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32 .\" from: @(#)sh.1 8.6 (Berkeley) 5/4/95
40 .Nd command interpreter (shell)
43 .Op Fl /+abCEefIimnPpsTuVvx
44 .Op Fl /+o Ar longname
50 utility is the standard command interpreter for the system.
51 The current version of
53 is in the process of being changed to
56 specification for the shell.
57 This version has many features which make
59 similar in some respects to the Korn shell, but it is not a Korn
65 plus a few Berkeley extensions, are being
66 incorporated into this shell.
67 This man page is not intended to be a tutorial nor a complete
68 specification of the shell.
70 The shell is a command that reads lines from
71 either a file or the terminal, interprets them, and
72 generally executes other commands.
73 It is the program that is started when a user logs into the system,
74 although a user can select a different shell with the
78 implements a language that has flow control constructs,
79 a macro facility that provides a variety of features in
80 addition to data storage, along with built-in history and line
82 It incorporates many features to
83 aid interactive use and has the advantage that the interpretative
84 language is common to both interactive and non-interactive
86 That is, commands can be typed directly
87 to the running shell or can be put into a file,
88 which can be executed directly by the shell.
91 .\" XXX This next sentence is incredibly confusing.
93 If no arguments are present and if the standard input of the shell
94 is connected to a terminal
98 the shell is considered an interactive shell.
100 generally prompts before each command and handles programming
101 and command errors differently (as described below).
102 When first starting, the shell inspects argument 0, and
103 if it begins with a dash
105 the shell is also considered a login shell.
106 This is normally done automatically by the system
107 when the user first logs in.
108 A login shell first reads commands
113 in a user's home directory,
115 If the environment variable
117 is set on entry to a shell, or is set in the
119 of a login shell, the shell then reads commands from the file named in
121 Therefore, a user should place commands that are to be executed only
124 file, and commands that are executed for every shell inside the
129 variable to some file by placing the following line in the file
131 in the home directory,
134 the filename desired:
136 .Dl "ENV=$HOME/.shinit; export ENV"
138 The first non-option argument specified on the command line
139 will be treated as the
140 name of a file from which to read commands (a shell script), and
141 the remaining arguments are set as the positional parameters
145 Otherwise, the shell reads commands
146 from its standard input.
148 Unlike older versions of
152 script is only sourced on invocation of interactive shells.
154 closes a well-known, and sometimes easily exploitable security
155 hole related to poorly thought out
158 .Ss Argument List Processing
159 All of the single letter options to
161 have a corresponding long name,
162 with the exception of
166 These long names are provided next to the single letter options
167 in the descriptions below.
168 The long name for an option may be specified as an argument to the
172 Once the shell is running,
173 the long name for an option may be specified as an argument to the
178 (described later in the section called
179 .Sx Built-in Commands ) .
180 Introducing an option with a dash
190 will stop option processing and will force the remaining
191 words on the command line to be treated as arguments.
196 options do not have long names.
197 They take arguments and are described after the single letter options.
198 .Bl -tag -width indent
199 .It Fl a Li allexport
200 Flag variables for export when assignments are made to them.
202 Enable asynchronous notification of background job
205 .It Fl C Li noclobber
206 Do not overwrite existing files with
211 command line editor (disables the
213 option if it has been set).
215 Exit immediately if any untested command fails in non-interactive mode.
216 The exit status of a command is considered to be
217 explicitly tested if the command is part of the list used to control
219 .Ic if , elif , while ,
222 if the command is the left
227 operator; or if the command is a pipeline preceded by the
230 If a shell function is executed and its exit status is explicitly
231 tested, all commands of the function are considered to be tested as
234 Disable pathname expansion.
235 .It Fl I Li ignoreeof
238 from input when in interactive mode.
239 .It Fl i Li interactive
240 Force the shell to behave interactively.
242 Turn on job control (set automatically when interactive).
244 If not interactive, read commands but do not
246 This is useful for checking the
247 syntax of shell scripts.
249 Change the default for the
255 (logical directory layout)
258 (physical directory layout).
259 .It Fl p Li privileged
260 Turn on privileged mode.
261 This mode is enabled on startup
262 if either the effective user or group ID is not equal to the
263 real user or group ID.
264 Turning this mode off sets the
265 effective user and group IDs to the real user and group IDs.
266 When this mode is enabled for interactive shells, the file
267 .Pa /etc/suid_profile
268 is sourced instead of
272 is sourced, and the contents of the
274 variable are ignored.
276 Read commands from standard input (set automatically
277 if no file arguments are present).
279 no effect when set after the shell has already started
280 running (i.e., when set with the
283 .It Fl T Li trapsasync
284 When waiting for a child, execute traps immediately.
285 If this option is not set,
286 traps are executed after the child exits,
289 This nonstandard option is useful for putting guarding shells around
290 children that block signals.
291 The surrounding shell may kill the child
292 or it may just return control to the tty and leave the child alone,
294 .Bd -literal -offset indent
295 sh -T -c "trap 'exit 1' 2 ; some-blocking-program"
298 Write a message to standard error when attempting
299 to expand a variable that is not set, and if the
300 shell is not interactive, exit immediately.
304 command line editor (disables
308 The shell writes its input to standard error
310 Useful for debugging.
313 (preceded by the value of the
316 to standard error before it is executed.
317 Useful for debugging.
322 option causes the commands to be read from the
324 operand instead of from the standard input.
325 Keep in mind that this option only accepts a single string as its
326 argument, hence multi-word strings must be quoted.
330 option takes as its only argument the long name of an option
331 to be enabled or disabled.
332 For example, the following two invocations of
334 both enable the built-in
337 .Bd -literal -offset indent
342 If used without an argument, the
344 option displays the current option settings in a human-readable format.
347 is used without an argument, the current option settings are output
348 in a format suitable for re-input into the shell.
349 .Ss Lexical Structure
350 The shell reads input in terms of lines from a file and breaks
351 it up into words at whitespace (blanks and tabs), and at
355 which are special to the shell.
