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44 .Nd command interpreter (shell)
47 .Op Fl /+abCEefIimnPpTuVvx
48 .Op Fl /+o Ar longname
54 .Op Fl /+abCEefIimnPpTuVvx
55 .Op Fl /+o Ar longname
62 .Op Fl /+abCEefIimnPpTuVvx
63 .Op Fl /+o Ar longname
69 utility is the standard command interpreter for the system.
70 The current version of
74 specification for the shell.
75 It only supports features
78 plus a few Berkeley extensions.
79 This man page is not intended to be a tutorial nor a complete
80 specification of the shell.
82 The shell is a command that reads lines from
83 either a file or the terminal, interprets them, and
84 generally executes other commands.
85 It is the program that is started when a user logs into the system,
86 although a user can select a different shell with the
90 implements a language that has flow control constructs,
91 a macro facility that provides a variety of features in
92 addition to data storage, along with built-in history and line
94 It incorporates many features to
95 aid interactive use and has the advantage that the interpretative
96 language is common to both interactive and non-interactive
98 That is, commands can be typed directly
99 to the running shell or can be put into a file,
100 which can be executed directly by the shell.
103 .\" XXX This next sentence is incredibly confusing.
105 If no arguments are present and if the standard input of the shell
106 is connected to a terminal
110 the shell is considered an interactive shell.
112 generally prompts before each command and handles programming
113 and command errors differently (as described below).
114 When first starting, the shell inspects argument 0, and
115 if it begins with a dash
117 the shell is also considered a login shell.
118 This is normally done automatically by the system
119 when the user first logs in.
120 A login shell first reads commands
125 in a user's home directory,
127 If the environment variable
129 is set on entry to a shell, or is set in the
131 of a login shell, the shell then subjects its value to parameter expansion
132 and arithmetic expansion and reads commands from the named file.
133 Therefore, a user should place commands that are to be executed only
136 file, and commands that are executed for every shell inside the
141 variable to some file by placing the following line in the file
143 in the home directory,
146 the filename desired:
148 .Dl "ENV=$HOME/.shinit; export ENV"
150 The first non-option argument specified on the command line
151 will be treated as the
152 name of a file from which to read commands (a shell script), and
153 the remaining arguments are set as the positional parameters
157 Otherwise, the shell reads commands
158 from its standard input.
160 Unlike older versions of
164 script is only sourced on invocation of interactive shells.
166 closes a well-known, and sometimes easily exploitable security
167 hole related to poorly thought out
170 .Ss Argument List Processing
171 All of the single letter options to
173 have a corresponding long name,
174 with the exception of
178 These long names are provided next to the single letter options
179 in the descriptions below.
180 The long name for an option may be specified as an argument to the
184 Once the shell is running,
185 the long name for an option may be specified as an argument to the
190 (described later in the section called
191 .Sx Built-in Commands ) .
192 Introducing an option with a dash
202 will stop option processing and will force the remaining
203 words on the command line to be treated as arguments.
208 options do not have long names.
209 They take arguments and are described after the single letter options.
210 .Bl -tag -width indent
211 .It Fl a Li allexport
212 Flag variables for export when assignments are made to them.
214 Enable asynchronous notification of background job
217 .It Fl C Li noclobber
218 Do not overwrite existing files with
223 command line editor (disables the
225 option if it has been set;
226 set automatically when interactive on terminals).
228 Exit immediately if any untested command fails in non-interactive mode.
229 The exit status of a command is considered to be
230 explicitly tested if the command is part of the list used to control
232 .Ic if , elif , while ,
235 if the command is the left
240 operator; or if the command is a pipeline preceded by the
243 If a shell function is executed and its exit status is explicitly
244 tested, all commands of the function are considered to be tested as
247 Disable pathname expansion.
249 A do-nothing option for
252 .It Fl I Li ignoreeof
255 from input when in interactive mode.
256 .It Fl i Li interactive
257 Force the shell to behave interactively.
259 Turn on job control (set automatically when interactive).
261 If not interactive, read commands but do not
263 This is useful for checking the
264 syntax of shell scripts.
266 Change the default for the
272 (logical directory layout)
275 (physical directory layout).
276 .It Fl p Li privileged
277 Turn on privileged mode.
278 This mode is enabled on startup
279 if either the effective user or group ID is not equal to the
280 real user or group ID.
281 Turning this mode off sets the
282 effective user and group IDs to the real user and group IDs.
283 When this mode is enabled for interactive shells, the file
284 .Pa /etc/suid_profile
285 is sourced instead of
289 is sourced, and the contents of the
291 variable are ignored.
293 Read commands from standard input (set automatically
294 if no file arguments are present).
296 no effect when set after the shell has already started
297 running (i.e., when set with the
300 .It Fl T Li trapsasync
301 When waiting for a child, execute traps immediately.
302 If this option is not set,
303 traps are executed after the child exits,
306 This nonstandard option is useful for putting guarding shells around
307 children that block signals.
308 The surrounding shell may kill the child
309 or it may just return control to the tty and leave the child alone,
311 .Bd -literal -offset indent
312 sh -T -c "trap 'exit 1' 2 ; some-blocking-program"
315 Write a message to standard error when attempting
316 to expand a variable, a positional parameter or
317 the special parameter
319 that is not set, and if the
320 shell is not interactive, exit immediately.
324 command line editor (disables
328 The shell writes its input to standard error
330 Useful for debugging.
333 (preceded by the value of the
335 variable subjected to parameter expansion and arithmetic expansion)
336 to standard error before it is executed.
337 Useful for debugging.
338 .It "\ \ " Em tabcomplete
339 Enables filename completion in the command line editor.
340 Typing a tab character will extend the current input word to match a
342 If more than one filename matches it is only extended to be the common prefix.
343 Typing a second tab character will list all the matching names.
344 Turned on by default in an interactive shell.
349 option causes the commands to be read from the
351 operand instead of from the standard input.
352 Keep in mind that this option only accepts a single string as its
353 argument, hence multi-word strings must be quoted.
357 option takes as its only argument the long name of an option
358 to be enabled or disabled.
359 For example, the following two invocations of
361 both enable the built-in
364 .Bd -literal -offset indent
369 If used without an argument, the
371 option displays the current option settings in a human-readable format.
374 is used without an argument, the current option settings are output
375 in a format suitable for re-input into the shell.
376 .Ss Lexical Structure
377 The shell reads input in terms of lines from a file and breaks
378 it up into words at whitespace (blanks and tabs), and at
382 which are special to the shell.
383 There are two types of operators: control operators and
384 redirection operators (their meaning is discussed later).
