2 .\" Copyright (c) 1991, 1993
3 .\" The Regents of the University of California. All rights reserved.
5 .\" This code is derived from software contributed to Berkeley by
8 .\" Redistribution and use in source and binary forms, with or without
9 .\" modification, are permitted provided that the following conditions
11 .\" 1. Redistributions of source code must retain the above copyright
12 .\" notice, this list of conditions and the following disclaimer.
13 .\" 2. Redistributions in binary form must reproduce the above copyright
14 .\" notice, this list of conditions and the following disclaimer in the
15 .\" documentation and/or other materials provided with the distribution.
16 .\" 4. Neither the name of the University nor the names of its contributors
17 .\" may be used to endorse or promote products derived from this software
18 .\" without specific prior written permission.
20 .\" THIS SOFTWARE IS PROVIDED BY THE REGENTS AND CONTRIBUTORS ``AS IS'' AND
21 .\" ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
22 .\" IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
23 .\" ARE DISCLAIMED. IN NO EVENT SHALL THE REGENTS OR CONTRIBUTORS BE LIABLE
24 .\" FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
25 .\" DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS
26 .\" OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION)
27 .\" HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT
28 .\" LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY
29 .\" OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
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
60 shell clone like pdksh.
62 designated by POSIX, plus a few Berkeley extensions, are being
63 incorporated into this shell.
64 This man page is not intended to be a tutorial nor a complete
65 specification of the shell.
67 The shell is a command that reads lines from
68 either a file or the terminal, interprets them, and
69 generally executes other commands.
70 It is the program that is started when a user logs into the system,
71 although a user can select a different shell with the
75 implements a language that has flow control constructs,
76 a macro facility that provides a variety of features in
77 addition to data storage, along with built-in history and line
79 It incorporates many features to
80 aid interactive use and has the advantage that the interpretative
81 language is common to both interactive and non-interactive
83 That is, commands can be typed directly
84 to the running shell or can be put into a file,
85 which can be executed directly by the shell.
88 .\" XXX This next sentence is incredibly confusing.
90 If no arguments are present and if the standard input of the shell
91 is connected to a terminal
95 the shell is considered an interactive shell.
97 generally prompts before each command and handles programming
98 and command errors differently (as described below).
99 When first starting, the shell inspects argument 0, and
100 if it begins with a dash
102 the shell is also considered a login shell.
103 This is normally done automatically by the system
104 when the user first logs in.
105 A login shell first reads commands
111 If the environment variable
113 is set on entry to a shell, or is set in the
115 of a login shell, the shell then reads commands from the file named in
117 Therefore, a user should place commands that are to be executed only
120 file, and commands that are executed for every shell inside the
125 variable to some file by placing the following line in the file
127 in the home directory,
130 the filename desired:
132 .Dl ENV=$HOME/.shinit; export ENV
134 The first non-option argument specified on the command line
135 will be treated as the
136 name of a file from which to read commands (a shell script), and
137 the remaining arguments are set as the positional parameters
138 of the shell ($1, $2, etc).
139 Otherwise, the shell reads commands
140 from its standard input.
142 Unlike older versions of
146 script is only sourced on invocation of interactive shells.
148 closes a well-known, and sometimes easily exploitable security
149 hole related to poorly thought out
152 .Ss Argument List Processing
153 All of the single letter options to
155 have a corresponding long name,
156 with the exception of
160 These long names are provided next to the single letter options
161 in the descriptions below.
162 The long name for an option may be specified as an argument to the
166 Once the shell is running,
167 the long name for an option may be specified as an argument to the
172 (described later in the section called
173 .Sx Built-in Commands ) .
174 Introducing an option with a dash
184 will stop option processing and will force the remaining
185 words on the command line to be treated as arguments.
190 options do not have long names.
191 They take arguments and are described after the single letter options.
192 .Bl -tag -width indent
193 .It Fl a Li allexport
194 Flag variables for export when assignments are made to them.
196 Enable asynchronous notification of background job
199 .It Fl C Li noclobber
200 Do not overwrite existing files with
205 command line editor (disables the
207 option if it has been set).
209 Exit immediately if any untested command fails in non-interactive mode.
210 The exit status of a command is considered to be
211 explicitly tested if the command is part of the list used to control
213 .Ic if , elif , while ,
216 if the command is the left
221 operator; or if the command is a pipeline preceded by the
224 If a shell function is executed and its exit status is explicitly
225 tested, all commands of the function are considered to be tested as
228 Disable pathname expansion.
229 .It Fl I Li ignoreeof
232 from input when in interactive mode.
233 .It Fl i Li interactive
234 Force the shell to behave interactively.
236 Turn on job control (set automatically when interactive).
238 If not interactive, read commands but do not
240 This is useful for checking the
241 syntax of shell scripts.
243 Change the default for the
249 (logical directory layout)
252 (physical directory layout).
253 .It Fl p Li privileged
254 Turn on privileged mode.
255 This mode is enabled on startup
256 if either the effective user or group id is not equal to the
257 real user or group id.
258 Turning this mode off sets the
259 effective user and group ids to the real user and group ids.
260 When this mode is enabled for interactive shells, the file
261 .Pa /etc/suid_profile
262 is sourced instead of
266 is sourced, and the contents of the
268 variable are ignored.
270 Read commands from standard input (set automatically
271 if no file arguments are present).
273 no effect when set after the shell has already started
274 running (i.e., when set with the
277 .It Fl T Li trapsasync
278 When waiting for a child, execute traps immediately.
279 If this option is not set,
280 traps are executed after the child exits,
283 This nonstandard option is useful for putting guarding shells around
284 children that block signals.
285 The surrounding shell may kill the child
286 or it may just return control to the tty and leave the child alone,
288 .Bd -literal -offset indent
289 sh -T -c "trap 'exit 1' 2 ; some-blocking-program"
293 Write a message to standard error when attempting
294 to expand a variable that is not set, and if the
295 shell is not interactive, exit immediately.