356 There are two types of operators: control operators and
357 redirection operators (their meaning is discussed later).
358 The following is a list of valid operators:
359 .Bl -tag -width indent
360 .It Control operators:
361 .Bl -column "XXX" "XXX" "XXX" "XXX" "XXX" -offset center -compact
362 .It Li & Ta Li && Ta Li ( Ta Li ) Ta Li \en
363 .It Li ;; Ta Li ; Ta Li | Ta Li ||
365 .It Redirection operators:
366 .Bl -column "XXX" "XXX" "XXX" "XXX" "XXX" -offset center -compact
367 .It Li < Ta Li > Ta Li << Ta Li >> Ta Li <>
368 .It Li <& Ta Li >& Ta Li <<- Ta Li >|
374 introduces a comment if used at the beginning of a word.
375 The word starting with
377 and the rest of the line are ignored.
379 Quoting is used to remove the special meaning of certain characters
380 or words to the shell, such as operators, whitespace, keywords,
383 There are three types of quoting: matched single quotes,
384 matched double quotes, and backslash.
385 .Bl -tag -width indent
387 Enclosing characters in single quotes preserves the literal
388 meaning of all the characters (except single quotes, making
389 it impossible to put single-quotes in a single-quoted string).
391 Enclosing characters within double quotes preserves the literal
392 meaning of all characters except dollar sign
398 The backslash inside double quotes is historically weird.
399 It remains literal unless it precedes the following characters,
400 which it serves to quote:
401 .Bl -column "XXX" "XXX" "XXX" "XXX" "XXX" -offset center -compact
402 .It Li $ Ta Li ` Ta Li \&" Ta Li \e\ Ta Li \en
405 A backslash preserves the literal meaning of the following
406 character, with the exception of the newline character
408 A backslash preceding a newline is treated as a line continuation.
411 Reserved words are words that have special meaning to the
412 shell and are recognized at the beginning of a line and
413 after a control operator.
414 The following are reserved words:
415 .Bl -column "doneXX" "elifXX" "elseXX" "untilXX" "whileX" -offset center
416 .It Li \&! Ta { Ta } Ta Ic case Ta Ic do
417 .It Ic done Ta Ic elif Ta Ic else Ta Ic esac Ta Ic fi
418 .It Ic for Ta Ic if Ta Ic then Ta Ic until Ta Ic while
421 An alias is a name and corresponding value set using the
424 Whenever a reserved word may occur (see above),
425 and after checking for reserved words, the shell
426 checks the word to see if it matches an alias.
427 If it does, it replaces it in the input stream with its value.
428 For example, if there is an alias called
440 Aliases provide a convenient way for naive users to
441 create shorthands for commands without having to learn how
442 to create functions with arguments.
444 used to create lexically obscure code.
445 This use is discouraged.
447 An alias name may be escaped in a command line, so that it is not
448 replaced by its alias value, by using quoting characters within or
449 adjacent to the alias name.
450 This is most often done by prefixing
451 an alias name with a backslash to execute a function, built-in, or
452 normal program with the same name.
457 The shell interprets the words it reads according to a
458 language, the specification of which is outside the scope
459 of this man page (refer to the BNF in the
462 Essentially though, a line is read and if
463 the first word of the line (or after a control operator)
464 is not a reserved word, then the shell has recognized a
466 Otherwise, a complex command or some
467 other special construct may have been recognized.
469 If a simple command has been recognized, the shell performs
470 the following actions:
473 Leading words of the form
475 are stripped off and assigned to the environment of
477 Redirection operators and
478 their arguments (as described below) are stripped
479 off and saved for processing.
481 The remaining words are expanded as described in
483 .Sx Word Expansions ,
484 and the first remaining word is considered the command
485 name and the command is located.
487 words are considered the arguments of the command.
488 If no command name resulted, then the
490 variable assignments recognized in 1) affect the
493 Redirections are performed as described in
497 Redirections are used to change where a command reads its input
499 In general, redirections open, close, or
500 duplicate an existing reference to a file.
502 used for redirection is:
504 .D1 Oo Ar n Oc Ar redir-op file
508 is one of the redirection operators mentioned
510 The following gives some examples of how these
511 operators can be used.
512 Note that stdin and stdout are commonly used abbreviations
513 for standard input and standard output respectively.
514 .Bl -tag -width "1234567890XX" -offset indent
515 .It Oo Ar n Oc Ns Li > Ar file
516 redirect stdout (or file descriptor
520 .It Oo Ar n Oc Ns Li >| Ar file
521 same as above, but override the
524 .It Oo Ar n Oc Ns Li >> Ar file
525 append stdout (or file descriptor
529 .It Oo Ar n Oc Ns Li < Ar file
530 redirect stdin (or file descriptor
534 .It Oo Ar n Oc Ns Li <> Ar file
535 redirect stdin (or file descriptor
539 .It Oo Ar n1 Oc Ns Li <& Ns Ar n2
540 duplicate stdin (or file descriptor
544 .It Oo Ar n Oc Ns Li <&-
545 close stdin (or file descriptor
547 .It Oo Ar n1 Oc Ns Li >& Ns Ar n2
548 duplicate stdout (or file descriptor
552 .It Oo Ar n Oc Ns Li >&-
553 close stdout (or file descriptor
557 The following redirection is often called a
559 .Bd -unfilled -offset indent
560 .Oo Ar n Oc Ns Li << Ar delimiter
566 All the text on successive lines up to the delimiter is
567 saved away and made available to the command on standard
568 input, or file descriptor
573 as specified on the initial line is quoted, then the
575 is treated literally, otherwise the text is subjected to
576 parameter expansion, command substitution, and arithmetic
577 expansion (as described in the section on
578 .Sx Word Expansions ) .
587 .Ss Search and Execution
588 There are three types of commands: shell functions,
589 built-in commands, and normal programs.
