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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.
609 There are two kinds of built-in commands: regular and special.
610 Assignments before special builtins persist after they finish
611 executing and assignment errors, redirection errors and certain
612 operand errors cause a script to be aborted.
613 Both regular and special builtins can affect the shell in ways
614 normal programs cannot.
616 Otherwise, if the command name does not match a function
617 or built-in command, the command is searched for as a normal
618 program in the file system (as described in the next section).
619 When a normal program is executed, the shell runs the program,
620 passing the arguments and the environment to the program.
621 If the program is not a normal executable file
622 (i.e., if it does not begin with the
632 the shell will interpret the program in a subshell.
633 The child shell will reinitialize itself in this case,
634 so that the effect will be
635 as if a new shell had been invoked to handle the ad-hoc shell script,
636 except that the location of hashed commands located in
637 the parent shell will be remembered by the child
638 (see the description of the
640 built-in command below).
642 Note that previous versions of this document
643 and the source code itself misleadingly and sporadically
644 refer to a shell script without a magic number
646 .Dq "shell procedure" .
648 When locating a command, the shell first looks to see if
649 it has a shell function by that name.
651 built-in command by that name.
652 If a built-in command is not found,
653 one of two things happen:
656 Command names containing a slash are simply executed without
657 performing any searches.
659 The shell searches each entry in the
662 in turn for the command.
665 variable should be a series of
666 entries separated by colons.
667 Each entry consists of a
669 The current directory
670 may be indicated implicitly by an empty directory name,
671 or explicitly by a single period.
673 .Ss Command Exit Status
674 Each command has an exit status that can influence the behavior
675 of other shell commands.
676 The paradigm is that a command exits
677 with zero for normal or success, and non-zero for failure,
678 error, or a false indication.
679 The man page for each command
680 should indicate the various exit codes and what they mean.
681 Additionally, the built-in commands return exit codes, as does
682 an executed shell function.
684 If a command is terminated by a signal, its exit status is 128 plus
686 Signal numbers are defined in the header file
689 Complex commands are combinations of simple commands
690 with control operators or reserved words, together creating a larger complex
692 More generally, a command is one of the following:
693 .Bl -item -offset indent
699 list or compound-list
706 Unless otherwise stated, the exit status of a command is
707 that of the last simple command executed by the command.
709 A pipeline is a sequence of one or more commands separated
710 by the control operator
712 The standard output of all but
713 the last command is connected to the standard input
715 The standard output of the last
716 command is inherited from the shell, as usual.
718 The format for a pipeline is:
720 .D1 Oo Li \&! Oc Ar command1 Op Li \&| Ar command2 ...
722 The standard output of
724 is connected to the standard input of
726 The standard input, standard output, or
727 both of a command is considered to be assigned by the
728 pipeline before any redirection specified by redirection
729 operators that are part of the command.
731 If the pipeline is not in the background (discussed later),
732 the shell waits for all commands to complete.
736 does not precede the pipeline, the
737 exit status is the exit status of the last command specified
739 Otherwise, the exit status is the logical
740 NOT of the exit status of the last command.
742 the last command returns zero, the exit status is 1; if
743 the last command returns greater than zero, the exit status
746 Because pipeline assignment of standard input or standard
747 output or both takes place before redirection, it can be
748 modified by redirection.
751 .Dl "command1 2>&1 | command2"
753 sends both the standard output and standard error of
755 to the standard input of
760 or newline terminator causes the preceding
762 (described below in the section called
763 .Sx Short-Circuit List Operators )
764 to be executed sequentially;
767 causes asynchronous execution of the preceding AND-OR-list.
769 Note that unlike some other shells,
771 executes each process in the pipeline as a child of the
774 Shell built-in commands are the exception to this rule.
775 They are executed in the current shell, although they do not affect its
776 environment when used in pipelines.
777 .Ss Background Commands (&)
778 If a command is terminated by the control operator ampersand
780 the shell executes the command asynchronously;
781 the shell does not wait for the command to finish
782 before executing the next command.
784 The format for running a command in background is:
786 .D1 Ar command1 Li & Op Ar command2 Li & Ar ...
788 If the shell is not interactive, the standard input of an
789 asynchronous command is set to
791 .Ss Lists (Generally Speaking)
792 A list is a sequence of zero or more commands separated by
793 newlines, semicolons, or ampersands,
794 and optionally terminated by one of these three characters.
796 list are executed in the order they are written.
