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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 asynchronously;
876 the shell does not wait for the command to finish
877 before executing the next command.
879 The format for running a command in background is:
881 .D1 Ar command1 Li & Op Ar command2 Li & Ar ...
883 If the shell is not interactive, the standard input of an
884 asynchronous command is set to
886 .Ss Lists (Generally Speaking)
887 A list is a sequence of zero or more commands separated by
888 newlines, semicolons, or ampersands,
889 and optionally terminated by one of these three characters.
891 list are executed in the order they are written.
892 If command is followed by an ampersand, the shell starts the
893 command and immediately proceeds onto the next command;
894 otherwise it waits for the command to terminate before
895 proceeding to the next one.
896 .Ss Short-Circuit List Operators
900 are AND-OR list operators.
902 executes the first command, and then executes the second command
903 if the exit status of the first command is zero.
905 is similar, but executes the second command if the exit
906 status of the first command is nonzero.
910 both have the same priority.
911 .Ss Flow-Control Constructs (if, while, for, case)
915 .Bd -unfilled -offset indent -compact
919 .Ic then Ar list Oc Ar ...
927 .Bd -unfilled -offset indent -compact
933 The two lists are executed repeatedly while the exit status of the
937 command is similar, but has the word
942 repeat until the exit status of the first list is zero.
947 .Bd -unfilled -offset indent -compact
948 .Ic for Ar variable Op Ic in Ar word ...
955 and the following words are omitted,
958 The words are expanded, and then the list is executed
959 repeatedly with the variable set to each word in turn.
964 commands may be replaced with
974 .D1 Ic break Op Ar num
975 .D1 Ic continue Op Ar num
979 command terminates the
988 command continues with the next iteration of the innermost loop.
989 These are implemented as special built-in commands.
994 .Bd -unfilled -offset indent -compact
995 .Ic case Ar word Ic in
996 .Ar pattern Ns Li ) Ar list Li ;;
1001 The pattern can actually be one or more patterns
1008 Tilde expansion, parameter expansion, command substitution,
1009 arithmetic expansion and quote removal are applied to the word.
1010 Then, each pattern is expanded in turn using tilde expansion,
1011 parameter expansion, command substitution and arithmetic expansion and
1012 the expanded form of the word is checked against it.
1013 If a match is found, the corresponding list is executed.
1014 If the selected list is terminated by the control operator
1018 execution continues with the next list,
1019 continuing until a list terminated with
1024 The exit code of the
1026 command is the exit code of the last command executed in the list or
1027 zero if no patterns were matched.
1028 .Ss Grouping Commands Together
1029 Commands may be grouped by writing either
1031 .D1 Li \&( Ns Ar list Ns Li \%)
1035 .D1 Li { Ar list Ns Li \&; }
1037 The first form executes the commands in a subshell environment.
1038 Note that built-in commands thus executed do not affect the current shell.
1039 The second form never forks another shell,
1040 so it is slightly more efficient.
1041 Grouping commands together this way allows the user to
1042 redirect their output as though they were one program:
1043 .Bd -literal -offset indent
1044 { echo -n "hello"; echo " world"; } > greeting
1047 The syntax of a function definition is
1049 .D1 Ar name Li \&( \&) Ar command
1051 A function definition is an executable statement; when
1052 executed it installs a function named
1055 exit status of zero.
1064 Variables may be declared to be local to a function by
1068 This should appear as the first statement of a function,
1071 .D1 Ic local Oo Ar variable ... Oc Op Fl
1075 command is implemented as a built-in command.
1077 When a variable is made local, it inherits the initial
1078 value and exported and readonly flags from the variable
1079 with the same name in the surrounding scope, if there is
1081 Otherwise, the variable is initially unset.
1083 uses dynamic scoping, so that if the variable
1085 is made local to function
1087 which then calls function
1089 references to the variable
1093 will refer to the variable
1097 not to the global variable named
1100 The only special parameter that can be made local is
1104 local causes any shell options that are
1107 command inside the function to be
1108 restored to their original values when the function
1115 .D1 Ic return Op Ar exitstatus
1117 It terminates the current executional scope, returning from the previous
1118 nested function, sourced script, or shell instance, in that order.
1121 command is implemented as a special built-in command.
1122 .Ss Variables and Parameters
1123 The shell maintains a set of parameters.
1125 denoted by a name is called a variable.