385 The following is a list of valid operators:
386 .Bl -tag -width indent
387 .It Control operators:
388 .Bl -column "XXX" "XXX" "XXX" "XXX" "XXX" -offset center -compact
389 .It Li & Ta Li && Ta Li ( Ta Li ) Ta Li \en
390 .It Li ;; Ta Li ;& Ta Li ; Ta Li | Ta Li ||
392 .It Redirection operators:
393 .Bl -column "XXX" "XXX" "XXX" "XXX" "XXX" -offset center -compact
394 .It Li < Ta Li > Ta Li << Ta Li >> Ta Li <>
395 .It Li <& Ta Li >& Ta Li <<- Ta Li >|
401 introduces a comment if used at the beginning of a word.
402 The word starting with
404 and the rest of the line are ignored.
408 characters (character code 0) are not allowed in shell input.
410 Quoting is used to remove the special meaning of certain characters
411 or words to the shell, such as operators, whitespace, keywords,
414 There are four types of quoting: matched single quotes,
415 dollar-single quotes,
416 matched double quotes, and backslash.
417 .Bl -tag -width indent
419 Enclosing characters in single quotes preserves the literal
420 meaning of all the characters (except single quotes, making
421 it impossible to put single-quotes in a single-quoted string).
422 .It Dollar-Single Quotes
423 Enclosing characters between
427 preserves the literal meaning of all characters
428 except backslashes and single quotes.
429 A backslash introduces a C-style escape sequence:
430 .Bl -tag -width xUnnnnnnnn
432 Alert (ring the terminal bell)
436 The control character denoted by
442 is a backslash, it must be doubled.
464 The byte whose octal value is
466 (one to three digits)
468 The byte whose hexadecimal value is
470 (one or more digits only the last two of which are used)
472 The Unicode code point
474 (four hexadecimal digits)
475 .It \eU Ns Ar nnnnnnnn
476 The Unicode code point
478 (eight hexadecimal digits)
481 The sequences for Unicode code points are currently only useful with
483 They reject code point 0 and UTF-16 surrogates.
485 If an escape sequence would produce a byte with value 0,
486 that byte and the rest of the string until the matching single-quote
489 Any other string starting with a backslash is an error.
491 Enclosing characters within double quotes preserves the literal
492 meaning of all characters except dollar sign
498 The backslash inside double quotes is historically weird.
499 It remains literal unless it precedes the following characters,
500 which it serves to quote:
501 .Bl -column "XXX" "XXX" "XXX" "XXX" "XXX" -offset center -compact
502 .It Li $ Ta Li ` Ta Li \&" Ta Li \e\ Ta Li \en
505 A backslash preserves the literal meaning of the following
506 character, with the exception of the newline character
508 A backslash preceding a newline is treated as a line continuation.
511 Keywords or reserved words are words that have special meaning to the
512 shell and are recognized at the beginning of a line and
513 after a control operator.
514 The following are keywords:
515 .Bl -column "doneXX" "elifXX" "elseXX" "untilXX" "whileX" -offset center
516 .It Li \&! Ta { Ta } Ta Ic case Ta Ic do
517 .It Ic done Ta Ic elif Ta Ic else Ta Ic esac Ta Ic fi
518 .It Ic for Ta Ic if Ta Ic then Ta Ic until Ta Ic while
521 An alias is a name and corresponding value set using the
524 Wherever the command word of a simple command may occur,
525 and after checking for keywords if a keyword may occur, the shell
526 checks the word to see if it matches an alias.
527 If it does, it replaces it in the input stream with its value.
528 For example, if there is an alias called
540 Aliases provide a convenient way for naive users to
541 create shorthands for commands without having to learn how
542 to create functions with arguments.
543 Using aliases in scripts is discouraged
544 because the command that defines them must be executed
545 before the code that uses them is parsed.
546 This is fragile and not portable.
548 An alias name may be escaped in a command line, so that it is not
549 replaced by its alias value, by using quoting characters within or
550 adjacent to the alias name.
551 This is most often done by prefixing
552 an alias name with a backslash to execute a function, built-in, or
553 normal program with the same name.
558 The shell interprets the words it reads according to a
559 language, the specification of which is outside the scope
560 of this man page (refer to the BNF in the
563 Essentially though, a line is read and if
564 the first word of the line (or after a control operator)
565 is not a keyword, then the shell has recognized a
567 Otherwise, a complex command or some
568 other special construct may have been recognized.
570 If a simple command has been recognized, the shell performs
571 the following actions:
574 Leading words of the form
576 are stripped off and assigned to the environment of
578 Redirection operators and
579 their arguments (as described below) are stripped
580 off and saved for processing.
582 The remaining words are expanded as described in
584 .Sx Word Expansions ,
585 and the first remaining word is considered the command
586 name and the command is located.
588 words are considered the arguments of the command.
589 If no command name resulted, then the
591 variable assignments recognized in 1) affect the
594 Redirections are performed as described in
598 Redirections are used to change where a command reads its input
600 In general, redirections open, close, or
601 duplicate an existing reference to a file.
603 used for redirection is:
605 .D1 Oo Ar n Oc Ar redir-op file
609 is one of the redirection operators mentioned
611 The following gives some examples of how these
612 operators can be used.
613 Note that stdin and stdout are commonly used abbreviations
614 for standard input and standard output respectively.
615 .Bl -tag -width "1234567890XX" -offset indent
616 .It Oo Ar n Oc Ns Li > Ar file
617 redirect stdout (or file descriptor
621 .It Oo Ar n Oc Ns Li >| Ar file
622 same as above, but override the
625 .It Oo Ar n Oc Ns Li >> Ar file
626 append stdout (or file descriptor
630 .It Oo Ar n Oc Ns Li < Ar file
631 redirect stdin (or file descriptor
635 .It Oo Ar n Oc Ns Li <> Ar file
636 redirect stdin (or file descriptor
640 .It Oo Ar n1 Oc Ns Li <& Ns Ar n2
641 duplicate stdin (or file descriptor
645 .It Oo Ar n Oc Ns Li <&-
646 close stdin (or file descriptor
648 .It Oo Ar n1 Oc Ns Li >& Ns Ar n2
649 duplicate stdout (or file descriptor
653 .It Oo Ar n Oc Ns Li >&-
654 close stdout (or file descriptor
658 The following redirection is often called a
660 .Bd -unfilled -offset indent
661 .Oo Ar n Oc Ns Li << Ar delimiter
667 All the text on successive lines up to the delimiter is
668 saved away and made available to the command on standard
669 input, or file descriptor
674 as specified on the initial line is quoted, then the
676 is treated literally, otherwise the text is subjected to
677 parameter expansion, command substitution, and arithmetic
678 expansion (as described in the section on
679 .Sx Word Expansions ) .
