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44 .Nd command interpreter (shell)
47 .Op Fl /+abCEefIimnPpTuVvx
48 .Op Fl /+o Ar longname
54 .Op Fl /+abCEefIimnPpTuVvx
55 .Op Fl /+o Ar longname
62 .Op Fl /+abCEefIimnPpTuVvx
63 .Op Fl /+o Ar longname
69 utility is the standard command interpreter for the system.
70 The current version of
74 specification for the shell.
75 It only supports features
78 plus a few Berkeley extensions.
79 This man page is not intended to be a tutorial nor a complete
80 specification of the shell.
82 The shell is a command that reads lines from
83 either a file or the terminal, interprets them, and
84 generally executes other commands.
85 It is the program that is started when a user logs into the system,
86 although a user can select a different shell with the
90 implements a language that has flow control constructs,
91 a macro facility that provides a variety of features in
92 addition to data storage, along with built-in history and line
94 It incorporates many features to
95 aid interactive use and has the advantage that the interpretative
96 language is common to both interactive and non-interactive
98 That is, commands can be typed directly
99 to the running shell or can be put into a file,
100 which can be executed directly by the shell.
103 .\" XXX This next sentence is incredibly confusing.
105 If no arguments are present and if the standard input of the shell
106 is connected to a terminal
110 the shell is considered an interactive shell.
112 generally prompts before each command and handles programming
113 and command errors differently (as described below).
114 When first starting, the shell inspects argument 0, and
115 if it begins with a dash
117 the shell is also considered a login shell.
118 This is normally done automatically by the system
119 when the user first logs in.
120 A login shell first reads commands
125 in a user's home directory,
127 If the environment variable
129 is set on entry to a shell, or is set in the
131 of a login shell, the shell then subjects its value to parameter expansion
132 and arithmetic expansion and reads commands from the named file.
133 Therefore, a user should place commands that are to be executed only
136 file, and commands that are executed for every shell inside the
141 variable to some file by placing the following line in the file
143 in the home directory,
146 the filename desired:
148 .Dl "ENV=$HOME/.shinit; export ENV"
150 The first non-option argument specified on the command line
151 will be treated as the
152 name of a file from which to read commands (a shell script), and
153 the remaining arguments are set as the positional parameters
157 Otherwise, the shell reads commands
158 from its standard input.
160 Unlike older versions of
164 script is only sourced on invocation of interactive shells.
166 closes a well-known, and sometimes easily exploitable security
167 hole related to poorly thought out
170 .Ss Argument List Processing
171 All of the single letter options to
173 have a corresponding long name,
174 with the exception of
178 These long names are provided next to the single letter options
179 in the descriptions below.
180 The long name for an option may be specified as an argument to the
184 Once the shell is running,
185 the long name for an option may be specified as an argument to the
190 (described later in the section called
191 .Sx Built-in Commands ) .
192 Introducing an option with a dash
202 will stop option processing and will force the remaining
203 words on the command line to be treated as arguments.
208 options do not have long names.
209 They take arguments and are described after the single letter options.
210 .Bl -tag -width indent
211 .It Fl a Li allexport
212 Flag variables for export when assignments are made to them.
214 Enable asynchronous notification of background job
217 .It Fl C Li noclobber
218 Do not overwrite existing files with
223 command line editor (disables the
225 option if it has been set;
226 set automatically when interactive on terminals).
228 Exit immediately if any untested command fails in non-interactive mode.
229 The exit status of a command is considered to be
230 explicitly tested if the command is part of the list used to control
232 .Ic if , elif , while ,
235 if the command is the left
240 operator; or if the command is a pipeline preceded by the
243 If a shell function is executed and its exit status is explicitly
244 tested, all commands of the function are considered to be tested as
247 Disable pathname expansion.
248 .It Fl I Li ignoreeof
251 from input when in interactive mode.
252 .It Fl i Li interactive
253 Force the shell to behave interactively.
255 Turn on job control (set automatically when interactive).
257 If not interactive, read commands but do not
259 This is useful for checking the
260 syntax of shell scripts.
262 Change the default for the
268 (logical directory layout)
271 (physical directory layout).
272 .It Fl p Li privileged
273 Turn on privileged mode.
274 This mode is enabled on startup
275 if either the effective user or group ID is not equal to the
276 real user or group ID.
277 Turning this mode off sets the
278 effective user and group IDs to the real user and group IDs.
279 When this mode is enabled for interactive shells, the file
280 .Pa /etc/suid_profile
281 is sourced instead of
285 is sourced, and the contents of the
287 variable are ignored.
289 Read commands from standard input (set automatically
290 if no file arguments are present).
292 no effect when set after the shell has already started
293 running (i.e., when set with the
296 .It Fl T Li trapsasync
297 When waiting for a child, execute traps immediately.
298 If this option is not set,
299 traps are executed after the child exits,
302 This nonstandard option is useful for putting guarding shells around
303 children that block signals.
304 The surrounding shell may kill the child
305 or it may just return control to the tty and leave the child alone,
307 .Bd -literal -offset indent
308 sh -T -c "trap 'exit 1' 2 ; some-blocking-program"
311 Write a message to standard error when attempting
312 to expand a variable, a positional parameter or
313 the special parameter
315 that is not set, and if the
316 shell is not interactive, exit immediately.
320 command line editor (disables
324 The shell writes its input to standard error
326 Useful for debugging.
329 (preceded by the value of the
331 variable subjected to parameter expansion and arithmetic expansion)
332 to standard error before it is executed.
333 Useful for debugging.
334 .It "\ \ " Em tabcomplete
335 Enables filename completion in the command line editor.
336 Typing a tab character will extend the current input word to match a
338 If more than one filename matches it is only extended to be the common prefix.
339 Typing a second tab character will list all the matching names.
340 Turned on by default in an interactive shell.
345 option causes the commands to be read from the
347 operand instead of from the standard input.
348 Keep in mind that this option only accepts a single string as its
349 argument, hence multi-word strings must be quoted.
353 option takes as its only argument the long name of an option
354 to be enabled or disabled.
355 For example, the following two invocations of
357 both enable the built-in
360 .Bd -literal -offset indent
365 If used without an argument, the
367 option displays the current option settings in a human-readable format.
370 is used without an argument, the current option settings are output
371 in a format suitable for re-input into the shell.
372 .Ss Lexical Structure
373 The shell reads input in terms of lines from a file and breaks
374 it up into words at whitespace (blanks and tabs), and at
378 which are special to the shell.
379 There are two types of operators: control operators and
380 redirection operators (their meaning is discussed later).