797 If command is followed by an ampersand, the shell starts the
798 command and immediately proceeds onto the next command;
799 otherwise it waits for the command to terminate before
800 proceeding to the next one.
801 .Ss Short-Circuit List Operators
805 are AND-OR list operators.
807 executes the first command, and then executes the second command
808 if the exit status of the first command is zero.
810 is similar, but executes the second command if the exit
811 status of the first command is nonzero.
815 both have the same priority.
816 .Ss Flow-Control Constructs (if, while, for, case)
820 .Bd -unfilled -offset indent -compact
824 .Ic then Ar list Oc Ar ...
832 .Bd -unfilled -offset indent -compact
838 The two lists are executed repeatedly while the exit status of the
842 command is similar, but has the word
847 repeat until the exit status of the first list is zero.
852 .Bd -unfilled -offset indent -compact
853 .Ic for Ar variable Op Ic in Ar word ...
860 and the following words are omitted,
863 The words are expanded, and then the list is executed
864 repeatedly with the variable set to each word in turn.
869 commands may be replaced with
879 .D1 Ic break Op Ar num
880 .D1 Ic continue Op Ar num
884 command terminates the
893 command continues with the next iteration of the innermost loop.
894 These are implemented as special built-in commands.
899 .Bd -unfilled -offset indent -compact
900 .Ic case Ar word Ic in
901 .Ar pattern Ns Li ) Ar list Li ;;
906 The pattern can actually be one or more patterns
915 command is the exit code of the last command executed in the list or
916 zero if no patterns were matched.
917 .Ss Grouping Commands Together
918 Commands may be grouped by writing either
920 .D1 Li \&( Ns Ar list Ns Li \%)
924 .D1 Li { Ar list Ns Li \&; }
926 The first form executes the commands in a subshell.
927 Note that built-in commands thus executed do not affect the current shell.
928 The second form does not fork another shell,
929 so it is slightly more efficient.
930 Grouping commands together this way allows the user to
931 redirect their output as though they were one program:
932 .Bd -literal -offset indent
933 { echo -n "hello"; echo " world"; } > greeting
936 The syntax of a function definition is
938 .D1 Ar name Li \&( \&) Ar command
940 A function definition is an executable statement; when
941 executed it installs a function named
953 Variables may be declared to be local to a function by
957 This should appear as the first statement of a function,
960 .D1 Ic local Oo Ar variable ... Oc Op Fl
964 command is implemented as a built-in command.
966 When a variable is made local, it inherits the initial
967 value and exported and readonly flags from the variable
968 with the same name in the surrounding scope, if there is
970 Otherwise, the variable is initially unset.
972 uses dynamic scoping, so that if the variable
974 is made local to function
976 which then calls function
978 references to the variable
982 will refer to the variable
986 not to the global variable named
989 The only special parameter that can be made local is
993 local causes any shell options that are
996 command inside the function to be
997 restored to their original values when the function
1004 .D1 Ic return Op Ar exitstatus
1006 It terminates the current executional scope, returning from the previous
1007 nested function, sourced script, or shell instance, in that order.
1010 command is implemented as a special built-in command.
1011 .Ss Variables and Parameters
1012 The shell maintains a set of parameters.
1014 denoted by a name is called a variable.
1016 the shell turns all the environment variables into shell
1018 New variables can be set using the form
1020 .D1 Ar name Ns = Ns Ar value
1022 Variables set by the user must have a name consisting solely
1023 of alphabetics, numerics, and underscores.
1024 The first letter of a variable name must not be numeric.
1025 A parameter can also be denoted by a number
1026 or a special character as explained below.
1027 .Ss Positional Parameters
1028 A positional parameter is a parameter denoted by a number greater than zero.
1029 The shell sets these initially to the values of its command line
1030 arguments that follow the name of the shell script.
1033 built-in command can also be used to set or reset them.
1034 .Ss Special Parameters
1035 A special parameter is a parameter denoted by a special one-character
1037 The special parameters recognized by the
1041 are shown in the following list, exactly as they would appear in input
1042 typed by the user or in the source of a shell script.
1045 Expands to the positional parameters, starting from one.
1047 the expansion occurs within a double-quoted string
1048 it expands to a single field with the value of each parameter
1049 separated by the first character of the
1056 Expands to the positional parameters, starting from one.
1058 the expansion occurs within double-quotes, each positional
1059 parameter expands as a separate argument.
