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1 '\" t
2 .\" Title: POSH
3 .\" Author: [see the "AUTHORS" section]
4 .\" Generator: DocBook XSL Stylesheets v1.75.2 <http://docbook.sf.net/>
5 .\" Date: 01/24/2011
6 .\" Manual: User commands
7 .\" Source: User commands
8 .\" Language: English
9 .\"
10 .TH "POSH" "1" "01/24/2011" "User commands" "User commands"
11 .\" -----------------------------------------------------------------
12 .\" * Define some portability stuff
13 .\" -----------------------------------------------------------------
14 .\" ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
15 .\" http://bugs.debian.org/507673
16 .\" http://lists.gnu.org/archive/html/groff/2009-02/msg00013.html
17 .\" ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
18 .ie \n(.g .ds Aq \(aq
19 .el .ds Aq '
20 .\" -----------------------------------------------------------------
21 .\" * set default formatting
22 .\" -----------------------------------------------------------------
23 .\" disable hyphenation
24 .nh
25 .\" disable justification (adjust text to left margin only)
26 .ad l
27 .\" -----------------------------------------------------------------
28 .\" * MAIN CONTENT STARTS HERE *
29 .\" -----------------------------------------------------------------
30 .SH "NAME"
31 posh \- Policy\-compliant Ordinary SHell
32 .SH "SYNOPSIS"
33 .HP \w'\fBposh\fR\ 'u
34 \fBposh\fR [+\-aCefilnuvx] [+\-o\ \fIoption\fR] [[\-c\ \fIcommand\-string\fR\ [\fIcommand\-name\fR]\ |\ \-s\ |\ \fIfile\fR\ ]\ [\fIargument\fR...]]
35 .SH "DESCRIPTION"
36 .PP
38 \fBposh\fR
39 is a reimplementation of the Bourne shell, a command interpreter for both interactive and script use\&.
40 .SS "Shell Startup"
41 .PP
42 The following options can be specified only on the command line:
43 .PP
44 \fB\-c\fR \fIcommand\-string\fR
45 .RS 4
46 the shell executes the command(s) contained in
47 \fIcommand\-string\fR
48 .RE
49 .PP
50 \fB\-i\fR
51 .RS 4
52 interactive mode \(em see below
53 .RE
54 .PP
55 \fB\-l\fR
56 .RS 4
57 login shell \(em see below interactive mode \(em see below
58 .RE
59 .PP
60 \fB\-s\fR
61 .RS 4
62 the shell reads commands from standard input; all non\-option arguments are positional parameters
63 .RE
64 .PP
65 In addition to the above, the options described in the
66 \fBset\fR
67 builtin command can also be used on the command line\&.
68 .PP
69 If neither the
70 \fB\-c\fR
71 nor the
72 \fB\-s\fR
73 options are specified, the first non\-option argument specifies the name of a file the shell reads commands from; if there are no non\-option arguments, the shell reads commands from standard input\&. The name of the shell (\fIi\&.e\&.\fR, the contents of the
74 \fB$0\fR) parameter is determined as follows: if the
75 \fB\-c\fR
76 option is used and there is a non\-option argument, it is used as the name; if commands are being read from a file, the file is used as the name; otherwise the name the shell was called with (\fIi\&.e\&.\fR, argv[0]) is used\&.
77 .PP
78 A shell is
79 \fBinteractive\fR
80 if the
81 \fB\-i\fR
82 option is used or if both standard input and standard error are attached to a tty\&. An interactive shell has job control enabled (if available), ignores the INT, QUIT and TERM signals, and prints prompts before reading input (see
83 \fBPS1\fR
84 and
85 \fBPS2\fR
86 parameters)\&.
87 .PP
88 A shell is
89 \fBprivileged\fR
90 if the
91 \fB\-p\fR
92 option is used or if the real user\-id or group\-id does not match the effective user\-id or group\-id (see
93 \fBgetuid\fR(2),
94 \fBgetgid\fR(2))\&. A privileged shell does not process $HOME/\&.profile\&. Instead the file /etc/suid_profile is processed\&. Clearing the privileged option causes the shell to set its effective user\-id (group\-id) to its real user\-id (group\-id)\&.
95 .PP
96 If the basename of the name the shell is called with (\fIi\&.e\&.\fR, argv[0]) starts with
97 \fB\-\fR
98 or if the
99 \fB\-l\fR
100 option is used, the shell is assumed to be a login shell and the shell reads and executes the contents of
101 /etc/profile
102 and
103 $HOME/\&.profile
104 if they exist and are readable\&.
105 .PP
106 The exit status of the shell is 127 if the command file specified on the command line could not be opened, or non\-zero if a fatal syntax error occurred during the execution of a script\&. In the absence of fatal errors, the exit status is that of the last command executed, or zero, if no command is executed\&.
107 .SS "Command Syntax"
108 .PP
109 The shell begins parsing its input by breaking it into words\&. Words, which are sequences of characters, are delimited by unquoted white\-space characters (space, tab and newline) or meta\-characters (<,
110 >,
111 |,
112 ;,
113 &,
114 (
115 and
116 ))\&. Aside from delimiting words, spaces and tabs are ignored, while newlines usually delimit commands\&. The meta\-characters are used in building the following tokens:
117 <,
118 <&,
119 <<,
120 >,
121 >&,
122 >>, etc\&. are used to specify redirections (see Input/Output Redirection below);
123 |
124 is used to create pipelines;
125 ;
126 is used to separate commands;
127 &
128 is used to create asynchronous pipelines;
129 &&
130 and
131 ||
132 are used to specify conditional execution;
133 ;;
134 is used in
135 case
136 statements; and lastly,
137 (
138 \&.\&.\&.
139 )
140 are used to create subshells\&.
141 .PP
142 White\-space and meta\-characters can be quoted individually using backslash (\fB\e\fR), or in groups using double (\fB"\fR) or single (\fB\*(Aq\fR) quotes\&. Note that the following characters are also treated specially by the shell and must be quoted if they are to represent themselves:
143 \fB\e\fR,
144 \fB"\fR,
145 \fB\*(Aq\fR,
146 \fB#\fR,
147 \fB$\fR,
148 \fB`\fR,
149 \fB~\fR,
150 \fB{\fR,
151 \fB}\fR,
152 \fB*\fR,
153 \fB?\fR
154 and
155 \fB[\fR\&. The first three of these are the above mentioned quoting characters (see Quoting below);
156 \fB#\fR, if used at the beginning of a word, introduces a comment \(em everything after the
157 \fB#\fR
158 up to the nearest newline is ignored;
159 \fB$\fR
160 is used to introduce parameter, command and arithmetic substitutions (see Substitution below);
161 \fB`\fR
162 introduces an old\-style command substitution (see Substitution below);
163 \fB~\fR
164 begins a directory expansion (see Tilde Expansion below);
165 \fB{\fR
166 and
167 \fB}\fR
168 delimit
169 \fBcsh\fR(1)
170 style alternations (see Brace Expansion below); and, finally,
171 \fB*\fR,
172 \fB?\fR
173 and
174 \fB[\fR
175 are used in file name generation (see File Name Patterns below)\&.
176 .PP
177 As words and tokens are parsed, the shell builds commands, of which there are two basic types:
178 \fIsimple\-commands\fR, typically programs that are executed, and
179 \fIcompound\-commands\fR, such as
180 \fBfor\fR
181 and
182 \fBif\fR
183 statements, grouping constructs and function definitions\&.
184 .PP
185 A simple\-command consists of some combination of parameter assignments (see Parameters below), input/output redirections (see Input/Output Redirections below), and command words; the only restriction is that parameter assignments come before any command words\&. The command words, if any, define the command that is to be executed and its arguments\&. The command may be a shell built\-in command, a function or an
186 \fIexternal command\fR,
187 \fIi\&.e\&.\fR, a separate executable file that is located using the
188 \fBPATH\fR
189 parameter (see Command Execution below)\&. Note that all command constructs have an
190 \fIexit status\fR: for external commands, this is related to the status returned by
191 \fBwait\fR(2)
192 (if the command could not be found, the exit status is 127, if it could not be executed, the exit status is 126); the exit status of other command constructs (built\-in commands, functions, compound\-commands, pipelines, lists,
193 \fIetc\&.\fR) are all well defined and are described where the construct is described\&. The exit status of a command consisting only of parameter assignments is that of the last command substitution performed during the parameter assignment or zero if there were no command substitutions\&.
194 .PP
195 Commands can be chained together using the
196 \fB|\fR
197 token to form
198 \fIpipelines\fR, in which the standard output of each command but the last is piped (see
199 \fBpipe\fR(2)) to the standard input of the following command\&. The exit status of a pipeline is that of its last command\&. A pipeline may be prefixed by the
200 \fB!\fR
201 reserved word which causes the exit status of the pipeline to be logically complemented: if the original status was 0 the complemented status will be 1, and if the original status was not 0, then the complemented status will be 0\&.