381 The following is a list of valid operators:
382 .Bl -tag -width indent
383 .It Control operators:
384 .Bl -column "XXX" "XXX" "XXX" "XXX" "XXX" -offset center -compact
385 .It Li & Ta Li && Ta Li ( Ta Li ) Ta Li \en
386 .It Li ;; Ta Li ; Ta Li | Ta Li ||
388 .It Redirection operators:
389 .Bl -column "XXX" "XXX" "XXX" "XXX" "XXX" -offset center -compact
390 .It Li < Ta Li > Ta Li << Ta Li >> Ta Li <>
391 .It Li <& Ta Li >& Ta Li <<- Ta Li >|
397 introduces a comment if used at the beginning of a word.
398 The word starting with
400 and the rest of the line are ignored.
404 characters (character code 0) are not allowed in shell input.
406 Quoting is used to remove the special meaning of certain characters
407 or words to the shell, such as operators, whitespace, keywords,
410 There are four types of quoting: matched single quotes,
411 dollar-single quotes,
412 matched double quotes, and backslash.
413 .Bl -tag -width indent
415 Enclosing characters in single quotes preserves the literal
416 meaning of all the characters (except single quotes, making
417 it impossible to put single-quotes in a single-quoted string).
418 .It Dollar-Single Quotes
419 Enclosing characters between
423 preserves the literal meaning of all characters
424 except backslashes and single quotes.
425 A backslash introduces a C-style escape sequence:
426 .Bl -tag -width xUnnnnnnnn
428 Alert (ring the terminal bell)
432 The control character denoted by
438 is a backslash, it must be doubled.
460 The byte whose octal value is
462 (one to three digits)
464 The byte whose hexadecimal value is
466 (one or more digits only the last two of which are used)
468 The Unicode code point
470 (four hexadecimal digits)
471 .It \eU Ns Ar nnnnnnnn
472 The Unicode code point
474 (eight hexadecimal digits)
477 The sequences for Unicode code points are currently only useful with
479 They reject code point 0 and UTF-16 surrogates.
481 If an escape sequence would produce a byte with value 0,
482 that byte and the rest of the string until the matching single-quote
485 Any other string starting with a backslash is an error.
487 Enclosing characters within double quotes preserves the literal
488 meaning of all characters except dollar sign
494 The backslash inside double quotes is historically weird.
495 It remains literal unless it precedes the following characters,
496 which it serves to quote:
497 .Bl -column "XXX" "XXX" "XXX" "XXX" "XXX" -offset center -compact
498 .It Li $ Ta Li ` Ta Li \&" Ta Li \e\ Ta Li \en
501 A backslash preserves the literal meaning of the following
502 character, with the exception of the newline character
504 A backslash preceding a newline is treated as a line continuation.
507 Keywords or reserved words are words that have special meaning to the
508 shell and are recognized at the beginning of a line and
509 after a control operator.
510 The following are keywords:
511 .Bl -column "doneXX" "elifXX" "elseXX" "untilXX" "whileX" -offset center
512 .It Li \&! Ta { Ta } Ta Ic case Ta Ic do
513 .It Ic done Ta Ic elif Ta Ic else Ta Ic esac Ta Ic fi
514 .It Ic for Ta Ic if Ta Ic then Ta Ic until Ta Ic while
517 An alias is a name and corresponding value set using the
520 Wherever the command word of a simple command may occur,
521 and after checking for keywords if a keyword may occur, the shell
522 checks the word to see if it matches an alias.
523 If it does, it replaces it in the input stream with its value.
524 For example, if there is an alias called
536 Aliases provide a convenient way for naive users to
537 create shorthands for commands without having to learn how
538 to create functions with arguments.
539 Using aliases in scripts is discouraged
540 because the command that defines them must be executed
541 before the code that uses them is parsed.
542 This is fragile and not portable.
544 An alias name may be escaped in a command line, so that it is not
545 replaced by its alias value, by using quoting characters within or
546 adjacent to the alias name.
547 This is most often done by prefixing
548 an alias name with a backslash to execute a function, built-in, or
549 normal program with the same name.
554 The shell interprets the words it reads according to a
555 language, the specification of which is outside the scope
556 of this man page (refer to the BNF in the
559 Essentially though, a line is read and if
560 the first word of the line (or after a control operator)
561 is not a keyword, then the shell has recognized a
563 Otherwise, a complex command or some
564 other special construct may have been recognized.
566 If a simple command has been recognized, the shell performs
567 the following actions:
570 Leading words of the form
572 are stripped off and assigned to the environment of
574 Redirection operators and
575 their arguments (as described below) are stripped
576 off and saved for processing.
578 The remaining words are expanded as described in
580 .Sx Word Expansions ,
581 and the first remaining word is considered the command
582 name and the command is located.
584 words are considered the arguments of the command.
585 If no command name resulted, then the
587 variable assignments recognized in 1) affect the
590 Redirections are performed as described in
594 Redirections are used to change where a command reads its input
596 In general, redirections open, close, or
597 duplicate an existing reference to a file.
599 used for redirection is:
601 .D1 Oo Ar n Oc Ar redir-op file
605 is one of the redirection operators mentioned
607 The following gives some examples of how these
608 operators can be used.
609 Note that stdin and stdout are commonly used abbreviations
610 for standard input and standard output respectively.
611 .Bl -tag -width "1234567890XX" -offset indent
612 .It Oo Ar n Oc Ns Li > Ar file
613 redirect stdout (or file descriptor
617 .It Oo Ar n Oc Ns Li >| Ar file
618 same as above, but override the
621 .It Oo Ar n Oc Ns Li >> Ar file
622 append stdout (or file descriptor
626 .It Oo Ar n Oc Ns Li < Ar file
627 redirect stdin (or file descriptor
631 .It Oo Ar n Oc Ns Li <> Ar file
632 redirect stdin (or file descriptor
636 .It Oo Ar n1 Oc Ns Li <& Ns Ar n2
637 duplicate stdin (or file descriptor
641 .It Oo Ar n Oc Ns Li <&-
642 close stdin (or file descriptor
644 .It Oo Ar n1 Oc Ns Li >& Ns Ar n2
645 duplicate stdout (or file descriptor
649 .It Oo Ar n Oc Ns Li >&-
650 close stdout (or file descriptor
654 The following redirection is often called a
656 .Bd -unfilled -offset indent
657 .Oo Ar n Oc Ns Li << Ar delimiter
663 All the text on successive lines up to the delimiter is
664 saved away and made available to the command on standard
665 input, or file descriptor
670 as specified on the initial line is quoted, then the
672 is treated literally, otherwise the text is subjected to
673 parameter expansion, command substitution, and arithmetic
674 expansion (as described in the section on
675 .Sx Word Expansions ) .
