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.
310 to standard error before it is executed.
311 Useful for debugging.
316 option causes the commands to be read from the
318 operand instead of from the standard input.
319 Keep in mind that this option only accepts a single string as its
320 argument, hence multi-word strings must be quoted.
324 option takes as its only argument the long name of an option
325 to be enabled or disabled.
326 For example, the following two invocations of
328 both enable the built-in
331 .Bd -literal -offset indent
336 If used without an argument, the
338 option displays the current option settings in a human-readable format.
341 is used without an argument, the current option settings are output
342 in a format suitable for re-input into the shell.
343 .Ss Lexical Structure
344 The shell reads input in terms of lines from a file and breaks
345 it up into words at whitespace (blanks and tabs), and at
349 which are special to the shell.
350 There are two types of operators: control operators and
351 redirection operators (their meaning is discussed later).
352 The following is a list of valid operators:
353 .Bl -tag -width indent
354 .It Control operators:
355 .Bl -column "XXX" "XXX" "XXX" "XXX" "XXX" -offset center -compact
356 .It Li & Ta Li && Ta Li ( Ta Li ) Ta Li \en
357 .It Li ;; Ta Li ; Ta Li | Ta Li ||
359 .It Redirection operators:
360 .Bl -column "XXX" "XXX" "XXX" "XXX" "XXX" -offset center -compact
361 .It Li < Ta Li > Ta Li << Ta Li >> Ta Li <>
362 .It Li <& Ta Li >& Ta Li <<- Ta Li >|
368 introduces a comment if used at the beginning of a word.
369 The word starting with
371 and the rest of the line are ignored.
373 Quoting is used to remove the special meaning of certain characters
374 or words to the shell, such as operators, whitespace, keywords,
377 There are three types of quoting: matched single quotes,
378 matched double quotes, and backslash.
379 .Bl -tag -width indent
381 Enclosing characters in single quotes preserves the literal
382 meaning of all the characters (except single quotes, making
383 it impossible to put single-quotes in a single-quoted string).
385 Enclosing characters within double quotes preserves the literal
386 meaning of all characters except dollarsign
392 The backslash inside double quotes is historically weird.
393 It remains literal unless it precedes the following characters,
394 which it serves to quote:
395 .Bl -column "XXX" "XXX" "XXX" "XXX" "XXX" -offset center -compact
396 .It Li $ Ta Li ` Ta Li \&" Ta Li \e\ Ta Li \en
399 A backslash preserves the literal meaning of the following
400 character, with the exception of the newline character
402 A backslash preceding a newline is treated as a line continuation.
405 Reserved words are words that have special meaning to the
406 shell and are recognized at the beginning of a line and
407 after a control operator.
408 The following are reserved words:
409 .Bl -column "doneXX" "elifXX" "elseXX" "untilXX" "whileX" -offset center
410 .It Li \&! Ta { Ta } Ta Ic case Ta Ic do
411 .It Ic done Ta Ic elif Ta Ic else Ta Ic esac Ta Ic fi
412 .It Ic for Ta Ic if Ta Ic then Ta Ic until Ta Ic while
415 An alias is a name and corresponding value set using the
418 Whenever a reserved word may occur (see above),
419 and after checking for reserved words, the shell
420 checks the word to see if it matches an alias.
421 If it does, it replaces it in the input stream with its value.
422 For example, if there is an alias called
427 .Bd -literal -offset indent
432 .Bd -literal -offset indent
436 Aliases provide a convenient way for naive users to
437 create shorthands for commands without having to learn how
438 to create functions with arguments.
440 used to create lexically obscure code.
441 This use is discouraged.
443 An alias name may be escaped in a command line, so that it is not
444 replaced by its alias value, by using quoting characters within or
445 adjacent to the alias name.
446 This is most often done by prefixing
447 an alias name with a backslash to execute a function, built-in, or
448 normal program with the same name.
453 The shell interprets the words it reads according to a
454 language, the specification of which is outside the scope
455 of this man page (refer to the BNF in the
458 Essentially though, a line is read and if
459 the first word of the line (or after a control operator)
460 is not a reserved word, then the shell has recognized a
462 Otherwise, a complex command or some
463 other special construct may have been recognized.
465 If a simple command has been recognized, the shell performs
466 the following actions:
469 Leading words of the form
471 are stripped off and assigned to the environment of
473 Redirection operators and
474 their arguments (as described below) are stripped
475 off and saved for processing.
477 The remaining words are expanded as described in
479 .Sx Word Expansions ,
480 and the first remaining word is considered the command
481 name and the command is located.
483 words are considered the arguments of the command.
484 If no command name resulted, then the
486 variable assignments recognized in 1) affect the
489 Redirections are performed as described in
493 Redirections are used to change where a command reads its input
495 In general, redirections open, close, or
496 duplicate an existing reference to a file.
498 used for redirection is:
500 .Dl [n] redir-op file
504 is one of the redirection operators mentioned
506 The following gives some examples of how these
507 operators can be used.
508 Note that stdin and stdout are commonly used abbreviations
509 for standard input and standard output respectively.
