884 that status is zero, the exit status is 1; if
885 that status is greater than zero, the exit status
888 Because pipeline assignment of standard input or standard
889 output or both takes place before redirection, it can be
890 modified by redirection.
893 .Dl "command1 2>&1 | command2"
895 sends both the standard output and standard error of
897 to the standard input of
902 or newline terminator causes the preceding
904 (described below in the section called
905 .Sx Short-Circuit List Operators )
906 to be executed sequentially;
909 causes asynchronous execution of the preceding AND-OR-list.
910 .Ss Background Commands (&)
911 If a command is terminated by the control operator ampersand
913 the shell executes the command in a subshell environment (see
914 .Sx Grouping Commands Together
915 below) and asynchronously;
916 the shell does not wait for the command to finish
917 before executing the next command.
919 The format for running a command in background is:
921 .D1 Ar command1 Li & Op Ar command2 Li & Ar ...
923 If the shell is not interactive, the standard input of an
924 asynchronous command is set to
927 The exit status is zero.
928 .Ss Lists (Generally Speaking)
929 A list is a sequence of zero or more commands separated by
930 newlines, semicolons, or ampersands,
931 and optionally terminated by one of these three characters.
933 list are executed in the order they are written.
934 If command is followed by an ampersand, the shell starts the
935 command and immediately proceeds onto the next command;
936 otherwise it waits for the command to terminate before
937 proceeding to the next one.
938 .Ss Short-Circuit List Operators
942 are AND-OR list operators.
944 executes the first command, and then executes the second command
945 if the exit status of the first command is zero.
947 is similar, but executes the second command if the exit
948 status of the first command is nonzero.
952 both have the same priority.
953 .Ss Flow-Control Constructs (if, while, for, case)
957 .Bd -unfilled -offset indent -compact
961 .Ic then Ar list Oc Ar ...
966 The exit status is that of selected
971 or zero if no list was selected.
976 .Bd -unfilled -offset indent -compact
982 The two lists are executed repeatedly while the exit status of the
986 command is similar, but has the word
991 repeat until the exit status of the first list is zero.
993 The exit status is that of the last execution of the second list,
994 or zero if it was never executed.
999 .Bd -unfilled -offset indent -compact
1000 .Ic for Ar variable Op Ic in Ar word ...
1007 and the following words are omitted,
1010 The words are expanded, and then the list is executed
1011 repeatedly with the variable set to each word in turn.
1016 commands may be replaced with
1026 .D1 Ic break Op Ar num
1027 .D1 Ic continue Op Ar num
1031 command terminates the
1040 command continues with the next iteration of the innermost loop.
1041 These are implemented as special built-in commands.
1046 .Bd -unfilled -offset indent -compact
1047 .Ic case Ar word Ic in
1048 .Ar pattern ) Ar list Li ;;
1053 The pattern can actually be one or more patterns
1060 Tilde expansion, parameter expansion, command substitution,
1061 arithmetic expansion and quote removal are applied to the word.
1062 Then, each pattern is expanded in turn using tilde expansion,
1063 parameter expansion, command substitution and arithmetic expansion and
1064 the expanded form of the word is checked against it.
1065 If a match is found, the corresponding list is executed.
1066 If the selected list is terminated by the control operator
1070 execution continues with the next list,
1071 continuing until a list terminated with
1076 .Ss Grouping Commands Together
1077 Commands may be grouped by writing either
1080 .Bd -literal -offset -ident
1086 .Bd -literal -offset -ident
1090 The first form executes the commands in a subshell environment.
1091 A subshell environment has its own copy of:
1094 The current working directory as set by
1097 The file creation mask as set by
1100 Resource limits as set by
1103 References to open files.
1110 Positional parameters and variables.
1119 These are copied from the parent shell environment,
1120 except that trapped (but not ignored) signals are reset to the default action
1121 and known jobs are cleared.
1122 Any changes do not affect the parent shell environment.
1124 A subshell environment may be implemented as a child process or differently.
1125 If job control is enabled in an interactive shell,
1126 commands grouped in parentheses can be suspended and continued as a unit.
1128 For compatibility with other shells,
1129 two open parentheses in sequence should be separated by whitespace.
1131 The second form never forks another shell,
1132 so it is slightly more efficient.
1133 Grouping commands together this way allows the user to
1134 redirect their output as though they were one program:
1135 .Bd -literal -offset indent
1136 { echo -n "hello"; echo " world"; } > greeting
1139 The syntax of a function definition is
1141 .D1 Ar name Li \&( \&) Ar command
1143 A function definition is an executable statement; when
1144 executed it installs a function named
1147 exit status of zero.
1156 Variables may be declared to be local to a function by
1160 This should appear as the first statement of a function,
1163 .D1 Ic local Oo Ar variable ... Oc Op Fl
1167 command is implemented as a built-in command.
1168 The exit status is zero
1169 unless the command is not in a function or a variable name is invalid.