590 The command is searched for (by name) in that order.
591 The three types of commands are all executed in a different way.
593 When a shell function is executed, all of the shell positional
596 which remains unchanged) are
597 set to the arguments of the shell function.
598 The variables which are explicitly placed in the environment of
599 the command (by placing assignments to them before the
600 function name) are made local to the function and are set
602 Then the command given in the function definition is executed.
603 The positional parameters are restored to their original values
604 when the command completes.
605 This all occurs within the current shell.
607 Shell built-in commands are executed internally to the shell, without
608 spawning a new process.
610 Otherwise, if the command name does not match a function
611 or built-in command, the command is searched for as a normal
612 program in the file system (as described in the next section).
613 When a normal program is executed, the shell runs the program,
614 passing the arguments and the environment to the program.
615 If the program is not a normal executable file
616 (i.e., if it does not begin with the
626 the shell will interpret the program in a subshell.
627 The child shell will reinitialize itself in this case,
628 so that the effect will be
629 as if a new shell had been invoked to handle the ad-hoc shell script,
630 except that the location of hashed commands located in
631 the parent shell will be remembered by the child
632 (see the description of the
634 built-in command below).
636 Note that previous versions of this document
637 and the source code itself misleadingly and sporadically
638 refer to a shell script without a magic number
640 .Dq "shell procedure" .
642 When locating a command, the shell first looks to see if
643 it has a shell function by that name.
645 built-in command by that name.
646 If a built-in command is not found,
647 one of two things happen:
650 Command names containing a slash are simply executed without
651 performing any searches.
653 The shell searches each entry in the
656 in turn for the command.
659 variable should be a series of
660 entries separated by colons.
661 Each entry consists of a
663 The current directory
664 may be indicated implicitly by an empty directory name,
665 or explicitly by a single period.
667 .Ss Command Exit Status
668 Each command has an exit status that can influence the behavior
669 of other shell commands.
670 The paradigm is that a command exits
671 with zero for normal or success, and non-zero for failure,
672 error, or a false indication.
673 The man page for each command
674 should indicate the various exit codes and what they mean.
675 Additionally, the built-in commands return exit codes, as does
676 an executed shell function.
678 If a command is terminated by a signal, its exit status is 128 plus
680 Signal numbers are defined in the header file
683 Complex commands are combinations of simple commands
684 with control operators or reserved words, together creating a larger complex
686 More generally, a command is one of the following:
687 .Bl -item -offset indent
693 list or compound-list
700 Unless otherwise stated, the exit status of a command is
701 that of the last simple command executed by the command.
703 A pipeline is a sequence of one or more commands separated
704 by the control operator
706 The standard output of all but
707 the last command is connected to the standard input
709 The standard output of the last
710 command is inherited from the shell, as usual.
712 The format for a pipeline is:
714 .D1 Oo Li \&! Oc Ar command1 Op Li \&| Ar command2 ...
716 The standard output of
718 is connected to the standard input of
720 The standard input, standard output, or
721 both of a command is considered to be assigned by the
722 pipeline before any redirection specified by redirection
723 operators that are part of the command.
725 If the pipeline is not in the background (discussed later),
726 the shell waits for all commands to complete.
730 does not precede the pipeline, the
731 exit status is the exit status of the last command specified
733 Otherwise, the exit status is the logical
734 NOT of the exit status of the last command.
736 the last command returns zero, the exit status is 1; if
737 the last command returns greater than zero, the exit status
740 Because pipeline assignment of standard input or standard
741 output or both takes place before redirection, it can be
742 modified by redirection.
745 .Dl "command1 2>&1 | command2"
747 sends both the standard output and standard error of
749 to the standard input of
754 or newline terminator causes the preceding
756 (described below in the section called
757 .Sx Short-Circuit List Operators )
758 to be executed sequentially;
761 causes asynchronous execution of the preceding AND-OR-list.
763 Note that unlike some other shells,
765 executes each process in the pipeline as a child of the
768 Shell built-in commands are the exception to this rule.
769 They are executed in the current shell, although they do not affect its
770 environment when used in pipelines.
771 .Ss Background Commands (&)
772 If a command is terminated by the control operator ampersand
774 the shell executes the command asynchronously;
775 the shell does not wait for the command to finish
776 before executing the next command.
778 The format for running a command in background is:
780 .D1 Ar command1 Li & Op Ar command2 Li & Ar ...
782 If the shell is not interactive, the standard input of an
783 asynchronous command is set to
785 .Ss Lists (Generally Speaking)
786 A list is a sequence of zero or more commands separated by
787 newlines, semicolons, or ampersands,
788 and optionally terminated by one of these three characters.
790 list are executed in the order they are written.
791 If command is followed by an ampersand, the shell starts the
792 command and immediately proceeds onto the next command;
793 otherwise it waits for the command to terminate before
794 proceeding to the next one.
795 .Ss Short-Circuit List Operators
799 are AND-OR list operators.
801 executes the first command, and then executes the second command
802 if the exit status of the first command is zero.
804 is similar, but executes the second command if the exit
805 status of the first command is nonzero.
809 both have the same priority.
810 .Ss Flow-Control Constructs (if, while, for, case)
814 .Bd -unfilled -offset indent -compact
818 .Ic then Ar list Oc Ar ...
826 .Bd -unfilled -offset indent -compact
832 The two lists are executed repeatedly while the exit status of the
836 command is similar, but has the word
841 repeat until the exit status of the first list is zero.
846 .Bd -unfilled -offset indent -compact
847 .Ic for Ar variable Op Ic in Ar word ...
854 and the following words are omitted,
857 The words are expanded, and then the list is executed
858 repeatedly with the variable set to each word in turn.
863 commands may be replaced with
873 .D1 Ic break Op Ar num
874 .D1 Ic continue Op Ar num
878 command terminates the
887 command continues with the next iteration of the innermost loop.