510 .Bl -tag -width "1234567890XX" -offset indent
512 redirect stdout (or file descriptor n) to file
514 same as above, but override the
518 append stdout (or file descriptor n) to file
520 redirect stdin (or file descriptor n) from file
522 redirect stdin (or file descriptor n) to and from file
524 duplicate stdin (or file descriptor n1) from file descriptor n2
526 close stdin (or file descriptor n)
528 duplicate stdout (or file descriptor n1) to file descriptor n2
530 close stdout (or file descriptor n)
533 The following redirection is often called a
535 .Bd -literal -offset indent
542 All the text on successive lines up to the delimiter is
543 saved away and made available to the command on standard
544 input, or file descriptor n if it is specified.
546 as specified on the initial line is quoted, then the here-doc-text
547 is treated literally, otherwise the text is subjected to
548 parameter expansion, command substitution, and arithmetic
549 expansion (as described in the section on
550 .Sx Word Expansions ) .
556 in the here-doc-text are stripped.
557 .Ss Search and Execution
558 There are three types of commands: shell functions,
559 built-in commands, and normal programs.
560 The command is searched for (by name) in that order.
561 The three types of commands are all executed in a different way.
563 When a shell function is executed, all of the shell positional
564 parameters (except $0, which remains unchanged) are
565 set to the arguments of the shell function.
566 The variables which are explicitly placed in the environment of
567 the command (by placing assignments to them before the
568 function name) are made local to the function and are set
570 Then the command given in the function definition is executed.
571 The positional parameters are restored to their original values
572 when the command completes.
573 This all occurs within the current shell.
575 Shell built-in commands are executed internally to the shell, without
576 spawning a new process.
578 Otherwise, if the command name does not match a function
579 or built-in command, the command is searched for as a normal
580 program in the file system (as described in the next section).
581 When a normal program is executed, the shell runs the program,
582 passing the arguments and the environment to the program.
583 If the program is not a normal executable file
584 (i.e., if it does not begin with the
594 the shell will interpret the program in a subshell.
595 The child shell will reinitialize itself in this case,
596 so that the effect will be
597 as if a new shell had been invoked to handle the ad-hoc shell script,
598 except that the location of hashed commands located in
599 the parent shell will be remembered by the child.
601 Note that previous versions of this document
602 and the source code itself misleadingly and sporadically
603 refer to a shell script without a magic number
605 .Qq shell procedure .
607 When locating a command, the shell first looks to see if
608 it has a shell function by that name.
610 built-in command by that name.
611 If a built-in command is not found,
612 one of two things happen:
615 Command names containing a slash are simply executed without
616 performing any searches.
618 The shell searches each entry in
620 in turn for the command.
623 variable should be a series of
624 entries separated by colons.
625 Each entry consists of a
627 The current directory
628 may be indicated implicitly by an empty directory name,
629 or explicitly by a single period.
631 .Ss Command Exit Status
632 Each command has an exit status that can influence the behavior
633 of other shell commands.
634 The paradigm is that a command exits
635 with zero for normal or success, and non-zero for failure,
636 error, or a false indication.
637 The man page for each command
638 should indicate the various exit codes and what they mean.
639 Additionally, the built-in commands return exit codes, as does
640 an executed shell function.
642 If a command is terminated by a signal, its exit status is 128 plus
644 Signal numbers are defined in the header file
647 Complex commands are combinations of simple commands
648 with control operators or reserved words, together creating a larger complex
650 More generally, a command is one of the following:
651 .Bl -item -offset indent
657 list or compound-list
664 Unless otherwise stated, the exit status of a command is
665 that of the last simple command executed by the command.
667 A pipeline is a sequence of one or more commands separated
668 by the control operator |.
669 The standard output of all but
670 the last command is connected to the standard input
672 The standard output of the last
673 command is inherited from the shell, as usual.
675 The format for a pipeline is:
677 .Dl [!] command1 [ | command2 ...]
679 The standard output of command1 is connected to the standard
681 The standard input, standard output, or
682 both of a command is considered to be assigned by the
683 pipeline before any redirection specified by redirection
684 operators that are part of the command.
686 If the pipeline is not in the background (discussed later),
687 the shell waits for all commands to complete.
691 does not precede the pipeline, the
692 exit status is the exit status of the last command specified
694 Otherwise, the exit status is the logical
695 NOT of the exit status of the last command.
697 the last command returns zero, the exit status is 1; if
698 the last command returns greater than zero, the exit status
701 Because pipeline assignment of standard input or standard
702 output or both takes place before redirection, it can be
703 modified by redirection.
706 .Dl $ command1 2>&1 | command2
708 sends both the standard output and standard error of
710 to the standard input of
715 or newline terminator causes the preceding
717 (described below in the section called
718 .Sx Short-Circuit List Operators )
719 to be executed sequentially;
722 causes asynchronous execution of the preceding AND-OR-list.
724 Note that unlike some other shells,
726 executes each process in the pipeline as a child of the
729 Shell built-in commands are the exception to this rule.
730 They are executed in the current shell, although they do not affect its
731 environment when used in pipelines.