1171 When a variable is made local, it inherits the initial
1172 value and exported and readonly flags from the variable
1173 with the same name in the surrounding scope, if there is
1175 Otherwise, the variable is initially unset.
1177 uses dynamic scoping, so that if the variable
1179 is made local to function
1181 which then calls function
1183 references to the variable
1187 will refer to the variable
1191 not to the global variable named
1194 The only special parameter that can be made local is
1198 local causes any shell options
1199 (including those that only have long names)
1203 command inside the function to be
1204 restored to their original values when the function
1211 .D1 Ic return Op Ar exitstatus
1213 It terminates the current executional scope, returning from the closest
1214 nested function or sourced script;
1215 if no function or sourced script is being executed,
1216 it exits the shell instance.
1219 command is implemented as a special built-in command.
1220 .Ss Variables and Parameters
1221 The shell maintains a set of parameters.
1225 of alphabetics, numerics, and underscores,
1226 and starting with an alphabetic or an underscore)
1227 is called a variable.
1229 the shell turns all environment variables with valid names into shell
1231 New variables can be set using the form
1233 .D1 Ar name Ns = Ns Ar value
1235 A parameter can also be denoted by a number
1236 or a special character as explained below.
1238 Assignments are expanded differently from other words:
1239 tilde expansion is also performed after the equals sign and after any colon
1240 and usernames are also terminated by colons,
1241 and field splitting and pathname expansion are not performed.
1243 This special expansion applies not only to assignments that form a simple
1244 command by themselves or precede a command word,
1245 but also to words passed to the
1250 built-in commands that have this form.
1251 For this, the builtin's name must be literal
1252 (not the result of an expansion)
1253 and may optionally be preceded by one or more literal instances of
1256 .Ss Positional Parameters
1257 A positional parameter is a parameter denoted by a number greater than zero.
1258 The shell sets these initially to the values of its command line
1259 arguments that follow the name of the shell script.
1262 built-in command can also be used to set or reset them.
1263 .Ss Special Parameters
1264 Special parameters are parameters denoted by a single special character
1266 They are shown in the following list, exactly as they would appear in input
1267 typed by the user or in the source of a shell script.
1270 Expands to the positional parameters, starting from one.
1272 the expansion occurs within a double-quoted string
1273 it expands to a single field with the value of each parameter
1274 separated by the first character of the
1281 Expands to the positional parameters, starting from one.
1283 the expansion occurs within double-quotes, each positional
1284 parameter expands as a separate argument.
1285 If there are no positional parameters, the
1288 generates zero arguments, even when
1291 What this basically means, for example, is
1304 .Bd -literal -offset indent
1308 Expands to the number of positional parameters.
1310 Expands to the exit status of the most recent pipeline.
1312 (hyphen) Expands to the current option flags (the single-letter
1313 option names concatenated into a string) as specified on
1316 built-in command, or implicitly
1319 Expands to the process ID of the invoked shell.
1321 retains the same value of
1325 Expands to the process ID of the most recent background
1326 command executed from the current shell.
1328 pipeline, the process ID is that of the last command in the
1330 If this parameter is referenced, the shell will remember
1331 the process ID and its exit status until the
1333 built-in command reports completion of the process.
1335 (zero) Expands to the name of the shell script if passed on the command line,
1338 operand if given (with
1340 or otherwise argument 0 passed to the shell.
1342 .Ss Special Variables
1343 The following variables are set by the shell or
1344 have special meaning to it:
1345 .Bl -tag -width ".Va HISTSIZE"
1347 The search path used with the
1351 The fallback editor used with the
1354 If not set, the default editor is
1357 The default editor used with the
1361 File used for persistent history storage.
1368 the shell will not load and save the history.
1370 The number of previous commands that are accessible.
1372 The user's home directory,
1373 used in tilde expansion and as a default directory for the
1377 Input Field Separators.
1378 This is initialized at startup to
1384 This value also applies if
1386 is unset, but not if it is set to the empty string.
1388 .Sx White Space Splitting
1389 section for more details.
1391 The current line number in the script or function.
1393 The name of a mail file, that will be checked for the arrival of new
1400 separated list of file names, for the shell to check for incoming
1402 This variable overrides the
1405 There is a maximum of 10 mailboxes that can be monitored at once.
1407 The index of the next argument to be processed by
1409 This is initialized to 1 at startup.
1411 The default search path for executables.
1414 section for details.
1416 The parent process ID of the invoked shell.
1417 This is set at startup
1418 unless this variable is in the environment.
1419 A later change of parent process ID is not reflected.
1420 A subshell retains the same value of
1423 The primary prompt string, which defaults to
1425 unless you are the superuser, in which case it defaults to
1428 may include any of the following formatting sequences,
1429 which are replaced by the given information:
1430 .Bl -tag -width indent
1432 This system's fully-qualified hostname (FQDN).
1434 This system's hostname.
1438 The final component of the current working directory.
1440 The entire path of the current working directory.
1444 for normal users and
1448 A literal backslash.
1451 The secondary prompt string, which defaults to
1454 may include any of the formatting sequences from
1457 The prefix for the trace output (if
1464 This clause describes the various expansions that are
1466 Not all expansions are performed on
1467 every word, as explained later.
