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10 .TH XARGS 1 "March 31, 2014"
11 .SH NAME
12 xargs \- construct argument lists and invoke utility
13 .SH SYNOPSIS
14 .LP
15 .nf
16 \fBxargs\fR [\fB-t\fR] [\fB-0\fR] [\fB-p\fR] [\fB-e\fR[\fIeofstr\fR]] [\fB-E\fR \fIeofstr\fR]
17 [\fB-I\fR \fIreplstr\fR] [\fB-i\fR[\fIreplstr\fR]] [\fB-L\fR \fInumber\fR] [\fB-l\fR[\fInumber\fR]]
18 [\fB-n\fR \fInumber\fR [\fB-x\fR]] [\fB-P\fR \fImaxprocs\fR] [\fB-s\fR \fIsize\fR]
19 [\fIutility\fR [\fIargument\fR...]]
20 .fi
21
22 .SH DESCRIPTION
23 .sp
24 .LP
25 The \fBxargs\fR utility constructs a command line consisting of the
26 \fIutility\fR and \fIargument\fR operands specified followed by as many
27 arguments read in sequence from standard input as fit in length and number
28 constraints specified by the options. The \fBxargs\fR utility then invokes the
29 constructed command line and waits for its completion. This sequence is
30 repeated until an end-of-file condition is detected on standard input or an
31 invocation of a constructed command line returns an exit status of \fB255\fR.
32 .sp
33 .LP
34 Arguments in the standard input must be separated by unquoted blank characters,
35 or unescaped blank characters or newline characters. A string of zero or more
36 non-double-quote (\fB"\fR) and non-newline characters can be quoted by
37 enclosing them in double-quotes. A string of zero or more non-apostrophe
38 (\fB\&'\fR) and non-newline characters can be quoted by enclosing them in
39 apostrophes. Any unquoted character can be escaped by preceding it with a
40 backslash (\fB\e\fR). The \fIutility\fR are executed one or more times until
41 the end-of-file is reached. The results are unspecified if the utility named by
42 \fIutility\fR attempts to read from its standard input.
43 .sp
44 .LP
45 The generated command line length is the sum of the size in bytes of the
46 utility name and each argument treated as strings, including a null byte
47 terminator for each of these strings. The \fBxargs\fR utility limits the
48 command line length such that when the command line is invoked, the combined
49 argument and environment lists can not exceed \fB{ARG_MAX}\(mi2048\fR bytes.
50 Within this constraint, if neither the \fB-n\fR nor the \fB-s\fR option is
51 specified, the default command line length is at least \fB{LINE_MAX}\fR.
52 .SH OPTIONS
53 .sp
54 .LP
55 The following options are supported:
56 .sp
57 .ne 2
58 .na
59 \fB\fB\fR\fB-e\fR\fB[\fR\fIeofstr\fR\fB]\fR\fR
60 .ad
61 .RS 15n
62 Uses \fIeofstr\fR as the logical end-of-file string. Underscore (\fB_\fR) is
63 assumed for the logical \fBEOF\fR string if neither \fB-e\fR nor \fB-E\fR is
64 used. When the \fIeofstr\fR option-argument is omitted, the logical \fBEOF\fR
65 string capability is disabled and underscores are taken literally. The
66 \fBxargs\fR utility reads standard input until either end-of-file or the
67 logical \fBEOF\fR string is encountered.
68 .RE
69
70 .sp
71 .ne 2
72 .na
73 \fB\fB-E\fR \fIeofstr\fR\fR
74 .ad
75 .RS 15n
76 Specifies a logical end-of-file string to replace the default underscore.
77 \fBxargs\fR reads standard input until either end-of-file or the logical EOF
78 string is encountered. When \fIeofstr\fR is a null string, the logical
79 end-of-file string capability is disabled and underscore characters are taken
80 literally.
81 .RE
82
83 .sp
84 .ne 2
85 .na
86 \fB\fB-I\fR \fIreplstr\fR\fR
87 .ad
88 .RS 15n
89 Insert mode. \fIutility\fR is executed for each line from standard input,
90 taking the entire line as a single argument, inserting it in \fIargument\fR
91 \fIs\fR for each occurrence of \fIreplstr\fR. A maximum of five arguments in
92 \fIargument\fRs can each contain one or more instances of \fIreplstr\fR. Any
93 blank characters at the beginning of each line are ignored. Constructed
94 arguments cannot grow larger than 255 bytes. Option \fB-x\fR is forced on. The
95 \fB-I\fR and \fB-i\fR options are mutually exclusive; the last one specified
96 takes effect.