732 .Ss Background Commands (&)
733 If a command is terminated by the control operator ampersand
735 the shell executes the command asynchronously;
736 the shell does not wait for the command to finish
737 before executing the next command.
739 The format for running a command in background is:
740 .Bd -literal -offset indent
741 command1 & [command2 & ...]
744 If the shell is not interactive, the standard input of an
745 asynchronous command is set to /dev/null.
746 .Ss Lists (Generally Speaking)
747 A list is a sequence of zero or more commands separated by
748 newlines, semicolons, or ampersands,
749 and optionally terminated by one of these three characters.
751 list are executed in the order they are written.
752 If command is followed by an ampersand, the shell starts the
753 command and immediately proceeds onto the next command;
754 otherwise it waits for the command to terminate before
755 proceeding to the next one.
756 .Ss Short-Circuit List Operators
760 are AND-OR list operators.
762 executes the first command, and then executes the second command
763 if the exit status of the first command is zero.
765 is similar, but executes the second command if the exit
766 status of the first command is nonzero.
770 both have the same priority.
771 .Ss Flow-Control Constructs (if, while, for, case)
776 .\" XXX Use .Dl to work around broken handling of .Ic inside .Bd and .Ed .
780 .Dl [ Ic elif Ar list
781 .Dl Ic then Ar list ] ...
782 .Dl [ Ic else Ar list ]
792 The two lists are executed repeatedly while the exit status of the
796 command is similar, but has the word
801 repeat until the exit status of the first list is zero.
806 .Dl Ic for Ar variable Op Ic in Ar word ...
812 and the following words are omitted,
815 The words are expanded, and then the list is executed
816 repeatedly with the variable set to each word in turn.
821 commands may be replaced with
831 .Dl Ic break Op Ar num
832 .Dl Ic continue Op Ar num
836 command terminates the
845 command continues with the next iteration of the innermost loop.
846 These are implemented as built-in commands.
851 .Dl Ic case Ar word Ic in
856 The pattern can actually be one or more patterns
863 .Ss Grouping Commands Together
864 Commands may be grouped by writing either
865 .Bd -literal -offset indent
870 .Bd -literal -offset indent
874 The first form executes the commands in a subshell.
875 Note that built-in commands thus executed do not affect the current shell.
876 The second form does not fork another shell,
877 so it is slightly more efficient.
878 Grouping commands together this way allows the user to
879 redirect their output as though they were one program:
880 .Bd -literal -offset indent
881 { echo -n "hello"; echo " world"; } > greeting
884 The syntax of a function definition is
885 .Bd -literal -offset indent
889 A function definition is an executable statement; when
890 executed it installs a function named name and returns an
892 The command is normally a list
898 Variables may be declared to be local to a function by
902 This should appear as the first statement of a function,
904 .Bd -ragged -offset indent
912 command is implemented as a built-in command.
914 When a variable is made local, it inherits the initial
915 value and exported and readonly flags from the variable
916 with the same name in the surrounding scope, if there is
918 Otherwise, the variable is initially unset.
920 uses dynamic scoping, so that if the variable
922 is made local to function
924 which then calls function
926 references to the variable
930 will refer to the variable
934 not to the global variable named
937 The only special parameter that can be made local is
941 local causes any shell options that are
942 changed via the set command inside the function to be
943 restored to their original values when the function
949 .Bd -ragged -offset indent
954 It terminates the current executional scope, returning from the previous
955 nested function, sourced script, or shell instance, in that order.
958 command is implemented as a built-in command.
959 .Ss Variables and Parameters
960 The shell maintains a set of parameters.
962 denoted by a name is called a variable.
964 the shell turns all the environment variables into shell
966 New variables can be set using the form
967 .Bd -literal -offset indent
971 Variables set by the user must have a name consisting solely
972 of alphabetics, numerics, and underscores.
973 The first letter of a variable name must not be numeric.
974 A parameter can also be denoted by a number
975 or a special character as explained below.
976 .Ss Positional Parameters
977 A positional parameter is a parameter denoted by a number greater than zero.
978 The shell sets these initially to the values of its command line
979 arguments that follow the name of the shell script.
982 built-in command can also be used to set or reset them.
983 .Ss Special Parameters
984 A special parameter is a parameter denoted by a special one-character
986 The special parameters recognized by the
990 are shown in the following list, exactly as they would appear in input
991 typed by the user or in the source of a shell script.
994 Expands to the positional parameters, starting from one.
996 the expansion occurs within a double-quoted string
997 it expands to a single field with the value of each parameter
998 separated by the first character of the
1007 Expands to the positional parameters, starting from one.
1009 the expansion occurs within double-quotes, each positional
1010 parameter expands as a separate argument.
1011 If there are no positional parameters, the
1014 generates zero arguments, even when
1017 What this basically means, for example, is
1026 .Bd -literal -offset indent
1030 Expands to the number of positional parameters.
1032 Expands to the exit status of the most recent pipeline.
1034 (hyphen) Expands to the current option flags (the single-letter
1035 option names concatenated into a string) as specified on
1036 invocation, by the set built-in command, or implicitly
1039 Expands to the process ID of the invoked shell.
1041 retains the same value of $ as its parent.