299 command line editor (disables
303 The shell writes its input to standard error
305 Useful for debugging.
308 (preceded by the value of the
311 to standard error before it is executed.
312 Useful for debugging.
317 option causes the commands to be read from the
319 operand instead of from the standard input.
320 Keep in mind that this option only accepts a single string as its
321 argument, hence multi-word strings must be quoted.
325 option takes as its only argument the long name of an option
326 to be enabled or disabled.
327 For example, the following two invocations of
329 both enable the built-in
332 .Bd -literal -offset indent
337 If used without an argument, the
339 option displays the current option settings in a human-readable format.
342 is used without an argument, the current option settings are output
343 in a format suitable for re-input into the shell.
344 .Ss Lexical Structure
345 The shell reads input in terms of lines from a file and breaks
346 it up into words at whitespace (blanks and tabs), and at
350 which are special to the shell.
351 There are two types of operators: control operators and
352 redirection operators (their meaning is discussed later).
353 The following is a list of valid operators:
354 .Bl -tag -width indent
355 .It Control operators:
356 .Bl -column "XXX" "XXX" "XXX" "XXX" "XXX" -offset center -compact
357 .It Li & Ta Li && Ta Li ( Ta Li ) Ta Li \en
358 .It Li ;; Ta Li ; Ta Li | Ta Li ||
360 .It Redirection operators:
361 .Bl -column "XXX" "XXX" "XXX" "XXX" "XXX" -offset center -compact
362 .It Li < Ta Li > Ta Li << Ta Li >> Ta Li <>
363 .It Li <& Ta Li >& Ta Li <<- Ta Li >|
369 introduces a comment if used at the beginning of a word.
370 The word starting with
372 and the rest of the line are ignored.
374 Quoting is used to remove the special meaning of certain characters
375 or words to the shell, such as operators, whitespace, keywords,
378 There are three types of quoting: matched single quotes,
379 matched double quotes, and backslash.
380 .Bl -tag -width indent
382 Enclosing characters in single quotes preserves the literal
383 meaning of all the characters (except single quotes, making
384 it impossible to put single-quotes in a single-quoted string).
386 Enclosing characters within double quotes preserves the literal
387 meaning of all characters except dollarsign
393 The backslash inside double quotes is historically weird.
394 It remains literal unless it precedes the following characters,
395 which it serves to quote:
396 .Bl -column "XXX" "XXX" "XXX" "XXX" "XXX" -offset center -compact
397 .It Li $ Ta Li ` Ta Li \&" Ta Li \e\ Ta Li \en
400 A backslash preserves the literal meaning of the following
401 character, with the exception of the newline character
403 A backslash preceding a newline is treated as a line continuation.
406 Reserved words are words that have special meaning to the
407 shell and are recognized at the beginning of a line and
408 after a control operator.
409 The following are reserved words:
410 .Bl -column "doneXX" "elifXX" "elseXX" "untilXX" "whileX" -offset center
411 .It Li \&! Ta { Ta } Ta Ic case Ta Ic do
412 .It Ic done Ta Ic elif Ta Ic else Ta Ic esac Ta Ic fi
413 .It Ic for Ta Ic if Ta Ic then Ta Ic until Ta Ic while
416 An alias is a name and corresponding value set using the
419 Whenever a reserved word may occur (see above),
420 and after checking for reserved words, the shell
421 checks the word to see if it matches an alias.
422 If it does, it replaces it in the input stream with its value.
423 For example, if there is an alias called
428 .Bd -literal -offset indent
433 .Bd -literal -offset indent
437 Aliases provide a convenient way for naive users to
438 create shorthands for commands without having to learn how
439 to create functions with arguments.
441 used to create lexically obscure code.
442 This use is discouraged.
444 An alias name may be escaped in a command line, so that it is not
445 replaced by its alias value, by using quoting characters within or
446 adjacent to the alias name.
447 This is most often done by prefixing
448 an alias name with a backslash to execute a function, built-in, or
449 normal program with the same name.
454 The shell interprets the words it reads according to a
455 language, the specification of which is outside the scope
456 of this man page (refer to the BNF in the
459 Essentially though, a line is read and if
460 the first word of the line (or after a control operator)
461 is not a reserved word, then the shell has recognized a
463 Otherwise, a complex command or some
464 other special construct may have been recognized.
466 If a simple command has been recognized, the shell performs
467 the following actions:
470 Leading words of the form
472 are stripped off and assigned to the environment of
474 Redirection operators and
475 their arguments (as described below) are stripped
476 off and saved for processing.
478 The remaining words are expanded as described in
480 .Sx Word Expansions ,
481 and the first remaining word is considered the command
482 name and the command is located.
484 words are considered the arguments of the command.
485 If no command name resulted, then the
487 variable assignments recognized in 1) affect the
490 Redirections are performed as described in
494 Redirections are used to change where a command reads its input
496 In general, redirections open, close, or
497 duplicate an existing reference to a file.
499 used for redirection is:
501 .Dl [n] redir-op file
505 is one of the redirection operators mentioned
507 The following gives some examples of how these
508 operators can be used.
509 Note that stdin and stdout are commonly used abbreviations
510 for standard input and standard output respectively.
511 .Bl -tag -width "1234567890XX" -offset indent
513 redirect stdout (or file descriptor n) to file
515 same as above, but override the
519 append stdout (or file descriptor n) to file
521 redirect stdin (or file descriptor n) from file
523 redirect stdin (or file descriptor n) to and from file
525 duplicate stdin (or file descriptor n1) from file descriptor n2
527 close stdin (or file descriptor n)
529 duplicate stdout (or file descriptor n1) to file descriptor n2
531 close stdout (or file descriptor n)
534 The following redirection is often called a
536 .Bd -literal -offset indent
543 All the text on successive lines up to the delimiter is
544 saved away and made available to the command on standard
545 input, or file descriptor n if it is specified.
