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10 .TH XARGS 1 "November 24, 2012"
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-s\fR \fIsize\fR] [\fIutility\fR [\fIargument\fR...]]
19 .fi
20
21 .SH DESCRIPTION
22 .sp
23 .LP
24 The \fBxargs\fR utility constructs a command line consisting of the
25 \fIutility\fR and \fIargument\fR operands specified followed by as many
26 arguments read in sequence from standard input as fit in length and number
27 constraints specified by the options. The \fBxargs\fR utility then invokes the
28 constructed command line and waits for its completion. This sequence is
29 repeated until an end-of-file condition is detected on standard input or an
30 invocation of a constructed command line returns an exit status of \fB255\fR.
31 .sp
32 .LP
33 Arguments in the standard input must be separated by unquoted blank characters,
34 or unescaped blank characters or newline characters. A string of zero or more
35 non-double-quote (\fB"\fR) and non-newline characters can be quoted by
36 enclosing them in double-quotes. A string of zero or more non-apostrophe
37 (\fB\&'\fR) and non-newline characters can be quoted by enclosing them in
38 apostrophes. Any unquoted character can be escaped by preceding it with a
39 backslash (\fB\e\fR). The \fIutility\fR are executed one or more times until
40 the end-of-file is reached. The results are unspecified if the utility named by
41 \fIutility\fR attempts to read from its standard input.
42 .sp
43 .LP
44 The generated command line length is the sum of the size in bytes of the
45 utility name and each argument treated as strings, including a null byte
46 terminator for each of these strings. The \fBxargs\fR utility limits the
47 command line length such that when the command line is invoked, the combined
48 argument and environment lists can not exceed \fB{ARG_MAX}\(mi2048\fR bytes.
49 Within this constraint, if neither the \fB-n\fR nor the \fB-s\fR option is
50 specified, the default command line length is at least \fB{LINE_MAX}\fR.
51 .SH OPTIONS
52 .sp
53 .LP
54 The following options are supported:
55 .sp
56 .ne 2
57 .na
58 \fB\fB\fR\fB-e\fR\fB[\fR\fIeofstr\fR\fB]\fR\fR
59 .ad
60 .RS 15n
61 Uses \fIeofstr\fR as the logical end-of-file string. Underscore (\fB_\fR) is
62 assumed for the logical \fBEOF\fR string if neither \fB-e\fR nor \fB-E\fR is
63 used. When the \fIeofstr\fR option-argument is omitted, the logical \fBEOF\fR
64 string capability is disabled and underscores are taken literally. The
65 \fBxargs\fR utility reads standard input until either end-of-file or the
66 logical \fBEOF\fR string is encountered.
67 .RE
68
69 .sp
70 .ne 2
71 .na
72 \fB\fB-E\fR \fIeofstr\fR\fR
73 .ad
74 .RS 15n
75 Specifies a logical end-of-file string to replace the default underscore.
76 \fBxargs\fR reads standard input until either end-of-file or the logical EOF
77 string is encountered. When \fIeofstr\fR is a null string, the logical
78 end-of-file string capability is disabled and underscore characters are taken
79 literally.
80 .RE
81
82 .sp
83 .ne 2
84 .na
85 \fB\fB-I\fR \fIreplstr\fR\fR
86 .ad
87 .RS 15n
88 Insert mode. \fIutility\fR is executed for each line from standard input,
89 taking the entire line as a single argument, inserting it in \fIargument\fR
90 \fIs\fR for each occurrence of \fIreplstr\fR. A maximum of five arguments in
91 \fIargument\fRs can each contain one or more instances of \fIreplstr\fR. Any
92 blank characters at the beginning of each line are ignored. Constructed
93 arguments cannot grow larger than 255 bytes. Option \fB-x\fR is forced on. The
94 \fB-I\fR and \fB-i\fR options are mutually exclusive; the last one specified
95 takes effect.
96 .RE
97
98 .sp
99 .ne 2
100 .na
101 \fB\fB\fR\fB-i\fR\fB[\fR\fIreplstr\fR\fB]\fR\fR
102 .ad
103 .RS 15n
104 This option is equivalent to \fB-I\fR \fIreplstr\fR. The string \fB{\|}\fR is
105 assumed for \fIreplstr\fR if the option-argument is omitted.