1469 Tilde expansions, parameter expansions, command substitutions,
1470 arithmetic expansions, and quote removals that occur within
1471 a single word expand to a single field.
1473 splitting or pathname expansion that can create multiple
1474 fields from a single word.
1475 The single exception to this rule is
1476 the expansion of the special parameter
1478 within double-quotes,
1479 as was described above.
1481 The order of word expansion is:
1484 Tilde Expansion, Parameter Expansion, Command Substitution,
1485 Arithmetic Expansion (these all occur at the same time).
1487 Field Splitting is performed on fields generated by step (1)
1492 Pathname Expansion (unless the
1494 option is in effect).
1501 character is used to introduce parameter expansion, command
1502 substitution, or arithmetic expansion.
1503 .Ss Tilde Expansion (substituting a user's home directory)
1504 A word beginning with an unquoted tilde character
1507 subjected to tilde expansion.
1508 All the characters up to a slash
1510 or the end of the word are treated as a username
1511 and are replaced with the user's home directory.
1513 username is missing (as in
1515 the tilde is replaced with the value of the
1517 variable (the current user's home directory).
1518 .Ss Parameter Expansion
1519 The format for parameter expansion is as follows:
1521 .D1 Li ${ Ns Ar expression Ns Li }
1525 consists of all characters until the matching
1529 escaped by a backslash or within a single-quoted or double-quoted
1530 string, and characters in
1531 embedded arithmetic expansions, command substitutions, and variable
1532 expansions, are not examined in determining the matching
1534 If the variants with
1540 occur within a double-quoted string,
1541 as an extension there may be unquoted parts
1542 (via double-quotes inside the expansion);
1544 within such parts are also not examined in determining the matching
1547 The simplest form for parameter expansion is:
1549 .D1 Li ${ Ns Ar parameter Ns Li }
1551 The value, if any, of
1555 The parameter name or symbol can be enclosed in braces, which are
1556 optional except for positional parameters with more than one digit or
1557 when parameter is followed by a character that could be interpreted as
1559 If a parameter expansion occurs inside double-quotes:
1562 Field splitting is not performed on the results of the
1563 expansion, with the exception of the special parameter
1566 Pathname expansion is not performed on the results of the
1570 In addition, a parameter expansion can be modified by using one of the
1572 .Bl -tag -width indent
1573 .It Li ${ Ns Ar parameter Ns Li :- Ns Ar word Ns Li }
1577 is unset or null, the expansion of
1579 is substituted; otherwise, the value of
1582 .It Li ${ Ns Ar parameter Ns Li := Ns Ar word Ns Li }
1583 Assign Default Values.
1586 is unset or null, the expansion of
1596 does not prevent field splitting or pathname expansion.
1597 Only variables, not positional
1598 parameters or special parameters, can be
1599 assigned in this way.
1600 .It Li ${ Ns Ar parameter Ns Li :? Ns Oo Ar word Oc Ns Li }
1601 Indicate Error if Null or Unset.
1604 is unset or null, the expansion of
1606 (or a message indicating it is unset if
1608 is omitted) is written to standard
1609 error and the shell exits with a nonzero
1611 Otherwise, the value of
1615 interactive shell need not exit.
1616 .It Li ${ Ns Ar parameter Ns Li :+ Ns Ar word Ns Li }
1617 Use Alternate Value.
1620 is unset or null, null is substituted;
1621 otherwise, the expansion of
1626 In the parameter expansions shown previously, use of the colon in the
1627 format results in a test for a parameter that is unset or null; omission
1628 of the colon results in a test for a parameter that is only unset.
1632 inherits the type of quoting
1633 (unquoted, double-quoted or here-document)
1634 from the surroundings,
1635 with the exception that a backslash that quotes a closing brace is removed
1636 during quote removal.
1637 .Bl -tag -width indent
1638 .It Li ${# Ns Ar parameter Ns Li }
1640 The length in characters of
1645 The following four varieties of parameter expansion provide for substring
1647 In each case, pattern matching notation
1649 .Sx Shell Patterns ) ,
1650 rather than regular expression notation,
1651 is used to evaluate the patterns.
1652 If parameter is one of the special parameters
1656 the result of the expansion is unspecified.
1657 Enclosing the full parameter expansion string in double-quotes does not
1658 cause the following four varieties of pattern characters to be quoted,
1659 whereas quoting characters within the braces has this effect.
1660 .Bl -tag -width indent
1661 .It Li ${ Ns Ar parameter Ns Li % Ns Ar word Ns Li }
1662 Remove Smallest Suffix Pattern.
1665 is expanded to produce a pattern.
1667 parameter expansion then results in
1669 with the smallest portion of the
1670 suffix matched by the pattern deleted.