547 as specified on the initial line is quoted, then the here-doc-text
548 is treated literally, otherwise the text is subjected to
549 parameter expansion, command substitution, and arithmetic
550 expansion (as described in the section on
551 .Sx Word Expansions ) .
557 in the here-doc-text are stripped.
558 .Ss Search and Execution
559 There are three types of commands: shell functions,
560 built-in commands, and normal programs.
561 The command is searched for (by name) in that order.
562 The three types of commands are all executed in a different way.
564 When a shell function is executed, all of the shell positional
565 parameters (except $0, which remains unchanged) are
566 set to the arguments of the shell function.
567 The variables which are explicitly placed in the environment of
568 the command (by placing assignments to them before the
569 function name) are made local to the function and are set
571 Then the command given in the function definition is executed.
572 The positional parameters are restored to their original values
573 when the command completes.
574 This all occurs within the current shell.
576 Shell built-in commands are executed internally to the shell, without
577 spawning a new process.
579 Otherwise, if the command name does not match a function
580 or built-in command, the command is searched for as a normal
581 program in the file system (as described in the next section).
582 When a normal program is executed, the shell runs the program,
583 passing the arguments and the environment to the program.
584 If the program is not a normal executable file
585 (i.e., if it does not begin with the
595 the shell will interpret the program in a subshell.
596 The child shell will reinitialize itself in this case,
597 so that the effect will be
598 as if a new shell had been invoked to handle the ad-hoc shell script,
599 except that the location of hashed commands located in
600 the parent shell will be remembered by the child.
602 Note that previous versions of this document
603 and the source code itself misleadingly and sporadically
604 refer to a shell script without a magic number
606 .Qq shell procedure .
608 When locating a command, the shell first looks to see if
609 it has a shell function by that name.
611 built-in command by that name.
612 If a built-in command is not found,
613 one of two things happen:
616 Command names containing a slash are simply executed without
617 performing any searches.
619 The shell searches each entry in
621 in turn for the command.
624 variable should be a series of
625 entries separated by colons.
626 Each entry consists of a
628 The current directory
629 may be indicated implicitly by an empty directory name,
630 or explicitly by a single period.
632 .Ss Command Exit Status
633 Each command has an exit status that can influence the behavior
634 of other shell commands.
635 The paradigm is that a command exits
636 with zero for normal or success, and non-zero for failure,
637 error, or a false indication.
638 The man page for each command
639 should indicate the various exit codes and what they mean.
640 Additionally, the built-in commands return exit codes, as does
641 an executed shell function.
643 If a command is terminated by a signal, its exit status is 128 plus
645 Signal numbers are defined in the header file
648 Complex commands are combinations of simple commands
649 with control operators or reserved words, together creating a larger complex
651 More generally, a command is one of the following:
652 .Bl -item -offset indent
658 list or compound-list
665 Unless otherwise stated, the exit status of a command is
666 that of the last simple command executed by the command.
668 A pipeline is a sequence of one or more commands separated
669 by the control operator |.
670 The standard output of all but
671 the last command is connected to the standard input
673 The standard output of the last
674 command is inherited from the shell, as usual.
676 The format for a pipeline is:
678 .Dl [!] command1 [ | command2 ...]
680 The standard output of command1 is connected to the standard
682 The standard input, standard output, or
683 both of a command is considered to be assigned by the
684 pipeline before any redirection specified by redirection
685 operators that are part of the command.
687 If the pipeline is not in the background (discussed later),
688 the shell waits for all commands to complete.
692 does not precede the pipeline, the
693 exit status is the exit status of the last command specified
695 Otherwise, the exit status is the logical
696 NOT of the exit status of the last command.
698 the last command returns zero, the exit status is 1; if
699 the last command returns greater than zero, the exit status
702 Because pipeline assignment of standard input or standard
703 output or both takes place before redirection, it can be
704 modified by redirection.
707 .Dl $ command1 2>&1 | command2
709 sends both the standard output and standard error of
711 to the standard input of
716 or newline terminator causes the preceding
718 (described below in the section called
719 .Sx Short-Circuit List Operators )
720 to be executed sequentially;
723 causes asynchronous execution of the preceding AND-OR-list.
725 Note that unlike some other shells,
727 executes each process in the pipeline as a child of the
730 Shell built-in commands are the exception to this rule.
731 They are executed in the current shell, although they do not affect its
732 environment when used in pipelines.
733 .Ss Background Commands (&)
734 If a command is terminated by the control operator ampersand
736 the shell executes the command asynchronously;
737 the shell does not wait for the command to finish
738 before executing the next command.
740 The format for running a command in background is:
741 .Bd -literal -offset indent
742 command1 & [command2 & ...]
745 If the shell is not interactive, the standard input of an
746 asynchronous command is set to /dev/null.
747 .Ss Lists (Generally Speaking)
748 A list is a sequence of zero or more commands separated by
749 newlines, semicolons, or ampersands,
750 and optionally terminated by one of these three characters.
752 list are executed in the order they are written.
753 If command is followed by an ampersand, the shell starts the
754 command and immediately proceeds onto the next command;
755 otherwise it waits for the command to terminate before
756 proceeding to the next one.
757 .Ss Short-Circuit List Operators
761 are AND-OR list operators.
763 executes the first command, and then executes the second command
764 if the exit status of the first command is zero.
766 is similar, but executes the second command if the exit
767 status of the first command is nonzero.
771 both have the same priority.
772 .Ss Flow-Control Constructs (if, while, for, case)
777 .\" XXX Use .Dl to work around broken handling of .Ic inside .Bd and .Ed .
781 .Dl [ Ic elif Ar list
782 .Dl Ic then Ar list ] ...
783 .Dl [ Ic else Ar list ]
793 The two lists are executed repeatedly while the exit status of the
797 command is similar, but has the word
802 repeat until the exit status of the first list is zero.
807 .Dl Ic for Ar variable Op Ic in Ar word ...