684 .Ss Search and Execution
685 There are three types of commands: shell functions,
686 built-in commands, and normal programs.
687 The command is searched for (by name) in that order.
688 The three types of commands are all executed in a different way.
690 When a shell function is executed, all of the shell positional
693 which remains unchanged) are
694 set to the arguments of the shell function.
695 The variables which are explicitly placed in the environment of
696 the command (by placing assignments to them before the
697 function name) are made local to the function and are set
699 Then the command given in the function definition is executed.
700 The positional parameters are restored to their original values
701 when the command completes.
702 This all occurs within the current shell.
704 Shell built-in commands are executed internally to the shell, without
705 spawning a new process.
706 There are two kinds of built-in commands: regular and special.
707 Assignments before special builtins persist after they finish
708 executing and assignment errors, redirection errors and certain
709 operand errors cause a script to be aborted.
710 Special builtins cannot be overridden with a function.
711 Both regular and special builtins can affect the shell in ways
712 normal programs cannot.
714 Otherwise, if the command name does not match a function
715 or built-in command, the command is searched for as a normal
716 program in the file system (as described in the next section).
717 When a normal program is executed, the shell runs the program,
718 passing the arguments and the environment to the program.
719 If the program is not a normal executable file
720 (i.e., if it does not begin with the
730 but appears to be a text file,
731 the shell will run a new instance of
735 Note that previous versions of this document
736 and the source code itself misleadingly and sporadically
737 refer to a shell script without a magic number
739 .Dq "shell procedure" .
741 When locating a command, the shell first looks to see if
742 it has a shell function by that name.
744 built-in command by that name.
745 If a built-in command is not found,
746 one of two things happen:
749 Command names containing a slash are simply executed without
750 performing any searches.
752 The shell searches each entry in the
755 in turn for the command.
758 variable should be a series of
759 entries separated by colons.
760 Each entry consists of a
762 The current directory
763 may be indicated implicitly by an empty directory name,
764 or explicitly by a single period.
766 .Ss Command Exit Status
767 Each command has an exit status that can influence the behavior
768 of other shell commands.
769 The paradigm is that a command exits
770 with zero for normal or success, and non-zero for failure,
771 error, or a false indication.
772 The man page for each command
773 should indicate the various exit codes and what they mean.
774 Additionally, the built-in commands return exit codes, as does
775 an executed shell function.
777 If a command is terminated by a signal, its exit status is 128 plus
779 Signal numbers are defined in the header file
782 Complex commands are combinations of simple commands
783 with control operators or keywords, together creating a larger complex
785 More generally, a command is one of the following:
786 .Bl -item -offset indent
792 list or compound-list
799 Unless otherwise stated, the exit status of a command is
800 that of the last simple command executed by the command.
802 A pipeline is a sequence of one or more commands separated
803 by the control operator
805 The standard output of all but
806 the last command is connected to the standard input
808 The standard output of the last
809 command is inherited from the shell, as usual.
811 The format for a pipeline is:
813 .D1 Oo Li \&! Oc Ar command1 Op Li \&| Ar command2 ...
815 The standard output of
817 is connected to the standard input of
819 The standard input, standard output, or
820 both of a command is considered to be assigned by the
821 pipeline before any redirection specified by redirection
822 operators that are part of the command.
824 Note that unlike some other shells,
826 executes each process in a pipeline with more than one command
827 in a subshell environment and as a child of the
831 If the pipeline is not in the background (discussed later),
832 the shell waits for all commands to complete.
836 does not precede the pipeline, the
837 exit status is the exit status of the last command specified
839 Otherwise, the exit status is the logical
840 NOT of the exit status of the last command.
842 the last command returns zero, the exit status is 1; if
843 the last command returns greater than zero, the exit status
846 Because pipeline assignment of standard input or standard
847 output or both takes place before redirection, it can be
848 modified by redirection.
851 .Dl "command1 2>&1 | command2"
853 sends both the standard output and standard error of
855 to the standard input of
860 or newline terminator causes the preceding
862 (described below in the section called
863 .Sx Short-Circuit List Operators )
864 to be executed sequentially;
867 causes asynchronous execution of the preceding AND-OR-list.
868 .Ss Background Commands (&)
869 If a command is terminated by the control operator ampersand
871 the shell executes the command asynchronously;
872 the shell does not wait for the command to finish
873 before executing the next command.
875 The format for running a command in background is:
877 .D1 Ar command1 Li & Op Ar command2 Li & Ar ...
879 If the shell is not interactive, the standard input of an
880 asynchronous command is set to
882 .Ss Lists (Generally Speaking)
883 A list is a sequence of zero or more commands separated by
884 newlines, semicolons, or ampersands,
885 and optionally terminated by one of these three characters.
887 list are executed in the order they are written.
888 If command is followed by an ampersand, the shell starts the
889 command and immediately proceeds onto the next command;
890 otherwise it waits for the command to terminate before
891 proceeding to the next one.
892 .Ss Short-Circuit List Operators
896 are AND-OR list operators.
898 executes the first command, and then executes the second command
899 if the exit status of the first command is zero.
901 is similar, but executes the second command if the exit
902 status of the first command is nonzero.
906 both have the same priority.
907 .Ss Flow-Control Constructs (if, while, for, case)
911 .Bd -unfilled -offset indent -compact
915 .Ic then Ar list Oc Ar ...
923 .Bd -unfilled -offset indent -compact
929 The two lists are executed repeatedly while the exit status of the
933 command is similar, but has the word
938 repeat until the exit status of the first list is zero.
943 .Bd -unfilled -offset indent -compact
944 .Ic for Ar variable Op Ic in Ar word ...
951 and the following words are omitted,
954 The words are expanded, and then the list is executed
955 repeatedly with the variable set to each word in turn.
960 commands may be replaced with
970 .D1 Ic break Op Ar num
971 .D1 Ic continue Op Ar num
975 command terminates the
984 command continues with the next iteration of the innermost loop.
985 These are implemented as special built-in commands.
990 .Bd -unfilled -offset indent -compact
991 .Ic case Ar word Ic in
992 .Ar pattern Ns Li ) Ar list Li ;;
997 The pattern can actually be one or more patterns
1004 The exit code of the
1006 command is the exit code of the last command executed in the list or
1007 zero if no patterns were matched.