1671 .It Li ${ Ns Ar parameter Ns Li %% Ns Ar word Ns Li }
1672 Remove Largest Suffix Pattern.
1675 is expanded to produce a pattern.
1677 parameter expansion then results in
1679 with the largest portion of the
1680 suffix matched by the pattern deleted.
1681 .It Li ${ Ns Ar parameter Ns Li # Ns Ar word Ns Li }
1682 Remove Smallest Prefix Pattern.
1685 is expanded to produce a pattern.
1687 parameter expansion then results in
1689 with the smallest portion of the
1690 prefix matched by the pattern deleted.
1691 .It Li ${ Ns Ar parameter Ns Li ## Ns Ar word Ns Li }
1692 Remove Largest Prefix Pattern.
1695 is expanded to produce a pattern.
1697 parameter expansion then results in
1699 with the largest portion of the
1700 prefix matched by the pattern deleted.
1702 .Ss Command Substitution
1703 Command substitution allows the output of a command to be substituted in
1704 place of the command name itself.
1705 Command substitution occurs when
1706 the command is enclosed as follows:
1708 .D1 Li $( Ns Ar command Ns Li )\&
1710 or the backquoted version:
1712 .D1 Li ` Ns Ar command Ns Li `
1714 The shell expands the command substitution by executing command
1715 and replacing the command substitution
1716 with the standard output of the command,
1717 removing sequences of one or more newlines at the end of the substitution.
1718 Embedded newlines before the end of the output are not removed;
1719 however, during field splitting, they may be translated into spaces
1720 depending on the value of
1722 and the quoting that is in effect.
1723 The command is executed in a subshell environment,
1724 except that the built-in commands
1729 return information about the parent shell environment
1732 returns information about the same process
1733 if they are the only command in a command substitution.
1735 If a command substitution of the
1737 form begins with a subshell,
1742 must be separated by whitespace
1743 to avoid ambiguity with arithmetic expansion.
1744 .Ss Arithmetic Expansion
1745 Arithmetic expansion provides a mechanism for evaluating an arithmetic
1746 expression and substituting its value.
1747 The format for arithmetic expansion is as follows:
1749 .D1 Li $(( Ns Ar expression Ns Li ))
1753 is treated as if it were in double-quotes, except
1754 that a double-quote inside the expression is not treated specially.
1756 shell expands all tokens in the
1758 for parameter expansion,
1759 command substitution,
1760 arithmetic expansion
1763 The allowed expressions are a subset of C expressions,
1765 .Bl -tag -width "Variables" -offset indent
1767 All values are of type
1770 Decimal, octal (starting with
1772 and hexadecimal (starting with
1776 Shell variables can be read and written
1777 and contain integer constants.
1780 .It Binary operators
1781 .Li "* / % + - << >> < <= > >= == != & ^ | && ||"\&
1782 .It Assignment operators
1783 .Li "= += -= *= /= %= <<= >>= &= ^= |="
1784 .It Conditional operator
1788 The result of the expression is substituted in decimal.
1789 .Ss White Space Splitting (Field Splitting)
1790 In certain contexts,
1791 after parameter expansion, command substitution, and
1792 arithmetic expansion the shell scans the results of
1793 expansions and substitutions that did not occur in double-quotes for
1794 field splitting and multiple fields can result.
1805 are treated differently from other characters in
1810 at the beginning or end of a word is discarded.
1812 Subsequently, a field is delimited by either
1815 a non-whitespace character in
1817 with any whitespace in
1821 one or more whitespace characters in
1825 If a word ends with a non-whitespace character in
1827 there is no empty field after this character.
1829 If no field is delimited, the word is discarded.
1830 In particular, if a word consists solely of an unquoted substitution
1831 and the result of the substitution is null,
1832 it is removed by field splitting even if
1835 .Ss Pathname Expansion (File Name Generation)
1839 file name generation is performed
1840 after word splitting is complete.
1842 viewed as a series of patterns, separated by slashes.
1844 process of expansion replaces the word with the names of
1845 all existing files whose names can be formed by replacing
1846 each pattern with a string that matches the specified pattern.
1847 There are two restrictions on this: first, a pattern cannot match
1848 a string containing a slash, and second,
1849 a pattern cannot match a string starting with a period
1850 unless the first character of the pattern is a period.
1851 The next section describes the patterns used for
1853 the four varieties of parameter expansion for substring processing and the
1857 A pattern consists of normal characters, which match themselves,
1858 and meta-characters.
1859 The meta-characters are
1864 These characters lose their special meanings if they are quoted.
1865 When command or variable substitution is performed and the dollar sign
1866 or back quotes are not double-quoted, the value of the
1867 variable or the output of the command is scanned for these
1868 characters and they are turned into meta-characters.
1872 matches any string of characters.
1875 matches any single character.
1878 introduces a character class.
1879 The end of the character class is indicated by a
1887 rather than introducing a character class.