1043 Expands to the process ID of the most recent background
1044 command executed from the current shell.
1046 pipeline, the process ID is that of the last command in the
1049 (zero) Expands to the name of the shell or shell script.
1052 This clause describes the various expansions that are
1054 Not all expansions are performed on
1055 every word, as explained later.
1057 Tilde expansions, parameter expansions, command substitutions,
1058 arithmetic expansions, and quote removals that occur within
1059 a single word expand to a single field.
1061 splitting or pathname expansion that can create multiple
1062 fields from a single word.
1063 The single exception to this rule is
1064 the expansion of the special parameter
1066 within double-quotes,
1067 as was described above.
1069 The order of word expansion is:
1072 Tilde Expansion, Parameter Expansion, Command Substitution,
1073 Arithmetic Expansion (these all occur at the same time).
1075 Field Splitting is performed on fields generated by step (1)
1080 Pathname Expansion (unless the
1082 option is in effect).
1089 character is used to introduce parameter expansion, command
1090 substitution, or arithmetic evaluation.
1091 .Ss Tilde Expansion (substituting a user's home directory)
1092 A word beginning with an unquoted tilde character
1095 subjected to tilde expansion.
1096 All the characters up to a slash
1098 or the end of the word are treated as a username
1099 and are replaced with the user's home directory.
1101 username is missing (as in ~/foobar), the tilde is replaced
1102 with the value of the HOME variable (the current user's
1104 .Ss Parameter Expansion
1105 The format for parameter expansion is as follows:
1106 .Bd -literal -offset indent
1110 where expression consists of all characters until the matching
1114 escaped by a backslash or within a quoted string, and characters in
1115 embedded arithmetic expansions, command substitutions, and variable
1116 expansions, are not examined in determining the matching
1119 The simplest form for parameter expansion is:
1120 .Bd -literal -offset indent
1124 The value, if any, of parameter is substituted.
1126 The parameter name or symbol can be enclosed in braces, which are
1127 optional except for positional parameters with more than one digit or
1128 when parameter is followed by a character that could be interpreted as
1130 If a parameter expansion occurs inside double-quotes:
1133 Pathname expansion is not performed on the results of the
1136 Field splitting is not performed on the results of the
1137 expansion, with the exception of the special parameter
1141 In addition, a parameter expansion can be modified by using one of the
1143 .Bl -tag -width indent
1144 .It Li ${parameter:-word}
1146 If parameter is unset or
1147 null, the expansion of word is
1148 substituted; otherwise, the value of
1149 parameter is substituted.
1150 .It Li ${parameter:=word}
1151 Assign Default Values.
1152 If parameter is unset
1153 or null, the expansion of word is
1154 assigned to parameter.
1156 final value of parameter is
1158 Only variables, not positional
1159 parameters or special parameters, can be
1160 assigned in this way.
1161 .It Li ${parameter:?[word]}
1162 Indicate Error if Null or Unset.
1164 parameter is unset or null, the expansion of
1165 word (or a message indicating it is unset if
1166 word is omitted) is written to standard
1167 error and the shell exits with a nonzero
1169 Otherwise, the value of
1170 parameter is substituted.
1172 interactive shell need not exit.
1173 .It Li ${parameter:+word}
1174 Use Alternate Value.
1175 If parameter is unset
1176 or null, null is substituted;
1177 otherwise, the expansion of word is
1181 In the parameter expansions shown previously, use of the colon in the
1182 format results in a test for a parameter that is unset or null; omission
1183 of the colon results in a test for a parameter that is only unset.
1184 .Bl -tag -width indent
1185 .It Li ${#parameter}
1187 The length in characters of
1188 the value of parameter.
1191 The following four varieties of parameter expansion provide for substring
1193 In each case, pattern matching notation
1195 .Sx Shell Patterns ) ,
1196 rather than regular expression notation,
1197 is used to evaluate the patterns.
1198 If parameter is one of the special parameters
1202 the result of the expansion is unspecified.
1203 Enclosing the full parameter expansion string in double-quotes does not
1204 cause the following four varieties of pattern characters to be quoted,
1205 whereas quoting characters within the braces has this effect.
1206 .Bl -tag -width indent
1207 .It Li ${parameter%word}
1208 Remove Smallest Suffix Pattern.
1210 is expanded to produce a pattern.
1212 parameter expansion then results in
1213 parameter, with the smallest portion of the
1214 suffix matched by the pattern deleted.
1215 .It Li ${parameter%%word}
1216 Remove Largest Suffix Pattern.
1218 is expanded to produce a pattern.
1220 parameter expansion then results in
1221 parameter, with the largest portion of the
1222 suffix matched by the pattern deleted.
1223 .It Li ${parameter#word}
1224 Remove Smallest Prefix Pattern.
1226 is expanded to produce a pattern.
1228 parameter expansion then results in
1229 parameter, with the smallest portion of the
1230 prefix matched by the pattern deleted.
1231 .It Li ${parameter##word}
1232 Remove Largest Prefix Pattern.
1234 is expanded to produce a pattern.