1127 the shell turns all the environment variables into shell
1129 New variables can be set using the form
1131 .D1 Ar name Ns = Ns Ar value
1133 Variables set by the user must have a name consisting solely
1134 of alphabetics, numerics, and underscores.
1135 The first letter of a variable name must not be numeric.
1136 A parameter can also be denoted by a number
1137 or a special character as explained below.
1138 .Ss Positional Parameters
1139 A positional parameter is a parameter denoted by a number greater than zero.
1140 The shell sets these initially to the values of its command line
1141 arguments that follow the name of the shell script.
1144 built-in command can also be used to set or reset them.
1145 .Ss Special Parameters
1146 Special parameters are parameters denoted by a single special character
1148 They are shown in the following list, exactly as they would appear in input
1149 typed by the user or in the source of a shell script.
1152 Expands to the positional parameters, starting from one.
1154 the expansion occurs within a double-quoted string
1155 it expands to a single field with the value of each parameter
1156 separated by the first character of the
1163 Expands to the positional parameters, starting from one.
1165 the expansion occurs within double-quotes, each positional
1166 parameter expands as a separate argument.
1167 If there are no positional parameters, the
1170 generates zero arguments, even when
1173 What this basically means, for example, is
1186 .Bd -literal -offset indent
1190 Expands to the number of positional parameters.
1192 Expands to the exit status of the most recent pipeline.
1194 (hyphen) Expands to the current option flags (the single-letter
1195 option names concatenated into a string) as specified on
1198 built-in command, or implicitly
1201 Expands to the process ID of the invoked shell.
1203 retains the same value of
1207 Expands to the process ID of the most recent background
1208 command executed from the current shell.
1210 pipeline, the process ID is that of the last command in the
1212 If this parameter is referenced, the shell will remember
1213 the process ID and its exit status until the
1215 built-in command reports completion of the process.
1217 (zero) Expands to the name of the shell script if passed on the command line,
1220 operand if given (with
1222 or otherwise argument 0 passed to the shell.
1224 .Ss Special Variables
1225 The following variables are set by the shell or
1226 have special meaning to it:
1227 .Bl -tag -width ".Va HISTSIZE"
1229 The search path used with the
1233 The fallback editor used with the
1236 If not set, the default editor is
1239 The default editor used with the
1243 The number of previous commands that are accessible.
1245 The user's home directory,
1246 used in tilde expansion and as a default directory for the
1250 Input Field Separators.
1251 This is normally set to
1257 .Sx White Space Splitting
1258 section for more details.
1260 The current line number in the script or function.
1262 The name of a mail file, that will be checked for the arrival of new
1269 separated list of file names, for the shell to check for incoming
1271 This variable overrides the
1274 There is a maximum of 10 mailboxes that can be monitored at once.
1276 The default search path for executables.
1279 section for details.
1281 The parent process ID of the invoked shell.
1282 This is set at startup
1283 unless this variable is in the environment.
1284 A later change of parent process ID is not reflected.
1285 A subshell retains the same value of
1288 The primary prompt string, which defaults to
1290 unless you are the superuser, in which case it defaults to
1293 The secondary prompt string, which defaults to
1296 The prefix for the trace output (if
1303 This clause describes the various expansions that are
1305 Not all expansions are performed on
1306 every word, as explained later.
1308 Tilde expansions, parameter expansions, command substitutions,
1309 arithmetic expansions, and quote removals that occur within
1310 a single word expand to a single field.
1312 splitting or pathname expansion that can create multiple
1313 fields from a single word.
1314 The single exception to this rule is
1315 the expansion of the special parameter
1317 within double-quotes,
1318 as was described above.
1320 The order of word expansion is:
1323 Tilde Expansion, Parameter Expansion, Command Substitution,
1324 Arithmetic Expansion (these all occur at the same time).
1326 Field Splitting is performed on fields generated by step (1)
1331 Pathname Expansion (unless the
1333 option is in effect).
1340 character is used to introduce parameter expansion, command
1341 substitution, or arithmetic expansion.
1342 .Ss Tilde Expansion (substituting a user's home directory)
1343 A word beginning with an unquoted tilde character
1346 subjected to tilde expansion.
1347 All the characters up to a slash
1349 or the end of the word are treated as a username
1350 and are replaced with the user's home directory.
1352 username is missing (as in
1354 the tilde is replaced with the value of the
1356 variable (the current user's home directory).