202 .PP
203 \fILists\fR
204 of commands can be created by separating pipelines by any of the following tokens:
205 \fB&&\fR,
206 \fB||\fR,
207 \fB&\fR,
208 \fB|&\fR
209 and
210 \fB;\fR\&. The first two are for conditional execution:
211 \fIcmd1\fR
212 \fB&&\fR
213 \fIcmd2\fR
214 executes
215 \fIcmd2\fR
216 only if the exit status of
217 \fIcmd1\fR
218 is zero;
219 \fB||\fR
220 is the opposite \(em
221 \fIcmd2\fR
222 is executed only if the exit status of
223 \fIcmd1\fR
224 is non\-zero\&.
225 \fB&&\fR
226 and
227 \fB||\fR
228 have equal precedence which is higher than that of
229 \fB&\fR,
230 \fB|&\fR
231 and
232 \fB;\fR, which also have equal precedence\&. The
233 \fB&\fR
234 token causes the preceding command to be executed asynchronously, that is, the shell starts the command, but does not wait for it to complete (the shell does keep track of the status of asynchronous commands \(em see Job Control below)\&. When an asynchronous command is started when job control is disabled (\fIi\&.e\&.\fR, in most scripts), the command is started with signals INT and QUIT ignored and with input redirected from /dev/null (however, redirections specified in the asynchronous command have precedence)\&. Note that a command must follow the
235 \fB&&\fR
236 and
237 \fB||\fR
238 operators, while a command need not follow
239 \fB&\fR,
240 \fB|&\fR
241 and
242 \fB;\fR\&. The exit status of a list is that of the last command executed, with the exception of asynchronous lists, for which the exit status is 0\&.
243 .PP
244 Compound commands are created using the following reserved words \(em these words are only recognized if they are unquoted and if they are used as the first word of a command (\fIi\&.e\&.\fR, they can\*(Aqt be preceded by parameter assignments or redirections):
245 .TS
246 center tab(:);
247 cB rB l l l.
248 T{
249 case
250 T}:T{
251 else
252 T}:T{
253 \ \&
254 T}:T{
255 \ \&
256 T}:T{
257 \ \&
258 T}
259 .T&
260 l l l l l
261 l l l l l
262 l l l l l.
263 T{
264 do
265 T}:T{
266 esac
267 T}:T{
268 if
269 T}:T{
270 time
271 T}:T{
272 [[
273 T}
274 T{
275 done
276 T}:T{
277 fi
278 T}:T{
279 in
280 T}:T{
281 until
282 T}:T{
283 {
284 T}
285 T{
286 elif
287 T}:T{
288 for
289 T}:T{
290 select
291 T}:T{
292 while
293 T}:T{
294 }
295 T}
296 .TE
297 .sp 1
298 .PP
299 \fBNote:\fR
300 Some shells (but not this one) execute control structure commands in a subshell when one or more of their file descriptors are redirected, so any environment changes inside them may fail\&. To be portable, the
301 \fBexec\fR
302 statement should be used instead to redirect file descriptors before the control structure\&.
303 .PP
304 In the following compound command descriptions, command lists (denoted as
305 \fIlist\fR) that are followed by reserved words must end with a semi\-colon, a newline or a (syntactically correct) reserved word\&. For example,
307 \fB{ echo foo; echo bar; }\fR
309 \fB{ echo foo; echo bar<newline>}\fR
311 \fB{ { echo foo; echo bar; } }\fR
312 are all valid, but
314 \fB{ echo foo; echo bar }\fR
315 is not\&.
316 .PP
317 \fB(\fR \fIlist\fR \fB)\fR
318 .RS 4
319 Execute
320 \fIlist\fR
321 in a subshell\&. There is no implicit way to pass environment changes from a subshell back to its parent\&.
322 .RE
323 .PP
324 \fB{\fR \fIlist\fR \fB}\fR
325 .RS 4
326 Compound construct;
327 \fIlist\fR
328 is executed, but not in a subshell\&. Note that
329 \fB{\fR
330 and
331 \fB}\fR
332 are reserved words, not meta\-characters\&.
333 .RE
334 .PP
335 \fBcase\fR \fIword\fR \fBin\fR [ [\fB(\fR] \fIpattern\fR [\fB|\fR \fIpattern\fR] \&.\&.\&. \fB)\fR \fIlist\fR \fB;;\fR ] \&.\&.\&. \fBesac\fR
336 .RS 4
337 The
338 \fBcase\fR
339 statement attempts to match
340 \fIword\fR
341 against the specified
342 \fIpattern\fRs; the
343 \fIlist\fR
344 associated with the first successfully matched pattern is executed\&. Patterns used in
345 \fBcase\fR
346 statements are the same as those used for file name patterns except that the restrictions regarding
347 \fB\&.\fR
348 and
349 \fB/\fR
350 are dropped\&. Note that any unquoted space before and after a pattern is stripped; any space with a pattern must be quoted\&. Both the word and the patterns are subject to parameter, command, and arithmetic substitution as well as tilde substitution\&. For historical reasons, open and close braces may be used instead of
351 \fBin\fR
352 and
353 \fBesac\fR
354 (\fIe\&.g\&.\fR,
355 \fBcase $foo { *) echo bar; }\fR)\&. The exit status of a
356 \fBcase\fR
357 statement is that of the executed
358 \fIlist\fR; if no
359 \fIlist\fR
360 is executed, the exit status is zero\&.
361 .RE
362 .PP
363 \fBfor\fR \fIname\fR [ \fBin\fR \fIword\fR \&.\&.\&. \fIterm\fR ] \fBdo\fR \fIlist\fR \fBdone\fR
364 .RS 4
365 where
366 \fIterm\fR
367 is either a newline or a
368 \fB;\fR\&. For each
369 \fIword\fR
370 in the specified word list, the parameter
371 \fIname\fR
372 is set to the word and
373 \fIlist\fR
374 is executed\&. If
375 \fBin\fR
376 is not used to specify a word list, the positional parameters (\fB"$1"\fR,
377 \fB"$2"\fR,
378 \fIetc\&.\fR) are used instead\&. For historical reasons, open and close braces may be used instead of
379 \fBdo\fR
380 and
381 \fBdone\fR
382 (\fIe\&.g\&.\fR,
383 \fBfor i; { echo $i; }\fR)\&. The exit status of a
384 \fBfor\fR
385 statement is the last exit status of
386 \fIlist\fR; if
387 \fIlist\fR
388 is never executed, the exit status is zero\&.
389 .RE
390 .PP
391 \fBif\fR \fIlist\fR \fBthen\fR \fIlist\fR [\fBelif\fR \fIlist\fR \fBthen\fR \fIlist\fR] \&.\&.\&. [\fBelse\fR \fIlist\fR] \fBfi\fR
392 .RS 4
393 If the exit status of the first
394 \fIlist\fR
395 is zero, the second
396 \fIlist\fR
397 is executed; otherwise the
398 \fIlist\fR
399 following the
400 \fBelif\fR, if any, is executed with similar consequences\&. If all the lists following the
401 \fBif\fR
402 and
403 \fBelif\fRs fail (\fIi\&.e\&.\fR, exit with non\-zero status), the
404 \fIlist\fR
405 following the
406 \fBelse\fR
407 is executed\&. The exit status of an
408 \fBif\fR
409 statement is that of non\-conditional
410 \fIlist\fR
411 that is executed; if no non\-conditional
412 \fIlist\fR
413 is executed, the exit status is zero\&.
414 .RE
415 .PP
416 \fBuntil\fR \fIlist\fR \fBdo\fR \fIlist\fR \fBdone\fR
417 .RS 4
418 This works like
419 \fBwhile\fR, except that the body is executed only while the exit status of the first
420 \fIlist\fR
421 is non\-zero\&.
422 .RE
423 .PP
424 \fBwhile\fR \fIlist\fR \fBdo\fR \fIlist\fR \fBdone\fR
425 .RS 4
426 A
427 \fBwhile\fR
428 is a prechecked loop\&. Its body is executed as often as the exit status of the first
429 \fIlist\fR
430 is zero\&. The exit status of a
431 \fBwhile\fR
432 statement is the last exit status of the
433 \fIlist\fR
434 in the body of the loop; if the body is not executed, the exit status is zero\&.
435 .RE
436 .PP
437 \fIname\fR \fB()\fR \fIcommand\fR
438 .RS 4
439 Defines the function
440 \fIname\fR\&. See Functions below\&. Note that redirections specified after a function definition are performed whenever the function is executed, not when the function definition is executed\&.