1236 parameter expansion then results in
1237 parameter, with the largest portion of the
1238 prefix matched by the pattern deleted.
1240 .Ss Command Substitution
1241 Command substitution allows the output of a command to be substituted in
1242 place of the command name itself.
1243 Command substitution occurs when
1244 the command is enclosed as follows:
1245 .Bd -literal -offset indent
1249 or the backquoted version:
1250 .Bd -literal -offset indent
1254 The shell expands the command substitution by executing command in a
1255 subshell environment and replacing the command substitution
1256 with the standard output of the command,
1257 removing sequences of one or more newlines at the end of the substitution.
1258 Embedded newlines before the end of the output are not removed;
1259 however, during field splitting, they may be translated into spaces
1260 depending on the value of
1262 and the quoting that is in effect.
1263 .Ss Arithmetic Expansion
1264 Arithmetic expansion provides a mechanism for evaluating an arithmetic
1265 expression and substituting its value.
1266 The format for arithmetic expansion is as follows:
1267 .Bd -literal -offset indent
1271 The expression is treated as if it were in double-quotes, except
1272 that a double-quote inside the expression is not treated specially.
1274 shell expands all tokens in the expression for parameter expansion,
1275 command substitution, and quote removal.
1277 Next, the shell treats this as an arithmetic expression and
1278 substitutes the value of the expression.
1279 .Ss White Space Splitting (Field Splitting)
1280 After parameter expansion, command substitution, and
1281 arithmetic expansion the shell scans the results of
1282 expansions and substitutions that did not occur in double-quotes for
1283 field splitting and multiple fields can result.
1285 The shell treats each character of the
1287 as a delimiter and uses
1288 the delimiters to split the results of parameter expansion and command
1289 substitution into fields.
1290 .Ss Pathname Expansion (File Name Generation)
1294 file name generation is performed
1295 after word splitting is complete.
1297 viewed as a series of patterns, separated by slashes.
1299 process of expansion replaces the word with the names of
1300 all existing files whose names can be formed by replacing
1301 each pattern with a string that matches the specified pattern.
1302 There are two restrictions on this: first, a pattern cannot match
1303 a string containing a slash, and second,
1304 a pattern cannot match a string starting with a period
1305 unless the first character of the pattern is a period.
1306 The next section describes the patterns used for both
1307 Pathname Expansion and the
1311 A pattern consists of normal characters, which match themselves,
1312 and meta-characters.
1313 The meta-characters are
1319 These characters lose their special meanings if they are quoted.
1320 When command or variable substitution is performed and the dollar sign
1321 or back quotes are not double-quoted, the value of the
1322 variable or the output of the command is scanned for these
1323 characters and they are turned into meta-characters.
1327 matches any string of characters.
1330 matches any single character.
1333 introduces a character class.
1334 The end of the character class is indicated by a
1342 rather than introducing a character class.
1343 A character class matches any of the characters between the square brackets.
1344 A range of characters may be specified using a minus sign.
1345 The character class may be complemented by making an exclamation point
1347 the first character of the character class.
1351 in a character class, make it the first character listed
1357 make it the first or last character listed.
1358 .Ss Built-in Commands
1359 This section lists the commands which
1360 are built-in because they need to perform some operation
1361 that cannot be performed by a separate process.
1363 these, a built-in version of the
1365 command is provided for efficiency.
1366 .Bl -tag -width indent
1368 A null command that returns a 0 (true) exit value.
1370 The commands in the specified file are read and executed by the shell.
1373 command may be used to return to the
1380 characters, it is used as is.
1381 Otherwise, the shell searches the
1384 If it is not found in the
1386 it is sought in the current working directory.
1387 .It Ic alias Oo Ar name Ns Oo = Ns Ar string Oc ... Oc
1389 .Ar name Ns = Ns Ar string
1390 is specified, the shell defines the alias
1396 is specified, the value of the alias
1399 With no arguments, the
1401 built-in command prints the names and values of all defined aliases
1404 Alias values are written with appropriate quoting so that they are
1405 suitable for re-input to the shell.
1409 .It Ic bg Op Ar job ...
1410 Continue the specified jobs
1411 (or the current job if no jobs are given)
1413 .It Ic builtin Ar cmd Op Ar arg ...
1414 Execute the specified built-in command,
1416 This is useful when the user wishes to override a shell function
1417 with the same name as a built-in command.
1418 .It Ic bind Oo Fl aeklrsv Oc Oo Ar key Oo Ar command Oc Oc
1419 List or alter key bindings for the line editor.
1420 This command is documented in
1422 .It Ic cd Oo Fl L | P Oc Op Ar directory
1423 Switch to the specified
1425 or to the directory specified in the
1427 environment variable if no
1436 then the directories listed in the
1439 searched for the specified
1443 is unset, the current directory is searched.
1446 is the same as that of
1448 In an interactive shell,
1451 command will print out the name of the directory
1452 that it actually switched to
1453 if this is different from the name that the user gave.
1454 These may be different either because the
1456 mechanism was used or because a symbolic link was crossed.