1357 .Ss Parameter Expansion
1358 The format for parameter expansion is as follows:
1360 .D1 Li ${ Ns Ar expression Ns Li }
1364 consists of all characters until the matching
1368 escaped by a backslash or within a single-quoted or double-quoted
1369 string, and characters in
1370 embedded arithmetic expansions, command substitutions, and variable
1371 expansions, are not examined in determining the matching
1373 If the variants with
1379 occur within a double-quoted string,
1380 as an extension there may be unquoted parts
1381 (via double-quotes inside the expansion);
1383 within such parts are also not examined in determining the matching
1386 The simplest form for parameter expansion is:
1388 .D1 Li ${ Ns Ar parameter Ns Li }
1390 The value, if any, of
1394 The parameter name or symbol can be enclosed in braces, which are
1395 optional except for positional parameters with more than one digit or
1396 when parameter is followed by a character that could be interpreted as
1398 If a parameter expansion occurs inside double-quotes:
1401 Pathname expansion is not performed on the results of the
1404 Field splitting is not performed on the results of the
1405 expansion, with the exception of the special parameter
1409 In addition, a parameter expansion can be modified by using one of the
1411 .Bl -tag -width indent
1412 .It Li ${ Ns Ar parameter Ns Li :- Ns Ar word Ns Li }
1416 is unset or null, the expansion of
1418 is substituted; otherwise, the value of
1421 .It Li ${ Ns Ar parameter Ns Li := Ns Ar word Ns Li }
1422 Assign Default Values.
1425 is unset or null, the expansion of
1435 does not prevent field splitting or pathname expansion.
1436 Only variables, not positional
1437 parameters or special parameters, can be
1438 assigned in this way.
1439 .It Li ${ Ns Ar parameter Ns Li :? Ns Oo Ar word Oc Ns Li }
1440 Indicate Error if Null or Unset.
1443 is unset or null, the expansion of
1445 (or a message indicating it is unset if
1447 is omitted) is written to standard
1448 error and the shell exits with a nonzero
1450 Otherwise, the value of
1454 interactive shell need not exit.
1455 .It Li ${ Ns Ar parameter Ns Li :+ Ns Ar word Ns Li }
1456 Use Alternate Value.
1459 is unset or null, null is substituted;
1460 otherwise, the expansion of
1465 In the parameter expansions shown previously, use of the colon in the
1466 format results in a test for a parameter that is unset or null; omission
1467 of the colon results in a test for a parameter that is only unset.
1471 inherits the type of quoting
1472 (unquoted, double-quoted or here-document)
1473 from the surroundings,
1474 with the exception that a backslash that quotes a closing brace is removed
1475 during quote removal.
1476 .Bl -tag -width indent
1477 .It Li ${# Ns Ar parameter Ns Li }
1479 The length in characters of
1484 The following four varieties of parameter expansion provide for substring
1486 In each case, pattern matching notation
1488 .Sx Shell Patterns ) ,
1489 rather than regular expression notation,
1490 is used to evaluate the patterns.
1491 If parameter is one of the special parameters
1495 the result of the expansion is unspecified.
1496 Enclosing the full parameter expansion string in double-quotes does not
1497 cause the following four varieties of pattern characters to be quoted,
1498 whereas quoting characters within the braces has this effect.
1499 .Bl -tag -width indent
1500 .It Li ${ Ns Ar parameter Ns Li % Ns Ar word Ns Li }
1501 Remove Smallest Suffix Pattern.
1504 is expanded to produce a pattern.
1506 parameter expansion then results in
1508 with the smallest portion of the
1509 suffix matched by the pattern deleted.
1510 .It Li ${ Ns Ar parameter Ns Li %% Ns Ar word Ns Li }
1511 Remove Largest Suffix Pattern.
1514 is expanded to produce a pattern.
1516 parameter expansion then results in
1518 with the largest portion of the
1519 suffix matched by the pattern deleted.
1520 .It Li ${ Ns Ar parameter Ns Li # Ns Ar word Ns Li }
1521 Remove Smallest Prefix Pattern.
1524 is expanded to produce a pattern.
1526 parameter expansion then results in
1528 with the smallest portion of the
1529 prefix matched by the pattern deleted.
1530 .It Li ${ Ns Ar parameter Ns Li ## Ns Ar word Ns Li }
1531 Remove Largest Prefix Pattern.
1534 is expanded to produce a pattern.
1536 parameter expansion then results in
1538 with the largest portion of the
1539 prefix matched by the pattern deleted.
1541 .Ss Command Substitution
1542 Command substitution allows the output of a command to be substituted in
1543 place of the command name itself.