106 .RE
107
108 .sp
109 .ne 2
110 .na
111 \fB\fB-L\fR \fInumber\fR\fR
112 .ad
113 .RS 15n
114 The \fIutility\fR is executed for each non-empty \fInumber\fR lines of
115 arguments from standard input. The last invocation of \fIutility\fR is with
116 fewer lines of arguments if fewer than \fInumber\fR remain. A line is
117 considered to end with the first newline character unless the last character of
118 the line is a blank character; a trailing blank character signals continuation
119 to the next non-empty line, inclusive. The \fB-L\fR, \fB-l\fR, and \fB-n\fR
120 options are mutually exclusive; the last one specified takes effect.
121 .RE
122
123 .sp
124 .ne 2
125 .na
126 \fB\fB-l[\fR\fInumber\fR\fB]\fR\fR
127 .ad
128 .RS 15n
129 (The letter ell.) This option is equivalent to \fB-L\fR \fInumber\fR. If
130 \fInumber\fR is omitted, \fB1\fR is assumed. Option \fB-x\fR is forced on.
131 .RE
132
133 .sp
134 .ne 2
135 .na
136 \fB\fB-n\fR \fInumber\fR\fR
137 .ad
138 .RS 15n
139 Invokes \fIutility\fR using as many standard input arguments as possible, up to
140 \fInumber\fR (a positive decimal integer) arguments maximum. Fewer arguments
141 are used if:
142 .RS +4
143 .TP
144 .ie t \(bu
145 .el o
146 The command line length accumulated exceeds the size specified by the \fB-s\fR
147 option (or \fB{LINE_MAX}\fR if there is no \fB-s\fR option), or
148 .RE
149 .RS +4
150 .TP
151 .ie t \(bu
152 .el o
153 The last iteration has fewer than \fInumber\fR, but not zero, operands
154 remaining.
155 .RE
156 .RE
157
158 .sp
159 .ne 2
160 .na
161 \fB-p\fR
162 .ad
163 .RS 15n
164 Prompt mode. The user is asked whether to execute \fIutility\fR at each
165 invocation. Trace mode (\fB-t\fR) is turned on to write the command instance to
166 be executed, followed by a prompt to standard error. An affirmative response
167 (specific to the user's locale) read from \fB/dev/tty\fR executes the command;
168 otherwise, that particular invocation of \fIutility\fR is skipped.
169 .RE
170
171 .sp
172 .ne 2
173 .na
174 \fB\fB-s\fR \fIsize\fR\fR
175 .ad
176 .RS 15n
177 Invokes \fIutility\fR using as many standard input arguments as possible
178 yielding a command line length less than \fIsize\fR (a positive decimal
179 integer) bytes. Fewer arguments are used if:
180 .RS +4
181 .TP
182 .ie t \(bu
183 .el o
184 The total number of arguments exceeds that specified by the \fB-n\fR option, or
185 .RE
186 .RS +4
187 .TP
188 .ie t \(bu
189 .el o
190 The total number of lines exceeds that specified by the \fB-L\fR option, or
191 .RE
192 .RS +4
193 .TP
194 .ie t \(bu
195 .el o
196 End of file is encountered on standard input before \fIsize\fR bytes are
197 accumulated.
198 .RE
199 Values of \fIsize\fR up to at least \fB{LINE_MAX}\fR bytes are supported,
200 provided that the constraints specified in DESCRIPTION are met. It is not
201 considered an error if a value larger than that supported by the implementation
202 or exceeding the constraints specified in DESCRIPTION is specified. \fBxargs\fR
203 uses the largest value it supports within the constraints.
204 .RE
205
206 .sp
207 .ne 2
208 .na
209 \fB\fB-t\fR\fR
210 .ad
211 .RS 6n
212 Enables trace mode. Each generated command line is written to standard error
213 just prior to invocation.
214 .RE
215
216 .sp
217 .ne 2
218 .na
219 \fB\fB-x\fR\fR
220 .ad
221 .RS 6n
222 Terminates if a command line containing \fInumber\fR arguments (see the
223 \fB-n\fR option above) or \fInumber\fR lines (see the \fB-L\fR option above)
224 does not fit in the implied or specified size (see the \fB-s\fR option above).