97 .RE
98
99 .sp
100 .ne 2
101 .na
102 \fB\fB\fR\fB-i\fR\fB[\fR\fIreplstr\fR\fB]\fR\fR
103 .ad
104 .RS 15n
105 This option is equivalent to \fB-I\fR \fIreplstr\fR. The string \fB{\|}\fR is
106 assumed for \fIreplstr\fR if the option-argument is omitted.
107 .RE
108
109 .sp
110 .ne 2
111 .na
112 \fB\fB-L\fR \fInumber\fR\fR
113 .ad
114 .RS 15n
115 The \fIutility\fR is executed for each non-empty \fInumber\fR lines of
116 arguments from standard input. The last invocation of \fIutility\fR is with
117 fewer lines of arguments if fewer than \fInumber\fR remain. A line is
118 considered to end with the first newline character unless the last character of
119 the line is a blank character; a trailing blank character signals continuation
120 to the next non-empty line, inclusive. The \fB-L\fR, \fB-l\fR, and \fB-n\fR
121 options are mutually exclusive; the last one specified takes effect.
122 .RE
123
124 .sp
125 .ne 2
126 .na
127 \fB\fB-l[\fR\fInumber\fR\fB]\fR\fR
128 .ad
129 .RS 15n
130 (The letter ell.) This option is equivalent to \fB-L\fR \fInumber\fR. If
131 \fInumber\fR is omitted, \fB1\fR is assumed. Option \fB-x\fR is forced on.
132 .RE
133
134 .sp
135 .ne 2
136 .na
137 \fB\fB-n\fR \fInumber\fR\fR
138 .ad
139 .RS 15n
140 Invokes \fIutility\fR using as many standard input arguments as possible, up to
141 \fInumber\fR (a positive decimal integer) arguments maximum. Fewer arguments
142 are used if:
143 .RS +4
144 .TP
145 .ie t \(bu
146 .el o
147 The command line length accumulated exceeds the size specified by the \fB-s\fR
148 option (or \fB{LINE_MAX}\fR if there is no \fB-s\fR option), or
149 .RE
150 .RS +4
151 .TP
152 .ie t \(bu
153 .el o
154 The last iteration has fewer than \fInumber\fR, but not zero, operands
155 remaining.
156 .RE
157 .RE
158
159 .sp
160 .ne 2
161 .na
162 \fB-p\fR
163 .ad
164 .RS 15n
165 Prompt mode. The user is asked whether to execute \fIutility\fR at each
166 invocation. Trace mode (\fB-t\fR) is turned on to write the command instance to
167 be executed, followed by a prompt to standard error. An affirmative response
168 (specific to the user's locale) read from \fB/dev/tty\fR executes the command;
169 otherwise, that particular invocation of \fIutility\fR is skipped.
170 .RE
171
172 .sp
173 .ne 2
174 .na
175 \fB\fB-P\fR \fImaxprocs\fR\fR
176 .ad
177 .RS 15n
178 Invokes \fIutility\fR using at most \fImaxprocs\fR (a positive decimal integer)
179 parallel child processes.
180 .RE
181
182 .sp
183 .ne 2
184 .na
185 \fB\fB-s\fR \fIsize\fR\fR
186 .ad
187 .RS 15n
188 Invokes \fIutility\fR using as many standard input arguments as possible
189 yielding a command line length less than \fIsize\fR (a positive decimal
190 integer) bytes. Fewer arguments are used if:
191 .RS +4
192 .TP
193 .ie t \(bu
194 .el o
195 The total number of arguments exceeds that specified by the \fB-n\fR option, or
196 .RE
197 .RS +4
198 .TP
199 .ie t \(bu
200 .el o
201 The total number of lines exceeds that specified by the \fB-L\fR option, or
202 .RE
203 .RS +4
204 .TP
205 .ie t \(bu
206 .el o
207 End of file is encountered on standard input before \fIsize\fR bytes are
208 accumulated.
209 .RE
210 Values of \fIsize\fR up to at least \fB{LINE_MAX}\fR bytes are supported,
211 provided that the constraints specified in DESCRIPTION are met. It is not
212 considered an error if a value larger than that supported by the implementation
213 or exceeding the constraints specified in DESCRIPTION is specified. \fBxargs\fR
214 uses the largest value it supports within the constraints.