1888 A character class matches any of the characters between the square brackets.
1889 A locale-dependent range of characters may be specified using a minus sign.
1890 A named class of characters (see
1892 may be specified by surrounding the name with
1897 .Ql \&[\&[:alpha:\&]\&]
1898 is a shell pattern that matches a single letter.
1899 The character class may be complemented by making an exclamation point
1901 the first character of the character class.
1904 has the same effect but is non-standard.
1908 in a character class, make it the first character listed
1916 make it the first or last character listed.
1917 .Ss Built-in Commands
1918 This section lists the built-in commands.
1919 .Bl -tag -width indent
1921 A null command that returns a 0 (true) exit value.
1923 The commands in the specified file are read and executed by the shell.
1926 command may be used to return to the
1933 characters, it is used as is.
1934 Otherwise, the shell searches the
1937 If it is not found in the
1939 it is sought in the current working directory.
1941 A built-in equivalent of
1943 .It Ic alias Oo Ar name Ns Oo = Ns Ar string Oc ... Oc
1945 .Ar name Ns = Ns Ar string
1946 is specified, the shell defines the alias
1952 is specified, the value of the alias
1955 With no arguments, the
1957 built-in command prints the names and values of all defined aliases
1960 Alias values are written with appropriate quoting so that they are
1961 suitable for re-input to the shell.
1965 .It Ic bg Op Ar job ...
1966 Continue the specified jobs
1967 (or the current job if no jobs are given)
1969 .It Ic bind Oo Fl aeklrsv Oc Oo Ar key Oo Ar command Oc Oc
1970 List or alter key bindings for the line editor.
1971 This command is documented in
1973 .It Ic break Op Ar num
1975 .Sx Flow-Control Constructs
1977 .It Ic builtin Ar cmd Op Ar arg ...
1978 Execute the specified built-in command,
1980 This is useful when the user wishes to override a shell function
1981 with the same name as a built-in command.
1982 .It Ic cd Oo Fl L | P Oc Oo Fl e Oc Op Ar directory
1984 Switch to the specified
1986 to the directory specified in the
1988 environment variable if no
1991 to the directory specified in the
1993 environment variable if
2003 then the directories listed in the
2006 searched for the specified
2010 is unset, the current directory is searched.
2013 is the same as that of
2015 In an interactive shell,
2018 command will print out the name of the directory
2019 that it actually switched to
2022 mechanism was used or if
2029 option is specified,
2031 is handled physically and symbolic links are resolved before
2033 components are processed.
2036 option is specified,
2038 is handled logically.
2039 This is the default.
2045 to return exit status 1 if the full pathname of the new directory
2046 cannot be determined reliably or at all.
2047 Normally this is not considered an error,
2048 although a warning is printed.
2050 If changing the directory fails, the exit status is greater than 1.
2051 If the directory is changed, the exit status is 0, or also 1 if
2058 .It Ic command Oo Fl p Oc Op Ar utility Op Ar argument ...
2059 .It Ic command Oo Fl p Oc Fl v Ar utility
2060 .It Ic command Oo Fl p Oc Fl V Ar utility
2061 The first form of invocation executes the specified
2063 ignoring shell functions in the search.
2066 is a special builtin,
2067 it is executed as if it were a regular builtin.
2071 option is specified, the command search is performed using a
2074 that is guaranteed to find all of the standard utilities.
2078 option is specified,
2080 is not executed but a description of its interpretation by the shell is
2082 For ordinary commands the output is the path name; for shell built-in
2083 commands, shell functions and keywords only the name is written.
2084 Aliases are printed as
2085 .Dq Ic alias Ar name Ns = Ns Ar value .
2089 option is identical to
2091 except for the output.
2093 .Dq Ar utility Ic is Ar description
2099 a special shell builtin,
2106 .It Ic continue Op Ar num
2108 .Sx Flow-Control Constructs
2110 .It Ic echo Oo Fl e | n Oc Op Ar string ...
2111 Print a space-separated list of the arguments to the standard output
2112 and append a newline character.
2113 .Bl -tag -width indent
2115 Suppress the output of the trailing newline.
2117 Process C-style backslash escape sequences.
2120 command understands the following character escapes:
2121 .Bl -tag -width indent
2123 Alert (ring the terminal bell)
2127 Suppress the trailing newline (this has the side-effect of truncating the
2128 line if it is not the last character)
2130 The ESC character (ASCII 0x1b)
2144 (Zero) The character whose octal value is
2150 is not enclosed in quotes then the backslash itself must be escaped
2151 with a backslash to protect it from the shell.
2153 .Bd -literal -offset indent
2162 $ echo -e a\e\e\e\eb
2171 options may be specified.
2172 .It Ic eval Ar string ...
2173 Concatenate all the arguments with spaces.
2174 Then re-parse and execute the command.
2175 .It Ic exec Op Ar command Op arg ...
2179 the shell process is replaced with the specified program
2180 (which must be a real program, not a shell built-in command or function).