1544 Command substitution occurs when
1545 the command is enclosed as follows:
1547 .D1 Li $( Ns Ar command Ns Li )\&
1549 or the backquoted version:
1551 .D1 Li ` Ns Ar command Ns Li `
1553 The shell expands the command substitution by executing command
1554 and replacing the command substitution
1555 with the standard output of the command,
1556 removing sequences of one or more newlines at the end of the substitution.
1557 Embedded newlines before the end of the output are not removed;
1558 however, during field splitting, they may be translated into spaces
1559 depending on the value of
1561 and the quoting that is in effect.
1562 The command is executed in a subshell environment,
1563 except that the built-in commands
1569 return information about the main shell environment
1570 if they are the only command in a command substitution.
1571 .Ss Arithmetic Expansion
1572 Arithmetic expansion provides a mechanism for evaluating an arithmetic
1573 expression and substituting its value.
1574 The format for arithmetic expansion is as follows:
1576 .D1 Li $(( Ns Ar expression Ns Li ))
1580 is treated as if it were in double-quotes, except
1581 that a double-quote inside the expression is not treated specially.
1583 shell expands all tokens in the
1585 for parameter expansion,
1586 command substitution,
1587 arithmetic expansion
1590 The allowed expressions are a subset of C expressions,
1592 .Bl -tag -width "Variables" -offset indent
1594 All values are of type
1597 Decimal, octal (starting with
1599 and hexadecimal (starting with
1603 Shell variables can be read and written
1604 and contain integer constants.
1607 .It Binary operators
1608 .Li "* / % + - << >> < <= > >= == != & ^ | && ||"
1609 .It Assignment operators
1610 .Li "= += -= *= /= %= <<= >>= &= ^= |="
1611 .It Conditional operator
1615 The result of the expression is substituted in decimal.
1616 .Ss White Space Splitting (Field Splitting)
1617 After parameter expansion, command substitution, and
1618 arithmetic expansion the shell scans the results of
1619 expansions and substitutions that did not occur in double-quotes for
1620 field splitting and multiple fields can result.
1622 The shell treats each character of the
1624 variable as a delimiter and uses
1625 the delimiters to split the results of parameter expansion and command
1626 substitution into fields.
1627 .Ss Pathname Expansion (File Name Generation)
1631 file name generation is performed
1632 after word splitting is complete.
1634 viewed as a series of patterns, separated by slashes.
1636 process of expansion replaces the word with the names of
1637 all existing files whose names can be formed by replacing
1638 each pattern with a string that matches the specified pattern.
1639 There are two restrictions on this: first, a pattern cannot match
1640 a string containing a slash, and second,
1641 a pattern cannot match a string starting with a period
1642 unless the first character of the pattern is a period.
1643 The next section describes the patterns used for
1645 the four varieties of parameter expansion for substring processing and the
1649 A pattern consists of normal characters, which match themselves,
1650 and meta-characters.
1651 The meta-characters are
1656 These characters lose their special meanings if they are quoted.
1657 When command or variable substitution is performed and the dollar sign
1658 or back quotes are not double-quoted, the value of the
1659 variable or the output of the command is scanned for these
1660 characters and they are turned into meta-characters.
1664 matches any string of characters.
1667 matches any single character.
1670 introduces a character class.
1671 The end of the character class is indicated by a
1679 rather than introducing a character class.
1680 A character class matches any of the characters between the square brackets.
1681 A locale-dependent range of characters may be specified using a minus sign.
1682 A named class of characters (see
1684 may be specified by surrounding the name with
1689 .Ql \&[\&[:alpha:\&]\&]
1690 is a shell pattern that matches a single letter.
1691 The character class may be complemented by making an exclamation point
1693 the first character of the character class.
1696 has the same effect but is non-standard.
1700 in a character class, make it the first character listed
1708 make it the first or last character listed.
1709 .Ss Built-in Commands
1710 This section lists the built-in commands.
1711 .Bl -tag -width indent
1713 A null command that returns a 0 (true) exit value.
1715 The commands in the specified file are read and executed by the shell.
1718 command may be used to return to the
1725 characters, it is used as is.
1726 Otherwise, the shell searches the
1729 If it is not found in the
1731 it is sought in the current working directory.
1733 A built-in equivalent of
1735 .It Ic alias Oo Ar name Ns Oo = Ns Ar string Oc Ar ... Oc
1737 .Ar name Ns = Ns Ar string
1738 is specified, the shell defines the alias
1744 is specified, the value of the alias
1747 With no arguments, the
1749 built-in command prints the names and values of all defined aliases
1752 Alias values are written with appropriate quoting so that they are
1753 suitable for re-input to the shell.