1060 If there are no positional parameters, the
1063 generates zero arguments, even when
1066 What this basically means, for example, is
1079 .Bd -literal -offset indent
1083 Expands to the number of positional parameters.
1085 Expands to the exit status of the most recent pipeline.
1087 (hyphen) Expands to the current option flags (the single-letter
1088 option names concatenated into a string) as specified on
1091 built-in command, or implicitly
1094 Expands to the process ID of the invoked shell.
1096 retains the same value of
1100 Expands to the process ID of the most recent background
1101 command executed from the current shell.
1103 pipeline, the process ID is that of the last command in the
1106 (zero) Expands to the name of the shell or shell script.
1109 This clause describes the various expansions that are
1111 Not all expansions are performed on
1112 every word, as explained later.
1114 Tilde expansions, parameter expansions, command substitutions,
1115 arithmetic expansions, and quote removals that occur within
1116 a single word expand to a single field.
1118 splitting or pathname expansion that can create multiple
1119 fields from a single word.
1120 The single exception to this rule is
1121 the expansion of the special parameter
1123 within double-quotes,
1124 as was described above.
1126 The order of word expansion is:
1129 Tilde Expansion, Parameter Expansion, Command Substitution,
1130 Arithmetic Expansion (these all occur at the same time).
1132 Field Splitting is performed on fields generated by step (1)
1137 Pathname Expansion (unless the
1139 option is in effect).
1146 character is used to introduce parameter expansion, command
1147 substitution, or arithmetic evaluation.
1148 .Ss Tilde Expansion (substituting a user's home directory)
1149 A word beginning with an unquoted tilde character
1152 subjected to tilde expansion.
1153 All the characters up to a slash
1155 or the end of the word are treated as a username
1156 and are replaced with the user's home directory.
1158 username is missing (as in
1160 the tilde is replaced with the value of the
1162 variable (the current user's home directory).
1163 .Ss Parameter Expansion
1164 The format for parameter expansion is as follows:
1166 .D1 Li ${ Ns Ar expression Ns Li }
1170 consists of all characters until the matching
1174 escaped by a backslash or within a quoted string, and characters in
1175 embedded arithmetic expansions, command substitutions, and variable
1176 expansions, are not examined in determining the matching
1179 The simplest form for parameter expansion is:
1181 .D1 Li ${ Ns Ar parameter Ns Li }
1183 The value, if any, of
1187 The parameter name or symbol can be enclosed in braces, which are
1188 optional except for positional parameters with more than one digit or
1189 when parameter is followed by a character that could be interpreted as
1191 If a parameter expansion occurs inside double-quotes:
1194 Pathname expansion is not performed on the results of the
1197 Field splitting is not performed on the results of the
1198 expansion, with the exception of the special parameter
1202 In addition, a parameter expansion can be modified by using one of the
1204 .Bl -tag -width indent
1205 .It Li ${ Ns Ar parameter Ns Li :- Ns Ar word Ns Li }
1209 is unset or null, the expansion of
1211 is substituted; otherwise, the value of
1214 .It Li ${ Ns Ar parameter Ns Li := Ns Ar word Ns Li }
1215 Assign Default Values.
1218 is unset or null, the expansion of
1226 Only variables, not positional
1227 parameters or special parameters, can be
1228 assigned in this way.
1229 .It Li ${ Ns Ar parameter Ns Li :? Ns Oo Ar word Oc Ns Li }
1230 Indicate Error if Null or Unset.
1233 is unset or null, the expansion of
1235 (or a message indicating it is unset if
1237 is omitted) is written to standard
1238 error and the shell exits with a nonzero
1240 Otherwise, the value of
1244 interactive shell need not exit.
1245 .It Li ${ Ns Ar parameter Ns Li :+ Ns Ar word Ns Li }
1246 Use Alternate Value.
1249 is unset or null, null is substituted;
1250 otherwise, the expansion of
1255 In the parameter expansions shown previously, use of the colon in the
1256 format results in a test for a parameter that is unset or null; omission
1257 of the colon results in a test for a parameter that is only unset.
1258 .Bl -tag -width indent
1259 .It Li ${# Ns Ar parameter Ns Li }
1261 The length in characters of
1266 The following four varieties of parameter expansion provide for substring
1268 In each case, pattern matching notation
1270 .Sx Shell Patterns ) ,
1271 rather than regular expression notation,
1272 is used to evaluate the patterns.
1273 If parameter is one of the special parameters
1277 the result of the expansion is unspecified.
1278 Enclosing the full parameter expansion string in double-quotes does not
1279 cause the following four varieties of pattern characters to be quoted,
1280 whereas quoting characters within the braces has this effect.