813 and the following words are omitted,
816 The words are expanded, and then the list is executed
817 repeatedly with the variable set to each word in turn.
822 commands may be replaced with
832 .Dl Ic break Op Ar num
833 .Dl Ic continue Op Ar num
837 command terminates the
846 command continues with the next iteration of the innermost loop.
847 These are implemented as built-in commands.
852 .Dl Ic case Ar word Ic in
857 The pattern can actually be one or more patterns
866 command is the exit code of the last command executed in the list or
867 zero if no patterns were matched.
868 .Ss Grouping Commands Together
869 Commands may be grouped by writing either
870 .Bd -literal -offset indent
875 .Bd -literal -offset indent
879 The first form executes the commands in a subshell.
880 Note that built-in commands thus executed do not affect the current shell.
881 The second form does not fork another shell,
882 so it is slightly more efficient.
883 Grouping commands together this way allows the user to
884 redirect their output as though they were one program:
885 .Bd -literal -offset indent
886 { echo -n "hello"; echo " world"; } > greeting
889 The syntax of a function definition is
890 .Bd -literal -offset indent
894 A function definition is an executable statement; when
895 executed it installs a function named name and returns an
897 The command is normally a list
903 Variables may be declared to be local to a function by
907 This should appear as the first statement of a function,
909 .Bd -ragged -offset indent
917 command is implemented as a built-in command.
919 When a variable is made local, it inherits the initial
920 value and exported and readonly flags from the variable
921 with the same name in the surrounding scope, if there is
923 Otherwise, the variable is initially unset.
925 uses dynamic scoping, so that if the variable
927 is made local to function
929 which then calls function
931 references to the variable
935 will refer to the variable
939 not to the global variable named
942 The only special parameter that can be made local is
946 local causes any shell options that are
947 changed via the set command inside the function to be
948 restored to their original values when the function
954 .Bd -ragged -offset indent
959 It terminates the current executional scope, returning from the previous
960 nested function, sourced script, or shell instance, in that order.
963 command is implemented as a built-in command.
964 .Ss Variables and Parameters
965 The shell maintains a set of parameters.
967 denoted by a name is called a variable.
969 the shell turns all the environment variables into shell
971 New variables can be set using the form
972 .Bd -literal -offset indent
976 Variables set by the user must have a name consisting solely
977 of alphabetics, numerics, and underscores.
978 The first letter of a variable name must not be numeric.
979 A parameter can also be denoted by a number
980 or a special character as explained below.
981 .Ss Positional Parameters
982 A positional parameter is a parameter denoted by a number greater than zero.
983 The shell sets these initially to the values of its command line
984 arguments that follow the name of the shell script.
987 built-in command can also be used to set or reset them.
988 .Ss Special Parameters
989 A special parameter is a parameter denoted by a special one-character
991 The special parameters recognized by the
995 are shown in the following list, exactly as they would appear in input
996 typed by the user or in the source of a shell script.
999 Expands to the positional parameters, starting from one.
1001 the expansion occurs within a double-quoted string
1002 it expands to a single field with the value of each parameter
1003 separated by the first character of the
1012 Expands to the positional parameters, starting from one.
1014 the expansion occurs within double-quotes, each positional
1015 parameter expands as a separate argument.
1016 If there are no positional parameters, the
1019 generates zero arguments, even when
1022 What this basically means, for example, is
1031 .Bd -literal -offset indent
1035 Expands to the number of positional parameters.
1037 Expands to the exit status of the most recent pipeline.
1039 (hyphen) Expands to the current option flags (the single-letter
1040 option names concatenated into a string) as specified on
1041 invocation, by the set built-in command, or implicitly
1044 Expands to the process ID of the invoked shell.
1046 retains the same value of $ as its parent.
1048 Expands to the process ID of the most recent background
1049 command executed from the current shell.
1051 pipeline, the process ID is that of the last command in the
1054 (zero) Expands to the name of the shell or shell script.
1057 This clause describes the various expansions that are
1059 Not all expansions are performed on
1060 every word, as explained later.
1062 Tilde expansions, parameter expansions, command substitutions,
1063 arithmetic expansions, and quote removals that occur within
1064 a single word expand to a single field.
1066 splitting or pathname expansion that can create multiple
1067 fields from a single word.
1068 The single exception to this rule is
1069 the expansion of the special parameter
1071 within double-quotes,
1072 as was described above.
1074 The order of word expansion is:
1077 Tilde Expansion, Parameter Expansion, Command Substitution,
1078 Arithmetic Expansion (these all occur at the same time).
1080 Field Splitting is performed on fields generated by step (1)
1085 Pathname Expansion (unless the
1087 option is in effect).
1094 character is used to introduce parameter expansion, command
1095 substitution, or arithmetic evaluation.
1096 .Ss Tilde Expansion (substituting a user's home directory)
1097 A word beginning with an unquoted tilde character
1100 subjected to tilde expansion.
1101 All the characters up to a slash
1103 or the end of the word are treated as a username
1104 and are replaced with the user's home directory.
1106 username is missing (as in ~/foobar), the tilde is replaced
1107 with the value of the HOME variable (the current user's
1109 .Ss Parameter Expansion
1110 The format for parameter expansion is as follows:
1111 .Bd -literal -offset indent
1115 where expression consists of all characters until the matching
1119 escaped by a backslash or within a quoted string, and characters in
1120 embedded arithmetic expansions, command substitutions, and variable
1121 expansions, are not examined in determining the matching
1124 The simplest form for parameter expansion is:
1125 .Bd -literal -offset indent
1129 The value, if any, of parameter is substituted.
1131 The parameter name or symbol can be enclosed in braces, which are
1132 optional except for positional parameters with more than one digit or
1133 when parameter is followed by a character that could be interpreted as
1135 If a parameter expansion occurs inside double-quotes:
1138 Pathname expansion is not performed on the results of the
1141 Field splitting is not performed on the results of the
1142 expansion, with the exception of the special parameter
1146 In addition, a parameter expansion can be modified by using one of the
1148 .Bl -tag -width indent
1149 .It Li ${parameter:-word}
1151 If parameter is unset or
1152 null, the expansion of word is
1153 substituted; otherwise, the value of
1154 parameter is substituted.