688 .Ss Search and Execution
689 There are three types of commands: shell functions,
690 built-in commands, and normal programs.
691 The command is searched for (by name) in that order.
692 The three types of commands are all executed in a different way.
694 When a shell function is executed, all of the shell positional
697 which remains unchanged) are
698 set to the arguments of the shell function.
699 The variables which are explicitly placed in the environment of
700 the command (by placing assignments to them before the
701 function name) are made local to the function and are set
703 Then the command given in the function definition is executed.
704 The positional parameters are restored to their original values
705 when the command completes.
706 This all occurs within the current shell.
708 Shell built-in commands are executed internally to the shell, without
709 spawning a new process.
710 There are two kinds of built-in commands: regular and special.
711 Assignments before special builtins persist after they finish
712 executing and assignment errors, redirection errors and certain
713 operand errors cause a script to be aborted.
714 Special builtins cannot be overridden with a function.
715 Both regular and special builtins can affect the shell in ways
716 normal programs cannot.
718 Otherwise, if the command name does not match a function
719 or built-in command, the command is searched for as a normal
720 program in the file system (as described in the next section).
721 When a normal program is executed, the shell runs the program,
722 passing the arguments and the environment to the program.
723 If the program is not a normal executable file
724 (i.e., if it does not begin with the
734 but appears to be a text file,
735 the shell will run a new instance of
739 Note that previous versions of this document
740 and the source code itself misleadingly and sporadically
741 refer to a shell script without a magic number
743 .Dq "shell procedure" .
745 When locating a command, the shell first looks to see if
746 it has a shell function by that name.
748 built-in command by that name.
749 If a built-in command is not found,
750 one of two things happen:
753 Command names containing a slash are simply executed without
754 performing any searches.
756 The shell searches each entry in the
759 in turn for the command.
762 variable should be a series of
763 entries separated by colons.
764 Each entry consists of a
766 The current directory
767 may be indicated implicitly by an empty directory name,
768 or explicitly by a single period.
770 .Ss Command Exit Status
771 Each command has an exit status that can influence the behavior
772 of other shell commands.
773 The paradigm is that a command exits
774 with zero for normal or success, and non-zero for failure,
775 error, or a false indication.
776 The man page for each command
777 should indicate the various exit codes and what they mean.
778 Additionally, the built-in commands return exit codes, as does
779 an executed shell function.
781 If a command is terminated by a signal, its exit status is 128 plus
783 Signal numbers are defined in the header file
786 Complex commands are combinations of simple commands
787 with control operators or keywords, together creating a larger complex
789 More generally, a command is one of the following:
790 .Bl -item -offset indent
796 list or compound-list
803 Unless otherwise stated, the exit status of a command is
804 that of the last simple command executed by the command.
806 A pipeline is a sequence of one or more commands separated
807 by the control operator
809 The standard output of all but
810 the last command is connected to the standard input
812 The standard output of the last
813 command is inherited from the shell, as usual.
815 The format for a pipeline is:
817 .D1 Oo Li \&! Oc Ar command1 Op Li \&| Ar command2 ...
819 The standard output of
821 is connected to the standard input of
823 The standard input, standard output, or
824 both of a command is considered to be assigned by the
825 pipeline before any redirection specified by redirection
826 operators that are part of the command.
828 Note that unlike some other shells,
830 executes each process in a pipeline with more than one command
831 in a subshell environment and as a child of the
835 If the pipeline is not in the background (discussed later),
836 the shell waits for all commands to complete.
840 does not precede the pipeline, the
841 exit status is the exit status of the last command specified
843 Otherwise, the exit status is the logical
844 NOT of the exit status of the last command.
846 the last command returns zero, the exit status is 1; if
847 the last command returns greater than zero, the exit status
850 Because pipeline assignment of standard input or standard
851 output or both takes place before redirection, it can be
852 modified by redirection.
855 .Dl "command1 2>&1 | command2"
857 sends both the standard output and standard error of
859 to the standard input of
864 or newline terminator causes the preceding
866 (described below in the section called
867 .Sx Short-Circuit List Operators )
868 to be executed sequentially;
871 causes asynchronous execution of the preceding AND-OR-list.
872 .Ss Background Commands (&)
873 If a command is terminated by the control operator ampersand
875 the shell executes the command in a subshell environment (see
876 .Sx Grouping Commands Together
877 below) and asynchronously;
878 the shell does not wait for the command to finish
879 before executing the next command.
881 The format for running a command in background is:
883 .D1 Ar command1 Li & Op Ar command2 Li & Ar ...
885 If the shell is not interactive, the standard input of an
886 asynchronous command is set to
888 .Ss Lists (Generally Speaking)
889 A list is a sequence of zero or more commands separated by
890 newlines, semicolons, or ampersands,
891 and optionally terminated by one of these three characters.
893 list are executed in the order they are written.
894 If command is followed by an ampersand, the shell starts the
895 command and immediately proceeds onto the next command;
896 otherwise it waits for the command to terminate before
897 proceeding to the next one.
898 .Ss Short-Circuit List Operators
902 are AND-OR list operators.
904 executes the first command, and then executes the second command
905 if the exit status of the first command is zero.
907 is similar, but executes the second command if the exit
908 status of the first command is nonzero.
912 both have the same priority.
913 .Ss Flow-Control Constructs (if, while, for, case)
917 .Bd -unfilled -offset indent -compact
921 .Ic then Ar list Oc Ar ...
929 .Bd -unfilled -offset indent -compact
935 The two lists are executed repeatedly while the exit status of the
939 command is similar, but has the word
944 repeat until the exit status of the first list is zero.
949 .Bd -unfilled -offset indent -compact
950 .Ic for Ar variable Op Ic in Ar word ...
957 and the following words are omitted,
960 The words are expanded, and then the list is executed
961 repeatedly with the variable set to each word in turn.
966 commands may be replaced with
976 .D1 Ic break Op Ar num
977 .D1 Ic continue Op Ar num
981 command terminates the
990 command continues with the next iteration of the innermost loop.
991 These are implemented as special built-in commands.
996 .Bd -unfilled -offset indent -compact
997 .Ic case Ar word Ic in
998 .Ar pattern Ns Li ) Ar list Li ;;
1003 The pattern can actually be one or more patterns
1010 Tilde expansion, parameter expansion, command substitution,
1011 arithmetic expansion and quote removal are applied to the word.
1012 Then, each pattern is expanded in turn using tilde expansion,
1013 parameter expansion, command substitution and arithmetic expansion and
1014 the expanded form of the word is checked against it.
1015 If a match is found, the corresponding list is executed.
1016 If the selected list is terminated by the control operator
1020 execution continues with the next list,
1021 continuing until a list terminated with
1026 The exit code of the
1028 command is the exit code of the last command executed in the list or
1029 zero if no patterns were matched.