1281 .Bl -tag -width indent
1282 .It Li ${ Ns Ar parameter Ns Li % Ns Ar word Ns Li }
1283 Remove Smallest Suffix Pattern.
1286 is expanded to produce a pattern.
1288 parameter expansion then results in
1290 with the smallest portion of the
1291 suffix matched by the pattern deleted.
1292 .It Li ${ Ns Ar parameter Ns Li %% Ns Ar word Ns Li }
1293 Remove Largest Suffix Pattern.
1296 is expanded to produce a pattern.
1298 parameter expansion then results in
1300 with the largest portion of the
1301 suffix matched by the pattern deleted.
1302 .It Li ${ Ns Ar parameter Ns Li # Ns Ar word Ns Li }
1303 Remove Smallest Prefix Pattern.
1306 is expanded to produce a pattern.
1308 parameter expansion then results in
1310 with the smallest portion of the
1311 prefix matched by the pattern deleted.
1312 .It Li ${ Ns Ar parameter Ns Li ## Ns Ar word Ns Li }
1313 Remove Largest Prefix Pattern.
1316 is expanded to produce a pattern.
1318 parameter expansion then results in
1320 with the largest portion of the
1321 prefix matched by the pattern deleted.
1323 .Ss Command Substitution
1324 Command substitution allows the output of a command to be substituted in
1325 place of the command name itself.
1326 Command substitution occurs when
1327 the command is enclosed as follows:
1329 .D1 Li $( Ns Ar command Ns Li )\&
1331 or the backquoted version:
1333 .D1 Li ` Ns Ar command Ns Li `
1335 The shell expands the command substitution by executing command in a
1336 subshell environment and replacing the command substitution
1337 with the standard output of the command,
1338 removing sequences of one or more newlines at the end of the substitution.
1339 Embedded newlines before the end of the output are not removed;
1340 however, during field splitting, they may be translated into spaces
1341 depending on the value of
1343 and the quoting that is in effect.
1344 .Ss Arithmetic Expansion
1345 Arithmetic expansion provides a mechanism for evaluating an arithmetic
1346 expression and substituting its value.
1347 The format for arithmetic expansion is as follows:
1349 .D1 Li $(( Ns Ar expression Ns Li ))
1353 is treated as if it were in double-quotes, except
1354 that a double-quote inside the expression is not treated specially.
1356 shell expands all tokens in the
1358 for parameter expansion,
1359 command substitution, and quote removal.
1361 Next, the shell treats this as an arithmetic expression and
1362 substitutes the value of the expression.
1363 .Ss White Space Splitting (Field Splitting)
1364 After parameter expansion, command substitution, and
1365 arithmetic expansion the shell scans the results of
1366 expansions and substitutions that did not occur in double-quotes for
1367 field splitting and multiple fields can result.
1369 The shell treats each character of the
1371 variable as a delimiter and uses
1372 the delimiters to split the results of parameter expansion and command
1373 substitution into fields.
1374 .Ss Pathname Expansion (File Name Generation)
1378 file name generation is performed
1379 after word splitting is complete.
1381 viewed as a series of patterns, separated by slashes.
1383 process of expansion replaces the word with the names of
1384 all existing files whose names can be formed by replacing
1385 each pattern with a string that matches the specified pattern.
1386 There are two restrictions on this: first, a pattern cannot match
1387 a string containing a slash, and second,
1388 a pattern cannot match a string starting with a period
1389 unless the first character of the pattern is a period.
1390 The next section describes the patterns used for both
1391 Pathname Expansion and the
1395 A pattern consists of normal characters, which match themselves,
1396 and meta-characters.
1397 The meta-characters are
1403 These characters lose their special meanings if they are quoted.
1404 When command or variable substitution is performed and the dollar sign
1405 or back quotes are not double-quoted, the value of the
1406 variable or the output of the command is scanned for these
1407 characters and they are turned into meta-characters.
1411 matches any string of characters.
1414 matches any single character.
1417 introduces a character class.
1418 The end of the character class is indicated by a
1426 rather than introducing a character class.
1427 A character class matches any of the characters between the square brackets.
1428 A range of characters may be specified using a minus sign.
1429 The character class may be complemented by making an exclamation point
1431 the first character of the character class.
1435 in a character class, make it the first character listed
1441 make it the first or last character listed.
1442 .Ss Built-in Commands
1443 This section lists the commands which
1444 are built-in because they need to perform some operation
1445 that cannot be performed by a separate process.