888 These are implemented as built-in commands.
893 .Bd -unfilled -offset indent -compact
894 .Ic case Ar word Ic in
895 .Ar pattern Ns Li ) Ar list Li ;;
900 The pattern can actually be one or more patterns
909 command is the exit code of the last command executed in the list or
910 zero if no patterns were matched.
911 .Ss Grouping Commands Together
912 Commands may be grouped by writing either
914 .D1 Li \&( Ns Ar list Ns Li \%)
918 .D1 Li { Ar list Ns Li \&; }
920 The first form executes the commands in a subshell.
921 Note that built-in commands thus executed do not affect the current shell.
922 The second form does not fork another shell,
923 so it is slightly more efficient.
924 Grouping commands together this way allows the user to
925 redirect their output as though they were one program:
926 .Bd -literal -offset indent
927 { echo -n "hello"; echo " world"; } > greeting
930 The syntax of a function definition is
932 .D1 Ar name Li \&( \&) Ar command
934 A function definition is an executable statement; when
935 executed it installs a function named
947 Variables may be declared to be local to a function by
951 This should appear as the first statement of a function,
954 .D1 Ic local Oo Ar variable ... Oc Op Fl
958 command is implemented as a built-in command.
960 When a variable is made local, it inherits the initial
961 value and exported and readonly flags from the variable
962 with the same name in the surrounding scope, if there is
964 Otherwise, the variable is initially unset.
966 uses dynamic scoping, so that if the variable
968 is made local to function
970 which then calls function
972 references to the variable
976 will refer to the variable
980 not to the global variable named
983 The only special parameter that can be made local is
987 local causes any shell options that are
990 command inside the function to be
991 restored to their original values when the function
998 .D1 Ic return Op Ar exitstatus
1000 It terminates the current executional scope, returning from the previous
1001 nested function, sourced script, or shell instance, in that order.
1004 command is implemented as a built-in command.
1005 .Ss Variables and Parameters
1006 The shell maintains a set of parameters.
1008 denoted by a name is called a variable.
1010 the shell turns all the environment variables into shell
1012 New variables can be set using the form
1014 .D1 Ar name Ns = Ns Ar value
1016 Variables set by the user must have a name consisting solely
1017 of alphabetics, numerics, and underscores.
1018 The first letter of a variable name must not be numeric.
1019 A parameter can also be denoted by a number
1020 or a special character as explained below.
1021 .Ss Positional Parameters
1022 A positional parameter is a parameter denoted by a number greater than zero.
1023 The shell sets these initially to the values of its command line
1024 arguments that follow the name of the shell script.
1027 built-in command can also be used to set or reset them.
1028 .Ss Special Parameters
1029 A special parameter is a parameter denoted by a special one-character
1031 The special parameters recognized by the
1035 are shown in the following list, exactly as they would appear in input
1036 typed by the user or in the source of a shell script.
1039 Expands to the positional parameters, starting from one.
1041 the expansion occurs within a double-quoted string
1042 it expands to a single field with the value of each parameter
1043 separated by the first character of the
1050 Expands to the positional parameters, starting from one.
1052 the expansion occurs within double-quotes, each positional
1053 parameter expands as a separate argument.
1054 If there are no positional parameters, the
1057 generates zero arguments, even when
1060 What this basically means, for example, is
1073 .Bd -literal -offset indent
1077 Expands to the number of positional parameters.
1079 Expands to the exit status of the most recent pipeline.
1081 (hyphen) Expands to the current option flags (the single-letter
1082 option names concatenated into a string) as specified on
1085 built-in command, or implicitly
1088 Expands to the process ID of the invoked shell.
1090 retains the same value of
1094 Expands to the process ID of the most recent background
1095 command executed from the current shell.
1097 pipeline, the process ID is that of the last command in the
1100 (zero) Expands to the name of the shell or shell script.
1103 This clause describes the various expansions that are
1105 Not all expansions are performed on
1106 every word, as explained later.
1108 Tilde expansions, parameter expansions, command substitutions,
1109 arithmetic expansions, and quote removals that occur within
1110 a single word expand to a single field.
1112 splitting or pathname expansion that can create multiple
1113 fields from a single word.
1114 The single exception to this rule is
1115 the expansion of the special parameter
1117 within double-quotes,
1118 as was described above.
1120 The order of word expansion is:
1123 Tilde Expansion, Parameter Expansion, Command Substitution,
1124 Arithmetic Expansion (these all occur at the same time).
1126 Field Splitting is performed on fields generated by step (1)
1131 Pathname Expansion (unless the
1133 option is in effect).
1140 character is used to introduce parameter expansion, command
1141 substitution, or arithmetic evaluation.
1142 .Ss Tilde Expansion (substituting a user's home directory)
1143 A word beginning with an unquoted tilde character
1146 subjected to tilde expansion.
1147 All the characters up to a slash
1149 or the end of the word are treated as a username
1150 and are replaced with the user's home directory.
1152 username is missing (as in
1154 the tilde is replaced with the value of the
1156 variable (the current user's home directory).
1157 .Ss Parameter Expansion
1158 The format for parameter expansion is as follows:
1160 .D1 Li ${ Ns Ar expression Ns Li }
1164 consists of all characters until the matching
1168 escaped by a backslash or within a quoted string, and characters in
1169 embedded arithmetic expansions, command substitutions, and variable
1170 expansions, are not examined in determining the matching
1173 The simplest form for parameter expansion is:
1175 .D1 Li ${ Ns Ar parameter Ns Li }
1177 The value, if any, of
1181 The parameter name or symbol can be enclosed in braces, which are
1182 optional except for positional parameters with more than one digit or
1183 when parameter is followed by a character that could be interpreted as
1185 If a parameter expansion occurs inside double-quotes:
1188 Pathname expansion is not performed on the results of the
1191 Field splitting is not performed on the results of the
1192 expansion, with the exception of the special parameter
1196 In addition, a parameter expansion can be modified by using one of the
1198 .Bl -tag -width indent
1199 .It Li ${ Ns Ar parameter Ns Li :- Ns Ar word Ns Li }
1203 is unset or null, the expansion of
1205 is substituted; otherwise, the value of
1208 .It Li ${ Ns Ar parameter Ns Li := Ns Ar word Ns Li }
1209 Assign Default Values.
1212 is unset or null, the expansion of
1220 Only variables, not positional
1221 parameters or special parameters, can be
1222 assigned in this way.