441 .RE
442 .PP
443 \fBtime\fR [ \fB\-p\fR ] [ \fIpipeline\fR ]
444 .RS 4
445 The
446 \fBtime\fR
447 reserved word is described in the Command Execution section\&.
448 .RE
449 .SS "Quoting"
450 .PP
451 Quoting is used to prevent the shell from treating characters or words specially\&. There are three methods of quoting: First,
452 \fB\e\fR
453 quotes the following character, unless it is at the end of a line, in which case both the
454 \fB\e\fR
455 and the newline are stripped\&. Second, a single quote (\fB\*(Aq\fR) quotes everything up to the next single quote (this may span lines)\&. Third, a double quote (\fB"\fR) quotes all characters, except
456 \fB$\fR,
457 \fB`\fR
458 and
459 \fB\e\fR, up to the next unquoted double quote\&.
460 \fB$\fR
461 and
462 \fB`\fR
463 inside double quotes have their usual meaning (\fIi\&.e\&.\fR, parameter, command or arithmetic substitution) except no field splitting is carried out on the results of double\-quoted substitutions\&. If a
464 \fB\e\fR
465 inside a double\-quoted string is followed by
466 \fB\e\fR,
467 \fB$\fR,
468 \fB`\fR
469 or
470 \fB"\fR, it is replaced by the second character; if it is followed by a newline, both the
471 \fB\e\fR
472 and the newline are stripped; otherwise, both the
473 \fB\e\fR
474 and the character following are unchanged\&.
475 .PP
476 Note: see POSIX Mode below for a special rule regarding sequences of the form
477 \fB"\fR\&.\&.\&.\fB`\fR\&.\&.\&.\fB\e"\fR\&.\&.\&.\fB`\fR\&.\&.\fB"\fR\&.
478 .SS "Substitution"
479 .PP
480 The first step the shell takes in executing a simple\-command is to perform substitutions on the words of the command\&. There are three kinds of substitution: parameter, command and arithmetic\&. Parameter substitutions, which are described in detail in the next section, take the form
481 \fB$name\fR
482 or
483 \fB${\fR\&.\&.\&.\fB}\fR; command substitutions take the form
484 \fB$(\fR\fIcommand\fR\fB)\fR
485 or
486 \fB`\fR\fIcommand\fR\fB`\fR; and arithmetic substitutions take the form
487 \fB$((\fR\fIexpression\fR\fB))\fR\&.
488 .PP
489 If a substitution appears outside of double quotes, the results of the substitution are generally subject to word or field splitting according to the current value of the
490 \fBIFS\fR
491 parameter\&. The
492 \fBIFS\fR
493 parameter specifies a list of characters which are used to break a string up into several words; any characters from the set space, tab and newline that appear in the IFS characters are called
494 \fIIFS white space\fR\&. Sequences of one or more IFS white space characters, in combination with zero or one non\-IFS white space characters delimit a field\&. As a special case, leading and trailing IFS white space is stripped (\fIi\&.e\&.\fR, no leading or trailing empty field is created by it); leading or trailing non\-IFS white space does create an empty field\&. Example: if
495 \fBIFS\fR
496 is set to `<space>:\*(Aq, the sequence of characters `<space>A<space>:<space><space>B::D\*(Aq contains four fields: `A\*(Aq, `B\*(Aq, `\*(Aq and `D\*(Aq\&. Note that if the
497 \fBIFS\fR
498 parameter is set to the null string, no field splitting is done; if the parameter is unset, the default value of space, tab and newline is used\&.
499 .PP
500 The results of substitution are, unless otherwise specified, also subject to brace expansion and file name expansion (see the relevant sections below)\&.
501 .PP
502 A command substitution is replaced by the output generated by the specified command, which is run in a subshell\&. For
503 \fB$(\fR\fIcommand\fR\fB)\fR
504 substitutions, normal quoting rules are used when
505 \fIcommand\fR
506 is parsed, however, for the
507 \fB`\fR\fIcommand\fR\fB`\fR
508 form, a
509 \fB\e\fR
510 followed by any of
511 \fB$\fR,
512 \fB`\fR
513 or
514 \fB\e\fR
515 is stripped (a
516 \fB\e\fR
517 followed by any other character is unchanged)\&. As a special case in command substitutions, a command of the form
518 \fB<\fR
519 \fIfile\fR
520 is interpreted to mean substitute the contents of
521 \fIfile\fR
522 ($(< foo) has the same effect as $(cat foo), but it is carried out more efficiently because no process is started)\&.
524 NOTE:
525 \fB$(\fR\fIcommand\fR\fB)\fR
526 expressions are currently parsed by finding the matching parenthesis, regardless of quoting\&. This will hopefully be fixed soon\&.
527 .PP
528 Arithmetic substitutions are replaced by the value of the specified expression\&. For example, the command
529 \fBecho $((2+3*4))\fR
530 prints 14\&. See Arithmetic Expressions for a description of an
531 \fIexpression\fR\&.
532 .SS "Parameters"
533 .PP
534 Parameters are shell variables; they can be assigned values and their values can be accessed using a parameter substitution\&. A parameter name is either one of the special single punctuation or digit character parameters described below, or a letter followed by zero or more letters or digits (`_\*(Aq counts as a letter)\&. The later form can be treated as arrays by appending an array index of the form:
535 \fB[\fR\fIexpr\fR\fB]\fR
536 where
537 \fIexpr\fR
538 is an arithmetic expression\&. Array indices are currently limited to the range 0 through 1023, inclusive\&. Parameter substitutions take the form
539 \fB$\fR\fIname\fR,
540 \fB${\fR\fIname\fR\fB}\fR
541 or
542 \fB${\fR\fIname\fR\fB[\fR\fIexpr\fR\fB]}\fR, where
543 \fIname\fR
544 is a parameter name\&. If substitution is performed on a parameter (or an array parameter element) that is not set, a null string is substituted unless the
545 \fBnounset\fR
546 option (\fBset \-o nounset\fR
547 or
548 \fBset \-u\fR) is set, in which case an error occurs\&.
549 .PP
550 Parameters can be assigned values in a number of ways\&. First, the shell implicitly sets some parameters like
551 \fB#\fR,
552 \fBPWD\fR, etc\&.; this is the only way the special single character parameters are set\&. Second, parameters are imported from the shell\*(Aqs environment at startup\&. Third, parameters can be assigned values on the command line, for example, `\fBFOO=bar\fR\*(Aq sets the parameter FOO to bar; multiple parameter assignments can be given on a single command line and they can be followed by a simple\-command, in which case the assignments are in effect only for the duration of the command (such assignments are also exported, see below for implications of this)\&. Note that both the parameter name and the
553 \fB=\fR
554 must be unquoted for the shell to recognize a parameter assignment\&. The fourth way of setting a parameter is with the
555 \fBexport\fR
556 and
557 \fBreadonly\fR
558 commands; see their descriptions in the Command Execution section\&. Fifth,
559 \fBfor\fR
560 and
561 \fBselect\fR
562 loops set parameters as well as the
563 \fBgetopts\fR,
564 \fBread\fR
565 and
566 \fBset \-A\fR
567 commands\&. Lastly, parameters can be assigned values using assignment operators inside arithmetic expressions (see Arithmetic Expressions below) or using the
568 \fB${\fR\fIname\fR\fB=\fR\fIvalue\fR\fB}\fR
569 form of parameter substitution (see below)\&.
570 .PP
571 Parameters with the export attribute (set using the
572 \fBexport\fR
573 command, or by parameter assignments followed by simple commands) are put in the environment (see
574 \fBenviron\fR(5)) of commands run by the shell as
575 \fIname\fR\fB=\fR\fIvalue\fR
576 pairs\&. The order in which parameters appear in the environment of a command is unspecified\&. When the shell starts up, it extracts parameters and their values from its environment and automatically sets the export attribute for those parameters\&.
577 .PP
578 Modifiers can be applied to the
579 \fB${\fR\fIname\fR\fB}\fR
580 form of parameter substitution:
581 .PP
582 \fB${\fR\fIname\fR\fB:\-\fR\fIword\fR\fB}\fR
583 .RS 4
584 if
585 \fIname\fR
586 is set and not null, it is substituted, otherwise
587 \fIword\fR
588 is substituted\&.
589 .RE
590 .PP
591 \fB${\fR\fIname\fR\fB:+\fR\fIword\fR\fB}\fR
592 .RS 4
593 if
594 \fIname\fR
595 is set and not null,
596 \fIword\fR
597 is substituted, otherwise nothing is substituted\&.
598 .RE
599 .PP
600 \fB${\fR\fIname\fR\fB:=\fR\fIword\fR\fB}\fR
601 .RS 4
602 if
603 \fIname\fR
604 is set and not null, it is substituted, otherwise it is assigned
605 \fIword\fR
606 and the resulting value of
607 \fIname\fR
608 is substituted\&.