1757 .It Ic bg Op Ar job ...
1758 Continue the specified jobs
1759 (or the current job if no jobs are given)
1761 .It Ic bind Oo Fl aeklrsv Oc Oo Ar key Oo Ar command Oc Oc
1762 List or alter key bindings for the line editor.
1763 This command is documented in
1765 .It Ic break Op Ar num
1767 .Sx Flow-Control Constructs
1769 .It Ic builtin Ar cmd Op Ar arg ...
1770 Execute the specified built-in command,
1772 This is useful when the user wishes to override a shell function
1773 with the same name as a built-in command.
1774 .It Ic cd Oo Fl L | P Oc Oo Fl e Oc Op Ar directory
1775 Switch to the specified
1777 or to the directory specified in the
1779 environment variable if no
1788 then the directories listed in the
1791 searched for the specified
1795 is unset, the current directory is searched.
1798 is the same as that of
1800 In an interactive shell,
1803 command will print out the name of the directory
1804 that it actually switched to
1805 if this is different from the name that the user gave.
1806 These may be different either because the
1808 mechanism was used or because a symbolic link was crossed.
1812 option is specified,
1814 is handled physically and symbolic links are resolved before
1816 components are processed.
1819 option is specified,
1821 is handled logically.
1822 This is the default.
1828 to return exit status 1 if the full pathname of the new directory
1829 cannot be determined reliably or at all.
1830 Normally this is not considered an error,
1831 although a warning is printed.
1836 .It Ic command Oo Fl p Oc Op Ar utility Op Ar argument ...
1837 .It Ic command Oo Fl p Oc Fl v Ar utility
1838 .It Ic command Oo Fl p Oc Fl V Ar utility
1839 The first form of invocation executes the specified
1841 ignoring shell functions in the search.
1844 is a special builtin,
1845 it is executed as if it were a regular builtin.
1849 option is specified, the command search is performed using a
1852 that is guaranteed to find all of the standard utilities.
1856 option is specified,
1858 is not executed but a description of its interpretation by the shell is
1860 For ordinary commands the output is the path name; for shell built-in
1861 commands, shell functions and keywords only the name is written.
1862 Aliases are printed as
1863 .Dq Ic alias Ar name Ns = Ns Ar value .
1867 option is identical to
1869 except for the output.
1871 .Dq Ar utility Ic is Ar description
1877 a special shell builtin,
1884 .It Ic continue Op Ar num
1886 .Sx Flow-Control Constructs
1888 .It Ic echo Oo Fl e | n Oc Op Ar string ...
1889 Print a space-separated list of the arguments to the standard output
1890 and append a newline character.
1891 .Bl -tag -width indent
1893 Suppress the output of the trailing newline.
1895 Process C-style backslash escape sequences.
1898 command understands the following character escapes:
1899 .Bl -tag -width indent
1901 Alert (ring the terminal bell)
1905 Suppress the trailing newline (this has the side-effect of truncating the
1906 line if it is not the last character)
1924 (Zero) The character whose octal value is
1930 is not enclosed in quotes then the backslash itself must be escaped
1931 with a backslash to protect it from the shell.
1933 .Bd -literal -offset indent
1942 $ echo -e a\e\e\e\eb
1951 options may be specified.
1952 .It Ic eval Ar string ...
1953 Concatenate all the arguments with spaces.
1954 Then re-parse and execute the command.
1955 .It Ic exec Op Ar command Op Ar arg ...
1959 the shell process is replaced with the specified program
1960 (which must be a real program, not a shell built-in command or function).
1961 Any redirections on the
1963 command are marked as permanent,
1964 so that they are not undone when the
1967 .It Ic exit Op Ar exitstatus
1968 Terminate the shell process.
1972 it is used as the exit status of the shell.
1973 Otherwise, if the shell is executing an
1975 trap, the exit status of the last command before the trap is used;
1976 if the shell is executing a trap for a signal,
1977 the shell exits by resending the signal to itself.
1978 Otherwise, the exit status of the preceding command is used.
1979 The exit status should be an integer between 0 and 255.
1980 .It Ic export Ar name ...
1981 .It Ic export Op Fl p
1982 The specified names are exported so that they will
1983 appear in the environment of subsequent commands.