1460 option is specified,
1462 is handled physically and symbolic links are resolved before
1464 components are processed.
1467 option is specified,
1469 is handled logically.
1470 This is the default.
1475 .It Ic command Oo Fl p Oc Op Ar utility Op Ar argument ...
1476 .It Ic command Oo Fl v | V Oc Op Ar utility
1477 The first form of invocation executes the specified
1479 as a simple command (see the
1485 option is specified, the command search is performed using a
1488 that is guaranteed to find all of the standard utilities.
1492 option is specified,
1494 is not executed but a description of its interpretation by the shell is
1496 For ordinary commands the output is the path name; for shell built-in
1497 commands, shell functions and keywords only the name is written.
1498 Aliases are printed as
1499 .Dq Ic alias Ar name Ns = Ns Ar value .
1503 option is identical to
1505 except for the output.
1507 .Dq Ar utility Ic is Ar description
1519 .It Ic echo Oo Fl e | n Oc Op Ar string ...
1520 Print a space-separated list of the arguments to the standard output
1521 and append a newline character.
1522 .Bl -tag -width indent
1524 Suppress the output of the trailing newline.
1526 Process C-style backslash escape sequences.
1528 understands the following character escapes:
1529 .Bl -tag -width indent
1531 Alert (ring the terminal bell)
1535 Suppress the trailing newline (this has the side-effect of truncating the
1536 line if it is not the last character)
1538 The ESC character (ASCII 0x1b)
1552 (Zero) The character whose octal value is nnn
1557 is not enclosed in quotes then the backslash itself must be escaped
1558 with a backslash to protect it from the shell.
1560 .Bd -literal -offset indent
1569 $ echo -e a\e\e\e\eb
1578 options may be specified.
1579 .It Ic eval Ar string ...
1580 Concatenate all the arguments with spaces.
1581 Then re-parse and execute the command.
1582 .It Ic exec Op Ar command Op arg ...
1586 the shell process is replaced with the specified program
1587 (which must be a real program, not a shell built-in command or function).
1588 Any redirections on the
1590 command are marked as permanent,
1591 so that they are not undone when the
1594 .It Ic exit Op Ar exitstatus
1595 Terminate the shell process.
1599 it is used as the exit status of the shell;
1600 otherwise the exit status of the preceding command is used.
1601 .It Ic export Ar name ...
1602 .It Ic export Op Fl p
1603 The specified names are exported so that they will
1604 appear in the environment of subsequent commands.
1605 The only way to un-export a variable is to
1608 The shell allows the value of a variable to be set
1609 at the same time as it is exported by writing
1610 .Bd -literal -offset indent
1614 With no arguments the export command lists the names
1615 of all exported variables.
1618 option is specified, the exported variables are printed as
1619 .Dq Ic export Ar name Ns = Ns Ar value
1620 lines, suitable for re-input to the shell.
1621 .It Ic fc Oo Fl e Ar editor Oc Op Ar first Op Ar last
1622 .It Ic fc Fl l Oo Fl nr Oc Op Ar first Op Ar last
1623 .It Ic fc Fl s Oo Ar old Ns = Ns Ar new Oc Op Ar first
1626 built-in command lists, or edits and re-executes,
1627 commands previously entered to an interactive shell.
1628 .Bl -tag -width indent
1630 Use the editor named by
1632 to edit the commands.
1633 The editor string is a command name,
1634 subject to search via the
1639 variable is used as a default when
1644 is null or unset, the value of the
1651 is used as the editor.
1653 List the commands rather than invoking
1655 The commands are written in the
1656 sequence indicated by the first and last operands, as
1659 with each command preceded by the command number.
1661 Suppress command numbers when listing with
1664 Reverse the order of the commands listed
1673 Re-execute the command without invoking an editor.
1676 Select the commands to list or edit.
1677 The number of previous commands that can be accessed
1678 are determined by the value of the
1685 or both are one of the following:
1686 .Bl -tag -width indent
1688 A positive number representing a command number;
1689 command numbers can be displayed with the
1693 A negative decimal number representing the
1694 command that was executed
1697 commands previously.
1698 For example, -1 is the immediately previous command.
1700 A string indicating the most recently entered command
1701 that begins with that string.
1704 operand is not also specified with
1706 the string form of the first operand cannot contain an embedded equal sign.
1710 The following environment variables affect the execution of
1712 .Bl -tag -width ".Ev HISTSIZE"
1714 Name of the editor to use for history editing.
1716 The number of previous commands that are accessible.
1721 or the current job to the foreground.
1722 .It Ic getopts Ar optstring Ar var
1728 command deprecates the older
1731 The first argument should be a series of letters, each possibly
1732 followed by a colon which indicates that the option takes an argument.
1733 The specified variable is set to the parsed option.
1735 the next argument is placed into the shell variable
1737 If an option takes an argument, it is placed into the shell variable
1739 If an invalid option is encountered,
1743 It returns a false value (1) when it encounters the end of the options.
1744 .It Ic hash Oo Fl rv Oc Op Ar command ...