2181 Any redirections on the
2183 command are marked as permanent,
2184 so that they are not undone when the
2187 .It Ic exit Op Ar exitstatus
2188 Terminate the shell process.
2192 it is used as the exit status of the shell.
2193 Otherwise, if the shell is executing an
2195 trap, the exit status of the last command before the trap is used;
2196 if the shell is executing a trap for a signal,
2197 the shell exits by resending the signal to itself.
2198 Otherwise, the exit status of the preceding command is used.
2199 The exit status should be an integer between 0 and 255.
2200 .It Ic export Ar name ...
2201 .It Ic export Op Fl p
2202 The specified names are exported so that they will
2203 appear in the environment of subsequent commands.
2204 The only way to un-export a variable is to
2207 The shell allows the value of a variable to be set
2208 at the same time as it is exported by writing
2210 .D1 Ic export Ar name Ns = Ns Ar value
2212 With no arguments the
2214 command lists the names
2215 of all exported variables.
2218 option is specified, the exported variables are printed as
2219 .Dq Ic export Ar name Ns = Ns Ar value
2220 lines, suitable for re-input to the shell.
2222 A null command that returns a non-zero (false) exit value.
2223 .It Ic fc Oo Fl e Ar editor Oc Op Ar first Op Ar last
2224 .It Ic fc Fl l Oo Fl nr Oc Op Ar first Op Ar last
2225 .It Ic fc Fl s Oo Ar old Ns = Ns Ar new Oc Op Ar first
2228 built-in command lists, or edits and re-executes,
2229 commands previously entered to an interactive shell.
2230 .Bl -tag -width indent
2232 Use the editor named by
2234 to edit the commands.
2237 string is a command name,
2238 subject to search via the
2243 variable is used as a default when
2248 is null or unset, the value of the
2255 is used as the editor.
2257 List the commands rather than invoking
2259 The commands are written in the
2260 sequence indicated by the
2264 operands, as affected by
2266 with each command preceded by the command number.
2268 Suppress command numbers when listing with
2271 Reverse the order of the commands listed
2280 Re-execute the command without invoking an editor.
2283 Select the commands to list or edit.
2284 The number of previous commands that can be accessed
2285 are determined by the value of the
2292 or both are one of the following:
2293 .Bl -tag -width indent
2294 .It Oo Cm + Oc Ns Ar num
2295 A positive number representing a command number;
2296 command numbers can be displayed with the
2300 A negative decimal number representing the
2301 command that was executed
2304 commands previously.
2305 For example, \-1 is the immediately previous command.
2307 A string indicating the most recently entered command
2308 that begins with that string.
2310 .Ar old Ns = Ns Ar new
2311 operand is not also specified with
2313 the string form of the first operand cannot contain an embedded equal sign.
2317 The following variables affect the execution of
2319 .Bl -tag -width ".Va HISTSIZE"
2321 Name of the editor to use for history editing.
2323 The number of previous commands that are accessible.
2328 or the current job to the foreground.
2329 .It Ic getopts Ar optstring var
2335 command deprecates the older
2338 The first argument should be a series of letters, each possibly
2339 followed by a colon which indicates that the option takes an argument.
2340 The specified variable is set to the parsed option.
2342 the next argument is placed into the shell variable
2344 If an option takes an argument, it is placed into the shell variable
2346 If an invalid option is encountered,
2350 It returns a false value (1) when it encounters the end of the options.
2351 A new set of arguments may be parsed by assigning
2353 .It Ic hash Oo Fl rv Oc Op Ar command ...
2354 The shell maintains a hash table which remembers the locations of commands.
2355 With no arguments whatsoever, the
2357 command prints out the contents of this table.
2361 command removes each specified
2363 from the hash table (unless they are functions) and then locates it.
2368 prints the locations of the commands as it finds them.
2373 command to delete all the entries in the hash table except for functions.
2374 .It Ic jobid Op Ar job
2375 Print the process IDs of the processes in the specified
2379 argument is omitted, use the current job.
2380 .It Ic jobs Oo Fl lps Oc Op Ar job ...
2381 Print information about the specified jobs, or all jobs if no
2384 The information printed includes job ID, status and command name.
2388 option is specified, the PID of each job is also printed.
2391 option is specified, only the process IDs for the process group leaders
2392 are printed, one per line.
2395 option is specified, only the PIDs of the job commands are printed, one per
2398 A built-in equivalent of
2400 that additionally supports sending signals to jobs.
2401 .It Ic local Oo Ar variable ... Oc Op Fl
2406 A built-in equivalent of
2408 .It Ic pwd Op Fl L | P
2409 Print the path of the current directory.
2410 The built-in command may
2411 differ from the program of the same name because the
2412 built-in command remembers what the current directory
2413 is rather than recomputing it each time.
2416 However, if the current directory is
2418 the built-in version of
2420 will continue to print the old name for the directory.
2424 option is specified, symbolic links are resolved.