1008 .Ss Grouping Commands Together
1009 Commands may be grouped by writing either
1011 .D1 Li \&( Ns Ar list Ns Li \%)
1015 .D1 Li { Ar list Ns Li \&; }
1017 The first form executes the commands in a subshell environment.
1018 Note that built-in commands thus executed do not affect the current shell.
1019 The second form never forks another shell,
1020 so it is slightly more efficient.
1021 Grouping commands together this way allows the user to
1022 redirect their output as though they were one program:
1023 .Bd -literal -offset indent
1024 { echo -n "hello"; echo " world"; } > greeting
1027 The syntax of a function definition is
1029 .D1 Ar name Li \&( \&) Ar command
1031 A function definition is an executable statement; when
1032 executed it installs a function named
1035 exit status of zero.
1044 Variables may be declared to be local to a function by
1048 This should appear as the first statement of a function,
1051 .D1 Ic local Oo Ar variable ... Oc Op Fl
1055 command is implemented as a built-in command.
1057 When a variable is made local, it inherits the initial
1058 value and exported and readonly flags from the variable
1059 with the same name in the surrounding scope, if there is
1061 Otherwise, the variable is initially unset.
1063 uses dynamic scoping, so that if the variable
1065 is made local to function
1067 which then calls function
1069 references to the variable
1073 will refer to the variable
1077 not to the global variable named
1080 The only special parameter that can be made local is
1084 local causes any shell options that are
1087 command inside the function to be
1088 restored to their original values when the function
1095 .D1 Ic return Op Ar exitstatus
1097 It terminates the current executional scope, returning from the previous
1098 nested function, sourced script, or shell instance, in that order.
1101 command is implemented as a special built-in command.
1102 .Ss Variables and Parameters
1103 The shell maintains a set of parameters.
1105 denoted by a name is called a variable.
1107 the shell turns all the environment variables into shell
1109 New variables can be set using the form
1111 .D1 Ar name Ns = Ns Ar value
1113 Variables set by the user must have a name consisting solely
1114 of alphabetics, numerics, and underscores.
1115 The first letter of a variable name must not be numeric.
1116 A parameter can also be denoted by a number
1117 or a special character as explained below.
1118 .Ss Positional Parameters
1119 A positional parameter is a parameter denoted by a number greater than zero.
1120 The shell sets these initially to the values of its command line
1121 arguments that follow the name of the shell script.
1124 built-in command can also be used to set or reset them.
1125 .Ss Special Parameters
1126 Special parameters are parameters denoted by a single special character
1128 They are shown in the following list, exactly as they would appear in input
1129 typed by the user or in the source of a shell script.
1132 Expands to the positional parameters, starting from one.
1134 the expansion occurs within a double-quoted string
1135 it expands to a single field with the value of each parameter
1136 separated by the first character of the
1143 Expands to the positional parameters, starting from one.
1145 the expansion occurs within double-quotes, each positional
1146 parameter expands as a separate argument.
1147 If there are no positional parameters, the
1150 generates zero arguments, even when
1153 What this basically means, for example, is
1166 .Bd -literal -offset indent
1170 Expands to the number of positional parameters.
1172 Expands to the exit status of the most recent pipeline.
1174 (hyphen) Expands to the current option flags (the single-letter
1175 option names concatenated into a string) as specified on
1178 built-in command, or implicitly
1181 Expands to the process ID of the invoked shell.
1183 retains the same value of
1187 Expands to the process ID of the most recent background
1188 command executed from the current shell.
1190 pipeline, the process ID is that of the last command in the
1192 If this parameter is referenced, the shell will remember
1193 the process ID and its exit status until the
1195 built-in command reports completion of the process.
1197 (zero) Expands to the name of the shell script if passed on the command line,
1200 operand if given (with
1202 or otherwise argument 0 passed to the shell.
1204 .Ss Special Variables
1205 The following variables are set by the shell or
1206 have special meaning to it:
1207 .Bl -tag -width ".Va HISTSIZE"
1209 The search path used with the
1213 The fallback editor used with the
1216 If not set, the default editor is
1219 The default editor used with the
1223 The number of previous commands that are accessible.
1225 The user's home directory,
1226 used in tilde expansion and as a default directory for the
1230 Input Field Separators.
1231 This is normally set to
1237 .Sx White Space Splitting
1238 section for more details.
1240 The current line number in the script or function.
1242 The name of a mail file, that will be checked for the arrival of new
1249 separated list of file names, for the shell to check for incoming
1251 This variable overrides the
1254 There is a maximum of 10 mailboxes that can be monitored at once.
1256 The default search path for executables.
1259 section for details.
1261 The parent process ID of the invoked shell.
1262 This is set at startup
1263 unless this variable is in the environment.
1264 A later change of parent process ID is not reflected.
1265 A subshell retains the same value of
1268 The primary prompt string, which defaults to
1270 unless you are the superuser, in which case it defaults to
1273 The secondary prompt string, which defaults to
1276 The prefix for the trace output (if
1283 This clause describes the various expansions that are
1285 Not all expansions are performed on
1286 every word, as explained later.
1288 Tilde expansions, parameter expansions, command substitutions,
1289 arithmetic expansions, and quote removals that occur within
1290 a single word expand to a single field.
1292 splitting or pathname expansion that can create multiple
1293 fields from a single word.
1294 The single exception to this rule is
1295 the expansion of the special parameter
1297 within double-quotes,
1298 as was described above.
1300 The order of word expansion is:
1303 Tilde Expansion, Parameter Expansion, Command Substitution,
1304 Arithmetic Expansion (these all occur at the same time).
1306 Field Splitting is performed on fields generated by step (1)
1311 Pathname Expansion (unless the
1313 option is in effect).
1320 character is used to introduce parameter expansion, command
1321 substitution, or arithmetic expansion.
1322 .Ss Tilde Expansion (substituting a user's home directory)
1323 A word beginning with an unquoted tilde character
1326 subjected to tilde expansion.
1327 All the characters up to a slash
1329 or the end of the word are treated as a username
1330 and are replaced with the user's home directory.
1332 username is missing (as in
1334 the tilde is replaced with the value of the
1336 variable (the current user's home directory).