1223 .It Li ${ Ns Ar parameter Ns Li :? Ns Oo Ar word Oc Ns Li }
1224 Indicate Error if Null or Unset.
1227 is unset or null, the expansion of
1229 (or a message indicating it is unset if
1231 is omitted) is written to standard
1232 error and the shell exits with a nonzero
1234 Otherwise, the value of
1238 interactive shell need not exit.
1239 .It Li ${ Ns Ar parameter Ns Li :+ Ns Ar word Ns Li }
1240 Use Alternate Value.
1243 is unset or null, null is substituted;
1244 otherwise, the expansion of
1249 In the parameter expansions shown previously, use of the colon in the
1250 format results in a test for a parameter that is unset or null; omission
1251 of the colon results in a test for a parameter that is only unset.
1252 .Bl -tag -width indent
1253 .It Li ${# Ns Ar parameter Ns Li }
1255 The length in characters of
1260 The following four varieties of parameter expansion provide for substring
1262 In each case, pattern matching notation
1264 .Sx Shell Patterns ) ,
1265 rather than regular expression notation,
1266 is used to evaluate the patterns.
1267 If parameter is one of the special parameters
1271 the result of the expansion is unspecified.
1272 Enclosing the full parameter expansion string in double-quotes does not
1273 cause the following four varieties of pattern characters to be quoted,
1274 whereas quoting characters within the braces has this effect.
1275 .Bl -tag -width indent
1276 .It Li ${ Ns Ar parameter Ns Li % Ns Ar word Ns Li }
1277 Remove Smallest Suffix Pattern.
1280 is expanded to produce a pattern.
1282 parameter expansion then results in
1284 with the smallest portion of the
1285 suffix matched by the pattern deleted.
1286 .It Li ${ Ns Ar parameter Ns Li %% Ns Ar word Ns Li }
1287 Remove Largest Suffix Pattern.
1290 is expanded to produce a pattern.
1292 parameter expansion then results in
1294 with the largest portion of the
1295 suffix matched by the pattern deleted.
1296 .It Li ${ Ns Ar parameter Ns Li # Ns Ar word Ns Li }
1297 Remove Smallest Prefix Pattern.
1300 is expanded to produce a pattern.
1302 parameter expansion then results in
1304 with the smallest portion of the
1305 prefix matched by the pattern deleted.
1306 .It Li ${ Ns Ar parameter Ns Li ## Ns Ar word Ns Li }
1307 Remove Largest Prefix Pattern.
1310 is expanded to produce a pattern.
1312 parameter expansion then results in
1314 with the largest portion of the
1315 prefix matched by the pattern deleted.
1317 .Ss Command Substitution
1318 Command substitution allows the output of a command to be substituted in
1319 place of the command name itself.
1320 Command substitution occurs when
1321 the command is enclosed as follows:
1323 .D1 Li $( Ns Ar command Ns Li )\&
1325 or the backquoted version:
1327 .D1 Li ` Ns Ar command Ns Li `
1329 The shell expands the command substitution by executing command in a
1330 subshell environment and replacing the command substitution
1331 with the standard output of the command,
1332 removing sequences of one or more newlines at the end of the substitution.
1333 Embedded newlines before the end of the output are not removed;
1334 however, during field splitting, they may be translated into spaces
1335 depending on the value of
1337 and the quoting that is in effect.
1338 .Ss Arithmetic Expansion
1339 Arithmetic expansion provides a mechanism for evaluating an arithmetic
1340 expression and substituting its value.
1341 The format for arithmetic expansion is as follows:
1343 .D1 Li $(( Ns Ar expression Ns Li ))
1347 is treated as if it were in double-quotes, except
1348 that a double-quote inside the expression is not treated specially.
1350 shell expands all tokens in the
1352 for parameter expansion,
1353 command substitution, and quote removal.
1355 Next, the shell treats this as an arithmetic expression and
1356 substitutes the value of the expression.
1357 .Ss White Space Splitting (Field Splitting)
1358 After parameter expansion, command substitution, and
1359 arithmetic expansion the shell scans the results of
1360 expansions and substitutions that did not occur in double-quotes for
1361 field splitting and multiple fields can result.
1363 The shell treats each character of the
1365 variable as a delimiter and uses
1366 the delimiters to split the results of parameter expansion and command
1367 substitution into fields.
1368 .Ss Pathname Expansion (File Name Generation)
1372 file name generation is performed
1373 after word splitting is complete.
1375 viewed as a series of patterns, separated by slashes.
1377 process of expansion replaces the word with the names of
1378 all existing files whose names can be formed by replacing
1379 each pattern with a string that matches the specified pattern.
1380 There are two restrictions on this: first, a pattern cannot match
1381 a string containing a slash, and second,
1382 a pattern cannot match a string starting with a period
1383 unless the first character of the pattern is a period.
1384 The next section describes the patterns used for both
1385 Pathname Expansion and the
1389 A pattern consists of normal characters, which match themselves,
1390 and meta-characters.
1391 The meta-characters are
1397 These characters lose their special meanings if they are quoted.
1398 When command or variable substitution is performed and the dollar sign
1399 or back quotes are not double-quoted, the value of the
1400 variable or the output of the command is scanned for these
1401 characters and they are turned into meta-characters.
1405 matches any string of characters.
1408 matches any single character.
1411 introduces a character class.
1412 The end of the character class is indicated by a
1420 rather than introducing a character class.
1421 A character class matches any of the characters between the square brackets.
1422 A range of characters may be specified using a minus sign.
1423 The character class may be complemented by making an exclamation point
1425 the first character of the character class.