1745 The shell maintains a hash table which remembers the locations of commands.
1746 With no arguments whatsoever, the
1748 command prints out the contents of this table.
1749 Entries which have not been looked at since the last
1751 command are marked with an asterisk;
1752 it is possible for these entries to be invalid.
1756 command removes each specified
1758 from the hash table (unless they are functions) and then locates it.
1763 prints the locations of the commands as it finds them.
1768 command to delete all the entries in the hash table except for functions.
1769 .It Ic jobid Op Ar job
1770 Print the process id's of the processes in the specified
1774 argument is omitted, use the current job.
1775 .It Ic jobs Oo Fl ls Oc Op Ar job ...
1776 Print information about the specified jobs, or all jobs if no
1779 The information printed includes job ID, status and command name.
1783 option is specified, the PID of each job is also printed.
1786 option is specified, only the PIDs of the jobs are printed, one per line.
1787 .It Ic local Oo Ar variable ... Oc Op Fl
1791 .It Ic pwd Op Fl L | P
1792 Print the path of the current directory.
1793 The built-in command may
1794 differ from the program of the same name because the
1795 built-in command remembers what the current directory
1796 is rather than recomputing it each time.
1799 However, if the current directory is
1801 the built-in version of
1803 will continue to print the old name for the directory.
1807 option is specified, symbolic links are resolved.
1810 option is specified, the shell's notion of the current directory
1811 is printed (symbolic links are not resolved).
1812 This is the default.
1813 .It Ic read Oo Fl p Ar prompt Oc Oo Fl t Ar timeout Oc Oo Fl er Oc Ar variable ...
1819 and the standard input is a terminal.
1821 read from the standard input.
1822 The trailing newline
1823 is deleted from the line and the line is split as
1824 described in the section on
1825 .Sx White Space Splitting (Field Splitting)
1827 the pieces are assigned to the variables in order.
1828 If there are more pieces than variables, the remaining
1829 pieces (along with the characters in
1831 that separated them)
1832 are assigned to the last variable.
1833 If there are more variables than pieces, the remaining
1834 variables are assigned the null string.
1836 Backslashes are treated specially, unless the
1840 If a backslash is followed by
1841 a newline, the backslash and the newline will be
1843 If a backslash is followed by any other
1844 character, the backslash will be deleted and the following
1845 character will be treated as though it were not in
1851 option is specified and the
1853 elapses before any input is supplied,
1856 command will return an exit status of 1 without assigning any values.
1859 value may optionally be followed by one of
1864 to explicitly specify seconds, minutes or hours.
1865 If none is supplied,
1871 option exists only for backward compatibility with older scripts.
1872 .It Ic readonly Oo Fl p Oc Op Ar name ...
1875 is marked as read only,
1876 so that it cannot be subsequently modified or unset.
1877 The shell allows the value of a variable to be set
1878 at the same time as it is marked read only
1879 by using the following form:
1880 .Bd -literal -offset indent
1884 With no arguments the
1886 command lists the names of all read only variables.
1889 option is specified, the read-only variables are printed as
1890 .Dq Ic readonly Ar name Ns = Ns Ar value
1891 lines, suitable for re-input to the shell.
1892 .It Ic return Op Ar exitstatus
1896 .It Ic set Oo Fl /+abCEefIimnpTuVvx Oc Oo Fl /+o Ar longname Oc Oo
1897 .Fl c Ar string Oc Op Fl - Ar arg ...
1900 command performs three different functions:
1903 With no arguments, it lists the values of all shell variables.
1905 If options are given,
1906 either in short form or using the long
1907 .Dq Fl /+o Ar longname
1909 it sets or clears the specified options as described in the section called
1910 .Sx Argument List Processing .
1914 option is specified,
1916 will replace the shell's positional parameters with the subsequent
1918 If no arguments follow the
1921 all the positional parameters will be cleared,
1922 which is equivalent to executing the command
1926 flag may be omitted when specifying arguments to be used
1927 as positional replacement parameters.
1928 This is not recommended,
1929 because the first argument may begin with a dash
1935 command will interpret as a request to enable or disable options.
1937 .It Ic setvar Ar variable Ar value
1938 Assigns the specified
1943 is intended to be used in functions that
1944 assign values to variables whose names are passed as parameters.
1945 In general it is better to write
1946 .Bd -literal -offset indent
1951 .It Ic shift Op Ar n
1952 Shift the positional parameters
1957 A shift sets the value of $1 to the value of $2,
1958 the value of $2 to the value of $3, and so on,
1959 decreasing the value of $# by one.
1960 If there are zero positional parameters, shifting does not do anything.
1962 Print the amount of time spent executing the shell and its children.
1963 The first output line shows the user and system times for the shell
1964 itself, the second one contains the user and system times for the
1966 .It Ic trap Oo Ar action Oc Ar signal ...
1968 Cause the shell to parse and execute
1973 The signals are specified by name or number.
1974 In addition, the pseudo-signal
1976 may be used to specify an action that is performed when the shell terminates.
1979 may be an empty string or a dash
1981 the former causes the specified signal to be ignored
1982 and the latter causes the default action to be taken.