1337 .Ss Parameter Expansion
1338 The format for parameter expansion is as follows:
1340 .D1 Li ${ Ns Ar expression Ns Li }
1344 consists of all characters until the matching
1348 escaped by a backslash or within a single-quoted or double-quoted
1349 string, and characters in
1350 embedded arithmetic expansions, command substitutions, and variable
1351 expansions, are not examined in determining the matching
1353 If the variants with
1359 occur within a double-quoted string,
1360 as an extension there may be unquoted parts
1361 (via double-quotes inside the expansion);
1363 within such parts are also not examined in determining the matching
1366 The simplest form for parameter expansion is:
1368 .D1 Li ${ Ns Ar parameter Ns Li }
1370 The value, if any, of
1374 The parameter name or symbol can be enclosed in braces, which are
1375 optional except for positional parameters with more than one digit or
1376 when parameter is followed by a character that could be interpreted as
1378 If a parameter expansion occurs inside double-quotes:
1381 Pathname expansion is not performed on the results of the
1384 Field splitting is not performed on the results of the
1385 expansion, with the exception of the special parameter
1389 In addition, a parameter expansion can be modified by using one of the
1391 .Bl -tag -width indent
1392 .It Li ${ Ns Ar parameter Ns Li :- Ns Ar word Ns Li }
1396 is unset or null, the expansion of
1398 is substituted; otherwise, the value of
1401 .It Li ${ Ns Ar parameter Ns Li := Ns Ar word Ns Li }
1402 Assign Default Values.
1405 is unset or null, the expansion of
1415 does not prevent field splitting or pathname expansion.
1416 Only variables, not positional
1417 parameters or special parameters, can be
1418 assigned in this way.
1419 .It Li ${ Ns Ar parameter Ns Li :? Ns Oo Ar word Oc Ns Li }
1420 Indicate Error if Null or Unset.
1423 is unset or null, the expansion of
1425 (or a message indicating it is unset if
1427 is omitted) is written to standard
1428 error and the shell exits with a nonzero
1430 Otherwise, the value of
1434 interactive shell need not exit.
1435 .It Li ${ Ns Ar parameter Ns Li :+ Ns Ar word Ns Li }
1436 Use Alternate Value.
1439 is unset or null, null is substituted;
1440 otherwise, the expansion of
1445 In the parameter expansions shown previously, use of the colon in the
1446 format results in a test for a parameter that is unset or null; omission
1447 of the colon results in a test for a parameter that is only unset.
1451 inherits the type of quoting
1452 (unquoted, double-quoted or here-document)
1453 from the surroundings,
1454 with the exception that a backslash that quotes a closing brace is removed
1455 during quote removal.
1456 .Bl -tag -width indent
1457 .It Li ${# Ns Ar parameter Ns Li }
1459 The length in characters of
1464 The following four varieties of parameter expansion provide for substring
1466 In each case, pattern matching notation
1468 .Sx Shell Patterns ) ,
1469 rather than regular expression notation,
1470 is used to evaluate the patterns.
1471 If parameter is one of the special parameters
1475 the result of the expansion is unspecified.
1476 Enclosing the full parameter expansion string in double-quotes does not
1477 cause the following four varieties of pattern characters to be quoted,
1478 whereas quoting characters within the braces has this effect.
1479 .Bl -tag -width indent
1480 .It Li ${ Ns Ar parameter Ns Li % Ns Ar word Ns Li }
1481 Remove Smallest Suffix Pattern.
1484 is expanded to produce a pattern.
1486 parameter expansion then results in
1488 with the smallest portion of the
1489 suffix matched by the pattern deleted.
1490 .It Li ${ Ns Ar parameter Ns Li %% Ns Ar word Ns Li }
1491 Remove Largest Suffix Pattern.
1494 is expanded to produce a pattern.
1496 parameter expansion then results in
1498 with the largest portion of the
1499 suffix matched by the pattern deleted.
1500 .It Li ${ Ns Ar parameter Ns Li # Ns Ar word Ns Li }
1501 Remove Smallest Prefix Pattern.
1504 is expanded to produce a pattern.
1506 parameter expansion then results in
1508 with the smallest portion of the
1509 prefix matched by the pattern deleted.
1510 .It Li ${ Ns Ar parameter Ns Li ## Ns Ar word Ns Li }
1511 Remove Largest Prefix Pattern.
1514 is expanded to produce a pattern.
1516 parameter expansion then results in
1518 with the largest portion of the
1519 prefix matched by the pattern deleted.
1521 .Ss Command Substitution
1522 Command substitution allows the output of a command to be substituted in
1523 place of the command name itself.
1524 Command substitution occurs when
1525 the command is enclosed as follows:
1527 .D1 Li $( Ns Ar command Ns Li )\&
1529 or the backquoted version:
1531 .D1 Li ` Ns Ar command Ns Li `
1533 The shell expands the command substitution by executing command
1534 and replacing the command substitution
1535 with the standard output of the command,
1536 removing sequences of one or more newlines at the end of the substitution.
1537 Embedded newlines before the end of the output are not removed;
1538 however, during field splitting, they may be translated into spaces
1539 depending on the value of
1541 and the quoting that is in effect.
1542 The command is executed in a subshell environment,
1543 except that the built-in commands
1549 return information about the main shell environment
1550 if they are the only command in a command substitution.
1551 .Ss Arithmetic Expansion
1552 Arithmetic expansion provides a mechanism for evaluating an arithmetic
1553 expression and substituting its value.
1554 The format for arithmetic expansion is as follows:
1556 .D1 Li $(( Ns Ar expression Ns Li ))
1560 is treated as if it were in double-quotes, except
1561 that a double-quote inside the expression is not treated specially.
1563 shell expands all tokens in the
1565 for parameter expansion,
1566 command substitution,
1567 arithmetic expansion
1570 The allowed expressions are a subset of C expressions,
1572 .Bl -tag -width "Variables" -offset indent
1574 All values are of type
1577 Decimal, octal (starting with
1579 and hexadecimal (starting with
1583 Shell variables can be read and written
1584 and contain integer constants.
1587 .It Binary operators
1588 .Li "* / % + - << >> < <= > >= == != & ^ | && ||"
1589 .It Assignment operators
1590 .Li "= += -= *= /= %= <<= >>= &= ^= |="
1591 .It Conditional operator
1595 The result of the expression is substituted in decimal.
1596 .Ss White Space Splitting (Field Splitting)
1597 After parameter expansion, command substitution, and
1598 arithmetic expansion the shell scans the results of
1599 expansions and substitutions that did not occur in double-quotes for
1600 field splitting and multiple fields can result.
1602 The shell treats each character of the
1604 variable as a delimiter and uses
1605 the delimiters to split the results of parameter expansion and command
1606 substitution into fields.
1607 .Ss Pathname Expansion (File Name Generation)
1611 file name generation is performed
1612 after word splitting is complete.