1429 in a character class, make it the first character listed
1435 make it the first or last character listed.
1436 .Ss Built-in Commands
1437 This section lists the commands which
1438 are built-in because they need to perform some operation
1439 that cannot be performed by a separate process.
1441 these, built-in versions of essential utilities
1442 are provided for efficiency.
1443 .Bl -tag -width indent
1445 A null command that returns a 0 (true) exit value.
1447 The commands in the specified file are read and executed by the shell.
1450 command may be used to return to the
1457 characters, it is used as is.
1458 Otherwise, the shell searches the
1461 If it is not found in the
1463 it is sought in the current working directory.
1465 A built-in equivalent of
1467 .It Ic alias Oo Ar name Ns Oo = Ns Ar string Oc ... Oc
1469 .Ar name Ns = Ns Ar string
1470 is specified, the shell defines the alias
1476 is specified, the value of the alias
1479 With no arguments, the
1481 built-in command prints the names and values of all defined aliases
1484 Alias values are written with appropriate quoting so that they are
1485 suitable for re-input to the shell.
1489 .It Ic bg Op Ar job ...
1490 Continue the specified jobs
1491 (or the current job if no jobs are given)
1493 .It Ic builtin Ar cmd Op Ar arg ...
1494 Execute the specified built-in command,
1496 This is useful when the user wishes to override a shell function
1497 with the same name as a built-in command.
1498 .It Ic bind Oo Fl aeklrsv Oc Oo Ar key Oo Ar command Oc Oc
1499 List or alter key bindings for the line editor.
1500 This command is documented in
1502 .It Ic cd Oo Fl L | P Oc Op Ar directory
1503 Switch to the specified
1505 or to the directory specified in the
1507 environment variable if no
1516 then the directories listed in the
1519 searched for the specified
1523 is unset, the current directory is searched.
1526 is the same as that of
1528 In an interactive shell,
1531 command will print out the name of the directory
1532 that it actually switched to
1533 if this is different from the name that the user gave.
1534 These may be different either because the
1536 mechanism was used or because a symbolic link was crossed.
1540 option is specified,
1542 is handled physically and symbolic links are resolved before
1544 components are processed.
1547 option is specified,
1549 is handled logically.
1550 This is the default.
1555 .It Ic command Oo Fl p Oc Op Ar utility Op Ar argument ...
1556 .It Ic command Oo Fl v | V Oc Op Ar utility
1557 The first form of invocation executes the specified
1559 as a simple command (see the
1565 option is specified, the command search is performed using a
1568 that is guaranteed to find all of the standard utilities.
1572 option is specified,
1574 is not executed but a description of its interpretation by the shell is
1576 For ordinary commands the output is the path name; for shell built-in
1577 commands, shell functions and keywords only the name is written.
1578 Aliases are printed as
1579 .Dq Ic alias Ar name Ns = Ns Ar value .
1583 option is identical to
1585 except for the output.
1587 .Dq Ar utility Ic is Ar description
1599 .It Ic echo Oo Fl e | n Oc Op Ar string ...
1600 Print a space-separated list of the arguments to the standard output
1601 and append a newline character.
1602 .Bl -tag -width indent
1604 Suppress the output of the trailing newline.
1606 Process C-style backslash escape sequences.
1609 command understands the following character escapes:
1610 .Bl -tag -width indent
1612 Alert (ring the terminal bell)
1616 Suppress the trailing newline (this has the side-effect of truncating the
1617 line if it is not the last character)
1635 (Zero) The character whose octal value is
1641 is not enclosed in quotes then the backslash itself must be escaped
1642 with a backslash to protect it from the shell.
1644 .Bd -literal -offset indent
1653 $ echo -e a\e\e\e\eb
1662 options may be specified.
1663 .It Ic eval Ar string ...
1664 Concatenate all the arguments with spaces.
1665 Then re-parse and execute the command.
1666 .It Ic exec Op Ar command Op arg ...
1670 the shell process is replaced with the specified program
1671 (which must be a real program, not a shell built-in command or function).
1672 Any redirections on the
1674 command are marked as permanent,
1675 so that they are not undone when the
1678 .It Ic exit Op Ar exitstatus
1679 Terminate the shell process.
1683 it is used as the exit status of the shell;
1684 otherwise the exit status of the preceding command is used.
1685 .It Ic export Ar name ...
1686 .It Ic export Op Fl p
1687 The specified names are exported so that they will
1688 appear in the environment of subsequent commands.
1689 The only way to un-export a variable is to
1692 The shell allows the value of a variable to be set
1693 at the same time as it is exported by writing
1695 .D1 Ic export Ar name Ns = Ns Ar value
1697 With no arguments the
1699 command lists the names
1700 of all exported variables.
1703 option is specified, the exported variables are printed as
1704 .Dq Ic export Ar name Ns = Ns Ar value
1705 lines, suitable for re-input to the shell.
1707 A null command that returns a non-zero (false) exit value.
1708 .It Ic fc Oo Fl e Ar editor Oc Op Ar first Op Ar last
1709 .It Ic fc Fl l Oo Fl nr Oc Op Ar first Op Ar last
1710 .It Ic fc Fl s Oo Ar old Ns = Ns Ar new Oc Op Ar first
1713 built-in command lists, or edits and re-executes,
1714 commands previously entered to an interactive shell.
1715 .Bl -tag -width indent
1717 Use the editor named by
1719 to edit the commands.
1722 string is a command name,
1723 subject to search via the
1728 variable is used as a default when
1733 is null or unset, the value of the
1740 is used as the editor.
1742 List the commands rather than invoking
1744 The commands are written in the
1745 sequence indicated by the
1749 operands, as affected by
1751 with each command preceded by the command number.