1030 .Ss Grouping Commands Together
1031 Commands may be grouped by writing either
1033 .D1 Li \&( Ns Ar list Ns Li \%)
1037 .D1 Li { Ar list Ns Li \&; }
1039 The first form executes the commands in a subshell environment.
1040 A subshell environment has its own copy of:
1043 The current working directory as set by
1046 The file creation mask as set by
1049 References to open files.
1056 Positional parameters and variables.
1065 These are copied from the parent shell environment,
1066 except that trapped (but not ignored) signals are reset to the default action
1067 and known jobs are cleared.
1068 Any changes do not affect the parent shell environment.
1070 A subshell environment may be implemented as a child process or differently.
1071 If job control is enabled in an interactive shell,
1072 commands grouped in parentheses can be suspended and continued as a unit.
1074 The second form never forks another shell,
1075 so it is slightly more efficient.
1076 Grouping commands together this way allows the user to
1077 redirect their output as though they were one program:
1078 .Bd -literal -offset indent
1079 { echo -n "hello"; echo " world"; } > greeting
1082 The syntax of a function definition is
1084 .D1 Ar name Li \&( \&) Ar command
1086 A function definition is an executable statement; when
1087 executed it installs a function named
1090 exit status of zero.
1099 Variables may be declared to be local to a function by
1103 This should appear as the first statement of a function,
1106 .D1 Ic local Oo Ar variable ... Oc Op Fl
1110 command is implemented as a built-in command.
1112 When a variable is made local, it inherits the initial
1113 value and exported and readonly flags from the variable
1114 with the same name in the surrounding scope, if there is
1116 Otherwise, the variable is initially unset.
1118 uses dynamic scoping, so that if the variable
1120 is made local to function
1122 which then calls function
1124 references to the variable
1128 will refer to the variable
1132 not to the global variable named
1135 The only special parameter that can be made local is
1139 local causes any shell options that are
1142 command inside the function to be
1143 restored to their original values when the function
1150 .D1 Ic return Op Ar exitstatus
1152 It terminates the current executional scope, returning from the previous
1153 nested function, sourced script, or shell instance, in that order.
1156 command is implemented as a special built-in command.
1157 .Ss Variables and Parameters
1158 The shell maintains a set of parameters.
1160 denoted by a name is called a variable.
1162 the shell turns all the environment variables into shell
1164 New variables can be set using the form
1166 .D1 Ar name Ns = Ns Ar value
1168 Variables set by the user must have a name consisting solely
1169 of alphabetics, numerics, and underscores.
1170 The first letter of a variable name must not be numeric.
1171 A parameter can also be denoted by a number
1172 or a special character as explained below.
1173 .Ss Positional Parameters
1174 A positional parameter is a parameter denoted by a number greater than zero.
1175 The shell sets these initially to the values of its command line
1176 arguments that follow the name of the shell script.
1179 built-in command can also be used to set or reset them.
1180 .Ss Special Parameters
1181 Special parameters are parameters denoted by a single special character
1183 They are shown in the following list, exactly as they would appear in input
1184 typed by the user or in the source of a shell script.
1187 Expands to the positional parameters, starting from one.
1189 the expansion occurs within a double-quoted string
1190 it expands to a single field with the value of each parameter
1191 separated by the first character of the
1198 Expands to the positional parameters, starting from one.
1200 the expansion occurs within double-quotes, each positional
1201 parameter expands as a separate argument.
1202 If there are no positional parameters, the
1205 generates zero arguments, even when
1208 What this basically means, for example, is
1221 .Bd -literal -offset indent
1225 Expands to the number of positional parameters.
1227 Expands to the exit status of the most recent pipeline.
1229 (hyphen) Expands to the current option flags (the single-letter
1230 option names concatenated into a string) as specified on
1233 built-in command, or implicitly
1236 Expands to the process ID of the invoked shell.
1238 retains the same value of
1242 Expands to the process ID of the most recent background
1243 command executed from the current shell.
1245 pipeline, the process ID is that of the last command in the
1247 If this parameter is referenced, the shell will remember
1248 the process ID and its exit status until the
1250 built-in command reports completion of the process.
1252 (zero) Expands to the name of the shell script if passed on the command line,
1255 operand if given (with
1257 or otherwise argument 0 passed to the shell.
1259 .Ss Special Variables
1260 The following variables are set by the shell or
1261 have special meaning to it:
1262 .Bl -tag -width ".Va HISTSIZE"
1264 The search path used with the
1268 The fallback editor used with the
1271 If not set, the default editor is
1274 The default editor used with the
1278 The number of previous commands that are accessible.
1280 The user's home directory,
1281 used in tilde expansion and as a default directory for the
1285 Input Field Separators.
1286 This is normally set to
1292 .Sx White Space Splitting
1293 section for more details.
1295 The current line number in the script or function.
1297 The name of a mail file, that will be checked for the arrival of new
1304 separated list of file names, for the shell to check for incoming
1306 This variable overrides the
1309 There is a maximum of 10 mailboxes that can be monitored at once.
1311 The default search path for executables.
1314 section for details.
1316 The parent process ID of the invoked shell.
1317 This is set at startup
1318 unless this variable is in the environment.
1319 A later change of parent process ID is not reflected.
1320 A subshell retains the same value of
1323 The primary prompt string, which defaults to
1325 unless you are the superuser, in which case it defaults to
1328 The secondary prompt string, which defaults to
1331 The prefix for the trace output (if
1338 This clause describes the various expansions that are
1340 Not all expansions are performed on
1341 every word, as explained later.
1343 Tilde expansions, parameter expansions, command substitutions,
1344 arithmetic expansions, and quote removals that occur within
1345 a single word expand to a single field.
1347 splitting or pathname expansion that can create multiple
1348 fields from a single word.
1349 The single exception to this rule is
1350 the expansion of the special parameter
1352 within double-quotes,
1353 as was described above.
1355 The order of word expansion is:
1358 Tilde Expansion, Parameter Expansion, Command Substitution,
1359 Arithmetic Expansion (these all occur at the same time).
1361 Field Splitting is performed on fields generated by step (1)
1366 Pathname Expansion (unless the
1368 option is in effect).
1375 character is used to introduce parameter expansion, command
1376 substitution, or arithmetic expansion.
1377 .Ss Tilde Expansion (substituting a user's home directory)
1378 A word beginning with an unquoted tilde character
1381 subjected to tilde expansion.
1382 All the characters up to a slash
1384 or the end of the word are treated as a username
1385 and are replaced with the user's home directory.
1387 username is missing (as in
1389 the tilde is replaced with the value of the
1391 variable (the current user's home directory).