1614 viewed as a series of patterns, separated by slashes.
1616 process of expansion replaces the word with the names of
1617 all existing files whose names can be formed by replacing
1618 each pattern with a string that matches the specified pattern.
1619 There are two restrictions on this: first, a pattern cannot match
1620 a string containing a slash, and second,
1621 a pattern cannot match a string starting with a period
1622 unless the first character of the pattern is a period.
1623 The next section describes the patterns used for both
1624 Pathname Expansion and the
1628 A pattern consists of normal characters, which match themselves,
1629 and meta-characters.
1630 The meta-characters are
1636 These characters lose their special meanings if they are quoted.
1637 When command or variable substitution is performed and the dollar sign
1638 or back quotes are not double-quoted, the value of the
1639 variable or the output of the command is scanned for these
1640 characters and they are turned into meta-characters.
1644 matches any string of characters.
1647 matches any single character.
1650 introduces a character class.
1651 The end of the character class is indicated by a
1659 rather than introducing a character class.
1660 A character class matches any of the characters between the square brackets.
1661 A range of characters may be specified using a minus sign.
1662 The character class may be complemented by making an exclamation point
1666 the first character of the character class.
1670 in a character class, make it the first character listed
1678 make it the first or last character listed.
1679 .Ss Built-in Commands
1680 This section lists the built-in commands.
1681 .Bl -tag -width indent
1683 A null command that returns a 0 (true) exit value.
1685 The commands in the specified file are read and executed by the shell.
1688 command may be used to return to the
1695 characters, it is used as is.
1696 Otherwise, the shell searches the
1699 If it is not found in the
1701 it is sought in the current working directory.
1703 A built-in equivalent of
1705 .It Ic alias Oo Ar name Ns Oo = Ns Ar string Oc Ar ... Oc
1707 .Ar name Ns = Ns Ar string
1708 is specified, the shell defines the alias
1714 is specified, the value of the alias
1717 With no arguments, the
1719 built-in command prints the names and values of all defined aliases
1722 Alias values are written with appropriate quoting so that they are
1723 suitable for re-input to the shell.
1727 .It Ic bg Op Ar job ...
1728 Continue the specified jobs
1729 (or the current job if no jobs are given)
1731 .It Ic bind Oo Fl aeklrsv Oc Oo Ar key Oo Ar command Oc Oc
1732 List or alter key bindings for the line editor.
1733 This command is documented in
1735 .It Ic break Op Ar num
1737 .Sx Flow-Control Constructs
1739 .It Ic builtin Ar cmd Op Ar arg ...
1740 Execute the specified built-in command,
1742 This is useful when the user wishes to override a shell function
1743 with the same name as a built-in command.
1744 .It Ic cd Oo Fl L | P Oc Oo Fl e Oc Op Ar directory
1745 Switch to the specified
1747 or to the directory specified in the
1749 environment variable if no
1758 then the directories listed in the
1761 searched for the specified
1765 is unset, the current directory is searched.
1768 is the same as that of
1770 In an interactive shell,
1773 command will print out the name of the directory
1774 that it actually switched to
1775 if this is different from the name that the user gave.
1776 These may be different either because the
1778 mechanism was used or because a symbolic link was crossed.
1782 option is specified,
1784 is handled physically and symbolic links are resolved before
1786 components are processed.
1789 option is specified,
1791 is handled logically.
1792 This is the default.
1798 to return exit status 1 if the full pathname of the new directory
1799 cannot be determined reliably or at all.
1800 Normally this is not considered an error,
1801 although a warning is printed.
1806 .It Ic command Oo Fl p Oc Op Ar utility Op Ar argument ...
1807 .It Ic command Oo Fl p Oc Fl v Ar utility
1808 .It Ic command Oo Fl p Oc Fl V Ar utility
1809 The first form of invocation executes the specified
1811 ignoring shell functions in the search.
1814 is a special builtin,
1815 it is executed as if it were a regular builtin.
1819 option is specified, the command search is performed using a
1822 that is guaranteed to find all of the standard utilities.
1826 option is specified,
1828 is not executed but a description of its interpretation by the shell is
1830 For ordinary commands the output is the path name; for shell built-in
1831 commands, shell functions and keywords only the name is written.
1832 Aliases are printed as
1833 .Dq Ic alias Ar name Ns = Ns Ar value .
1837 option is identical to
1839 except for the output.
1841 .Dq Ar utility Ic is Ar description
1847 a special shell builtin,
1854 .It Ic continue Op Ar num
1856 .Sx Flow-Control Constructs
1858 .It Ic echo Oo Fl e | n Oc Op Ar string ...
1859 Print a space-separated list of the arguments to the standard output
1860 and append a newline character.
1861 .Bl -tag -width indent
1863 Suppress the output of the trailing newline.
1865 Process C-style backslash escape sequences.
1868 command understands the following character escapes:
1869 .Bl -tag -width indent
1871 Alert (ring the terminal bell)
1875 Suppress the trailing newline (this has the side-effect of truncating the
1876 line if it is not the last character)
1894 (Zero) The character whose octal value is
1900 is not enclosed in quotes then the backslash itself must be escaped
1901 with a backslash to protect it from the shell.
1903 .Bd -literal -offset indent
1912 $ echo -e a\e\e\e\eb
1921 options may be specified.
1922 .It Ic eval Ar string ...
1923 Concatenate all the arguments with spaces.
1924 Then re-parse and execute the command.
1925 .It Ic exec Op Ar command Op Ar arg ...
1929 the shell process is replaced with the specified program
1930 (which must be a real program, not a shell built-in command or function).
1931 Any redirections on the
1933 command are marked as permanent,
1934 so that they are not undone when the
1937 .It Ic exit Op Ar exitstatus
1938 Terminate the shell process.
1942 it is used as the exit status of the shell.
1943 Otherwise, if the shell is executing an
1945 trap, the exit status of the last command before the trap is used;
1946 if the shell is executing a trap for a signal,
1947 the shell exits by resending the signal to itself.
1948 Otherwise, the exit status of the preceding command is used.
1949 The exit status should be an integer between 0 and 255.
1950 .It Ic export Ar name ...
1951 .It Ic export Op Fl p
1952 The specified names are exported so that they will
1953 appear in the environment of subsequent commands.
1954 The only way to un-export a variable is to
1957 The shell allows the value of a variable to be set
1958 at the same time as it is exported by writing
1960 .D1 Ic export Ar name Ns = Ns Ar value
1962 With no arguments the
1964 command lists the names
1965 of all exported variables.