215 .RE
216
217 .sp
218 .ne 2
219 .na
220 \fB\fB-t\fR\fR
221 .ad
222 .RS 6n
223 Enables trace mode. Each generated command line is written to standard error
224 just prior to invocation.
225 .RE
226
227 .sp
228 .ne 2
229 .na
230 \fB\fB-x\fR\fR
231 .ad
232 .RS 6n
233 Terminates if a command line containing \fInumber\fR arguments (see the
234 \fB-n\fR option above) or \fInumber\fR lines (see the \fB-L\fR option above)
235 does not fit in the implied or specified size (see the \fB-s\fR option above).
236 .RE
237
238 .sp
239 .ne 2
240 .na
241 \fB-0\fR
242 .ad
243 .RS 6n
244 Null separator mode. Instead of using white space or new lines to
245 delimit arguments, zero bytes are used. This is suitable for use with
246 the -print0 argument to \fBfind\fR(1).
247 .RE
248
249 .SH OPERANDS
250 .sp
251 .LP
252 The following operands are supported:
253 .sp
254 .ne 2
255 .na
256 \fB\fIutility\fR\fR
257 .ad
258 .RS 12n
259 The name of the utility to be invoked, found by search path using the
260 \fBPATH\fR environment variable. (ee \fBenviron\fR(5).) If \fIutility\fR is
261 omitted, the default is the \fBecho\fR(1) utility. If the \fIutility\fR operand
262 names any of the special built-in utilities in \fBshell_builtins\fR(1), the
263 results are undefined.
264 .RE
265
266 .sp
267 .ne 2
268 .na
269 \fB\fIargument\fR\fR
270 .ad
271 .RS 12n
272 An initial option or operand for the invocation of \fIutility\fR.
273 .RE
274
275 .SH USAGE
276 .sp
277 .LP
278 The \fB255\fR exit status allows a utility being used by \fBxargs\fR to tell
279 \fBxargs\fR to terminate if it knows no further invocations using the current
280 data stream succeeds. Thus, \fIutility\fR should explicitly \fBexit\fR with an
281 appropriate value to avoid accidentally returning with \fB255\fR.
282 .sp
283 .LP
284 Notice that input is parsed as lines. Blank characters separate arguments. If
285 \fBxargs\fR is used to bundle output of commands like \fBfind\fR \fIdir\fR
286 \fB-print\fR or \fBls\fR into commands to be executed, unexpected results are
287 likely if any filenames contain any blank characters or newline characters.
288 This can be fixed by using \fBfind\fR to call a script that converts each file
289 found into a quoted string that is then piped to \fBxargs\fR. Notice that the
290 quoting rules used by \fBxargs\fR are not the same as in the shell. They were
291 not made consistent here because existing applications depend on the current
292 rules and the shell syntax is not fully compatible with it. An easy rule that
293 can be used to transform any string into a quoted form that \fBxargs\fR
294 interprets correctly is to precede each character in the string with a
295 backslash (\fB\e\fR).
296 .sp
297 .LP
298 On implementations with a large value for \fB{ARG_MAX}\fR, \fBxargs\fR can
299 produce command lines longer than \fB{LINE_MAX}\fR. For invocation of
300 utilities, this is not a problem. If \fBxargs\fR is being used to create a text
301 file, users should explicitly set the maximum command line length with the
302 \fB-s\fR option.
303 .sp
304 .LP
305 The \fBxargs\fR utility returns exit status \fB127\fR if an error occurs so
306 that applications can distinguish "failure to find a utility" from "invoked
307 utility exited with an error indication." The value \fB127\fR was chosen
308 because it is not commonly used for other meanings; most utilities use small
309 values for "normal error conditions" and the values above \fB128\fR can be
310 confused with termination due to receipt of a signal. The value \fB126\fR was
311 chosen in a similar manner to indicate that the utility could be found, but not
312 invoked.