1392 .Ss Parameter Expansion
1393 The format for parameter expansion is as follows:
1395 .D1 Li ${ Ns Ar expression Ns Li }
1399 consists of all characters until the matching
1403 escaped by a backslash or within a single-quoted or double-quoted
1404 string, and characters in
1405 embedded arithmetic expansions, command substitutions, and variable
1406 expansions, are not examined in determining the matching
1408 If the variants with
1414 occur within a double-quoted string,
1415 as an extension there may be unquoted parts
1416 (via double-quotes inside the expansion);
1418 within such parts are also not examined in determining the matching
1421 The simplest form for parameter expansion is:
1423 .D1 Li ${ Ns Ar parameter Ns Li }
1425 The value, if any, of
1429 The parameter name or symbol can be enclosed in braces, which are
1430 optional except for positional parameters with more than one digit or
1431 when parameter is followed by a character that could be interpreted as
1433 If a parameter expansion occurs inside double-quotes:
1436 Pathname expansion is not performed on the results of the
1439 Field splitting is not performed on the results of the
1440 expansion, with the exception of the special parameter
1444 In addition, a parameter expansion can be modified by using one of the
1446 .Bl -tag -width indent
1447 .It Li ${ Ns Ar parameter Ns Li :- Ns Ar word Ns Li }
1451 is unset or null, the expansion of
1453 is substituted; otherwise, the value of
1456 .It Li ${ Ns Ar parameter Ns Li := Ns Ar word Ns Li }
1457 Assign Default Values.
1460 is unset or null, the expansion of
1470 does not prevent field splitting or pathname expansion.
1471 Only variables, not positional
1472 parameters or special parameters, can be
1473 assigned in this way.
1474 .It Li ${ Ns Ar parameter Ns Li :? Ns Oo Ar word Oc Ns Li }
1475 Indicate Error if Null or Unset.
1478 is unset or null, the expansion of
1480 (or a message indicating it is unset if
1482 is omitted) is written to standard
1483 error and the shell exits with a nonzero
1485 Otherwise, the value of
1489 interactive shell need not exit.
1490 .It Li ${ Ns Ar parameter Ns Li :+ Ns Ar word Ns Li }
1491 Use Alternate Value.
1494 is unset or null, null is substituted;
1495 otherwise, the expansion of
1500 In the parameter expansions shown previously, use of the colon in the
1501 format results in a test for a parameter that is unset or null; omission
1502 of the colon results in a test for a parameter that is only unset.
1506 inherits the type of quoting
1507 (unquoted, double-quoted or here-document)
1508 from the surroundings,
1509 with the exception that a backslash that quotes a closing brace is removed
1510 during quote removal.
1511 .Bl -tag -width indent
1512 .It Li ${# Ns Ar parameter Ns Li }
1514 The length in characters of
1519 The following four varieties of parameter expansion provide for substring
1521 In each case, pattern matching notation
1523 .Sx Shell Patterns ) ,
1524 rather than regular expression notation,
1525 is used to evaluate the patterns.
1526 If parameter is one of the special parameters
1530 the result of the expansion is unspecified.
1531 Enclosing the full parameter expansion string in double-quotes does not
1532 cause the following four varieties of pattern characters to be quoted,
1533 whereas quoting characters within the braces has this effect.
1534 .Bl -tag -width indent
1535 .It Li ${ Ns Ar parameter Ns Li % Ns Ar word Ns Li }
1536 Remove Smallest Suffix Pattern.
1539 is expanded to produce a pattern.
1541 parameter expansion then results in
1543 with the smallest portion of the
1544 suffix matched by the pattern deleted.
1545 .It Li ${ Ns Ar parameter Ns Li %% Ns Ar word Ns Li }
1546 Remove Largest Suffix Pattern.
1549 is expanded to produce a pattern.
1551 parameter expansion then results in
1553 with the largest portion of the
1554 suffix matched by the pattern deleted.
1555 .It Li ${ Ns Ar parameter Ns Li # Ns Ar word Ns Li }
1556 Remove Smallest Prefix Pattern.
1559 is expanded to produce a pattern.
1561 parameter expansion then results in
1563 with the smallest portion of the
1564 prefix matched by the pattern deleted.
1565 .It Li ${ Ns Ar parameter Ns Li ## Ns Ar word Ns Li }
1566 Remove Largest Prefix Pattern.
1569 is expanded to produce a pattern.
1571 parameter expansion then results in
1573 with the largest portion of the
1574 prefix matched by the pattern deleted.
1576 .Ss Command Substitution
1577 Command substitution allows the output of a command to be substituted in
1578 place of the command name itself.
1579 Command substitution occurs when
1580 the command is enclosed as follows:
1582 .D1 Li $( Ns Ar command Ns Li )\&
1584 or the backquoted version:
1586 .D1 Li ` Ns Ar command Ns Li `
1588 The shell expands the command substitution by executing command
1589 and replacing the command substitution
1590 with the standard output of the command,
1591 removing sequences of one or more newlines at the end of the substitution.
1592 Embedded newlines before the end of the output are not removed;
1593 however, during field splitting, they may be translated into spaces
1594 depending on the value of
1596 and the quoting that is in effect.
1597 The command is executed in a subshell environment,
1598 except that the built-in commands
1603 return information about the parent shell environment
1606 returns information about the same process
1607 if they are the only command in a command substitution.
1608 .Ss Arithmetic Expansion
1609 Arithmetic expansion provides a mechanism for evaluating an arithmetic
1610 expression and substituting its value.
1611 The format for arithmetic expansion is as follows:
1613 .D1 Li $(( Ns Ar expression Ns Li ))
1617 is treated as if it were in double-quotes, except
1618 that a double-quote inside the expression is not treated specially.
1620 shell expands all tokens in the
1622 for parameter expansion,
1623 command substitution,
1624 arithmetic expansion
1627 The allowed expressions are a subset of C expressions,
1629 .Bl -tag -width "Variables" -offset indent
1631 All values are of type
1634 Decimal, octal (starting with
1636 and hexadecimal (starting with
1640 Shell variables can be read and written
1641 and contain integer constants.
1644 .It Binary operators
1645 .Li "* / % + - << >> < <= > >= == != & ^ | && ||"
1646 .It Assignment operators
1647 .Li "= += -= *= /= %= <<= >>= &= ^= |="
1648 .It Conditional operator
1652 The result of the expression is substituted in decimal.
1653 .Ss White Space Splitting (Field Splitting)
1654 After parameter expansion, command substitution, and
1655 arithmetic expansion the shell scans the results of
1656 expansions and substitutions that did not occur in double-quotes for
1657 field splitting and multiple fields can result.