1984 The only way to un-export a variable is to
1987 The shell allows the value of a variable to be set
1988 at the same time as it is exported by writing
1990 .D1 Ic export Ar name Ns = Ns Ar value
1992 With no arguments the
1994 command lists the names
1995 of all exported variables.
1998 option is specified, the exported variables are printed as
1999 .Dq Ic export Ar name Ns = Ns Ar value
2000 lines, suitable for re-input to the shell.
2002 A null command that returns a non-zero (false) exit value.
2003 .It Ic fc Oo Fl e Ar editor Oc Op Ar first Op Ar last
2004 .It Ic fc Fl l Oo Fl nr Oc Op Ar first Op Ar last
2005 .It Ic fc Fl s Oo Ar old Ns = Ns Ar new Oc Op Ar first
2008 built-in command lists, or edits and re-executes,
2009 commands previously entered to an interactive shell.
2010 .Bl -tag -width indent
2012 Use the editor named by
2014 to edit the commands.
2017 string is a command name,
2018 subject to search via the
2023 variable is used as a default when
2028 is null or unset, the value of the
2035 is used as the editor.
2037 List the commands rather than invoking
2039 The commands are written in the
2040 sequence indicated by the
2044 operands, as affected by
2046 with each command preceded by the command number.
2048 Suppress command numbers when listing with
2051 Reverse the order of the commands listed
2060 Re-execute the command without invoking an editor.
2063 Select the commands to list or edit.
2064 The number of previous commands that can be accessed
2065 are determined by the value of the
2072 or both are one of the following:
2073 .Bl -tag -width indent
2074 .It Oo Cm + Oc Ns Ar num
2075 A positive number representing a command number;
2076 command numbers can be displayed with the
2080 A negative decimal number representing the
2081 command that was executed
2084 commands previously.
2085 For example, \-1 is the immediately previous command.
2087 A string indicating the most recently entered command
2088 that begins with that string.
2090 .Ar old Ns = Ns Ar new
2091 operand is not also specified with
2093 the string form of the first operand cannot contain an embedded equal sign.
2097 The following variables affect the execution of
2099 .Bl -tag -width ".Va HISTSIZE"
2101 Name of the editor to use for history editing.
2103 The number of previous commands that are accessible.
2108 or the current job to the foreground.
2109 .It Ic getopts Ar optstring var
2116 command deprecates the older
2119 The first argument should be a series of letters, each possibly
2120 followed by a colon which indicates that the option takes an argument.
2121 The specified variable is set to the parsed option.
2123 the next argument is placed into the shell variable
2125 If an option takes an argument, it is placed into the shell variable
2127 If an invalid option is encountered,
2131 It returns a false value (1) when it encounters the end of the options.
2132 .It Ic hash Oo Fl rv Oc Op Ar command ...
2133 The shell maintains a hash table which remembers the locations of commands.
2134 With no arguments whatsoever, the
2136 command prints out the contents of this table.
2137 Entries which have not been looked at since the last
2139 command are marked with an asterisk;
2140 it is possible for these entries to be invalid.
2144 command removes each specified
2146 from the hash table (unless they are functions) and then locates it.
2151 prints the locations of the commands as it finds them.
2156 command to delete all the entries in the hash table except for functions.
2157 .It Ic jobid Op Ar job
2158 Print the process IDs of the processes in the specified
2162 argument is omitted, use the current job.
2163 .It Ic jobs Oo Fl lps Oc Op Ar job ...
2164 Print information about the specified jobs, or all jobs if no
2167 The information printed includes job ID, status and command name.
2171 option is specified, the PID of each job is also printed.
2174 option is specified, only the process IDs for the process group leaders
2175 are printed, one per line.
2178 option is specified, only the PIDs of the job commands are printed, one per
2181 A built-in equivalent of
2183 that additionally supports sending signals to jobs.
2184 .It Ic local Oo Ar variable ... Oc Op Fl
2189 A built-in equivalent of
2191 .It Ic pwd Op Fl L | P
2192 Print the path of the current directory.
2193 The built-in command may
2194 differ from the program of the same name because the
2195 built-in command remembers what the current directory
2196 is rather than recomputing it each time.
2199 However, if the current directory is
2201 the built-in version of
2203 will continue to print the old name for the directory.
2207 option is specified, symbolic links are resolved.
2210 option is specified, the shell's notion of the current directory
2211 is printed (symbolic links are not resolved).