1155 .It Li ${parameter:=word}
1156 Assign Default Values.
1157 If parameter is unset
1158 or null, the expansion of word is
1159 assigned to parameter.
1161 final value of parameter is
1163 Only variables, not positional
1164 parameters or special parameters, can be
1165 assigned in this way.
1166 .It Li ${parameter:?[word]}
1167 Indicate Error if Null or Unset.
1169 parameter is unset or null, the expansion of
1170 word (or a message indicating it is unset if
1171 word is omitted) is written to standard
1172 error and the shell exits with a nonzero
1174 Otherwise, the value of
1175 parameter is substituted.
1177 interactive shell need not exit.
1178 .It Li ${parameter:+word}
1179 Use Alternate Value.
1180 If parameter is unset
1181 or null, null is substituted;
1182 otherwise, the expansion of word is
1186 In the parameter expansions shown previously, use of the colon in the
1187 format results in a test for a parameter that is unset or null; omission
1188 of the colon results in a test for a parameter that is only unset.
1189 .Bl -tag -width indent
1190 .It Li ${#parameter}
1192 The length in characters of
1193 the value of parameter.
1196 The following four varieties of parameter expansion provide for substring
1198 In each case, pattern matching notation
1200 .Sx Shell Patterns ) ,
1201 rather than regular expression notation,
1202 is used to evaluate the patterns.
1203 If parameter is one of the special parameters
1207 the result of the expansion is unspecified.
1208 Enclosing the full parameter expansion string in double-quotes does not
1209 cause the following four varieties of pattern characters to be quoted,
1210 whereas quoting characters within the braces has this effect.
1211 .Bl -tag -width indent
1212 .It Li ${parameter%word}
1213 Remove Smallest Suffix Pattern.
1215 is expanded to produce a pattern.
1217 parameter expansion then results in
1218 parameter, with the smallest portion of the
1219 suffix matched by the pattern deleted.
1220 .It Li ${parameter%%word}
1221 Remove Largest Suffix Pattern.
1223 is expanded to produce a pattern.
1225 parameter expansion then results in
1226 parameter, with the largest portion of the
1227 suffix matched by the pattern deleted.
1228 .It Li ${parameter#word}
1229 Remove Smallest Prefix Pattern.
1231 is expanded to produce a pattern.
1233 parameter expansion then results in
1234 parameter, with the smallest portion of the
1235 prefix matched by the pattern deleted.
1236 .It Li ${parameter##word}
1237 Remove Largest Prefix Pattern.
1239 is expanded to produce a pattern.
1241 parameter expansion then results in
1242 parameter, with the largest portion of the
1243 prefix matched by the pattern deleted.
1245 .Ss Command Substitution
1246 Command substitution allows the output of a command to be substituted in
1247 place of the command name itself.
1248 Command substitution occurs when
1249 the command is enclosed as follows:
1250 .Bd -literal -offset indent
1254 or the backquoted version:
1255 .Bd -literal -offset indent
1259 The shell expands the command substitution by executing command in a
1260 subshell environment and replacing the command substitution
1261 with the standard output of the command,
1262 removing sequences of one or more newlines at the end of the substitution.
1263 Embedded newlines before the end of the output are not removed;
1264 however, during field splitting, they may be translated into spaces
1265 depending on the value of
1267 and the quoting that is in effect.
1268 .Ss Arithmetic Expansion
1269 Arithmetic expansion provides a mechanism for evaluating an arithmetic
1270 expression and substituting its value.
1271 The format for arithmetic expansion is as follows:
1272 .Bd -literal -offset indent
1276 The expression is treated as if it were in double-quotes, except
1277 that a double-quote inside the expression is not treated specially.
1279 shell expands all tokens in the expression for parameter expansion,
1280 command substitution, and quote removal.
1282 Next, the shell treats this as an arithmetic expression and
1283 substitutes the value of the expression.
1284 .Ss White Space Splitting (Field Splitting)
1285 After parameter expansion, command substitution, and
1286 arithmetic expansion the shell scans the results of
1287 expansions and substitutions that did not occur in double-quotes for
1288 field splitting and multiple fields can result.
1290 The shell treats each character of the
1292 as a delimiter and uses
1293 the delimiters to split the results of parameter expansion and command
1294 substitution into fields.
1295 .Ss Pathname Expansion (File Name Generation)
1299 file name generation is performed
1300 after word splitting is complete.
1302 viewed as a series of patterns, separated by slashes.
1304 process of expansion replaces the word with the names of
1305 all existing files whose names can be formed by replacing
1306 each pattern with a string that matches the specified pattern.
1307 There are two restrictions on this: first, a pattern cannot match
1308 a string containing a slash, and second,
1309 a pattern cannot match a string starting with a period
1310 unless the first character of the pattern is a period.
1311 The next section describes the patterns used for both
1312 Pathname Expansion and the
1316 A pattern consists of normal characters, which match themselves,
1317 and meta-characters.
1318 The meta-characters are
1324 These characters lose their special meanings if they are quoted.
1325 When command or variable substitution is performed and the dollar sign
1326 or back quotes are not double-quoted, the value of the
1327 variable or the output of the command is scanned for these
1328 characters and they are turned into meta-characters.
1332 matches any string of characters.
1335 matches any single character.
1338 introduces a character class.
1339 The end of the character class is indicated by a
1347 rather than introducing a character class.
1348 A character class matches any of the characters between the square brackets.
1349 A range of characters may be specified using a minus sign.
1350 The character class may be complemented by making an exclamation point
1352 the first character of the character class.
1356 in a character class, make it the first character listed
1362 make it the first or last character listed.