1659 The shell treats each character of the
1661 variable as a delimiter and uses
1662 the delimiters to split the results of parameter expansion and command
1663 substitution into fields.
1664 .Ss Pathname Expansion (File Name Generation)
1668 file name generation is performed
1669 after word splitting is complete.
1671 viewed as a series of patterns, separated by slashes.
1673 process of expansion replaces the word with the names of
1674 all existing files whose names can be formed by replacing
1675 each pattern with a string that matches the specified pattern.
1676 There are two restrictions on this: first, a pattern cannot match
1677 a string containing a slash, and second,
1678 a pattern cannot match a string starting with a period
1679 unless the first character of the pattern is a period.
1680 The next section describes the patterns used for
1682 the four varieties of parameter expansion for substring processing and the
1686 A pattern consists of normal characters, which match themselves,
1687 and meta-characters.
1688 The meta-characters are
1693 These characters lose their special meanings if they are quoted.
1694 When command or variable substitution is performed and the dollar sign
1695 or back quotes are not double-quoted, the value of the
1696 variable or the output of the command is scanned for these
1697 characters and they are turned into meta-characters.
1701 matches any string of characters.
1704 matches any single character.
1707 introduces a character class.
1708 The end of the character class is indicated by a
1716 rather than introducing a character class.
1717 A character class matches any of the characters between the square brackets.
1718 A locale-dependent range of characters may be specified using a minus sign.
1719 A named class of characters (see
1721 may be specified by surrounding the name with
1726 .Ql \&[\&[:alpha:\&]\&]
1727 is a shell pattern that matches a single letter.
1728 The character class may be complemented by making an exclamation point
1730 the first character of the character class.
1733 has the same effect but is non-standard.
1737 in a character class, make it the first character listed
1745 make it the first or last character listed.
1746 .Ss Built-in Commands
1747 This section lists the built-in commands.
1748 .Bl -tag -width indent
1750 A null command that returns a 0 (true) exit value.
1752 The commands in the specified file are read and executed by the shell.
1755 command may be used to return to the
1762 characters, it is used as is.
1763 Otherwise, the shell searches the
1766 If it is not found in the
1768 it is sought in the current working directory.
1770 A built-in equivalent of
1772 .It Ic alias Oo Ar name Ns Oo = Ns Ar string Oc Ar ... Oc
1774 .Ar name Ns = Ns Ar string
1775 is specified, the shell defines the alias
1781 is specified, the value of the alias
1784 With no arguments, the
1786 built-in command prints the names and values of all defined aliases
1789 Alias values are written with appropriate quoting so that they are
1790 suitable for re-input to the shell.
1794 .It Ic bg Op Ar job ...
1795 Continue the specified jobs
1796 (or the current job if no jobs are given)
1798 .It Ic bind Oo Fl aeklrsv Oc Oo Ar key Oo Ar command Oc Oc
1799 List or alter key bindings for the line editor.
1800 This command is documented in
1802 .It Ic break Op Ar num
1804 .Sx Flow-Control Constructs
1806 .It Ic builtin Ar cmd Op Ar arg ...
1807 Execute the specified built-in command,
1809 This is useful when the user wishes to override a shell function
1810 with the same name as a built-in command.
1811 .It Ic cd Oo Fl L | P Oc Oo Fl e Oc Op Ar directory
1812 Switch to the specified
1814 or to the directory specified in the
1816 environment variable if no
1825 then the directories listed in the
1828 searched for the specified
1832 is unset, the current directory is searched.
1835 is the same as that of
1837 In an interactive shell,
1840 command will print out the name of the directory
1841 that it actually switched to
1842 if this is different from the name that the user gave.
1843 These may be different either because the
1845 mechanism was used or because a symbolic link was crossed.
1849 option is specified,
1851 is handled physically and symbolic links are resolved before
1853 components are processed.
1856 option is specified,
1858 is handled logically.
1859 This is the default.
1865 to return exit status 1 if the full pathname of the new directory
1866 cannot be determined reliably or at all.
1867 Normally this is not considered an error,
1868 although a warning is printed.
1873 .It Ic command Oo Fl p Oc Op Ar utility Op Ar argument ...
1874 .It Ic command Oo Fl p Oc Fl v Ar utility
1875 .It Ic command Oo Fl p Oc Fl V Ar utility
1876 The first form of invocation executes the specified
1878 ignoring shell functions in the search.
1881 is a special builtin,
1882 it is executed as if it were a regular builtin.
1886 option is specified, the command search is performed using a
1889 that is guaranteed to find all of the standard utilities.
1893 option is specified,
1895 is not executed but a description of its interpretation by the shell is
1897 For ordinary commands the output is the path name; for shell built-in
1898 commands, shell functions and keywords only the name is written.
1899 Aliases are printed as
1900 .Dq Ic alias Ar name Ns = Ns Ar value .
1904 option is identical to
1906 except for the output.
1908 .Dq Ar utility Ic is Ar description
1914 a special shell builtin,
1921 .It Ic continue Op Ar num
1923 .Sx Flow-Control Constructs
1925 .It Ic echo Oo Fl e | n Oc Op Ar string ...
1926 Print a space-separated list of the arguments to the standard output
1927 and append a newline character.
1928 .Bl -tag -width indent
1930 Suppress the output of the trailing newline.
1932 Process C-style backslash escape sequences.
1935 command understands the following character escapes:
1936 .Bl -tag -width indent
1938 Alert (ring the terminal bell)
1942 Suppress the trailing newline (this has the side-effect of truncating the
1943 line if it is not the last character)
1961 (Zero) The character whose octal value is
1967 is not enclosed in quotes then the backslash itself must be escaped
1968 with a backslash to protect it from the shell.
1970 .Bd -literal -offset indent
1979 $ echo -e a\e\e\e\eb
1988 options may be specified.
1989 .It Ic eval Ar string ...
1990 Concatenate all the arguments with spaces.
1991 Then re-parse and execute the command.
1992 .It Ic exec Op Ar command Op Ar arg ...
1996 the shell process is replaced with the specified program
1997 (which must be a real program, not a shell built-in command or function).
1998 Any redirections on the
2000 command are marked as permanent,
2001 so that they are not undone when the
2004 .It Ic exit Op Ar exitstatus
2005 Terminate the shell process.
2009 it is used as the exit status of the shell.
2010 Otherwise, if the shell is executing an
2012 trap, the exit status of the last command before the trap is used;
2013 if the shell is executing a trap for a signal,
2014 the shell exits by resending the signal to itself.
2015 Otherwise, the exit status of the preceding command is used.
2016 The exit status should be an integer between 0 and 255.
2017 .It Ic export Ar name ...