313 .SH EXAMPLES
314 .LP
315 \fBExample 1 \fRUsing the xargs command
316 .sp
317 .LP
318 The following example moves all files from directory \fB$1\fR to directory
319 \fB$2\fR, and echo each move command just before doing it:
320
321 .sp
322 .in +2
323 .nf
324 example% \fBls $1 | xargs -I {} -t mv $1/{} $2/{}\fR
325 .fi
326 .in -2
327 .sp
328
329 .sp
330 .LP
331 The following command combines the output of the parenthesised commands onto
332 one line, which is then written to the end of file \fBlog\fR:
333
334 .sp
335 .in +2
336 .nf
337 example% \fB(logname; date; printf "%s\en" "$0 $*") | xargs >>log\fR
338 .fi
339 .in -2
340 .sp
341
342 .sp
343 .LP
344 The following command invokes \fBdiff\fR with successive pairs of arguments
345 originally typed as command line arguments (assuming there are no embedded
346 blank characters in the elements of the original argument list):
347
348 .sp
349 .in +2
350 .nf
351 example% \fBprintf "%s\en" "$*" | xargs -n 2 -x diff\fR
352 .fi
353 .in -2
354 .sp
355
356 .sp
357 .LP
358 The user is asked which files in the current directory are to be archived. The
359 files are archived into \fBarch\fR \fB;\fR a, one at a time, or b, many at a
360 time:
361
362 .sp
363 .in +2
364 .nf
365 example% \fBls | xargs -p -L 1 ar -r arch
366 ls | xargs -p -L 1 | xargs ar -r arch\fR
367 .fi
368 .in -2
369 .sp
370
371 .sp
372 .LP
373 The following executes with successive pairs of arguments originally typed as
374 command line arguments:
375
376 .sp
377 .in +2
378 .nf
379 example% \fBecho $* | xargs -n 2 diff\fR
380 .fi
381 .in -2
382 .sp
383
384 .SH ENVIRONMENT VARIABLES
385 .sp
386 .LP
387 See \fBenviron\fR(5) for descriptions of the following environment variables
388 that affect the execution of \fBxargs\fR: \fBLANG\fR, \fBLC_ALL\fR,
389 \fBLC_COLLATE\fR, \fBLC_CTYPE\fR, \fBLC_MESSAGES\fR, and \fBNLSPATH\fR.
390 .sp
391 .ne 2
392 .na
393 \fB\fBPATH\fR\fR
394 .ad
395 .RS 8n
396 Determine the location of \fIutility\fR.
397 .RE
398
399 .sp
400 .LP
401 Affirmative responses are processed using the extended regular expression
402 defined for the \fByesexpr\fR keyword in the \fBLC_MESSAGES\fR category of the
403 user's locale. The locale specified in the \fBLC_COLLATE\fR category defines
404 the behavior of ranges, equivalence classes, and multi-character collating
405 elements used in the expression defined for \fByesexpr\fR. The locale specified
406 in \fBLC_CTYPE\fR determines the locale for interpretation of sequences of
407 bytes of text data a characters, the behavior of character classes used in the
408 expression defined for the \fByesexpr\fR. See \fBlocale\fR(5).
409 .SH EXIT STATUS
410 .sp
411 .LP
412 The following exit values are returned:
413 .sp
414 .ne 2
415 .na
416 \fB\fB0\fR\fR
417 .ad
418 .RS 12n
419 All invocations of \fIutility\fR returned exit status \fB0\fR.
420 .RE
421
422 .sp
423 .ne 2
424 .na
425 \fB\fB1\(mi125\fR\fR
426 .ad
427 .RS 12n
428 A command line meeting the specified requirements could not be assembled, one
429 or more of the invocations of \fIutility\fR returned a non-zero exit status, or
430 some other error occurred.
431 .RE
432
433 .sp
434 .ne 2
435 .na
436 \fB\fB126\fR\fR
437 .ad
438 .RS 12n
439 The utility specified by \fIutility\fR was found but could not be invoked.
440 .RE
441
442 .sp
443 .ne 2
444 .na
445 \fB\fB127\fR\fR
446 .ad
447 .RS 12n
448 The utility specified by \fIutility\fR could not be found.
449 .RE
450
451 .sp
452 .LP
453 If a command line meeting the specified requirements cannot be assembled, the
454 utility cannot be invoked, an invocation of the utility is terminated by a
455 signal, or an invocation of the utility exits with exit status \fB255\fR, the
456 \fBxargs\fR utility writes a diagnostic message and exit without processing any
457 remaining input.
458 .SH ATTRIBUTES
459 .sp
460 .LP
461 See \fBattributes\fR(5) for descriptions of the following attributes:
462 .sp
463
464 .sp
465 .TS
466 box;
467 c | c
468 l | l .
469 ATTRIBUTE TYPE ATTRIBUTE VALUE
470 _
471 CSI Enabled
472 _
473 Interface Stability Standard
474 .TE
475
476 .SH SEE ALSO
477 .sp
478 .LP
479 \fBecho\fR(1), \fBshell_builtins\fR(1), \fBattributes\fR(5), \fBenviron\fR(5),
480 \fBstandards\fR(5)