609 .RE
610 .PP
611 \fB${\fR\fIname\fR\fB:?\fR\fIword\fR\fB}\fR
612 .RS 4
613 if
614 \fIname\fR
615 is set and not null, it is substituted, otherwise
616 \fIword\fR
617 is printed on standard error (preceded by
618 \fIname\fR:) and an error occurs (normally causing termination of a shell script, function or \&.\-script)\&. If word is omitted the string `parameter null or not set\*(Aq is used instead\&.
619 .RE
620 .PP
621 In the above modifiers, the
622 \fB:\fR
623 can be omitted, in which case the conditions only depend on
624 \fIname\fR
625 being set (as opposed to set and not null)\&. If
626 \fIword\fR
627 is needed, parameter, command, arithmetic and tilde substitution are performed on it; if
628 \fIword\fR
629 is not needed, it is not evaluated\&.
630 .PP
631 The following forms of parameter substitution can also be used:
632 .PP
633 \fB${#\fR\fIname\fR\fB}\fR
634 .RS 4
635 The number of positional parameters if
636 \fIname\fR
637 is
638 \fB*\fR,
639 \fB@\fR
640 or is not specified, or the length of the string value of parameter
641 \fIname\fR\&.
642 .RE
643 .PP
644 \fB${#\fR\fIname\fR\fB[*]}\fR, \fB${#\fR\fIname\fR\fB[@]}\fR
645 .RS 4
646 The number of elements in the array
647 \fIname\fR\&.
648 .RE
649 .PP
650 \fB${\fR\fIname\fR\fB#\fR\fIpattern\fR\fB}\fR, \fB${\fR\fIname\fR\fB##\fR\fIpattern\fR\fB}\fR
651 .RS 4
652 If
653 \fIpattern\fR
654 matches the beginning of the value of parameter
655 \fIname\fR, the matched text is deleted from the result of substitution\&. A single
656 \fB#\fR
657 results in the shortest match, two
658 \fB#\fR\*(Aqs results in the longest match\&.
659 .RE
660 .PP
661 \fB${\fR\fIname\fR\fB%\fR\fIpattern\fR\fB}\fR, \fB${\fR\fIname\fR\fB%%\fR\fIpattern\fR\fB}\fR
662 .RS 4
663 Like
664 \fB${\fR\&.\&.\fB#\fR\&.\&.\fB}\fR
665 substitution, but it deletes from the end of the value\&.
666 .RE
667 .PP
668 The following special parameters are implicitly set by the shell and cannot be set directly using assignments:
669 .PP
670 \fB!\fR
671 .RS 4
672 Process id of the last background process started\&. If no background processes have been started, the parameter is not set\&.
673 .RE
674 .PP
675 \fB#\fR
676 .RS 4
677 The number of positional parameters (\fIi\&.e\&.\fR,
678 \fB$1\fR,
679 \fB$2\fR,
680 \fIetc\&.\fR)\&.
681 .RE
682 .PP
683 \fB$\fR
684 .RS 4
685 The process ID of the shell, or the PID of the original shell if it is a subshell\&.
686 .RE
687 .PP
688 \fB\-\fR
689 .RS 4
690 The concatenation of the current single letter options (see
691 \fBset\fR
692 command below for list of options)\&.
693 .RE
694 .PP
695 \fB?\fR
696 .RS 4
697 The exit status of the last non\-asynchronous command executed\&. If the last command was killed by a signal,
698 \fB$?\fR
699 is set to 128 plus the signal number\&.
700 .RE
701 .PP
702 \fI0\fR
703 .RS 4
704 The name the shell was invoked with (that is,
705 \fIargv[0]\fR), or the
706 \fB\fIcommand\-name\fR\fR
707 if it was invoked with the
708 \fB\-c\fR
709 option and the
710 \fB\fIcommand\-name\fR\fR
711 was supplied, or the
712 \fIfile\fR
713 argument, if it was supplied\&. If the
714 \fBposix\fR
715 option is not set,
716 \fB$0\fR
717 is the name of the current function or script\&.
718 .RE
719 .PP
720 \fI1\fR \&.\&.\&. \fI9\fR
721 .RS 4
722 The first nine positional parameters that were supplied to the shell, function or
723 \fB\&.\fR\-script\&. Further positional parameters may be accessed using
724 \fI${\fR\fI\fInumber\fR\fR\fI}\fR\&.
725 .RE
726 .PP
727 \fI*\fR
728 .RS 4
729 All positional parameters (except parameter 0),
730 \fIi\&.e\&.\fR,
731 \fB$1 $2 $3\fR\&.\&.\&.\&. If used outside of double quotes, parameters are separate words (which are subjected to word splitting); if used within double quotes, parameters are separated by the first character of the
732 \fBIFS\fR
733 parameter (or the empty string if
734 \fBIFS\fR
735 is null)\&.
736 .RE
737 .PP
738 \fI@\fR
739 .RS 4
740 Same as
741 \fB$*\fR, unless it is used inside double quotes, in which case a separate word is generated for each positional parameter \- if there are no positional parameters, no word is generated ("$@" can be used to access arguments, verbatim, without loosing null arguments or splitting arguments with spaces)\&.
742 .RE
743 .PP
744 The following parameters are set and/or used by the shell:
745 .PP
746 "\fBCDPATH\fR"
747 .RS 4
748 Search path for the
749 \fBcd\fR
750 built\-in command\&. Works the same way as
751 \fBPATH\fR
752 for those directories not beginning with
753 \fB/\fR
754 in
755 \fBcd\fR
756 commands\&. Note that if CDPATH is set and does not contain
757 \&.
758 nor an empty path, the current directory is not searched\&.
759 .RE
760 .PP
761 \fBCOLUMNS\fR
762 .RS 4
763 Set to the number of columns on the terminal or window\&. Currently set to the
764 \fBcols\fR
765 value as reported by
766 \fBstty\fR(1)
767 if that value is non\-zero\&. This parameter is used by the interactive line editing modes, and by
768 \fBselect\fR,
769 \fBset \-o\fR
770 and
771 \fBkill \-l\fR
772 commands to format information in columns\&.
773 .RE
774 .PP
775 \fBERRNO\fR
776 .RS 4
777 Integer value of the shell\*(Aqs errno variable \(em indicates the reason the last system call failed\&.
778 .sp
779 Not implemented yet\&.
780 .RE
781 .PP
782 \fBEXECSHELL\fR
783 .RS 4
784 If set, this parameter is assumed to contain the shell that is to be used to execute commands that
785 \fBexecve\fR(2)
786 fails to execute and which do not start with a `\fB#!\fR
787 \fIshell\fR\*(Aq sequence\&.
788 .RE
789 .PP
790 \fBFCEDIT\fR
791 .RS 4
792 The editor used by the
793 \fBfc\fR
794 command (see below)\&.
795 .RE
796 .PP
797 \fBFPATH\fR
798 .RS 4
799 Like
800 \fBPATH\fR, but used when an undefined function is executed to locate the file defining the function\&. It is also searched when a command can\*(Aqt be found using
801 \fBPATH\fR\&. See Functions below for more information\&.
802 .RE
803 .PP
804 \fBHOME\fR
805 .RS 4
806 The default directory for the
807 \fBcd\fR
808 command and the value substituted for an unqualified
809 \fB~\fR
810 (see Tilde Expansion below)\&.
811 .RE
812 .PP
813 \fBIFS\fR
814 .RS 4
815 Internal field separator, used during substitution and by the
816 \fBread\fR
817 command, to split values into distinct arguments; normally set to space, tab and newline\&. See Substitution above for details\&.
819 \fBNote:\fR
820 this parameter is not imported from the environment when the shell is started\&.
821 .RE
822 .PP
823 \fBPOSH_VERSION\fR
824 .RS 4
825 The version of posh (readonly)\&.
826 .RE
827 .PP
828 \fBLINENO\fR
829 .RS 4
830 The line number of the function or shell script that is currently being executed\&.
831 .RE
832 .PP
833 \fBLINES\fR
834 .RS 4
835 Set to the number of lines on the terminal or window\&.
836 .sp
837 Not implemented yet\&.
838 .RE
839 .PP
840 \fBOLDPWD\fR
841 .RS 4
842 The previous working directory\&. Unset if
843 \fBcd\fR
844 has not successfully changed directories since the shell started, or if the shell doesn\*(Aqt know where it is\&.
845 .RE
846 .PP
847 \fBOPTARG\fR
848 .RS 4
849 When using
850 \fBgetopts\fR, it contains the argument for a parsed option, if it requires one\&.
851 .RE
852 .PP
853 \fBOPTIND\fR
854 .RS 4
855 The index of the last argument processed when using
856 \fBgetopts\fR\&. Assigning 1 to this parameter causes
857 \fBgetopts\fR
858 to process arguments from the beginning the next time it is invoked\&.