1968 option is specified, the exported variables are printed as
1969 .Dq Ic export Ar name Ns = Ns Ar value
1970 lines, suitable for re-input to the shell.
1972 A null command that returns a non-zero (false) exit value.
1973 .It Ic fc Oo Fl e Ar editor Oc Op Ar first Op Ar last
1974 .It Ic fc Fl l Oo Fl nr Oc Op Ar first Op Ar last
1975 .It Ic fc Fl s Oo Ar old Ns = Ns Ar new Oc Op Ar first
1978 built-in command lists, or edits and re-executes,
1979 commands previously entered to an interactive shell.
1980 .Bl -tag -width indent
1982 Use the editor named by
1984 to edit the commands.
1987 string is a command name,
1988 subject to search via the
1993 variable is used as a default when
1998 is null or unset, the value of the
2005 is used as the editor.
2007 List the commands rather than invoking
2009 The commands are written in the
2010 sequence indicated by the
2014 operands, as affected by
2016 with each command preceded by the command number.
2018 Suppress command numbers when listing with
2021 Reverse the order of the commands listed
2030 Re-execute the command without invoking an editor.
2033 Select the commands to list or edit.
2034 The number of previous commands that can be accessed
2035 are determined by the value of the
2042 or both are one of the following:
2043 .Bl -tag -width indent
2044 .It Oo Cm + Oc Ns Ar num
2045 A positive number representing a command number;
2046 command numbers can be displayed with the
2050 A negative decimal number representing the
2051 command that was executed
2054 commands previously.
2055 For example, \-1 is the immediately previous command.
2057 A string indicating the most recently entered command
2058 that begins with that string.
2060 .Ar old Ns = Ns Ar new
2061 operand is not also specified with
2063 the string form of the first operand cannot contain an embedded equal sign.
2067 The following variables affect the execution of
2069 .Bl -tag -width ".Va HISTSIZE"
2071 Name of the editor to use for history editing.
2073 The number of previous commands that are accessible.
2078 or the current job to the foreground.
2079 .It Ic getopts Ar optstring var
2086 command deprecates the older
2089 The first argument should be a series of letters, each possibly
2090 followed by a colon which indicates that the option takes an argument.
2091 The specified variable is set to the parsed option.
2093 the next argument is placed into the shell variable
2095 If an option takes an argument, it is placed into the shell variable
2097 If an invalid option is encountered,
2101 It returns a false value (1) when it encounters the end of the options.
2102 .It Ic hash Oo Fl rv Oc Op Ar command ...
2103 The shell maintains a hash table which remembers the locations of commands.
2104 With no arguments whatsoever, the
2106 command prints out the contents of this table.
2107 Entries which have not been looked at since the last
2109 command are marked with an asterisk;
2110 it is possible for these entries to be invalid.
2114 command removes each specified
2116 from the hash table (unless they are functions) and then locates it.
2121 prints the locations of the commands as it finds them.
2126 command to delete all the entries in the hash table except for functions.
2127 .It Ic jobid Op Ar job
2128 Print the process IDs of the processes in the specified
2132 argument is omitted, use the current job.
2133 .It Ic jobs Oo Fl lps Oc Op Ar job ...
2134 Print information about the specified jobs, or all jobs if no
2137 The information printed includes job ID, status and command name.
2141 option is specified, the PID of each job is also printed.
2144 option is specified, only the process IDs for the process group leaders
2145 are printed, one per line.
2148 option is specified, only the PIDs of the job commands are printed, one per
2151 A built-in equivalent of
2153 that additionally supports sending signals to jobs.
2154 .It Ic local Oo Ar variable ... Oc Op Fl
2159 A built-in equivalent of
2161 .It Ic pwd Op Fl L | P
2162 Print the path of the current directory.
2163 The built-in command may
2164 differ from the program of the same name because the
2165 built-in command remembers what the current directory
2166 is rather than recomputing it each time.
2169 However, if the current directory is
2171 the built-in version of
2173 will continue to print the old name for the directory.
2177 option is specified, symbolic links are resolved.
2180 option is specified, the shell's notion of the current directory
2181 is printed (symbolic links are not resolved).
2182 This is the default.
2183 .It Ic read Oo Fl p Ar prompt Oc Oo
2184 .Fl t Ar timeout Oc Oo Fl er Oc Ar variable ...
2190 and the standard input is a terminal.
2192 read from the standard input.
2193 The trailing newline
2194 is deleted from the line and the line is split as
2195 described in the section on
2196 .Sx White Space Splitting (Field Splitting)
2198 the pieces are assigned to the variables in order.
2199 If there are more pieces than variables, the remaining
2200 pieces (along with the characters in
2202 that separated them)
2203 are assigned to the last variable.
2204 If there are more variables than pieces, the remaining
2205 variables are assigned the null string.
2207 Backslashes are treated specially, unless the
2211 If a backslash is followed by
2212 a newline, the backslash and the newline will be
2214 If a backslash is followed by any other
2215 character, the backslash will be deleted and the following
2216 character will be treated as though it were not in
2222 option is specified and the
2224 elapses before a complete line of input is supplied,
2227 command will return an exit status of 1 without assigning any values.
2230 value may optionally be followed by one of
2235 to explicitly specify seconds, minutes or hours.
2236 If none is supplied,
2242 option exists only for backward compatibility with older scripts.
2243 .It Ic readonly Oo Fl p Oc Op Ar name ...
2246 is marked as read only,
2247 so that it cannot be subsequently modified or unset.
2248 The shell allows the value of a variable to be set
2249 at the same time as it is marked read only
2250 by using the following form:
2252 .D1 Ic readonly Ar name Ns = Ns Ar value
2254 With no arguments the
2256 command lists the names of all read only variables.
2259 option is specified, the read-only variables are printed as
2260 .Dq Ic readonly Ar name Ns = Ns Ar value
2261 lines, suitable for re-input to the shell.
2262 .It Ic return Op Ar exitstatus
2266 .It Ic set Oo Fl /+abCEefIimnpTuVvx Oc Oo Fl /+o Ar longname Oc Oo
2267 .Fl c Ar string Oc Op Fl - Ar arg ...
2270 command performs three different functions:
2273 With no arguments, it lists the values of all shell variables.
2275 If options are given,
2276 either in short form or using the long
2277 .Dq Fl /+o Ar longname
2279 it sets or clears the specified options as described in the section called
2280 .Sx Argument List Processing .