2212 This is the default.
2213 .It Ic read Oo Fl p Ar prompt Oc Oo
2214 .Fl t Ar timeout Oc Oo Fl er Oc Ar variable ...
2220 and the standard input is a terminal.
2222 read from the standard input.
2223 The trailing newline
2224 is deleted from the line and the line is split as
2225 described in the section on
2226 .Sx White Space Splitting (Field Splitting)
2228 the pieces are assigned to the variables in order.
2229 If there are more pieces than variables, the remaining
2230 pieces (along with the characters in
2232 that separated them)
2233 are assigned to the last variable.
2234 If there are more variables than pieces, the remaining
2235 variables are assigned the null string.
2237 Backslashes are treated specially, unless the
2241 If a backslash is followed by
2242 a newline, the backslash and the newline will be
2244 If a backslash is followed by any other
2245 character, the backslash will be deleted and the following
2246 character will be treated as though it were not in
2252 option is specified and the
2254 elapses before a complete line of input is supplied,
2257 command will return an exit status of 1 without assigning any values.
2260 value may optionally be followed by one of
2265 to explicitly specify seconds, minutes or hours.
2266 If none is supplied,
2272 option exists only for backward compatibility with older scripts.
2273 .It Ic readonly Oo Fl p Oc Op Ar name ...
2276 is marked as read only,
2277 so that it cannot be subsequently modified or unset.
2278 The shell allows the value of a variable to be set
2279 at the same time as it is marked read only
2280 by using the following form:
2282 .D1 Ic readonly Ar name Ns = Ns Ar value
2284 With no arguments the
2286 command lists the names of all read only variables.
2289 option is specified, the read-only variables are printed as
2290 .Dq Ic readonly Ar name Ns = Ns Ar value
2291 lines, suitable for re-input to the shell.
2292 .It Ic return Op Ar exitstatus
2296 .It Ic set Oo Fl /+abCEefIimnpTuVvx Oc Oo Fl /+o Ar longname Oc Oo
2297 .Fl c Ar string Oc Op Fl - Ar arg ...
2300 command performs three different functions:
2303 With no arguments, it lists the values of all shell variables.
2305 If options are given,
2306 either in short form or using the long
2307 .Dq Fl /+o Ar longname
2309 it sets or clears the specified options as described in the section called
2310 .Sx Argument List Processing .
2314 option is specified,
2316 will replace the shell's positional parameters with the subsequent
2318 If no arguments follow the
2321 all the positional parameters will be cleared,
2322 which is equivalent to executing the command
2326 flag may be omitted when specifying arguments to be used
2327 as positional replacement parameters.
2328 This is not recommended,
2329 because the first argument may begin with a dash
2335 command will interpret as a request to enable or disable options.
2337 .It Ic setvar Ar variable value
2338 Assigns the specified
2344 command is intended to be used in functions that
2345 assign values to variables whose names are passed as parameters.
2346 In general it is better to write
2347 .Dq Ar variable Ns = Ns Ar value
2350 .It Ic shift Op Ar n
2351 Shift the positional parameters
2356 A shift sets the value of
2365 decreasing the value of
2368 If there are zero positional parameters, shifting does not do anything.
2370 A built-in equivalent of
2373 Print the amount of time spent executing the shell and its children.
2374 The first output line shows the user and system times for the shell
2375 itself, the second one contains the user and system times for the
2377 .It Ic trap Oo Ar action Oc Ar signal ...
2379 Cause the shell to parse and execute
2384 The signals are specified by name or number.
2385 In addition, the pseudo-signal
2387 may be used to specify an
2389 that is performed when the shell terminates.
2392 may be an empty string or a dash
2394 the former causes the specified signal to be ignored
2395 and the latter causes the default action to be taken.
2398 is another way to request the default action, for compatibility reasons this
2399 usage is not recommended though.
2400 In a subshell environment,
2401 the shell resets trapped (but not ignored) signals to the default action.
2404 command has no effect on signals that were ignored on entry to the shell.
2410 command to display a list of valid signal names.
2412 A null command that returns a 0 (true) exit value.
2413 .It Ic type Op Ar name ...
2416 as a command and print the resolution of the command search.
2417 Possible resolutions are:
2418 shell keyword, alias, special shell builtin, shell builtin, command,
2421 For aliases the alias expansion is printed;
2422 for commands and tracked aliases
2423 the complete pathname of the command is printed.
2424 .It Ic ulimit Oo Fl HSabcdflmnstuv Oc Op Ar limit
2425 Set or display resource limits (see
2429 is specified, the named resource will be set;
2430 otherwise the current resource value will be displayed.