2427 option is specified, the shell's notion of the current directory
2428 is printed (symbolic links are not resolved).
2429 This is the default.
2430 .It Ic read Oo Fl p Ar prompt Oc Oo
2431 .Fl t Ar timeout Oc Oo Fl er Oc Ar variable ...
2437 and the standard input is a terminal.
2439 read from the standard input.
2440 The trailing newline
2441 is deleted from the line and the line is split as
2442 described in the section on
2443 .Sx White Space Splitting (Field Splitting)\&
2445 the pieces are assigned to the variables in order.
2446 If there are more pieces than variables, the remaining
2447 pieces (along with the characters in
2449 that separated them)
2450 are assigned to the last variable.
2451 If there are more variables than pieces, the remaining
2452 variables are assigned the null string.
2454 Backslashes are treated specially, unless the
2458 If a backslash is followed by
2459 a newline, the backslash and the newline will be
2461 If a backslash is followed by any other
2462 character, the backslash will be deleted and the following
2463 character will be treated as though it were not in
2469 option is specified and the
2471 elapses before a complete line of input is supplied,
2474 command will return an exit status as if terminated by
2476 without assigning any values.
2479 value may optionally be followed by one of
2484 to explicitly specify seconds, minutes or hours.
2485 If none is supplied,
2491 option exists only for backward compatibility with older scripts.
2493 The exit status is 0 on success, 1 on end of file,
2494 between 2 and 128 if an error occurs
2495 and greater than 128 if a trapped signal interrupts
2497 .It Ic readonly Oo Fl p Oc Op Ar name ...
2500 is marked as read only,
2501 so that it cannot be subsequently modified or unset.
2502 The shell allows the value of a variable to be set
2503 at the same time as it is marked read only
2504 by using the following form:
2506 .D1 Ic readonly Ar name Ns = Ns Ar value
2508 With no arguments the
2510 command lists the names of all read only variables.
2513 option is specified, the read-only variables are printed as
2514 .Dq Ic readonly Ar name Ns = Ns Ar value
2515 lines, suitable for re-input to the shell.
2516 .It Ic return Op Ar exitstatus
2520 .It Ic set Oo Fl /+abCEefIimnpTuVvx Oc Oo Fl /+o Ar longname
2521 .Oc Op Fl - Ar arg ...
2524 command performs three different functions:
2527 With no arguments, it lists the values of all shell variables.
2529 If options are given,
2530 either in short form or using the long
2531 .Dq Fl /+o Ar longname
2533 it sets or clears the specified options as described in the section called
2534 .Sx Argument List Processing .
2538 option is specified,
2540 will replace the shell's positional parameters with the subsequent
2542 If no arguments follow the
2545 all the positional parameters will be cleared,
2546 which is equivalent to executing the command
2550 flag may be omitted when specifying arguments to be used
2551 as positional replacement parameters.
2552 This is not recommended,
2553 because the first argument may begin with a dash
2559 command will interpret as a request to enable or disable options.
2561 .It Ic setvar Ar variable value
2562 Assigns the specified
2568 command is intended to be used in functions that
2569 assign values to variables whose names are passed as parameters.
2570 In general it is better to write
2571 .Dq Ar variable Ns = Ns Ar value
2574 .It Ic shift Op Ar n
2575 Shift the positional parameters
2580 A shift sets the value of
2589 decreasing the value of
2592 For portability, shifting if there are zero positional parameters
2593 should be avoided, since the shell may abort.
2595 A built-in equivalent of
2598 Print the amount of time spent executing the shell process and its children.
2599 The first output line shows the user and system times for the shell process
2600 itself, the second one contains the user and system times for the
2602 .It Ic trap Oo Ar action Oc Ar signal ...
2604 Cause the shell to parse and execute
2609 The signals are specified by name or number.
2610 In addition, the pseudo-signal
2612 may be used to specify an
2614 that is performed when the shell terminates.
2617 may be an empty string or a dash
2619 the former causes the specified signal to be ignored
2620 and the latter causes the default action to be taken.
2623 and using only signal numbers is another way to request the default action.
2624 In a subshell or utility environment,
2625 the shell resets trapped (but not ignored) signals to the default action.
2628 command has no effect on signals that were ignored on entry to the shell.
2634 command to display a list of valid signal names.
2636 A null command that returns a 0 (true) exit value.
2637 .It Ic type Op Ar name ...
2640 as a command and print the resolution of the command search.
2641 Possible resolutions are:
2642 shell keyword, alias, special shell builtin, shell builtin, command,
2645 For aliases the alias expansion is printed;
2646 for commands and tracked aliases
2647 the complete pathname of the command is printed.
2648 .It Ic ulimit Oo Fl HSabcdfklmnopstuvw Oc Op Ar limit
2649 Set or display resource limits (see
2653 is specified, the named resource will be set;
2654 otherwise the current resource value will be displayed.
2658 is specified, the hard limits will be set or displayed.