2284 option is specified,
2286 will replace the shell's positional parameters with the subsequent
2288 If no arguments follow the
2291 all the positional parameters will be cleared,
2292 which is equivalent to executing the command
2296 flag may be omitted when specifying arguments to be used
2297 as positional replacement parameters.
2298 This is not recommended,
2299 because the first argument may begin with a dash
2305 command will interpret as a request to enable or disable options.
2307 .It Ic setvar Ar variable value
2308 Assigns the specified
2314 command is intended to be used in functions that
2315 assign values to variables whose names are passed as parameters.
2316 In general it is better to write
2317 .Dq Ar variable Ns = Ns Ar value
2320 .It Ic shift Op Ar n
2321 Shift the positional parameters
2326 A shift sets the value of
2335 decreasing the value of
2338 If there are zero positional parameters, shifting does not do anything.
2340 A built-in equivalent of
2343 Print the amount of time spent executing the shell and its children.
2344 The first output line shows the user and system times for the shell
2345 itself, the second one contains the user and system times for the
2347 .It Ic trap Oo Ar action Oc Ar signal ...
2349 Cause the shell to parse and execute
2354 The signals are specified by name or number.
2355 In addition, the pseudo-signal
2357 may be used to specify an
2359 that is performed when the shell terminates.
2362 may be an empty string or a dash
2364 the former causes the specified signal to be ignored
2365 and the latter causes the default action to be taken.
2368 is another way to request the default action, for compatibility reasons this
2369 usage is not recommended though.
2370 In a subshell environment,
2371 the shell resets trapped (but not ignored) signals to the default action.
2374 command has no effect on signals that were ignored on entry to the shell.
2380 command to display a list of valid signal names.
2382 A null command that returns a 0 (true) exit value.
2383 .It Ic type Op Ar name ...
2386 as a command and print the resolution of the command search.
2387 Possible resolutions are:
2388 shell keyword, alias, special shell builtin, shell builtin, command,
2391 For aliases the alias expansion is printed;
2392 for commands and tracked aliases
2393 the complete pathname of the command is printed.
2394 .It Ic ulimit Oo Fl HSabcdflmnstuv Oc Op Ar limit
2395 Set or display resource limits (see
2399 is specified, the named resource will be set;
2400 otherwise the current resource value will be displayed.
2404 is specified, the hard limits will be set or displayed.
2405 While everybody is allowed to reduce a hard limit,
2406 only the superuser can increase it.
2410 specifies the soft limits instead.
2411 When displaying limits,
2417 The default is to display the soft limits,
2418 and to set both the hard and the soft limits.
2424 command to display all resources.
2427 is not acceptable in this mode.
2429 The remaining options specify which resource value is to be
2430 displayed or modified.
2431 They are mutually exclusive.
2432 .Bl -tag -width indent
2434 The maximum size of socket buffer usage, in bytes.
2435 .It Fl c Ar coredumpsize
2436 The maximal size of core dump files, in 512-byte blocks.
2437 .It Fl d Ar datasize
2438 The maximal size of the data segment of a process, in kilobytes.
2439 .It Fl f Ar filesize
2440 The maximal size of a file, in 512-byte blocks.
2441 .It Fl l Ar lockedmem
2442 The maximal size of memory that can be locked by a process, in
2444 .It Fl m Ar memoryuse
2445 The maximal resident set size of a process, in kilobytes.
2447 The maximal number of descriptors that could be opened by a process.
2448 .It Fl s Ar stacksize
2449 The maximal size of the stack segment, in kilobytes.
2451 The maximal amount of CPU time to be used by each process, in seconds.
2452 .It Fl u Ar userproc
2453 The maximal number of simultaneous processes for this user ID.
2454 .It Fl v Ar virtualmem
2455 The maximal virtual size of a process, in kilobytes.
2457 .It Ic umask Oo Fl S Oc Op Ar mask
2458 Set the file creation mask (see
2460 to the octal or symbolic (see
2464 If the argument is omitted, the current mask value is printed.
2467 option is specified, the output is symbolic, otherwise the output is octal.
2468 .It Ic unalias Oo Fl a Oc Op Ar name ...
2469 The specified alias names are removed.
2472 is specified, all aliases are removed.
2473 .It Ic unset Oo Fl fv Oc Ar name ...
2474 The specified variables or functions are unset and unexported.
2477 option is specified or no options are given, the
2479 arguments are treated as variable names.
2482 option is specified, the
2484 arguments are treated as function names.
2485 .It Ic wait Op Ar job
2486 Wait for the specified
2488 to complete and return the exit status of the last process in the
2490 If the argument is omitted, wait for all jobs to complete
2491 and return an exit status of zero.
2493 .Ss Commandline Editing
2496 is being used interactively from a terminal, the current command
2497 and the command history
2501 .Sx Built-in Commands )
2504 command line editing.
2505 This mode uses commands similar
2506 to a subset of those described in the
2524 can be switched between insert mode and command mode by typing
2528 while in command mode will pass the line to the shell.
2531 .Dq Li "set -o emacs"
2534 command can be used to enable a subset of
2536 command line editing features.
2538 The following environment variables affect the execution of
2540 .Bl -tag -width ".Ev LANGXXXXXX"
2542 Initialization file for interactive shells.
2543 .It Ev LANG , Ev LC_*
2545 These are inherited by children of the shell,
2546 and is used in a limited manner by the shell itself.
2548 An absolute pathname for the current directory,
2549 possibly containing symbolic links.
2550 This is used and updated by the shell.
2552 The default terminal setting for the shell.
2553 This is inherited by children of the shell, and is used in the history
2557 Additionally, all environment variables are turned into shell variables
2559 which may affect the shell as described under
2560 .Sx Special Variables .
2562 Errors that are detected by the shell, such as a syntax error, will
2563 cause the shell to exit with a non-zero exit status.
2564 If the shell is not an interactive shell, the execution of the shell
2565 file will be aborted.
2566 Otherwise the shell will return the exit status of the last command
2569 builtin is used with a numeric argument, it
2570 will return the argument.
2576 .Xr emacs 1 Pq Pa pkgsrc/editors/emacs ,
2590 command, the Thompson shell, appeared in
2592 It was superseded in
2594 by the Bourne shell, which inherited the name
2599 was rewritten in 1989 under the
2601 license after the Bourne shell from
2606 was originally written by
2607 .An Kenneth Almquist .
2611 utility does not recognize multibyte characters other than UTF-8.
2614 and the line editing library
2616 do not recognize multibyte characters.
2618 The characters generated by filename completion should probably be quoted
2619 to ensure that the filename is still valid after the input line has been
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