1363 .Ss Built-in Commands
1364 This section lists the commands which
1365 are built-in because they need to perform some operation
1366 that cannot be performed by a separate process.
1368 these, built-in versions of essential utilities
1369 are provided for efficiency.
1370 .Bl -tag -width indent
1372 A null command that returns a 0 (true) exit value.
1374 The commands in the specified file are read and executed by the shell.
1377 command may be used to return to the
1384 characters, it is used as is.
1385 Otherwise, the shell searches the
1388 If it is not found in the
1390 it is sought in the current working directory.
1392 A built-in equivalent of
1394 .It Ic alias Oo Ar name Ns Oo = Ns Ar string Oc ... Oc
1396 .Ar name Ns = Ns Ar string
1397 is specified, the shell defines the alias
1403 is specified, the value of the alias
1406 With no arguments, the
1408 built-in command prints the names and values of all defined aliases
1411 Alias values are written with appropriate quoting so that they are
1412 suitable for re-input to the shell.
1416 .It Ic bg Op Ar job ...
1417 Continue the specified jobs
1418 (or the current job if no jobs are given)
1420 .It Ic builtin Ar cmd Op Ar arg ...
1421 Execute the specified built-in command,
1423 This is useful when the user wishes to override a shell function
1424 with the same name as a built-in command.
1425 .It Ic bind Oo Fl aeklrsv Oc Oo Ar key Oo Ar command Oc Oc
1426 List or alter key bindings for the line editor.
1427 This command is documented in
1429 .It Ic cd Oo Fl L | P Oc Op Ar directory
1430 Switch to the specified
1432 or to the directory specified in the
1434 environment variable if no
1443 then the directories listed in the
1446 searched for the specified
1450 is unset, the current directory is searched.
1453 is the same as that of
1455 In an interactive shell,
1458 command will print out the name of the directory
1459 that it actually switched to
1460 if this is different from the name that the user gave.
1461 These may be different either because the
1463 mechanism was used or because a symbolic link was crossed.
1467 option is specified,
1469 is handled physically and symbolic links are resolved before
1471 components are processed.
1474 option is specified,
1476 is handled logically.
1477 This is the default.
1482 .It Ic command Oo Fl p Oc Op Ar utility Op Ar argument ...
1483 .It Ic command Oo Fl v | V Oc Op Ar utility
1484 The first form of invocation executes the specified
1486 as a simple command (see the
1492 option is specified, the command search is performed using a
1495 that is guaranteed to find all of the standard utilities.
1499 option is specified,
1501 is not executed but a description of its interpretation by the shell is
1503 For ordinary commands the output is the path name; for shell built-in
1504 commands, shell functions and keywords only the name is written.
1505 Aliases are printed as
1506 .Dq Ic alias Ar name Ns = Ns Ar value .
1510 option is identical to
1512 except for the output.
1514 .Dq Ar utility Ic is Ar description
1526 .It Ic echo Oo Fl e | n Oc Op Ar string ...
1527 Print a space-separated list of the arguments to the standard output
1528 and append a newline character.
1529 .Bl -tag -width indent
1531 Suppress the output of the trailing newline.
1533 Process C-style backslash escape sequences.
1535 understands the following character escapes:
1536 .Bl -tag -width indent
1538 Alert (ring the terminal bell)
1542 Suppress the trailing newline (this has the side-effect of truncating the
1543 line if it is not the last character)
1545 The ESC character (ASCII 0x1b)
1559 (Zero) The character whose octal value is nnn
1564 is not enclosed in quotes then the backslash itself must be escaped
1565 with a backslash to protect it from the shell.
1567 .Bd -literal -offset indent
1576 $ echo -e a\e\e\e\eb
1585 options may be specified.
1586 .It Ic eval Ar string ...
1587 Concatenate all the arguments with spaces.
1588 Then re-parse and execute the command.
1589 .It Ic exec Op Ar command Op arg ...
1593 the shell process is replaced with the specified program
1594 (which must be a real program, not a shell built-in command or function).
1595 Any redirections on the
1597 command are marked as permanent,
1598 so that they are not undone when the
1601 .It Ic exit Op Ar exitstatus
1602 Terminate the shell process.
1606 it is used as the exit status of the shell;
1607 otherwise the exit status of the preceding command is used.
1608 .It Ic export Ar name ...
1609 .It Ic export Op Fl p
1610 The specified names are exported so that they will
1611 appear in the environment of subsequent commands.
1612 The only way to un-export a variable is to
1615 The shell allows the value of a variable to be set
1616 at the same time as it is exported by writing
1617 .Bd -literal -offset indent
1621 With no arguments the export command lists the names
1622 of all exported variables.
1625 option is specified, the exported variables are printed as
1626 .Dq Ic export Ar name Ns = Ns Ar value
1627 lines, suitable for re-input to the shell.
1629 A null command that returns a non-zero (false) exit value.
1630 .It Ic fc Oo Fl e Ar editor Oc Op Ar first Op Ar last
1631 .It Ic fc Fl l Oo Fl nr Oc Op Ar first Op Ar last
1632 .It Ic fc Fl s Oo Ar old Ns = Ns Ar new Oc Op Ar first
1635 built-in command lists, or edits and re-executes,
1636 commands previously entered to an interactive shell.
1637 .Bl -tag -width indent
1639 Use the editor named by
1641 to edit the commands.
1642 The editor string is a command name,
1643 subject to search via the
1648 variable is used as a default when
1653 is null or unset, the value of the
1660 is used as the editor.
1662 List the commands rather than invoking
1664 The commands are written in the
1665 sequence indicated by the first and last operands, as
1668 with each command preceded by the command number.
1670 Suppress command numbers when listing with
1673 Reverse the order of the commands listed
1682 Re-execute the command without invoking an editor.
1685 Select the commands to list or edit.
1686 The number of previous commands that can be accessed
1687 are determined by the value of the
1694 or both are one of the following:
1695 .Bl -tag -width indent
1697 A positive number representing a command number;
1698 command numbers can be displayed with the
1702 A negative decimal number representing the
1703 command that was executed
1706 commands previously.