225 .RE
226
227 .sp
228 .ne 2
229 .na
230 \fB-0\fR
231 .ad
232 .RS 6n
233 Null separator mode. Instead of using white space or new lines to
234 delimit arguments, zero bytes are used. This is suitable for use with
235 the -print0 argument to \fBfind\fR(1).
236 .RE
237
238 .SH OPERANDS
239 .sp
240 .LP
241 The following operands are supported:
242 .sp
243 .ne 2
244 .na
245 \fB\fIutility\fR\fR
246 .ad
247 .RS 12n
248 The name of the utility to be invoked, found by search path using the
249 \fBPATH\fR environment variable. (ee \fBenviron\fR(5).) If \fIutility\fR is
250 omitted, the default is the \fBecho\fR(1) utility. If the \fIutility\fR operand
251 names any of the special built-in utilities in \fBshell_builtins\fR(1), the
252 results are undefined.
253 .RE
254
255 .sp
256 .ne 2
257 .na
258 \fB\fIargument\fR\fR
259 .ad
260 .RS 12n
261 An initial option or operand for the invocation of \fIutility\fR.
262 .RE
263
264 .SH USAGE
265 .sp
266 .LP
267 The \fB255\fR exit status allows a utility being used by \fBxargs\fR to tell
268 \fBxargs\fR to terminate if it knows no further invocations using the current
269 data stream succeeds. Thus, \fIutility\fR should explicitly \fBexit\fR with an
270 appropriate value to avoid accidentally returning with \fB255\fR.
271 .sp
272 .LP
273 Notice that input is parsed as lines. Blank characters separate arguments. If
274 \fBxargs\fR is used to bundle output of commands like \fBfind\fR \fIdir\fR
275 \fB-print\fR or \fBls\fR into commands to be executed, unexpected results are
276 likely if any filenames contain any blank characters or newline characters.
277 This can be fixed by using \fBfind\fR to call a script that converts each file
278 found into a quoted string that is then piped to \fBxargs\fR. Notice that the
279 quoting rules used by \fBxargs\fR are not the same as in the shell. They were
280 not made consistent here because existing applications depend on the current
281 rules and the shell syntax is not fully compatible with it. An easy rule that
282 can be used to transform any string into a quoted form that \fBxargs\fR
283 interprets correctly is to precede each character in the string with a
284 backslash (\fB\e\fR).
285 .sp
286 .LP
287 On implementations with a large value for \fB{ARG_MAX}\fR, \fBxargs\fR can
288 produce command lines longer than \fB{LINE_MAX}\fR. For invocation of
289 utilities, this is not a problem. If \fBxargs\fR is being used to create a text
290 file, users should explicitly set the maximum command line length with the
291 \fB-s\fR option.
292 .sp
293 .LP
294 The \fBxargs\fR utility returns exit status \fB127\fR if an error occurs so
295 that applications can distinguish "failure to find a utility" from "invoked
296 utility exited with an error indication." The value \fB127\fR was chosen
297 because it is not commonly used for other meanings; most utilities use small
298 values for "normal error conditions" and the values above \fB128\fR can be
299 confused with termination due to receipt of a signal. The value \fB126\fR was
300 chosen in a similar manner to indicate that the utility could be found, but not
301 invoked.