1447 these, built-in versions of essential utilities
1448 are provided for efficiency.
1449 .Bl -tag -width indent
1451 A null command that returns a 0 (true) exit value.
1453 The commands in the specified file are read and executed by the shell.
1456 command may be used to return to the
1463 characters, it is used as is.
1464 Otherwise, the shell searches the
1467 If it is not found in the
1469 it is sought in the current working directory.
1471 A built-in equivalent of
1473 .It Ic alias Oo Ar name Ns Oo = Ns Ar string Oc ... Oc
1475 .Ar name Ns = Ns Ar string
1476 is specified, the shell defines the alias
1482 is specified, the value of the alias
1485 With no arguments, the
1487 built-in command prints the names and values of all defined aliases
1490 Alias values are written with appropriate quoting so that they are
1491 suitable for re-input to the shell.
1495 .It Ic bg Op Ar job ...
1496 Continue the specified jobs
1497 (or the current job if no jobs are given)
1499 .It Ic builtin Ar cmd Op Ar arg ...
1500 Execute the specified built-in command,
1502 This is useful when the user wishes to override a shell function
1503 with the same name as a built-in command.
1504 .It Ic bind Oo Fl aeklrsv Oc Oo Ar key Oo Ar command Oc Oc
1505 List or alter key bindings for the line editor.
1506 This command is documented in
1508 .It Ic cd Oo Fl L | P Oc Op Ar directory
1509 Switch to the specified
1511 or to the directory specified in the
1513 environment variable if no
1522 then the directories listed in the
1525 searched for the specified
1529 is unset, the current directory is searched.
1532 is the same as that of
1534 In an interactive shell,
1537 command will print out the name of the directory
1538 that it actually switched to
1539 if this is different from the name that the user gave.
1540 These may be different either because the
1542 mechanism was used or because a symbolic link was crossed.
1546 option is specified,
1548 is handled physically and symbolic links are resolved before
1550 components are processed.
1553 option is specified,
1555 is handled logically.
1556 This is the default.
1561 .It Ic command Oo Fl p Oc Op Ar utility Op Ar argument ...
1562 .It Ic command Oo Fl v | V Oc Op Ar utility
1563 The first form of invocation executes the specified
1565 as a simple command (see the
1571 option is specified, the command search is performed using a
1574 that is guaranteed to find all of the standard utilities.
1578 option is specified,
1580 is not executed but a description of its interpretation by the shell is
1582 For ordinary commands the output is the path name; for shell built-in
1583 commands, shell functions and keywords only the name is written.
1584 Aliases are printed as
1585 .Dq Ic alias Ar name Ns = Ns Ar value .
1589 option is identical to
1591 except for the output.
1593 .Dq Ar utility Ic is Ar description
1599 a special shell builtin,
1606 .It Ic echo Oo Fl e | n Oc Op Ar string ...
1607 Print a space-separated list of the arguments to the standard output
1608 and append a newline character.
1609 .Bl -tag -width indent
1611 Suppress the output of the trailing newline.
1613 Process C-style backslash escape sequences.
1616 command understands the following character escapes:
1617 .Bl -tag -width indent
1619 Alert (ring the terminal bell)
1623 Suppress the trailing newline (this has the side-effect of truncating the
1624 line if it is not the last character)
1642 (Zero) The character whose octal value is
1648 is not enclosed in quotes then the backslash itself must be escaped
1649 with a backslash to protect it from the shell.
1651 .Bd -literal -offset indent
1660 $ echo -e a\e\e\e\eb
1669 options may be specified.
1670 .It Ic eval Ar string ...
1671 Concatenate all the arguments with spaces.
1672 Then re-parse and execute the command.
1673 .It Ic exec Op Ar command Op arg ...
1677 the shell process is replaced with the specified program
1678 (which must be a real program, not a shell built-in command or function).
1679 Any redirections on the
1681 command are marked as permanent,
1682 so that they are not undone when the
1685 .It Ic exit Op Ar exitstatus
1686 Terminate the shell process.
1690 it is used as the exit status of the shell;
1691 otherwise the exit status of the preceding command is used.
1692 The exit status should be an integer between 0 and 255.
1693 .It Ic export Ar name ...
1694 .It Ic export Op Fl p
1695 The specified names are exported so that they will
1696 appear in the environment of subsequent commands.