1707 For example, -1 is the immediately previous command.
1709 A string indicating the most recently entered command
1710 that begins with that string.
1713 operand is not also specified with
1715 the string form of the first operand cannot contain an embedded equal sign.
1719 The following environment variables affect the execution of
1721 .Bl -tag -width ".Ev HISTSIZE"
1723 Name of the editor to use for history editing.
1725 The number of previous commands that are accessible.
1730 or the current job to the foreground.
1731 .It Ic getopts Ar optstring Ar var
1737 command deprecates the older
1740 The first argument should be a series of letters, each possibly
1741 followed by a colon which indicates that the option takes an argument.
1742 The specified variable is set to the parsed option.
1744 the next argument is placed into the shell variable
1746 If an option takes an argument, it is placed into the shell variable
1748 If an invalid option is encountered,
1752 It returns a false value (1) when it encounters the end of the options.
1753 .It Ic hash Oo Fl rv Oc Op Ar command ...
1754 The shell maintains a hash table which remembers the locations of commands.
1755 With no arguments whatsoever, the
1757 command prints out the contents of this table.
1758 Entries which have not been looked at since the last
1760 command are marked with an asterisk;
1761 it is possible for these entries to be invalid.
1765 command removes each specified
1767 from the hash table (unless they are functions) and then locates it.
1772 prints the locations of the commands as it finds them.
1777 command to delete all the entries in the hash table except for functions.
1778 .It Ic jobid Op Ar job
1779 Print the process id's of the processes in the specified
1783 argument is omitted, use the current job.
1784 .It Ic jobs Oo Fl lps Oc Op Ar job ...
1785 Print information about the specified jobs, or all jobs if no
1788 The information printed includes job ID, status and command name.
1792 option is specified, the PID of each job is also printed.
1795 option is specified, only the process IDs for the process group leaders
1796 are printed, one per line.
1799 option is specified, only the PIDs of the job commands are printed, one per
1801 .It Ic local Oo Ar variable ... Oc Op Fl
1805 .It Ic pwd Op Fl L | P
1806 Print the path of the current directory.
1807 The built-in command may
1808 differ from the program of the same name because the
1809 built-in command remembers what the current directory
1810 is rather than recomputing it each time.
1813 However, if the current directory is
1815 the built-in version of
1817 will continue to print the old name for the directory.
1821 option is specified, symbolic links are resolved.
1824 option is specified, the shell's notion of the current directory
1825 is printed (symbolic links are not resolved).
1826 This is the default.
1827 .It Ic read Oo Fl p Ar prompt Oc Oo Fl t Ar timeout Oc Oo Fl er Oc Ar variable ...
1833 and the standard input is a terminal.
1835 read from the standard input.
1836 The trailing newline
1837 is deleted from the line and the line is split as
1838 described in the section on
1839 .Sx White Space Splitting (Field Splitting)
1841 the pieces are assigned to the variables in order.
1842 If there are more pieces than variables, the remaining
1843 pieces (along with the characters in
1845 that separated them)
1846 are assigned to the last variable.
1847 If there are more variables than pieces, the remaining
1848 variables are assigned the null string.
1850 Backslashes are treated specially, unless the
1854 If a backslash is followed by
1855 a newline, the backslash and the newline will be
1857 If a backslash is followed by any other
1858 character, the backslash will be deleted and the following
1859 character will be treated as though it were not in
1865 option is specified and the
1867 elapses before any input is supplied,
1870 command will return an exit status of 1 without assigning any values.
1873 value may optionally be followed by one of
1878 to explicitly specify seconds, minutes or hours.
1879 If none is supplied,
1885 option exists only for backward compatibility with older scripts.
1886 .It Ic readonly Oo Fl p Oc Op Ar name ...
1889 is marked as read only,
1890 so that it cannot be subsequently modified or unset.
1891 The shell allows the value of a variable to be set
1892 at the same time as it is marked read only
1893 by using the following form:
1894 .Bd -literal -offset indent
1898 With no arguments the
1900 command lists the names of all read only variables.
1903 option is specified, the read-only variables are printed as
1904 .Dq Ic readonly Ar name Ns = Ns Ar value
1905 lines, suitable for re-input to the shell.
1906 .It Ic return Op Ar exitstatus
1910 .It Ic set Oo Fl /+abCEefIimnpTuVvx Oc Oo Fl /+o Ar longname Oc Oo
1911 .Fl c Ar string Oc Op Fl - Ar arg ...
1914 command performs three different functions:
1917 With no arguments, it lists the values of all shell variables.
1919 If options are given,
1920 either in short form or using the long
1921 .Dq Fl /+o Ar longname
1923 it sets or clears the specified options as described in the section called
1924 .Sx Argument List Processing .
1928 option is specified,
1930 will replace the shell's positional parameters with the subsequent
1932 If no arguments follow the
1935 all the positional parameters will be cleared,
1936 which is equivalent to executing the command
1940 flag may be omitted when specifying arguments to be used
1941 as positional replacement parameters.
1942 This is not recommended,
1943 because the first argument may begin with a dash
1949 command will interpret as a request to enable or disable options.
1951 .It Ic setvar Ar variable Ar value
1952 Assigns the specified
1957 is intended to be used in functions that
1958 assign values to variables whose names are passed as parameters.
1959 In general it is better to write
1960 .Bd -literal -offset indent
1965 .It Ic shift Op Ar n
1966 Shift the positional parameters
1971 A shift sets the value of $1 to the value of $2,
1972 the value of $2 to the value of $3, and so on,
1973 decreasing the value of $# by one.