859 .RE
860 .PP
861 \fBPATH\fR
862 .RS 4
863 A colon separated list of directories that are searched when looking for commands and
864 \&.\*(Aqd files\&. An empty string resulting from a leading or trailing colon, or two adjacent colons is treated as a `\&.\*(Aq, the current directory\&.
865 .RE
866 .PP
867 \fBPPID\fR
868 .RS 4
869 The process ID of the shell\*(Aqs parent (readonly)\&.
870 .RE
871 .PP
872 \fBPS1\fR
873 .RS 4
874 The primary prompt for interactive shells\&. The prompt is printed verbatim (\fIi\&.e\&.\fR, no substitutions are done)\&. Default is \(oq$\ \&\(cq for non\-root users, `\fB#\ \&\fR\*(Aq for root\&.\&.
875 .RE
876 .PP
877 \fBPS2\fR
878 .RS 4
879 Secondary prompt string, by default `\fB>\fR
880 \*(Aq, used when more input is needed to complete a command\&.
881 .RE
882 .PP
883 \fBPS4\fR
884 .RS 4
885 Used to prefix commands that are printed during execution tracing (see
886 \fBset \-x\fR
887 command below)\&. The prompt is printed verbatim (\fIi\&.e\&.\fR, no substitutions are done)\&. Default is `\fB+\ \&\fR\*(Aq\&.
888 .RE
889 .PP
890 \fBPWD\fR
891 .RS 4
892 The current working directory\&. Maybe unset or null if shell doesn\*(Aqt know where it is\&.
893 .RE
894 .PP
895 \fBREPLY\fR
896 .RS 4
897 Default parameter for the
898 \fBread\fR
899 command if no names are given\&. Also used in
900 \fBselect\fR
901 loops to store the value that is read from standard input\&.
902 .RE
903 .PP
904 \fBTMPDIR\fR
905 .RS 4
906 The directory shell temporary files are created in\&. If this parameter is not set, or does not contain the absolute path of a writable directory, temporary files are created in
907 /tmp\&.
908 .RE
909 .SS "Tilde Expansion"
910 .PP
911 Tilde expansion, which is done in parallel with parameter substitution, is done on words starting with an unquoted
912 \fB~\fR\&. The characters following the tilde, up to the first
913 \fB/\fR, if any, are assumed to be a login name\&. If the login name is empty,
914 \fB+\fR
915 or
916 \fB\-\fR, the value of the
917 \fBHOME\fR,
918 \fBPWD\fR, or
919 \fBOLDPWD\fR
920 parameter is substituted, respectively\&. Otherwise, the password file is searched for the login name, and the tilde expression is substituted with the user\*(Aqs home directory\&. If the login name is not found in the password file or if any quoting or parameter substitution occurs in the login name, no substitution is performed\&.
921 .PP
922 In parameter assignments (those preceding a simple\-command or those occurring in the arguments of
923 \fBalias\fR,
924 \fBexport\fR, and
925 \fBreadonly\fR, tilde expansion is done after any unquoted colon (\fB:\fR), and login names are also delimited by colons\&.
926 .PP
927 The home directory of previously expanded login names are cached and re\-used\&. The
928 \fBalias \-d\fR
929 command may be used to list, change and add to this cache (\fIe\&.g\&.\fR, `alias \-d fac=/usr/local/facilities; cd ~fac/bin\*(Aq)\&.
930 .SS "File Name Patterns"
931 .PP
932 A file name pattern is a word containing one or more unquoted
933 \fB?\fR
934 or
935 \fB*\fR
936 characters or
937 \fB[\fR\&.\&.\fB]\fR
938 sequences\&. Once brace expansion has been performed, the shell replaces file name patterns with the sorted names of all the files that match the pattern (if no files match, the word is left unchanged)\&. The pattern elements have the following meaning:
939 .PP
940 "\fB?\fR"
941 .RS 4
942 matches any single character\&.
943 .RE
944 .PP
945 \fB*\fR
946 .RS 4
947 matches any sequence of characters\&.
948 .RE
949 .PP
950 \fB[\fR\&.\&.\fB]\fR
951 .RS 4
952 matches any of the characters inside the brackets\&. Ranges of characters can be specified by separating two characters by a
953 \fB\-\fR,
954 \fIe\&.g\&.\fR,
955 \fB[a0\-9]\fR
956 matches the letter
957 \fBa\fR
958 or any digit\&. In order to represent itself, a
959 \fB\-\fR
960 must either be quoted or the first or last character in the character list\&. Similarly, a
961 \fB]\fR
962 must be quoted or the first character in the list if it is represent itself instead of the end of the list\&. Also, a
963 \fB!\fR
964 appearing at the start of the list has special meaning (see below), so to represent itself it must be quoted or appear later in the list\&.
965 .RE
966 .PP
967 \fB[!\fR\&.\&.\fB]\fR
968 .RS 4
969 like
970 \fB[\fR\&.\&.\fB]\fR, except it matches any character not inside the brackets\&.
971 .RE
972 .PP
973 Note that posh currently never matches
974 \&.
975 and
976 \&.\&., but the original ksh, Bourne sh and bash do, so this may have to change (too bad)\&.
977 .PP
978 Note that none of the above pattern elements match either a period (\&.) at the start of a file name or a slash (\fB/\fR), even if they are explicitly used in a
979 \fB[\fR\&.\&.\fB]\fR
980 sequence; also, the names
981 \&.
982 and
983 \&.\&.
984 are never matched, even by the pattern
985 \fB\&.*\fR\&.
986 .PP
987 The POSIX character classes (\fIi\&.e\&.\fR,
988 \fB[:\fR\fIclass\-name\fR\fB:]\fR
989 inside a
990 \fB[\fR\&.\&.\fB]\fR
991 expression) are not yet implemented\&.
992 .SS "Input/Output Redirection"
993 .PP
994 When a command is executed, its standard input, standard output and standard error (file descriptors 0, 1 and 2, respectively) are normally inherited from the shell\&. Three exceptions to this are commands in pipelines, for which standard input and/or standard output are those set up by the pipeline, asynchronous commands created when job control is disabled, for which standard input is initially set to be from
995 /dev/null, and commands for which any of the following redirections have been specified:
996 .PP
997 "\fB>\fR \fIfile\fR"
998 .RS 4
999 standard output is redirected to
1000 \fIfile\fR\&. If
1001 \fIfile\fR
1002 does not exist, it is created; if it does exist, is a regular file and the
1003 \fBnoclobber\fR
1004 option is set, an error occurs, otherwise the file is truncated\&. Note that this means the command
1005 \fIcmd < foo > foo\fR
1006 will open
1007 \fIfoo\fR
1008 for reading and then truncate it when it opens it for writing, before
1009 \fIcmd\fR
1010 gets a chance to actually read
1011 \fIfoo\fR\&.
1012 .RE
1013 .PP
1014 "\fB>|\fR \fIfile\fR"
1015 .RS 4
1016 same as
1017 \fB>\fR, except the file is truncated, even if the
1018 \fBnoclobber\fR
1019 option is set\&.
1020 .RE
1021 .PP
1022 "\fB>>\fR \fIfile\fR"
1023 .RS 4
1024 same as
1025 \fB>\fR, except the file an existing file is appended to instead of being truncated\&. Also, the file is opened in append mode, so writes always go to the end of the file (see
1026 \fBopen\fR(2))\&.
1027 .RE
1028 .PP
1029 "\fB<\fR \fIfile\fR"
1030 .RS 4
1031 standard input is redirected from
1032 \fIfile\fR, which is opened for reading\&.
1033 .RE
1034 .PP
1035 "\fB<>\fR \fIfile\fR"
1036 .RS 4
1037 same as
1038 \fB<\fR, except the file is opened for reading and writing\&.
1039 .RE
1040 .PP
1041 "\fB<<\fR \fImarker\fR"
1042 .RS 4
1043 after reading the command line containing this kind of redirection (called a here document), the shell copies lines from the command source into a temporary file until a line matching
1044 \fImarker\fR
1045 is read\&. When the command is executed, standard input is redirected from the temporary file\&. If
1046 \fImarker\fR
1047 contains no quoted characters, the contents of the temporary file are processed as if enclosed in double quotes each time the command is executed, so parameter, command and arithmetic substitutions are performed, along with backslash (\fB\e\fR) escapes for
1048 \fB$\fR,
1049 \fB`\fR,
1050 \fB\e\fR
1051 and
1052 \fB\enewline\fR\&. If multiple here documents are used on the same command line, they are saved in order\&.
1053 .RE
1054 .PP
1055 "\fB<<\-\fR \fImarker\fR"
1056 .RS 4
1057 same as
1058 \fB<<\fR, except leading tabs are stripped from lines in the here document\&.