1985 is another way to request the default action, for compatibility reasons this
1986 usage is not recommended though.
1987 When the shell forks off a subshell,
1988 it resets trapped (but not ignored) signals to the default action.
1991 command has no effect on signals that were ignored on entry to the shell.
1997 command to display a list of valid signal names.
1998 .It Ic type Op Ar name ...
2001 as a command and print the resolution of the command search.
2002 Possible resolutions are:
2003 shell keyword, alias, shell built-in command, command, tracked alias
2005 For aliases the alias expansion is printed;
2006 for commands and tracked aliases
2007 the complete pathname of the command is printed.
2008 .It Ic ulimit Oo Fl HSabcdflmnstuv Oc Op Ar limit
2009 Set or display resource limits (see
2013 is specified, the named resource will be set;
2014 otherwise the current resource value will be displayed.
2018 is specified, the hard limits will be set or displayed.
2019 While everybody is allowed to reduce a hard limit,
2020 only the superuser can increase it.
2024 specifies the soft limits instead.
2025 When displaying limits,
2031 The default is to display the soft limits,
2032 and to set both the hard and the soft limits.
2038 command to display all resources.
2041 is not acceptable in this mode.
2043 The remaining options specify which resource value is to be
2044 displayed or modified.
2045 They are mutually exclusive.
2046 .Bl -tag -width indent
2048 The maximum size of socket buffer usage, in bytes.
2049 .It Fl c Ar coredumpsize
2050 The maximal size of core dump files, in 512-byte blocks.
2051 .It Fl d Ar datasize
2052 The maximal size of the data segment of a process, in kilobytes.
2053 .It Fl f Ar filesize
2054 The maximal size of a file, in 512-byte blocks.
2055 .It Fl l Ar lockedmem
2056 The maximal size of memory that can be locked by a process, in
2058 .It Fl m Ar memoryuse
2059 The maximal resident set size of a process, in kilobytes.
2061 The maximal number of descriptors that could be opened by a process.
2062 .It Fl s Ar stacksize
2063 The maximal size of the stack segment, in kilobytes.
2065 The maximal amount of CPU time to be used by each process, in seconds.
2066 .It Fl u Ar userproc
2067 The maximal number of simultaneous processes for this user ID.
2068 .It Fl v Ar virtualmem
2069 The maximal virtual size of a process, in kilobytes.
2071 .It Ic umask Oo Fl S Oc Op Ar mask
2072 Set the file creation mask (see
2074 to the octal or symbolic (see
2078 If the argument is omitted, the current mask value is printed.
2081 option is specified, the output is symbolic, otherwise the output is octal.
2082 .It Ic unalias Oo Fl a Oc Op Ar name ...
2083 The specified alias names are removed.
2086 is specified, all aliases are removed.
2087 .It Ic unset Oo Fl fv Oc Ar name ...
2088 The specified variables or functions are unset and unexported.
2091 option is specified or no options are given, the
2093 arguments are treated as variable names.
2096 option is specified, the
2098 arguments are treated as function names.
2099 .It Ic wait Op Ar job
2100 Wait for the specified
2102 to complete and return the exit status of the last process in the
2104 If the argument is omitted, wait for all jobs to complete
2105 and return an exit status of zero.
2107 .Ss Commandline Editing
2110 is being used interactively from a terminal, the current command
2111 and the command history
2115 .Sx Built-in Commands )
2116 can be edited using vi-mode command line editing.
2117 This mode uses commands similar
2118 to a subset of those described in the vi man page.
2123 enables vi-mode editing and places
2125 into vi insert mode.
2126 With vi-mode enabled,
2128 can be switched between insert mode and command mode by typing
2132 while in command mode will pass the line to the shell.
2138 command can be used to enable a subset of
2139 emacs-style command line editing features.
2141 The following environment variables affect the execution of
2143 .Bl -tag -width ".Ev HISTSIZE"
2145 The search path used with the
2149 The fallback editor used with the
2152 If not set, the default editor is
2155 The default editor used with the
2159 The number of previous commands that are accessible.
2161 The starting directory of
2164 Input Field Separators.
2165 This is normally set to
2171 .Sx White Space Splitting
2172 section for more details.
2174 The name of a mail file, that will be checked for the arrival of new
2181 separated list of file names, for the shell to check for incoming
2183 This environment setting overrides the
2186 There is a maximum of 10 mailboxes that can be monitored at once.
2188 The default search path for executables.
2191 section for details.
2193 The primary prompt string, which defaults to
2195 unless you are the superuser, in which case it defaults to
2198 The secondary prompt string, which defaults to
2201 The default terminal setting for the shell.
2202 This is inherited by children of the shell, and is used in the history
2206 Errors that are detected by the shell, such as a syntax error, will
2207 cause the shell to exit with a non-zero exit status.
2208 If the shell is not an interactive shell, the execution of the shell
2209 file will be aborted.
2210 Otherwise the shell will return the exit status of the last command
2211 executed, or if the exit builtin is used with a numeric argument, it
2212 will return the argument.
2236 utility does not recognize multibyte characters.
projects / FreeBSD / FreeBSD.git / blob