1974 If there are zero positional parameters, shifting does not do anything.
1976 A built-in equivalent of
1979 Print the amount of time spent executing the shell and its children.
1980 The first output line shows the user and system times for the shell
1981 itself, the second one contains the user and system times for the
1983 .It Ic trap Oo Ar action Oc Ar signal ...
1985 Cause the shell to parse and execute
1990 The signals are specified by name or number.
1991 In addition, the pseudo-signal
1993 may be used to specify an action that is performed when the shell terminates.
1996 may be an empty string or a dash
1998 the former causes the specified signal to be ignored
1999 and the latter causes the default action to be taken.
2002 is another way to request the default action, for compatibility reasons this
2003 usage is not recommended though.
2004 When the shell forks off a subshell,
2005 it resets trapped (but not ignored) signals to the default action.
2008 command has no effect on signals that were ignored on entry to the shell.
2014 command to display a list of valid signal names.
2016 A null command that returns a 0 (true) exit value.
2017 .It Ic type Op Ar name ...
2020 as a command and print the resolution of the command search.
2021 Possible resolutions are:
2022 shell keyword, alias, shell built-in command, command, tracked alias
2024 For aliases the alias expansion is printed;
2025 for commands and tracked aliases
2026 the complete pathname of the command is printed.
2027 .It Ic ulimit Oo Fl HSabcdflmnstuv Oc Op Ar limit
2028 Set or display resource limits (see
2032 is specified, the named resource will be set;
2033 otherwise the current resource value will be displayed.
2037 is specified, the hard limits will be set or displayed.
2038 While everybody is allowed to reduce a hard limit,
2039 only the superuser can increase it.
2043 specifies the soft limits instead.
2044 When displaying limits,
2050 The default is to display the soft limits,
2051 and to set both the hard and the soft limits.
2057 command to display all resources.
2060 is not acceptable in this mode.
2062 The remaining options specify which resource value is to be
2063 displayed or modified.
2064 They are mutually exclusive.
2065 .Bl -tag -width indent
2067 The maximum size of socket buffer usage, in bytes.
2068 .It Fl c Ar coredumpsize
2069 The maximal size of core dump files, in 512-byte blocks.
2070 .It Fl d Ar datasize
2071 The maximal size of the data segment of a process, in kilobytes.
2072 .It Fl f Ar filesize
2073 The maximal size of a file, in 512-byte blocks.
2074 .It Fl l Ar lockedmem
2075 The maximal size of memory that can be locked by a process, in
2077 .It Fl m Ar memoryuse
2078 The maximal resident set size of a process, in kilobytes.
2080 The maximal number of descriptors that could be opened by a process.
2081 .It Fl s Ar stacksize
2082 The maximal size of the stack segment, in kilobytes.
2084 The maximal amount of CPU time to be used by each process, in seconds.
2085 .It Fl u Ar userproc
2086 The maximal number of simultaneous processes for this user ID.
2087 .It Fl v Ar virtualmem
2088 The maximal virtual size of a process, in kilobytes.
2090 .It Ic umask Oo Fl S Oc Op Ar mask
2091 Set the file creation mask (see
2093 to the octal or symbolic (see
2097 If the argument is omitted, the current mask value is printed.
2100 option is specified, the output is symbolic, otherwise the output is octal.
2101 .It Ic unalias Oo Fl a Oc Op Ar name ...
2102 The specified alias names are removed.
2105 is specified, all aliases are removed.
2106 .It Ic unset Oo Fl fv Oc Ar name ...
2107 The specified variables or functions are unset and unexported.
2110 option is specified or no options are given, the
2112 arguments are treated as variable names.
2115 option is specified, the
2117 arguments are treated as function names.
2118 .It Ic wait Op Ar job
2119 Wait for the specified
2121 to complete and return the exit status of the last process in the
2123 If the argument is omitted, wait for all jobs to complete
2124 and return an exit status of zero.
2126 .Ss Commandline Editing
2129 is being used interactively from a terminal, the current command
2130 and the command history
2134 .Sx Built-in Commands )
2135 can be edited using vi-mode command line editing.
2136 This mode uses commands similar
2137 to a subset of those described in the vi man page.
2142 enables vi-mode editing and places
2144 into vi insert mode.
2145 With vi-mode enabled,
2147 can be switched between insert mode and command mode by typing
2151 while in command mode will pass the line to the shell.
2157 command can be used to enable a subset of
2158 emacs-style command line editing features.
2160 The following environment variables affect the execution of
2162 .Bl -tag -width ".Ev HISTSIZE"
2164 The search path used with the
2168 The fallback editor used with the
2171 If not set, the default editor is
2174 The default editor used with the
2178 The number of previous commands that are accessible.
2180 The starting directory of
2183 Input Field Separators.
2184 This is normally set to
2190 .Sx White Space Splitting
2191 section for more details.
2193 The name of a mail file, that will be checked for the arrival of new
2200 separated list of file names, for the shell to check for incoming
2202 This environment setting overrides the
2205 There is a maximum of 10 mailboxes that can be monitored at once.
2207 The default search path for executables.
2210 section for details.
2212 The primary prompt string, which defaults to
2214 unless you are the superuser, in which case it defaults to
2217 The secondary prompt string, which defaults to
2220 The prefix for the trace output (if
2226 The default terminal setting for the shell.
2227 This is inherited by children of the shell, and is used in the history
2231 Errors that are detected by the shell, such as a syntax error, will
2232 cause the shell to exit with a non-zero exit status.
2233 If the shell is not an interactive shell, the execution of the shell
2234 file will be aborted.
2235 Otherwise the shell will return the exit status of the last command
2236 executed, or if the exit builtin is used with a numeric argument, it
2237 will return the argument.
2256 command, the Thompson shell, appeared in
2258 It was superseded in
2260 by the Bourne shell, which inherited the name
2265 was rewritten in 1989 under the
2267 license after the Bourne shell from
2272 was originally written by Kenneth Almquist.
2276 utility does not recognize multibyte characters.
projects / FreeBSD / FreeBSD.git / blob