2018 .It Ic export Op Fl p
2019 The specified names are exported so that they will
2020 appear in the environment of subsequent commands.
2021 The only way to un-export a variable is to
2024 The shell allows the value of a variable to be set
2025 at the same time as it is exported by writing
2027 .D1 Ic export Ar name Ns = Ns Ar value
2029 With no arguments the
2031 command lists the names
2032 of all exported variables.
2035 option is specified, the exported variables are printed as
2036 .Dq Ic export Ar name Ns = Ns Ar value
2037 lines, suitable for re-input to the shell.
2039 A null command that returns a non-zero (false) exit value.
2040 .It Ic fc Oo Fl e Ar editor Oc Op Ar first Op Ar last
2041 .It Ic fc Fl l Oo Fl nr Oc Op Ar first Op Ar last
2042 .It Ic fc Fl s Oo Ar old Ns = Ns Ar new Oc Op Ar first
2045 built-in command lists, or edits and re-executes,
2046 commands previously entered to an interactive shell.
2047 .Bl -tag -width indent
2049 Use the editor named by
2051 to edit the commands.
2054 string is a command name,
2055 subject to search via the
2060 variable is used as a default when
2065 is null or unset, the value of the
2072 is used as the editor.
2074 List the commands rather than invoking
2076 The commands are written in the
2077 sequence indicated by the
2081 operands, as affected by
2083 with each command preceded by the command number.
2085 Suppress command numbers when listing with
2088 Reverse the order of the commands listed
2097 Re-execute the command without invoking an editor.
2100 Select the commands to list or edit.
2101 The number of previous commands that can be accessed
2102 are determined by the value of the
2109 or both are one of the following:
2110 .Bl -tag -width indent
2111 .It Oo Cm + Oc Ns Ar num
2112 A positive number representing a command number;
2113 command numbers can be displayed with the
2117 A negative decimal number representing the
2118 command that was executed
2121 commands previously.
2122 For example, \-1 is the immediately previous command.
2124 A string indicating the most recently entered command
2125 that begins with that string.
2127 .Ar old Ns = Ns Ar new
2128 operand is not also specified with
2130 the string form of the first operand cannot contain an embedded equal sign.
2134 The following variables affect the execution of
2136 .Bl -tag -width ".Va HISTSIZE"
2138 Name of the editor to use for history editing.
2140 The number of previous commands that are accessible.
2145 or the current job to the foreground.
2146 .It Ic getopts Ar optstring var
2153 command deprecates the older
2156 The first argument should be a series of letters, each possibly
2157 followed by a colon which indicates that the option takes an argument.
2158 The specified variable is set to the parsed option.
2160 the next argument is placed into the shell variable
2162 If an option takes an argument, it is placed into the shell variable
2164 If an invalid option is encountered,
2168 It returns a false value (1) when it encounters the end of the options.
2169 .It Ic hash Oo Fl rv Oc Op Ar command ...
2170 The shell maintains a hash table which remembers the locations of commands.
2171 With no arguments whatsoever, the
2173 command prints out the contents of this table.
2174 Entries which have not been looked at since the last
2176 command are marked with an asterisk;
2177 it is possible for these entries to be invalid.
2181 command removes each specified
2183 from the hash table (unless they are functions) and then locates it.
2188 prints the locations of the commands as it finds them.
2193 command to delete all the entries in the hash table except for functions.
2194 .It Ic jobid Op Ar job
2195 Print the process IDs of the processes in the specified
2199 argument is omitted, use the current job.
2200 .It Ic jobs Oo Fl lps Oc Op Ar job ...
2201 Print information about the specified jobs, or all jobs if no
2204 The information printed includes job ID, status and command name.
2208 option is specified, the PID of each job is also printed.
2211 option is specified, only the process IDs for the process group leaders
2212 are printed, one per line.
2215 option is specified, only the PIDs of the job commands are printed, one per
2218 A built-in equivalent of
2220 that additionally supports sending signals to jobs.
2221 .It Ic local Oo Ar variable ... Oc Op Fl
2226 A built-in equivalent of
2228 .It Ic pwd Op Fl L | P
2229 Print the path of the current directory.
2230 The built-in command may
2231 differ from the program of the same name because the
2232 built-in command remembers what the current directory
2233 is rather than recomputing it each time.
2236 However, if the current directory is
2238 the built-in version of
2240 will continue to print the old name for the directory.
2244 option is specified, symbolic links are resolved.
2247 option is specified, the shell's notion of the current directory
2248 is printed (symbolic links are not resolved).
2249 This is the default.
2250 .It Ic read Oo Fl p Ar prompt Oc Oo
2251 .Fl t Ar timeout Oc Oo Fl er Oc Ar variable ...
2257 and the standard input is a terminal.
2259 read from the standard input.
2260 The trailing newline
2261 is deleted from the line and the line is split as
2262 described in the section on
2263 .Sx White Space Splitting (Field Splitting)
2265 the pieces are assigned to the variables in order.
2266 If there are more pieces than variables, the remaining
2267 pieces (along with the characters in
2269 that separated them)
2270 are assigned to the last variable.
2271 If there are more variables than pieces, the remaining
2272 variables are assigned the null string.
2274 Backslashes are treated specially, unless the
2278 If a backslash is followed by
2279 a newline, the backslash and the newline will be
2281 If a backslash is followed by any other
2282 character, the backslash will be deleted and the following
2283 character will be treated as though it were not in
2289 option is specified and the
2291 elapses before a complete line of input is supplied,
2294 command will return an exit status of 1 without assigning any values.
2297 value may optionally be followed by one of
2302 to explicitly specify seconds, minutes or hours.
2303 If none is supplied,
2309 option exists only for backward compatibility with older scripts.
2310 .It Ic readonly Oo Fl p Oc Op Ar name ...
2313 is marked as read only,
2314 so that it cannot be subsequently modified or unset.
2315 The shell allows the value of a variable to be set
2316 at the same time as it is marked read only
2317 by using the following form:
2319 .D1 Ic readonly Ar name Ns = Ns Ar value
2321 With no arguments the
2323 command lists the names of all read only variables.
2326 option is specified, the read-only variables are printed as
2327 .Dq Ic readonly Ar name Ns = Ns Ar value
2328 lines, suitable for re-input to the shell.
2329 .It Ic return Op Ar exitstatus
2333 .It Ic set Oo Fl /+abCEefIimnpTuVvx Oc Oo Fl /+o Ar longname Oc Oo
2334 .Fl c Ar string Oc Op Fl - Ar arg ...
2337 command performs three different functions:
2340 With no arguments, it lists the values of all shell variables.
2342 If options are given,
2343 either in short form or using the long
2344 .Dq Fl /+o Ar longname
2346 it sets or clears the specified options as described in the section called
2347 .Sx Argument List Processing .