302 .SH EXAMPLES
303 .LP
304 \fBExample 1 \fRUsing the xargs command
305 .sp
306 .LP
307 The following example moves all files from directory \fB$1\fR to directory
308 \fB$2\fR, and echo each move command just before doing it:
309
310 .sp
311 .in +2
312 .nf
313 example% \fBls $1 | xargs -I {} -t mv $1/{} $2/{}\fR
314 .fi
315 .in -2
316 .sp
317
318 .sp
319 .LP
320 The following command combines the output of the parenthesised commands onto
321 one line, which is then written to the end of file \fBlog\fR:
322
323 .sp
324 .in +2
325 .nf
326 example% \fB(logname; date; printf "%s\en" "$0 $*") | xargs >>log\fR
327 .fi
328 .in -2
329 .sp
330
331 .sp
332 .LP
333 The following command invokes \fBdiff\fR with successive pairs of arguments
334 originally typed as command line arguments (assuming there are no embedded
335 blank characters in the elements of the original argument list):
336
337 .sp
338 .in +2
339 .nf
340 example% \fBprintf "%s\en" "$*" | xargs -n 2 -x diff\fR
341 .fi
342 .in -2
343 .sp
344
345 .sp
346 .LP
347 The user is asked which files in the current directory are to be archived. The
348 files are archived into \fBarch\fR \fB;\fR a, one at a time, or b, many at a
349 time:
350
351 .sp
352 .in +2
353 .nf
354 example% \fBls | xargs -p -L 1 ar -r arch
355 ls | xargs -p -L 1 | xargs ar -r arch\fR
356 .fi
357 .in -2
358 .sp
359
360 .sp
361 .LP
362 The following executes with successive pairs of arguments originally typed as
363 command line arguments:
364
365 .sp
366 .in +2
367 .nf
368 example% \fBecho $* | xargs -n 2 diff\fR
369 .fi
370 .in -2
371 .sp
372
373 .SH ENVIRONMENT VARIABLES
374 .sp
375 .LP
376 See \fBenviron\fR(5) for descriptions of the following environment variables
377 that affect the execution of \fBxargs\fR: \fBLANG\fR, \fBLC_ALL\fR,
378 \fBLC_COLLATE\fR, \fBLC_CTYPE\fR, \fBLC_MESSAGES\fR, and \fBNLSPATH\fR.
379 .sp
380 .ne 2
381 .na
382 \fB\fBPATH\fR\fR
383 .ad
384 .RS 8n
385 Determine the location of \fIutility\fR.
386 .RE
387
388 .sp
389 .LP
390 Affirmative responses are processed using the extended regular expression
391 defined for the \fByesexpr\fR keyword in the \fBLC_MESSAGES\fR category of the
392 user's locale. The locale specified in the \fBLC_COLLATE\fR category defines
393 the behavior of ranges, equivalence classes, and multi-character collating
394 elements used in the expression defined for \fByesexpr\fR. The locale specified
395 in \fBLC_CTYPE\fR determines the locale for interpretation of sequences of
396 bytes of text data a characters, the behavior of character classes used in the
397 expression defined for the \fByesexpr\fR. See \fBlocale\fR(5).
398 .SH EXIT STATUS
399 .sp
400 .LP
401 The following exit values are returned:
402 .sp
403 .ne 2
404 .na
405 \fB\fB0\fR\fR
406 .ad
407 .RS 12n
408 All invocations of \fIutility\fR returned exit status \fB0\fR.
409 .RE
410
411 .sp
412 .ne 2
413 .na
414 \fB\fB1\(mi125\fR\fR
415 .ad
416 .RS 12n
417 A command line meeting the specified requirements could not be assembled, one
418 or more of the invocations of \fIutility\fR returned a non-zero exit status, or
419 some other error occurred.
420 .RE
421
422 .sp
423 .ne 2
424 .na
425 \fB\fB126\fR\fR
426 .ad
427 .RS 12n
428 The utility specified by \fIutility\fR was found but could not be invoked.
429 .RE
430
431 .sp
432 .ne 2
433 .na
434 \fB\fB127\fR\fR
435 .ad
436 .RS 12n
437 The utility specified by \fIutility\fR could not be found.
438 .RE
439
440 .sp
441 .LP
442 If a command line meeting the specified requirements cannot be assembled, the
443 utility cannot be invoked, an invocation of the utility is terminated by a
444 signal, or an invocation of the utility exits with exit status \fB255\fR, the
445 \fBxargs\fR utility writes a diagnostic message and exit without processing any
446 remaining input.
447 .SH ATTRIBUTES
448 .sp
449 .LP
450 See \fBattributes\fR(5) for descriptions of the following attributes:
451 .sp
452
453 .sp
454 .TS
455 box;
456 c | c
457 l | l .
458 ATTRIBUTE TYPE ATTRIBUTE VALUE
459 _
460 CSI Enabled
461 _
462 Interface Stability Standard
463 .TE
464
465 .SH SEE ALSO
466 .sp
467 .LP
468 \fBecho\fR(1), \fBshell_builtins\fR(1), \fBattributes\fR(5), \fBenviron\fR(5),
469 \fBstandards\fR(5)