1697 The only way to un-export a variable is to
1700 The shell allows the value of a variable to be set
1701 at the same time as it is exported by writing
1703 .D1 Ic export Ar name Ns = Ns Ar value
1705 With no arguments the
1707 command lists the names
1708 of all exported variables.
1711 option is specified, the exported variables are printed as
1712 .Dq Ic export Ar name Ns = Ns Ar value
1713 lines, suitable for re-input to the shell.
1715 A null command that returns a non-zero (false) exit value.
1716 .It Ic fc Oo Fl e Ar editor Oc Op Ar first Op Ar last
1717 .It Ic fc Fl l Oo Fl nr Oc Op Ar first Op Ar last
1718 .It Ic fc Fl s Oo Ar old Ns = Ns Ar new Oc Op Ar first
1721 built-in command lists, or edits and re-executes,
1722 commands previously entered to an interactive shell.
1723 .Bl -tag -width indent
1725 Use the editor named by
1727 to edit the commands.
1730 string is a command name,
1731 subject to search via the
1736 variable is used as a default when
1741 is null or unset, the value of the
1748 is used as the editor.
1750 List the commands rather than invoking
1752 The commands are written in the
1753 sequence indicated by the
1757 operands, as affected by
1759 with each command preceded by the command number.
1761 Suppress command numbers when listing with
1764 Reverse the order of the commands listed
1773 Re-execute the command without invoking an editor.
1776 Select the commands to list or edit.
1777 The number of previous commands that can be accessed
1778 are determined by the value of the
1785 or both are one of the following:
1786 .Bl -tag -width indent
1787 .It Oo Cm + Oc Ns Ar num
1788 A positive number representing a command number;
1789 command numbers can be displayed with the
1793 A negative decimal number representing the
1794 command that was executed
1797 commands previously.
1798 For example, \-1 is the immediately previous command.
1800 A string indicating the most recently entered command
1801 that begins with that string.
1803 .Ar old Ns = Ns Ar new
1804 operand is not also specified with
1806 the string form of the first operand cannot contain an embedded equal sign.
1810 The following environment variables affect the execution of
1812 .Bl -tag -width ".Ev HISTSIZE"
1814 Name of the editor to use for history editing.
1816 The number of previous commands that are accessible.
1821 or the current job to the foreground.
1822 .It Ic getopts Ar optstring var
1829 command deprecates the older
1832 The first argument should be a series of letters, each possibly
1833 followed by a colon which indicates that the option takes an argument.
1834 The specified variable is set to the parsed option.
1836 the next argument is placed into the shell variable
1838 If an option takes an argument, it is placed into the shell variable
1840 If an invalid option is encountered,
1844 It returns a false value (1) when it encounters the end of the options.
1845 .It Ic hash Oo Fl rv Oc Op Ar command ...
1846 The shell maintains a hash table which remembers the locations of commands.
1847 With no arguments whatsoever, the
1849 command prints out the contents of this table.
1850 Entries which have not been looked at since the last
1852 command are marked with an asterisk;
1853 it is possible for these entries to be invalid.
1857 command removes each specified
1859 from the hash table (unless they are functions) and then locates it.
1864 prints the locations of the commands as it finds them.
1869 command to delete all the entries in the hash table except for functions.
1870 .It Ic jobid Op Ar job
1871 Print the process IDs of the processes in the specified
1875 argument is omitted, use the current job.
1876 .It Ic jobs Oo Fl lps Oc Op Ar job ...
1877 Print information about the specified jobs, or all jobs if no
1880 The information printed includes job ID, status and command name.
1884 option is specified, the PID of each job is also printed.
1887 option is specified, only the process IDs for the process group leaders
1888 are printed, one per line.
1891 option is specified, only the PIDs of the job commands are printed, one per
1893 .It Ic local Oo Ar variable ... Oc Op Fl
1897 .It Ic pwd Op Fl L | P
1898 Print the path of the current directory.
1899 The built-in command may
1900 differ from the program of the same name because the
1901 built-in command remembers what the current directory
1902 is rather than recomputing it each time.
1905 However, if the current directory is
1907 the built-in version of
1909 will continue to print the old name for the directory.
1913 option is specified, symbolic links are resolved.
1916 option is specified, the shell's notion of the current directory
1917 is printed (symbolic links are not resolved).
1918 This is the default.
1919 .It Ic read Oo Fl p Ar prompt Oc Oo
1920 .Fl t Ar timeout Oc Oo Fl er Oc Ar variable ...
1926 and the standard input is a terminal.
1928 read from the standard input.