2351 option is specified,
2353 will replace the shell's positional parameters with the subsequent
2355 If no arguments follow the
2358 all the positional parameters will be cleared,
2359 which is equivalent to executing the command
2363 flag may be omitted when specifying arguments to be used
2364 as positional replacement parameters.
2365 This is not recommended,
2366 because the first argument may begin with a dash
2372 command will interpret as a request to enable or disable options.
2374 .It Ic setvar Ar variable value
2375 Assigns the specified
2381 command is intended to be used in functions that
2382 assign values to variables whose names are passed as parameters.
2383 In general it is better to write
2384 .Dq Ar variable Ns = Ns Ar value
2387 .It Ic shift Op Ar n
2388 Shift the positional parameters
2393 A shift sets the value of
2402 decreasing the value of
2405 If there are zero positional parameters, shifting does not do anything.
2407 A built-in equivalent of
2410 Print the amount of time spent executing the shell process and its children.
2411 The first output line shows the user and system times for the shell process
2412 itself, the second one contains the user and system times for the
2414 .It Ic trap Oo Ar action Oc Ar signal ...
2416 Cause the shell to parse and execute
2421 The signals are specified by name or number.
2422 In addition, the pseudo-signal
2424 may be used to specify an
2426 that is performed when the shell terminates.
2429 may be an empty string or a dash
2431 the former causes the specified signal to be ignored
2432 and the latter causes the default action to be taken.
2435 is another way to request the default action, for compatibility reasons this
2436 usage is not recommended though.
2437 In a subshell or utility environment,
2438 the shell resets trapped (but not ignored) signals to the default action.
2441 command has no effect on signals that were ignored on entry to the shell.
2447 command to display a list of valid signal names.
2449 A null command that returns a 0 (true) exit value.
2450 .It Ic type Op Ar name ...
2453 as a command and print the resolution of the command search.
2454 Possible resolutions are:
2455 shell keyword, alias, special shell builtin, shell builtin, command,
2458 For aliases the alias expansion is printed;
2459 for commands and tracked aliases
2460 the complete pathname of the command is printed.
2461 .It Ic ulimit Oo Fl HSabcdflmnstuv Oc Op Ar limit
2462 Set or display resource limits (see
2466 is specified, the named resource will be set;
2467 otherwise the current resource value will be displayed.
2471 is specified, the hard limits will be set or displayed.
2472 While everybody is allowed to reduce a hard limit,
2473 only the superuser can increase it.
2477 specifies the soft limits instead.
2478 When displaying limits,
2484 The default is to display the soft limits,
2485 and to set both the hard and the soft limits.
2491 command to display all resources.
2494 is not acceptable in this mode.
2496 The remaining options specify which resource value is to be
2497 displayed or modified.
2498 They are mutually exclusive.
2499 .Bl -tag -width indent
2501 The maximum size of socket buffer usage, in bytes.
2502 .It Fl c Ar coredumpsize
2503 The maximal size of core dump files, in 512-byte blocks.
2504 .It Fl d Ar datasize
2505 The maximal size of the data segment of a process, in kilobytes.
2506 .It Fl f Ar filesize
2507 The maximal size of a file, in 512-byte blocks.
2508 .It Fl l Ar lockedmem
2509 The maximal size of memory that can be locked by a process, in
2511 .It Fl m Ar memoryuse
2512 The maximal resident set size of a process, in kilobytes.
2514 The maximal number of descriptors that could be opened by a process.
2515 .It Fl s Ar stacksize
2516 The maximal size of the stack segment, in kilobytes.
2518 The maximal amount of CPU time to be used by each process, in seconds.
2519 .It Fl u Ar userproc
2520 The maximal number of simultaneous processes for this user ID.
2521 .It Fl v Ar virtualmem
2522 The maximal virtual size of a process, in kilobytes.
2524 .It Ic umask Oo Fl S Oc Op Ar mask
2525 Set the file creation mask (see
2527 to the octal or symbolic (see
2531 If the argument is omitted, the current mask value is printed.
2534 option is specified, the output is symbolic, otherwise the output is octal.
2535 .It Ic unalias Oo Fl a Oc Op Ar name ...
2536 The specified alias names are removed.
2539 is specified, all aliases are removed.
2540 .It Ic unset Oo Fl fv Oc Ar name ...
2541 The specified variables or functions are unset and unexported.
2544 option is specified or no options are given, the
2546 arguments are treated as variable names.
2549 option is specified, the
2551 arguments are treated as function names.
2552 .It Ic wait Op Ar job
2553 Wait for the specified
2555 to complete and return the exit status of the last process in the
2557 If the argument is omitted, wait for all jobs to complete
2558 and return an exit status of zero.
2560 .Ss Commandline Editing
2563 is being used interactively from a terminal, the current command
2564 and the command history
2568 .Sx Built-in Commands )
2571 command line editing.
2572 This mode uses commands similar
2573 to a subset of those described in the
2591 can be switched between insert mode and command mode by typing
2595 while in command mode will pass the line to the shell.
2598 .Dq Li "set -o emacs"
2601 command can be used to enable a subset of
2603 command line editing features.
2605 The following environment variables affect the execution of
2607 .Bl -tag -width ".Ev LANGXXXXXX"
2609 Initialization file for interactive shells.
2610 .It Ev LANG , Ev LC_*
2612 These are inherited by children of the shell,
2613 and is used in a limited manner by the shell itself.
2615 An absolute pathname for the current directory,
2616 possibly containing symbolic links.
2617 This is used and updated by the shell.
2619 The default terminal setting for the shell.
2620 This is inherited by children of the shell, and is used in the history
2624 Additionally, all environment variables are turned into shell variables
2626 which may affect the shell as described under
2627 .Sx Special Variables .
2629 Errors that are detected by the shell, such as a syntax error, will
2630 cause the shell to exit with a non-zero exit status.
2631 If the shell is not an interactive shell, the execution of the shell
2632 file will be aborted.
2633 Otherwise the shell will return the exit status of the last command
2636 builtin is used with a numeric argument, it
2637 will return the argument.
2643 .Xr emacs 1 Pq Pa pkgsrc/editors/emacs ,
2658 command, the Thompson shell, appeared in
2660 It was superseded in
2662 by the Bourne shell, which inherited the name
2667 was rewritten in 1989 under the
2669 license after the Bourne shell from
2674 was originally written by
2675 .An Kenneth Almquist .
2679 utility does not recognize multibyte characters other than UTF-8.
2682 and the line editing library
2684 do not recognize multibyte characters.
2686 The characters generated by filename completion should probably be quoted
2687 to ensure that the filename is still valid after the input line has been