1753 Suppress command numbers when listing with
1756 Reverse the order of the commands listed
1765 Re-execute the command without invoking an editor.
1768 Select the commands to list or edit.
1769 The number of previous commands that can be accessed
1770 are determined by the value of the
1777 or both are one of the following:
1778 .Bl -tag -width indent
1779 .It Oo Cm + Oc Ns Ar num
1780 A positive number representing a command number;
1781 command numbers can be displayed with the
1785 A negative decimal number representing the
1786 command that was executed
1789 commands previously.
1790 For example, \-1 is the immediately previous command.
1792 A string indicating the most recently entered command
1793 that begins with that string.
1795 .Ar old Ns = Ns Ar new
1796 operand is not also specified with
1798 the string form of the first operand cannot contain an embedded equal sign.
1802 The following environment variables affect the execution of
1804 .Bl -tag -width ".Ev HISTSIZE"
1806 Name of the editor to use for history editing.
1808 The number of previous commands that are accessible.
1813 or the current job to the foreground.
1814 .It Ic getopts Ar optstring var
1821 command deprecates the older
1824 The first argument should be a series of letters, each possibly
1825 followed by a colon which indicates that the option takes an argument.
1826 The specified variable is set to the parsed option.
1828 the next argument is placed into the shell variable
1830 If an option takes an argument, it is placed into the shell variable
1832 If an invalid option is encountered,
1836 It returns a false value (1) when it encounters the end of the options.
1837 .It Ic hash Oo Fl rv Oc Op Ar command ...
1838 The shell maintains a hash table which remembers the locations of commands.
1839 With no arguments whatsoever, the
1841 command prints out the contents of this table.
1842 Entries which have not been looked at since the last
1844 command are marked with an asterisk;
1845 it is possible for these entries to be invalid.
1849 command removes each specified
1851 from the hash table (unless they are functions) and then locates it.
1856 prints the locations of the commands as it finds them.
1861 command to delete all the entries in the hash table except for functions.
1862 .It Ic jobid Op Ar job
1863 Print the process IDs of the processes in the specified
1867 argument is omitted, use the current job.
1868 .It Ic jobs Oo Fl lps Oc Op Ar job ...
1869 Print information about the specified jobs, or all jobs if no
1872 The information printed includes job ID, status and command name.
1876 option is specified, the PID of each job is also printed.
1879 option is specified, only the process IDs for the process group leaders
1880 are printed, one per line.
1883 option is specified, only the PIDs of the job commands are printed, one per
1885 .It Ic local Oo Ar variable ... Oc Op Fl
1889 .It Ic pwd Op Fl L | P
1890 Print the path of the current directory.
1891 The built-in command may
1892 differ from the program of the same name because the
1893 built-in command remembers what the current directory
1894 is rather than recomputing it each time.
1897 However, if the current directory is
1899 the built-in version of
1901 will continue to print the old name for the directory.
1905 option is specified, symbolic links are resolved.
1908 option is specified, the shell's notion of the current directory
1909 is printed (symbolic links are not resolved).
1910 This is the default.
1911 .It Ic read Oo Fl p Ar prompt Oc Oo
1912 .Fl t Ar timeout Oc Oo Fl er Oc Ar variable ...
1918 and the standard input is a terminal.
1920 read from the standard input.
1921 The trailing newline
1922 is deleted from the line and the line is split as
1923 described in the section on
1924 .Sx White Space Splitting (Field Splitting)
1926 the pieces are assigned to the variables in order.
1927 If there are more pieces than variables, the remaining
1928 pieces (along with the characters in
1930 that separated them)
1931 are assigned to the last variable.
1932 If there are more variables than pieces, the remaining
1933 variables are assigned the null string.
1935 Backslashes are treated specially, unless the
1939 If a backslash is followed by
1940 a newline, the backslash and the newline will be
1942 If a backslash is followed by any other
1943 character, the backslash will be deleted and the following
1944 character will be treated as though it were not in
1950 option is specified and the
1952 elapses before any input is supplied,
1955 command will return an exit status of 1 without assigning any values.
1958 value may optionally be followed by one of
1963 to explicitly specify seconds, minutes or hours.
1964 If none is supplied,
1970 option exists only for backward compatibility with older scripts.
1971 .It Ic readonly Oo Fl p Oc Op Ar name ...
1974 is marked as read only,
1975 so that it cannot be subsequently modified or unset.
1976 The shell allows the value of a variable to be set
1977 at the same time as it is marked read only
1978 by using the following form:
1980 .D1 Ic readonly Ar name Ns = Ns Ar value
1982 With no arguments the
1984 command lists the names of all read only variables.
1987 option is specified, the read-only variables are printed as
1988 .Dq Ic readonly Ar name Ns = Ns Ar value
1989 lines, suitable for re-input to the shell.
1990 .It Ic return Op Ar exitstatus
1994 .It Ic set Oo Fl /+abCEefIimnpTuVvx Oc Oo Fl /+o Ar longname Oc Oo
1995 .Fl c Ar string Oc Op Fl - Ar arg ...
1998 command performs three different functions:
2001 With no arguments, it lists the values of all shell variables.
2003 If options are given,
2004 either in short form or using the long
2005 .Dq Fl /+o Ar longname
2007 it sets or clears the specified options as described in the section called
2008 .Sx Argument List Processing .
2012 option is specified,
2014 will replace the shell's positional parameters with the subsequent
2016 If no arguments follow the
2019 all the positional parameters will be cleared,
2020 which is equivalent to executing the command
2024 flag may be omitted when specifying arguments to be used
2025 as positional replacement parameters.
2026 This is not recommended,
2027 because the first argument may begin with a dash
2033 command will interpret as a request to enable or disable options.
2035 .It Ic setvar Ar variable value
2036 Assigns the specified
2042 command is intended to be used in functions that
2043 assign values to variables whose names are passed as parameters.