1929 The trailing newline
1930 is deleted from the line and the line is split as
1931 described in the section on
1932 .Sx White Space Splitting (Field Splitting)
1934 the pieces are assigned to the variables in order.
1935 If there are more pieces than variables, the remaining
1936 pieces (along with the characters in
1938 that separated them)
1939 are assigned to the last variable.
1940 If there are more variables than pieces, the remaining
1941 variables are assigned the null string.
1943 Backslashes are treated specially, unless the
1947 If a backslash is followed by
1948 a newline, the backslash and the newline will be
1950 If a backslash is followed by any other
1951 character, the backslash will be deleted and the following
1952 character will be treated as though it were not in
1958 option is specified and the
1960 elapses before a complete line of input is supplied,
1963 command will return an exit status of 1 without assigning any values.
1966 value may optionally be followed by one of
1971 to explicitly specify seconds, minutes or hours.
1972 If none is supplied,
1978 option exists only for backward compatibility with older scripts.
1979 .It Ic readonly Oo Fl p Oc Op Ar name ...
1982 is marked as read only,
1983 so that it cannot be subsequently modified or unset.
1984 The shell allows the value of a variable to be set
1985 at the same time as it is marked read only
1986 by using the following form:
1988 .D1 Ic readonly Ar name Ns = Ns Ar value
1990 With no arguments the
1992 command lists the names of all read only variables.
1995 option is specified, the read-only variables are printed as
1996 .Dq Ic readonly Ar name Ns = Ns Ar value
1997 lines, suitable for re-input to the shell.
1998 .It Ic return Op Ar exitstatus
2002 .It Ic set Oo Fl /+abCEefIimnpTuVvx Oc Oo Fl /+o Ar longname Oc Oo
2003 .Fl c Ar string Oc Op Fl - Ar arg ...
2006 command performs three different functions:
2009 With no arguments, it lists the values of all shell variables.
2011 If options are given,
2012 either in short form or using the long
2013 .Dq Fl /+o Ar longname
2015 it sets or clears the specified options as described in the section called
2016 .Sx Argument List Processing .
2020 option is specified,
2022 will replace the shell's positional parameters with the subsequent
2024 If no arguments follow the
2027 all the positional parameters will be cleared,
2028 which is equivalent to executing the command
2032 flag may be omitted when specifying arguments to be used
2033 as positional replacement parameters.
2034 This is not recommended,
2035 because the first argument may begin with a dash
2041 command will interpret as a request to enable or disable options.
2043 .It Ic setvar Ar variable value
2044 Assigns the specified
2050 command is intended to be used in functions that
2051 assign values to variables whose names are passed as parameters.
2052 In general it is better to write
2053 .Dq Ar variable Ns = Ns Ar value
2056 .It Ic shift Op Ar n
2057 Shift the positional parameters
2062 A shift sets the value of
2071 decreasing the value of
2074 If there are zero positional parameters, shifting does not do anything.
2076 A built-in equivalent of
2079 Print the amount of time spent executing the shell and its children.
2080 The first output line shows the user and system times for the shell
2081 itself, the second one contains the user and system times for the
2083 .It Ic trap Oo Ar action Oc Ar signal ...
2085 Cause the shell to parse and execute
2090 The signals are specified by name or number.
2091 In addition, the pseudo-signal
2093 may be used to specify an
2095 that is performed when the shell terminates.
2098 may be an empty string or a dash
2100 the former causes the specified signal to be ignored
2101 and the latter causes the default action to be taken.
2104 is another way to request the default action, for compatibility reasons this
2105 usage is not recommended though.
2106 When the shell forks off a subshell,
2107 it resets trapped (but not ignored) signals to the default action.
2110 command has no effect on signals that were ignored on entry to the shell.
2116 command to display a list of valid signal names.
2118 A null command that returns a 0 (true) exit value.
2119 .It Ic type Op Ar name ...
2122 as a command and print the resolution of the command search.
2123 Possible resolutions are:
2124 shell keyword, alias, special shell builtin, shell builtin, command,
2127 For aliases the alias expansion is printed;
2128 for commands and tracked aliases
2129 the complete pathname of the command is printed.
2130 .It Ic ulimit Oo Fl HSabcdflmnpstuv Oc Op Ar limit
2131 Set or display resource limits (see
2135 is specified, the named resource will be set;
2136 otherwise the current resource value will be displayed.
2140 is specified, the hard limits will be set or displayed.
2141 While everybody is allowed to reduce a hard limit,
2142 only the superuser can increase it.