1059 .RE
1060 .PP
1061 "\fB<&\fR \fIfd\fR"
1062 .RS 4
1063 standard input is duplicated from file descriptor
1064 \fIfd\fR\&.
1065 \fIfd\fR
1066 can be a single digit, indicating the number of an existing file descriptor, the letter
1067 \fBp\fR, indicating the file descriptor associated with the output of the current co\-process, or the character
1068 \fB\-\fR, indicating standard input is to be closed\&.
1069 .RE
1070 .PP
1071 "\fB>&\fR \fIfd\fR"
1072 .RS 4
1073 same as
1074 \fB<&\fR, except the operation is done on standard output\&.
1075 .RE
1076 .PP
1077 In any of the above redirections, the file descriptor that is redirected (\fIi\&.e\&.\fR, standard input or standard output) can be explicitly given by preceding the redirection with a single digit\&. Parameter, command and arithmetic substitutions, tilde substitutions and (if the shell is interactive) file name generation are all performed on the
1078 \fIfile\fR,
1079 \fImarker\fR
1080 and
1081 \fIfd\fR
1082 arguments of redirections\&. Note however, that the results of any file name generation are only used if a single file is matched; if multiple files match, the word with the unexpanded file name generation characters is used\&.
1083 .PP
1084 For simple\-commands, redirections may appear anywhere in the command, for compound\-commands (\fBif\fR
1085 statements,
1086 \fIetc\&.\fR), any redirections must appear at the end\&. Redirections are processed after pipelines are created and in the order they are given, so
1088 \fBcat /foo/bar 2>&1 > /dev/null | cat \-n\fR
1089 will print an error with a line number prepended to it\&.
1090 .SS "Arithmetic Expressions"
1091 .PP
1092 Integer arithmetic expressions can be used inside
1093 \fB$((\fR\&.\&.\fB))\fR
1094 expressions, inside array references (\fIe\&.g\&.\fR,
1095 \fIname\fR\fB[\fR\fIexpr\fR\fB]\fR), as numeric arguments to the
1096 \fBtest\fR
1097 command, and as the value of an assignment to an integer parameter\&.
1098 .PP
1099 Expression may contain alpha\-numeric parameter identifiers, array references, and integer constants and may be combined with the following C operators (listed and grouped in increasing order of precedence)\&.
1100 .PP
1101 Unary operators:
1102 .RS 4
1103 \fB+ \- ! ~ ++ \-\-\fR
1104 .RE
1105 .PP
1106 Binary operators:
1107 .RS 4
1108 \fB,\fR
1110 \fB= *= /= %= += \-= <<= >>= &= ^= |=\fR
1112 \fB||\fR
1114 \fB&&\fR
1116 \fB|\fR
1118 \fB^\fR
1120 \fB&\fR
1122 \fB== !=\fR
1124 \fB< <= >= >\fR
1126 \fB<< >>\fR
1128 \fB+ \-\fR
1130 \fB* / %\fR
1131 .RE
1132 .PP
1133 Ternary operator:
1134 .RS 4
1135 \fB?:\fR
1136 (precedence is immediately higher than assignment)
1137 .RE
1138 .PP
1139 Grouping operators:
1140 .RS 4
1141 \fB( )\fR
1142 .RE
1143 .PP
1144 Integer constants may be specified with arbitrary bases using the notation
1145 \fIbase\fR\fB#\fR\fInumber\fR, where
1146 \fIbase\fR
1147 is a decimal integer specifying the base, and
1148 \fInumber\fR
1149 is a number in the specified base\&.
1150 .PP
1151 The operators are evaluated as follows:
1152 .PP
1153 "unary \fB+\fR"
1154 .RS 4
1155 result is the argument (included for completeness)\&.
1156 .RE
1157 .PP
1158 "unary \fB\-\fR"
1159 .RS 4
1160 negation\&.
1161 .RE
1162 .PP
1163 "\fB!\fR"
1164 .RS 4
1165 logical not; the result is 1 if argument is zero, 0 if not\&.
1166 .RE
1167 .PP
1168 "\fB~\fR"
1169 .RS 4
1170 arithmetic (bit\-wise) not\&.
1171 .RE
1172 .PP
1173 "\fB++\fR"
1174 .RS 4
1175 increment; must be applied to a parameter (not a literal or other expression) \- the parameter is incremented by 1\&. When used as a prefix operator, the result is the incremented value of the parameter, when used as a postfix operator, the result is the original value of the parameter\&.
1176 .RE
1177 .PP
1178 "\fB++\fR"
1179 .RS 4
1180 similar to
1181 \fB++\fR, except the parameter is decremented by 1\&.
1182 .RE
1183 .PP
1184 "\fB,\fR"
1185 .RS 4
1186 separates two arithmetic expressions; the left hand side is evaluated first, then the right\&. The result is value of the expression on the right hand side\&.
1187 .RE
1188 .PP
1189 "\fB=\fR"
1190 .RS 4
1191 assignment; variable on the left is set to the value on the right\&.
1192 .RE
1193 .PP
1194 "\fB*= /= %= += \-= <<= >>= &= ^= |=\fR"
1195 .RS 4
1196 assignment operators;
1197 \fI<var> <op>\fR\fB=\fR
1198 \fI<expr>\fR
1199 is the same as
1200 \fI<var>\fR
1201 \fB=\fR
1202 \fI<var> <op>\fR
1203 \fB(\fR
1204 \fI<expr>\fR
1205 \fB)\fR\&.
1206 .RE
1207 .PP
1208 "\fB||\fR"
1209 .RS 4
1210 logical or; the result is 1 if either argument is non\-zero, 0 if not\&. The right argument is evaluated only if the left argument is zero\&.
1211 .RE
1212 .PP
1213 "\fB&&\fR"
1214 .RS 4
1215 logical and; the result is 1 if both arguments are non\-zero, 0 if not\&. The right argument is evaluated only if the left argument is non\-zero\&.
1216 .RE
1217 .PP
1218 "\fB|\fR"
1219 .RS 4
1220 arithmetic (bit\-wise) or\&.
1221 .RE
1222 .PP
1223 "\fB^\fR"
1224 .RS 4
1225 arithmetic (bit\-wise) exclusive\-or\&.
1226 .RE
1227 .PP
1228 "\fB&\fR"
1229 .RS 4
1230 arithmetic (bit\-wise) and\&.
1231 .RE
1232 .PP
1233 "\fB==\fR"
1234 .RS 4
1235 equal; the result is 1 if both arguments are equal, 0 if not\&.
1236 .RE
1237 .PP
1238 "\fB!=\fR"
1239 .RS 4
1240 not equal; the result is 0 if both arguments are equal, 1 if not\&.
1241 .RE
1242 .PP
1243 "\fB<\fR"
1244 .RS 4
1245 less than; the result is 1 if the left argument is less than the right, 0 if not\&.
1246 .RE
1247 .PP
1248 "\fB<= >= >\fR"
1249 .RS 4
1250 less than or equal, greater than or equal, greater than\&. See <\&.
1251 .RE
1252 .PP
1253 "\fB<< >>\fR"
1254 .RS 4
1255 shift left (right); the result is the left argument with its bits shifted left (right) by the amount given in the right argument\&.
1256 .RE
1257 .PP
1258 "\fB+ \- * /\fR"
1259 .RS 4
1260 addition, subtraction, multiplication, and division\&.
1261 .RE
1262 .PP
1263 "\fB%\fR"
1264 .RS 4
1265 remainder; the result is the remainder of the division of the left argument by the right\&. The sign of the result is unspecified if either argument is negative\&.
1266 .RE
1267 .PP
1268 "\fI<arg1>\fR \fB?\fR \fI<arg2>\fR \fB:\fR \fI<arg3>\fR"
1269 .RS 4
1270 if
1271 \fI<arg1>\fR
1272 is non\-zero, the result is
1273 \fI<arg2>\fR, otherwise
1274 \fI<arg3>\fR\&.
1275 .RE
1276 .SS "Functions"
1277 .PP
1278 Functions are defined using the Bourne/POSIX shell
1279 \fIname\fR\fB()\fR
1280 syntax\&. Functions are like
1281 \&.\-scripts in that they are executed in the current environment, however, unlike
1282 \&.\-scripts, shell arguments (\fIi\&.e\&.\fR, positional parameters,
1283 \fB$1\fR,
1284 \fIetc\&.\fR) are never visible inside them\&. When the shell is determining the location of a command, functions are searched after special built\-in commands, and before regular and non\-regular built\-ins, and before the
1285 \fBPATH\fR
1286 is searched\&.
1287 .PP
1288 An existing function may be deleted using
1289 \fBunset \-f\fR
1290 \fIfunction\-name\fR\&.