2434 is specified, the hard limits will be set or displayed.
2435 While everybody is allowed to reduce a hard limit,
2436 only the superuser can increase it.
2440 specifies the soft limits instead.
2441 When displaying limits,
2447 The default is to display the soft limits,
2448 and to set both the hard and the soft limits.
2454 command to display all resources.
2457 is not acceptable in this mode.
2459 The remaining options specify which resource value is to be
2460 displayed or modified.
2461 They are mutually exclusive.
2462 .Bl -tag -width indent
2464 The maximum size of socket buffer usage, in bytes.
2465 .It Fl c Ar coredumpsize
2466 The maximal size of core dump files, in 512-byte blocks.
2467 .It Fl d Ar datasize
2468 The maximal size of the data segment of a process, in kilobytes.
2469 .It Fl f Ar filesize
2470 The maximal size of a file, in 512-byte blocks.
2471 .It Fl l Ar lockedmem
2472 The maximal size of memory that can be locked by a process, in
2474 .It Fl m Ar memoryuse
2475 The maximal resident set size of a process, in kilobytes.
2477 The maximal number of descriptors that could be opened by a process.
2478 .It Fl s Ar stacksize
2479 The maximal size of the stack segment, in kilobytes.
2481 The maximal amount of CPU time to be used by each process, in seconds.
2482 .It Fl u Ar userproc
2483 The maximal number of simultaneous processes for this user ID.
2484 .It Fl v Ar virtualmem
2485 The maximal virtual size of a process, in kilobytes.
2487 .It Ic umask Oo Fl S Oc Op Ar mask
2488 Set the file creation mask (see
2490 to the octal or symbolic (see
2494 If the argument is omitted, the current mask value is printed.
2497 option is specified, the output is symbolic, otherwise the output is octal.
2498 .It Ic unalias Oo Fl a Oc Op Ar name ...
2499 The specified alias names are removed.
2502 is specified, all aliases are removed.
2503 .It Ic unset Oo Fl fv Oc Ar name ...
2504 The specified variables or functions are unset and unexported.
2507 option is specified or no options are given, the
2509 arguments are treated as variable names.
2512 option is specified, the
2514 arguments are treated as function names.
2515 .It Ic wait Op Ar job
2516 Wait for the specified
2518 to complete and return the exit status of the last process in the
2520 If the argument is omitted, wait for all jobs to complete
2521 and return an exit status of zero.
2523 .Ss Commandline Editing
2526 is being used interactively from a terminal, the current command
2527 and the command history
2531 .Sx Built-in Commands )
2534 command line editing.
2535 This mode uses commands similar
2536 to a subset of those described in the
2554 can be switched between insert mode and command mode by typing
2558 while in command mode will pass the line to the shell.
2561 .Dq Li "set -o emacs"
2564 command can be used to enable a subset of
2566 command line editing features.
2568 The following environment variables affect the execution of
2570 .Bl -tag -width ".Ev LANGXXXXXX"
2572 Initialization file for interactive shells.
2573 .It Ev LANG , Ev LC_*
2575 These are inherited by children of the shell,
2576 and is used in a limited manner by the shell itself.
2578 An absolute pathname for the current directory,
2579 possibly containing symbolic links.
2580 This is used and updated by the shell.
2582 The default terminal setting for the shell.
2583 This is inherited by children of the shell, and is used in the history
2587 Additionally, all environment variables are turned into shell variables
2589 which may affect the shell as described under
2590 .Sx Special Variables .
2592 Errors that are detected by the shell, such as a syntax error, will
2593 cause the shell to exit with a non-zero exit status.
2594 If the shell is not an interactive shell, the execution of the shell
2595 file will be aborted.
2596 Otherwise the shell will return the exit status of the last command
2599 builtin is used with a numeric argument, it
2600 will return the argument.
2606 .Xr emacs 1 Pq Pa pkgsrc/editors/emacs ,
2621 command, the Thompson shell, appeared in
2623 It was superseded in
2625 by the Bourne shell, which inherited the name
2630 was rewritten in 1989 under the
2632 license after the Bourne shell from
2637 was originally written by
2638 .An Kenneth Almquist .
2642 utility does not recognize multibyte characters other than UTF-8.
2645 and the line editing library
2647 do not recognize multibyte characters.
2649 The characters generated by filename completion should probably be quoted
2650 to ensure that the filename is still valid after the input line has been