2146 specifies the soft limits instead.
2147 When displaying limits,
2153 The default is to display the soft limits,
2154 and to set both the hard and the soft limits.
2160 command to display all resources.
2163 is not acceptable in this mode.
2165 The remaining options specify which resource value is to be
2166 displayed or modified.
2167 They are mutually exclusive.
2168 .Bl -tag -width indent
2170 The maximum size of socket buffer usage, in bytes.
2171 .It Fl c Ar coredumpsize
2172 The maximal size of core dump files, in 512-byte blocks.
2173 .It Fl d Ar datasize
2174 The maximal size of the data segment of a process, in kilobytes.
2175 .It Fl f Ar filesize
2176 The maximal size of a file, in 512-byte blocks.
2177 .It Fl l Ar lockedmem
2178 The maximal size of memory that can be locked by a process, in
2180 .It Fl m Ar memoryuse
2181 The maximal resident set size of a process, in kilobytes.
2183 The maximal number of descriptors that could be opened by a process.
2184 .It Fl p Ar pseudoterminals
2185 The maximal number of pseudo-terminals for this user ID.
2186 .It Fl s Ar stacksize
2187 The maximal size of the stack segment, in kilobytes.
2189 The maximal amount of CPU time to be used by each process, in seconds.
2190 .It Fl u Ar userproc
2191 The maximal number of simultaneous processes for this user ID.
2192 .It Fl v Ar virtualmem
2193 The maximal virtual size of a process, in kilobytes.
2195 .It Ic umask Oo Fl S Oc Op Ar mask
2196 Set the file creation mask (see
2198 to the octal or symbolic (see
2202 If the argument is omitted, the current mask value is printed.
2205 option is specified, the output is symbolic, otherwise the output is octal.
2206 .It Ic unalias Oo Fl a Oc Op Ar name ...
2207 The specified alias names are removed.
2210 is specified, all aliases are removed.
2211 .It Ic unset Oo Fl fv Oc Ar name ...
2212 The specified variables or functions are unset and unexported.
2215 option is specified or no options are given, the
2217 arguments are treated as variable names.
2220 option is specified, the
2222 arguments are treated as function names.
2223 .It Ic wait Op Ar job
2224 Wait for the specified
2226 to complete and return the exit status of the last process in the
2228 If the argument is omitted, wait for all jobs to complete
2229 and return an exit status of zero.
2231 .Ss Commandline Editing
2234 is being used interactively from a terminal, the current command
2235 and the command history
2239 .Sx Built-in Commands )
2242 command line editing.
2243 This mode uses commands similar
2244 to a subset of those described in the
2262 can be switched between insert mode and command mode by typing
2266 while in command mode will pass the line to the shell.
2269 .Dq Li "set -o emacs"
2272 command can be used to enable a subset of
2274 command line editing features.
2276 The following environment variables affect the execution of
2278 .Bl -tag -width ".Ev HISTSIZE"
2280 The search path used with the
2284 The fallback editor used with the
2287 If not set, the default editor is
2290 The default editor used with the
2294 The number of previous commands that are accessible.
2296 The starting directory of
2299 Input Field Separators.
2300 This is normally set to
2306 .Sx White Space Splitting
2307 section for more details.
2309 The name of a mail file, that will be checked for the arrival of new
2316 separated list of file names, for the shell to check for incoming
2318 This environment setting overrides the
2321 There is a maximum of 10 mailboxes that can be monitored at once.
2323 The default search path for executables.
2326 section for details.
2328 The primary prompt string, which defaults to
2330 unless you are the superuser, in which case it defaults to
2333 The secondary prompt string, which defaults to
2336 The prefix for the trace output (if
2342 The default terminal setting for the shell.
2343 This is inherited by children of the shell, and is used in the history
2347 Errors that are detected by the shell, such as a syntax error, will
2348 cause the shell to exit with a non-zero exit status.
2349 If the shell is not an interactive shell, the execution of the shell
2350 file will be aborted.
2351 Otherwise the shell will return the exit status of the last command
2354 builtin is used with a numeric argument, it
2355 will return the argument.
2374 command, the Thompson shell, appeared in
2376 It was superseded in
2378 by the Bourne shell, which inherited the name
2383 was rewritten in 1989 under the
2385 license after the Bourne shell from
2390 was originally written by
2391 .An Kenneth Almquist .
2395 utility does not recognize multibyte characters.
projects / FreeBSD / releng / 8.0.git / blob