1291 .PP
1292 Since functions are executed in the current shell environment, parameter assignments made inside functions are visible after the function completes\&.
1293 .PP
1294 The exit status of a function is that of the last command executed in the function\&. A function can be made to finish immediately using the
1295 \fBreturn\fR
1296 command; this may also be used to explicitly specify the exit status\&.
1297 .SS "Command Execution"
1298 .PP
1299 After evaluation of command line arguments, redirections and parameter assignments, the type of command is determined: a special built\-in, a function, a regular built\-in or the name of a file to execute found using the
1300 \fBPATH\fR
1301 parameter\&. The checks are made in the above order\&. Special built\-in commands differ from other commands in that the
1302 \fBPATH\fR
1303 parameter is not used to find them, an error during their execution can cause a non\-interactive shell to exit and parameter assignments that are specified before the command are kept after the command completes\&. Just to confuse things, if the posix option is turned off (see
1304 \fBset\fR
1305 command below) some special commands are very special in that no field splitting, file globbing, brace expansion nor tilde expansion is performed on arguments that look like assignments\&. Regular built\-in commands are different only in that the
1306 \fBPATH\fR
1307 parameter is not used to find them\&.
1308 .SS "Job Control"
1309 .PP
1310 Job control refers to the shell\*(Aqs ability to monitor and control
1311 \fBjobs\fR, which are processes or groups of processes created for commands or pipelines\&. At a minimum, the shell keeps track of the status of the background (\fIi\&.e\&.\fR, asynchronous) jobs that currently exist; this information can be displayed using the
1312 \fBjobs\fR
1313 command\&. If job control is fully enabled (using
1314 \fBset \-m\fR
1315 or
1316 \fBset \-o monitor\fR), as it is for interactive shells, the processes of a job are placed in their own process group, foreground jobs can be stopped by typing the suspend character from the terminal (normally ^Z), jobs can be restarted in either the foreground or background, using the
1317 \fBfg\fR
1318 and
1319 \fBbg\fR
1320 commands, respectively, and the state of the terminal is saved or restored when a foreground job is stopped or restarted, respectively\&.
1321 .PP
1322 Note that only commands that create processes (\fIe\&.g\&.\fR, asynchronous commands, subshell commands, and non\-built\-in, non\-function commands) can be stopped; commands like
1323 \fBread\fR
1324 cannot be\&.
1325 .PP
1326 When a job is created, it is assigned a job\-number\&. For interactive shells, this number is printed inside
1327 \fB[\fR\&.\&.\fB]\fR, followed by the process\-ids of the processes in the job when an asynchronous command is run\&. A job may be referred to in
1328 \fBbg\fR,
1329 \fBfg\fR,
1330 \fBjobs\fR,
1331 \fBkill\fR
1332 and
1333 \fBwait\fR
1334 commands either by the process id of the last process in the command pipeline (as stored in the
1335 \fB$!\fR
1336 parameter) or by prefixing the job\-number with a percent sign (\fB%\fR)\&. Other percent sequences can also be used to refer to jobs:
1337 .TS
1338 center tab(:);
1339 cB rB cB s.
1340 T{
1341 %+
1342 T}:T{
1343 %+
1344 T}:T{
1345 The most recently stopped job, or, if there are no stopped jobs, the oldest
1346 running job\&.
1347 T}
1348 .T&
1349 c l l l
1350 c l l l
1351 c l l l
1352 c l l l
1353 c l l l.
1354 T{
1355 %%, \fI%\fR
1356 T}:T{
1357 %%, \fI%\fR
1358 T}:T{
1359 Same as \fB%+\fR\&.
1360 T}:T{
1361 \ \&
1362 T}
1363 T{
1364 %\-
1365 T}:T{
1366 %\-
1367 T}:T{
1368 The job that would be the \fB%+\fR job, if the later did not exist\&.
1369 T}:T{
1370 \ \&
1371 T}
1372 T{
1373 %\fIn\fR
1374 T}:T{
1375 %\fIn\fR
1376 T}:T{
1377 The job with job\-number \fIn\fR\&.
1378 T}:T{
1379 \ \&
1380 T}
1381 T{
1382 %?\fIstring\fR
1383 T}:T{
1384 %?\fIstring\fR
1385 T}:T{
1386 The job containing the string \fIstring\fR (an error occurs if multiple jobs
1387 are matched)\&.
1388 T}:T{
1389 \ \&
1390 T}
1391 T{
1392 %\fIstring\fR
1393 T}:T{
1394 %\fIstring\fR
1395 T}:T{
1396 The job starting with string \fIstring\fR (an error occurs if multiple jobs
1397 are matched)\&.
1398 T}:T{
1399 \ \&
1400 T}
1401 .TE
1402 .sp 1
1403 .PP
1404 When a job changes state (\fIe\&.g\&.\fR, a background job finishes or foreground job is stopped), the shell prints the following status information:
1405 \fB[\fR\fInumber\fR\fB]\fR
1406 \fIflag status command\fR
1407 where
1408 .PP
1409 "\ \&\fInumber\fR"
1410 .RS 4
1411 is the job\-number of the job\&.
1412 .RE
1413 .PP
1414 "\ \&\fIflag\fR"
1415 .RS 4
1416 is
1417 \fB+\fR
1418 or
1419 \fB\-\fR
1420 if the job is the
1421 \fB%+\fR
1422 or
1423 \fB%\-\fR
1424 job, respectively, or space if it is neither\&.
1425 .RE
1426 .PP
1427 "\ \&\fIstatus\fR"
1428 .RS 4
1429 indicates the current state of the job and can be
1430 .RE
1431 .PP
1432 "\fBRunning\fR"
1433 .RS 4
1434 the job has neither stopped or exited (note that running does not necessarily mean consuming CPU time \(em the process could be blocked waiting for some event)\&.
1435 .RE
1436 .PP
1437 "\fBDone\fR [\fB(\fR\fInumber\fR\fB)\fR]"
1438 .RS 4
1439 the job exited\&.
1440 \fInumber\fR
1441 is the exit status of the job, which is omitted if the status is zero\&.
1442 .RE
1443 .PP
1444 "\fBStopped\fR [\fB(\fR\fIsignal\fR\fB)\fR]"
1445 .RS 4
1446 the job was stopped by the indicated
1447 \fIsignal\fR
1448 (if no signal is given, the job was stopped by SIGTSTP)\&.
1449 .RE
1450 .PP
1451 "\fIsignal\-description\fR [\fB(core dumped)\fR]"
1452 .RS 4
1453 the job was killed by a signal (\fIe\&.g\&.\fR, Memory\ \&fault, Hangup,
1454 \fIetc\&.\fR
1455 \(em use
1456 \fBkill \-l\fR
1457 for a list of signal descriptions)\&. The
1458 \fB(core\ \&dumped)\fR
1459 message indicates the process created a core file\&.
1460 .RE
1461 .PP
1462 "\ \&\fIcommand\fR"
1463 .RS 4
1464 is the command that created the process\&. If there are multiple processes in the job, then each process will have a line showing its
1465 \fIcommand\fR
1466 and possibly its
1467 \fIstatus\fR, if it is different from the status of the previous process\&.
1468 .RE
1469 .PP
1470 When an attempt is made to exit the shell while there are jobs in the stopped state, the shell warns the user that there are stopped jobs and does not exit\&. If another attempt is immediately made to exit the shell, the stopped jobs are sent a
1471 \fBHUP\fR
1472 signal and the shell exits\&. Similarly, if the
1473 \fBnohup\fR
1474 option is not set and there are running jobs when an attempt is made to exit a login shell, the shell warns the user and does not exit\&. If another attempt is immediately made to exit the shell, the running jobs are sent a
1475 \fBHUP\fR
1476 signal and the shell exits\&.
1477 .SH "BUILTIN UTILITIES"
1478 .PP
1479 posh implements the following builtin utilities:
1480 .sp
1481 .RS 4
1482 .ie n \{\
1483 \h'-04'\(bu\h'+03'\c
1484 .\}
1485 .el \{\
1486 .sp -1
1487 .IP \(bu 2.3
1488 .\}
1489 \&.