2659 While everybody is allowed to reduce a hard limit,
2660 only the superuser can increase it.
2664 specifies the soft limits instead.
2665 When displaying limits,
2671 The default is to display the soft limits,
2672 and to set both the hard and the soft limits.
2678 command to display all resources.
2681 is not acceptable in this mode.
2683 The remaining options specify which resource value is to be
2684 displayed or modified.
2685 They are mutually exclusive.
2686 .Bl -tag -width indent
2688 The maximum size of socket buffer usage, in bytes.
2689 .It Fl c Ar coredumpsize
2690 The maximal size of core dump files, in 512-byte blocks.
2693 to 0 prevents core dump files from being created.
2694 .It Fl d Ar datasize
2695 The maximal size of the data segment of a process, in kilobytes.
2696 .It Fl f Ar filesize
2697 The maximal size of a file, in 512-byte blocks.
2699 The maximal number of kqueues
2703 .It Fl l Ar lockedmem
2704 The maximal size of memory that can be locked by a process, in
2706 .It Fl m Ar memoryuse
2707 The maximal resident set size of a process, in kilobytes.
2709 The maximal number of descriptors that could be opened by a process.
2711 The maximal number of process-shared locks
2715 .It Fl p Ar pseudoterminals
2716 The maximal number of pseudo-terminals for this user ID.
2717 .It Fl s Ar stacksize
2718 The maximal size of the stack segment, in kilobytes.
2720 The maximal amount of CPU time to be used by each process, in seconds.
2721 .It Fl u Ar userproc
2722 The maximal number of simultaneous processes for this user ID.
2723 .It Fl v Ar virtualmem
2724 The maximal virtual size of a process, in kilobytes.
2726 The maximum amount of swap space reserved or used for this user ID,
2729 .It Ic umask Oo Fl S Oc Op Ar mask
2730 Set the file creation mask (see
2732 to the octal or symbolic (see
2736 If the argument is omitted, the current mask value is printed.
2739 option is specified, the output is symbolic, otherwise the output is octal.
2740 .It Ic unalias Oo Fl a Oc Op Ar name ...
2741 The specified alias names are removed.
2744 is specified, all aliases are removed.
2745 .It Ic unset Oo Fl fv Oc Ar name ...
2746 The specified variables or functions are unset and unexported.
2749 option is specified or no options are given, the
2751 arguments are treated as variable names.
2754 option is specified, the
2756 arguments are treated as function names.
2757 .It Ic wait Op Ar job ...
2758 Wait for each specified
2760 to complete and return the exit status of the last process in the
2765 specified is unknown to the shell, it is treated as if it
2766 were a known job that exited with exit status 127.
2767 If no operands are given, wait for all jobs to complete
2768 and return an exit status of zero.
2770 .Ss Command Line Editing
2773 is being used interactively from a terminal, the current command
2774 and the command history
2778 .Sx Built-in Commands )
2781 command line editing.
2782 This mode uses commands similar
2783 to a subset of those described in the
2801 can be switched between insert mode and command mode by typing
2805 while in command mode will pass the line to the shell.
2808 .Dq Li "set -o emacs"
2811 command can be used to enable a subset of
2813 command line editing features.
2815 The following environment variables affect the execution of
2817 .Bl -tag -width ".Ev LANGXXXXXX"
2819 Initialization file for interactive shells.
2820 .It Ev LANG , Ev LC_*
2822 These are inherited by children of the shell,
2823 and is used in a limited manner by the shell itself.
2825 The previous current directory.
2826 This is used and updated by
2829 An absolute pathname for the current directory,
2830 possibly containing symbolic links.
2831 This is used and updated by the shell.
2833 The default terminal setting for the shell.
2834 This is inherited by children of the shell, and is used in the history
2838 Additionally, environment variables are turned into shell variables
2840 which may affect the shell as described under
2841 .Sx Special Variables .
2843 .Bl -tag -width "/etc/suid_profileXX" -compact
2845 User's login profile.
2847 System login profile.
2850 .It Pa /etc/suid_profile
2851 Privileged shell profile.
2856 cannot be found, the exit status will be 127;
2857 if it cannot be opened for another reason, the exit status will be 126.
2858 Other errors that are detected by the shell, such as a syntax error, will
2859 cause the shell to exit with a non-zero exit status.
2860 If the shell is not an interactive shell, the execution of the shell
2861 file will be aborted.
2862 Otherwise the shell will return the exit status of the last command
2865 builtin is used with a numeric argument, it
2866 will return the argument.
2872 .Xr emacs 1 Pq Pa ports/editors/emacs ,
2887 command, the Thompson shell, appeared in
2889 It was superseded in
2891 by the Bourne shell, which inherited the name
2896 was rewritten in 1989 under the
2898 license after the Bourne shell from
2903 was originally written by
2904 .An Kenneth Almquist .
2908 utility does not recognize multibyte characters other than UTF-8.
2911 does not recognize multibyte characters.