2044 In general it is better to write
2045 .Dq Ar variable Ns = Ns Ar value
2048 .It Ic shift Op Ar n
2049 Shift the positional parameters
2054 A shift sets the value of
2063 decreasing the value of
2066 If there are zero positional parameters, shifting does not do anything.
2068 A built-in equivalent of
2071 Print the amount of time spent executing the shell and its children.
2072 The first output line shows the user and system times for the shell
2073 itself, the second one contains the user and system times for the
2075 .It Ic trap Oo Ar action Oc Ar signal ...
2077 Cause the shell to parse and execute
2082 The signals are specified by name or number.
2083 In addition, the pseudo-signal
2085 may be used to specify an
2087 that is performed when the shell terminates.
2090 may be an empty string or a dash
2092 the former causes the specified signal to be ignored
2093 and the latter causes the default action to be taken.
2096 is another way to request the default action, for compatibility reasons this
2097 usage is not recommended though.
2098 When the shell forks off a subshell,
2099 it resets trapped (but not ignored) signals to the default action.
2102 command has no effect on signals that were ignored on entry to the shell.
2108 command to display a list of valid signal names.
2110 A null command that returns a 0 (true) exit value.
2111 .It Ic type Op Ar name ...
2114 as a command and print the resolution of the command search.
2115 Possible resolutions are:
2116 shell keyword, alias, shell built-in command, command, tracked alias
2118 For aliases the alias expansion is printed;
2119 for commands and tracked aliases
2120 the complete pathname of the command is printed.
2121 .It Ic ulimit Oo Fl HSabcdflmnstuv Oc Op Ar limit
2122 Set or display resource limits (see
2126 is specified, the named resource will be set;
2127 otherwise the current resource value will be displayed.
2131 is specified, the hard limits will be set or displayed.
2132 While everybody is allowed to reduce a hard limit,
2133 only the superuser can increase it.
2137 specifies the soft limits instead.
2138 When displaying limits,
2144 The default is to display the soft limits,
2145 and to set both the hard and the soft limits.
2151 command to display all resources.
2154 is not acceptable in this mode.
2156 The remaining options specify which resource value is to be
2157 displayed or modified.
2158 They are mutually exclusive.
2159 .Bl -tag -width indent
2161 The maximum size of socket buffer usage, in bytes.
2162 .It Fl c Ar coredumpsize
2163 The maximal size of core dump files, in 512-byte blocks.
2164 .It Fl d Ar datasize
2165 The maximal size of the data segment of a process, in kilobytes.
2166 .It Fl f Ar filesize
2167 The maximal size of a file, in 512-byte blocks.
2168 .It Fl l Ar lockedmem
2169 The maximal size of memory that can be locked by a process, in
2171 .It Fl m Ar memoryuse
2172 The maximal resident set size of a process, in kilobytes.
2174 The maximal number of descriptors that could be opened by a process.
2175 .It Fl s Ar stacksize
2176 The maximal size of the stack segment, in kilobytes.
2178 The maximal amount of CPU time to be used by each process, in seconds.
2179 .It Fl u Ar userproc
2180 The maximal number of simultaneous processes for this user ID.
2181 .It Fl v Ar virtualmem
2182 The maximal virtual size of a process, in kilobytes.
2184 .It Ic umask Oo Fl S Oc Op Ar mask
2185 Set the file creation mask (see
2187 to the octal or symbolic (see
2191 If the argument is omitted, the current mask value is printed.
2194 option is specified, the output is symbolic, otherwise the output is octal.
2195 .It Ic unalias Oo Fl a Oc Op Ar name ...
2196 The specified alias names are removed.
2199 is specified, all aliases are removed.
2200 .It Ic unset Oo Fl fv Oc Ar name ...
2201 The specified variables or functions are unset and unexported.
2204 option is specified or no options are given, the
2206 arguments are treated as variable names.
2209 option is specified, the
2211 arguments are treated as function names.
2212 .It Ic wait Op Ar job
2213 Wait for the specified
2215 to complete and return the exit status of the last process in the
2217 If the argument is omitted, wait for all jobs to complete
2218 and return an exit status of zero.
2220 .Ss Commandline Editing
2223 is being used interactively from a terminal, the current command
2224 and the command history
2228 .Sx Built-in Commands )
2231 command line editing.
2232 This mode uses commands similar
2233 to a subset of those described in the
2251 can be switched between insert mode and command mode by typing
2255 while in command mode will pass the line to the shell.
2258 .Dq Li "set -o emacs"
2261 command can be used to enable a subset of
2263 command line editing features.
2265 The following environment variables affect the execution of
2267 .Bl -tag -width ".Ev HISTSIZE"
2269 The search path used with the
2273 The fallback editor used with the
2276 If not set, the default editor is
2279 The default editor used with the
2283 The number of previous commands that are accessible.
2285 The starting directory of
2288 Input Field Separators.
2289 This is normally set to
2295 .Sx White Space Splitting
2296 section for more details.
2298 The name of a mail file, that will be checked for the arrival of new
2305 separated list of file names, for the shell to check for incoming
2307 This environment setting overrides the
2310 There is a maximum of 10 mailboxes that can be monitored at once.
2312 The default search path for executables.
2315 section for details.
2317 The primary prompt string, which defaults to
2319 unless you are the superuser, in which case it defaults to
2322 The secondary prompt string, which defaults to
2325 The prefix for the trace output (if
2331 The default terminal setting for the shell.
2332 This is inherited by children of the shell, and is used in the history
2336 Errors that are detected by the shell, such as a syntax error, will
2337 cause the shell to exit with a non-zero exit status.
2338 If the shell is not an interactive shell, the execution of the shell
2339 file will be aborted.
2340 Otherwise the shell will return the exit status of the last command
2343 builtin is used with a numeric argument, it
2344 will return the argument.
2363 command, the Thompson shell, appeared in
2365 It was superseded in
2367 by the Bourne shell, which inherited the name
2372 was rewritten in 1989 under the
2374 license after the Bourne shell from
2379 was originally written by
2380 .An Kenneth Almquist .
2384 utility does not recognize multibyte characters.
projects / FreeBSD / releng / 7.2.git / blob