1490 .RE
1491 .sp
1492 .RS 4
1493 .ie n \{\
1494 \h'-04'\(bu\h'+03'\c
1495 .\}
1496 .el \{\
1497 .sp -1
1498 .IP \(bu 2.3
1499 .\}
1500 :
1501 .RE
1502 .sp
1503 .RS 4
1504 .ie n \{\
1505 \h'-04'\(bu\h'+03'\c
1506 .\}
1507 .el \{\
1508 .sp -1
1509 .IP \(bu 2.3
1510 .\}
1511 [
1512 .RE
1513 .sp
1514 .RS 4
1515 .ie n \{\
1516 \h'-04'\(bu\h'+03'\c
1517 .\}
1518 .el \{\
1519 .sp -1
1520 .IP \(bu 2.3
1521 .\}
1522 break
1523 .RE
1524 .sp
1525 .RS 4
1526 .ie n \{\
1527 \h'-04'\(bu\h'+03'\c
1528 .\}
1529 .el \{\
1530 .sp -1
1531 .IP \(bu 2.3
1532 .\}
1533 builtin
1534 .RE
1535 .sp
1536 .RS 4
1537 .ie n \{\
1538 \h'-04'\(bu\h'+03'\c
1539 .\}
1540 .el \{\
1541 .sp -1
1542 .IP \(bu 2.3
1543 .\}
1544 continue
1545 .RE
1546 .sp
1547 .RS 4
1548 .ie n \{\
1549 \h'-04'\(bu\h'+03'\c
1550 .\}
1551 .el \{\
1552 .sp -1
1553 .IP \(bu 2.3
1554 .\}
1555 eval
1556 .RE
1557 .sp
1558 .RS 4
1559 .ie n \{\
1560 \h'-04'\(bu\h'+03'\c
1561 .\}
1562 .el \{\
1563 .sp -1
1564 .IP \(bu 2.3
1565 .\}
1566 exec
1567 .RE
1568 .sp
1569 .RS 4
1570 .ie n \{\
1571 \h'-04'\(bu\h'+03'\c
1572 .\}
1573 .el \{\
1574 .sp -1
1575 .IP \(bu 2.3
1576 .\}
1577 exit
1578 .RE
1579 .sp
1580 .RS 4
1581 .ie n \{\
1582 \h'-04'\(bu\h'+03'\c
1583 .\}
1584 .el \{\
1585 .sp -1
1586 .IP \(bu 2.3
1587 .\}
1588 false
1589 .RE
1590 .sp
1591 .RS 4
1592 .ie n \{\
1593 \h'-04'\(bu\h'+03'\c
1594 .\}
1595 .el \{\
1596 .sp -1
1597 .IP \(bu 2.3
1598 .\}
1599 return
1600 .RE
1601 .sp
1602 .RS 4
1603 .ie n \{\
1604 \h'-04'\(bu\h'+03'\c
1605 .\}
1606 .el \{\
1607 .sp -1
1608 .IP \(bu 2.3
1609 .\}
1610 set
1611 .RE
1612 .sp
1613 .RS 4
1614 .ie n \{\
1615 \h'-04'\(bu\h'+03'\c
1616 .\}
1617 .el \{\
1618 .sp -1
1619 .IP \(bu 2.3
1620 .\}
1621 shift
1622 .RE
1623 .sp
1624 .RS 4
1625 .ie n \{\
1626 \h'-04'\(bu\h'+03'\c
1627 .\}
1628 .el \{\
1629 .sp -1
1630 .IP \(bu 2.3
1631 .\}
1632 times
1633 .RE
1634 .sp
1635 .RS 4
1636 .ie n \{\
1637 \h'-04'\(bu\h'+03'\c
1638 .\}
1639 .el \{\
1640 .sp -1
1641 .IP \(bu 2.3
1642 .\}
1643 trap
1644 .RE
1645 .sp
1646 .RS 4
1647 .ie n \{\
1648 \h'-04'\(bu\h'+03'\c
1649 .\}
1650 .el \{\
1651 .sp -1
1652 .IP \(bu 2.3
1653 .\}
1654 wait
1655 .RE
1656 .sp
1657 .RS 4
1658 .ie n \{\
1659 \h'-04'\(bu\h'+03'\c
1660 .\}
1661 .el \{\
1662 .sp -1
1663 .IP \(bu 2.3
1664 .\}
1665 read
1666 .RE
1667 .sp
1668 .RS 4
1669 .ie n \{\
1670 \h'-04'\(bu\h'+03'\c
1671 .\}
1672 .el \{\
1673 .sp -1
1674 .IP \(bu 2.3
1675 .\}
1676 test
1677 .RE
1678 .sp
1679 .RS 4
1680 .ie n \{\
1681 \h'-04'\(bu\h'+03'\c
1682 .\}
1683 .el \{\
1684 .sp -1
1685 .IP \(bu 2.3
1686 .\}
1687 true
1688 .RE
1689 .sp
1690 .RS 4
1691 .ie n \{\
1692 \h'-04'\(bu\h'+03'\c
1693 .\}
1694 .el \{\
1695 .sp -1
1696 .IP \(bu 2.3
1697 .\}
1698 umask
1699 .RE
1700 .sp
1701 .RS 4
1702 .ie n \{\
1703 \h'-04'\(bu\h'+03'\c
1704 .\}
1705 .el \{\
1706 .sp -1
1707 .IP \(bu 2.3
1708 .\}
1709 unset
1710 .RE
1711 .sp
1712 .RS 4
1713 .ie n \{\
1714 \h'-04'\(bu\h'+03'\c
1715 .\}
1716 .el \{\
1717 .sp -1
1718 .IP \(bu 2.3
1719 .\}
1720 cd
1721 .RE
1722 .sp
1723 .RS 4
1724 .ie n \{\
1725 \h'-04'\(bu\h'+03'\c
1726 .\}
1727 .el \{\
1728 .sp -1
1729 .IP \(bu 2.3
1730 .\}
1731 command
1732 .RE
1733 .sp
1734 .RS 4
1735 .ie n \{\
1736 \h'-04'\(bu\h'+03'\c
1737 .\}
1738 .el \{\
1739 .sp -1
1740 .IP \(bu 2.3
1741 .\}
1742 echo
1743 .RE
1744 .sp
1745 .RS 4
1746 .ie n \{\
1747 \h'-04'\(bu\h'+03'\c
1748 .\}
1749 .el \{\
1750 .sp -1
1751 .IP \(bu 2.3
1752 .\}
1753 export
1754 .RE
1755 .sp
1756 .RS 4
1757 .ie n \{\
1758 \h'-04'\(bu\h'+03'\c
1759 .\}
1760 .el \{\
1761 .sp -1
1762 .IP \(bu 2.3
1763 .\}
1764 getopts
1765 .RE
1766 .sp
1767 .RS 4
1768 .ie n \{\
1769 \h'-04'\(bu\h'+03'\c
1770 .\}
1771 .el \{\
1772 .sp -1
1773 .IP \(bu 2.3
1774 .\}
1775 kill
1776 .RE
1777 .sp
1778 .RS 4
1779 .ie n \{\
1780 \h'-04'\(bu\h'+03'\c
1781 .\}
1782 .el \{\
1783 .sp -1
1784 .IP \(bu 2.3
1785 .\}
1786 local
1787 .RE
1788 .sp
1789 .RS 4
1790 .ie n \{\
1791 \h'-04'\(bu\h'+03'\c
1792 .\}
1793 .el \{\
1794 .sp -1
1795 .IP \(bu 2.3
1796 .\}
1797 pwd
1798 .RE
1799 .sp
1800 .RS 4
1801 .ie n \{\
1802 \h'-04'\(bu\h'+03'\c
1803 .\}
1804 .el \{\
1805 .sp -1
1806 .IP \(bu 2.3
1807 .\}
1808 readonly
1809 .RE
1810 .SH "FILES"
1811 .PP
1813 ~/\&.profile
1814 /etc/profile
1815 /etc/suid_profile
1816 .SH "BUGS"
1817 .PP
1818 Any bugs in posh should be reported via the Debian BTS\&. Legitimate bugs are inconsistencies between manpage and behavior, and inconsistencies between behavior and Debian policy (currently SUSv3 compliance with the following exceptions: echo \-n, binary \-a and \-o to test, local scoping)\&.
1819 .SH "VERSION"
1820 .PP
1821 This page documents the Policy\-compliant Ordinary SHell\&.
1822 .SH "AUTHORS"
1823 .PP
1824 This shell is based on pdksh\&.
1825 .SH "SEE ALSO"
1826 .PP
1828 \fBawk\fR(1),
1829 \fBksh\fR(1),
1830 \fBdash\fR(1),
1831 \fBed\fR(1),
1832 \fBgetconf\fR(1),
1833 \fBgetopt\fR(1),
1834 \fBsed\fR(1),
1835 \fBstty\fR(1),
1836 \fBvi\fR(1),
1837 \fBdup\fR(2),
1838 \fBexecve\fR(2),
1839 \fBgetgid\fR(2),
1840 \fBgetuid\fR(2),
1841 \fBopen\fR(2),
1842 \fBpipe\fR(2),
1843 \fBwait\fR(2),
1844 \fBgetopt\fR(3),
1845 \fBrand\fR(3),
1846 \fBsignal\fR(3),
1847 \fBsystem\fR(3),
1848 \fBenviron\fR(5)