1XARGS(1) General Commands Manual XARGS(1)
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6 xargs - build and execute command lines from standard input
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9 xargs [-0prtx] [-E eof-str] [-e[eof-str]] [--eof[=eof-str]] [--null]
10 [-d delimiter] [--delimiter delimiter] [-I replace-str] [-i[replace-
11 str]] [--replace[=replace-str]] [-l[max-lines]] [-L max-lines]
12 [--max-lines[=max-lines]] [-n max-args] [--max-args=max-args] [-s max-
13 chars] [--max-chars=max-chars] [-P max-procs] [--max-procs=max-procs]
14 [--process-slot-var=name] [--interactive] [--verbose] [--exit]
15 [--no-run-if-empty] [--arg-file=file] [--show-limits] [--version]
16 [--help] [command [initial-arguments]]
17
19 This manual page documents the GNU version of xargs. xargs reads items
20 from the standard input, delimited by blanks (which can be protected
21 with double or single quotes or a backslash) or newlines, and executes
22 the command (default is /bin/echo) one or more times with any initial-
23 arguments followed by items read from standard input. Blank lines on
24 the standard input are ignored.
25 The command line for command is built up until it reaches a system-de‐
27 fined limit (unless the -n and -L options are used). The specified
28 command will be invoked as many times as necessary to use up the list
29 of input items. In general, there will be many fewer invocations of
30 command than there were items in the input. This will normally have
31 significant performance benefits. Some commands can usefully be exe‐
32 cuted in parallel too; see the -P option.
33 Because Unix filenames can contain blanks and newlines, this default
35 behaviour is often problematic; filenames containing blanks and/or new‐
36 lines are incorrectly processed by xargs. In these situations it is
37 better to use the -0 option, which prevents such problems. When using
38 this option you will need to ensure that the program which produces the
39 input for xargs also uses a null character as a separator. If that
40 program is GNU find for example, the -print0 option does this for you.
41 If any invocation of the command exits with a status of 255, xargs will
43 stop immediately without reading any further input. An error message
44 is issued on stderr when this happens.
45
47 -0, --null
48 Input items are terminated by a null character instead of by
49 whitespace, and the quotes and backslash are not special (every
50 character is taken literally). Disables the end of file string,
51 which is treated like any other argument. Useful when input
52 items might contain white space, quote marks, or backslashes.
53 The GNU find -print0 option produces input suitable for this
54 mode.
55 -a file, --arg-file=file
58 Read items from file instead of standard input. If you use this
59 option, stdin remains unchanged when commands are run. Other‐
60 wise, stdin is redirected from /dev/null.
61 --delimiter=delim, -d delim
64 Input items are terminated by the specified character. The
65 specified delimiter may be a single character, a C-style charac‐
66 ter escape such as \n, or an octal or hexadecimal escape code.
67 Octal and hexadecimal escape codes are understood as for the
68 printf command. Multibyte characters are not supported. When
69 processing the input, quotes and backslash are not special; ev‐
70 ery character in the input is taken literally. The -d option
71 disables any end-of-file string, which is treated like any other
72 argument. You can use this option when the input consists of
73 simply newline-separated items, although it is almost always
74 better to design your program to use --null where this is possi‐
75 ble.
76 -E eof-str
79 Set the end of file string to eof-str. If the end of file
80 string occurs as a line of input, the rest of the input is ig‐
81 nored. If neither -E nor -e is used, no end of file string is
82 used.
83 -e[eof-str], --eof[=eof-str]
85 This option is a synonym for the -E option. Use -E instead, be‐
86 cause it is POSIX compliant while this option is not. If eof-
87 str is omitted, there is no end of file string. If neither -E
88 nor -e is used, no end of file string is used.
89 -I replace-str
91 Replace occurrences of replace-str in the initial-arguments with
92 names read from standard input. Also, unquoted blanks do not
93 terminate input items; instead the separator is the newline
94 character. Implies -x and -L 1.
95 -i[replace-str], --replace[=replace-str]
97 This option is a synonym for -Ireplace-str if replace-str is
98 specified. If the replace-str argument is missing, the effect
99 is the same as -I{}. This option is deprecated; use -I instead.
100 -L max-lines
102 Use at most max-lines nonblank input lines per command line.
103 Trailing blanks cause an input line to be logically continued on
104 the next input line. Implies -x.
105 -l[max-lines], --max-lines[=max-lines]
107 Synonym for the -L option. Unlike -L, the max-lines argument is
108 optional. If max-lines is not specified, it defaults to one.
109 The -l option is deprecated since the POSIX standard specifies
110 -L instead.
111 -n max-args, --max-args=max-args
113 Use at most max-args arguments per command line. Fewer than
114 max-args arguments will be used if the size (see the -s option)
115 is exceeded, unless the -x option is given, in which case xargs
116 will exit.
117 -P max-procs, --max-procs=max-procs
119 Run up to max-procs processes at a time; the default is 1. If
120 max-procs is 0, xargs will run as many processes as possible at
121 a time. Use the -n option or the -L option with -P; otherwise
122 chances are that only one exec will be done. While xargs is
123 running, you can send its process a SIGUSR1 signal to increase
124 the number of commands to run simultaneously, or a SIGUSR2 to
125 decrease the number. You cannot increase it above an implemen‐
126 tation-defined limit (which is shown with --show-limits). You
127 cannot decrease it below 1. xargs never terminates its com‐
128 mands; when asked to decrease, it merely waits for more than one
129 existing command to terminate before starting another.
130 Please note that it is up to the called processes to properly
132 manage parallel access to shared resources. For example, if
133 more than one of them tries to print to stdout, the ouptut will
134 be produced in an indeterminate order (and very likely mixed up)
135 unless the processes collaborate in some way to prevent this.
136 Using some kind of locking scheme is one way to prevent such
137 problems. In general, using a locking scheme will help ensure
138 correct output but reduce performance. If you don't want to
139 tolerate the performance difference, simply arrange for each
140 process to produce a separate output file (or otherwise use sep‐
141 arate resources).
142 -p, --interactive
144 Prompt the user about whether to run each command line and read
145 a line from the terminal. Only run the command line if the re‐
146 sponse starts with `y' or `Y'. Implies -t.
147 --process-slot-var=name
149 Set the environment variable name to a unique value in each run‐
150 ning child process. Values are reused once child processes ex‐
151 it. This can be used in a rudimentary load distribution scheme,
152 for example.
153 -r, --no-run-if-empty
155 If the standard input does not contain any nonblanks, do not run
156 the command. Normally, the command is run once even if there is
157 no input. This option is a GNU extension.
158 -s max-chars, --max-chars=max-chars
160 Use at most max-chars characters per command line, including the
161 command and initial-arguments and the terminating nulls at the
162 ends of the argument strings. The largest allowed value is sys‐
163 tem-dependent, and is calculated as the argument length limit
164 for exec, less the size of your environment, less 2048 bytes of
165 headroom. If this value is more than 128KiB, 128Kib is used as
166 the default value; otherwise, the default value is the maximum.
167 1KiB is 1024 bytes. xargs automatically adapts to tighter con‐
168 straints.
169 --show-limits
171 Display the limits on the command-line length which are imposed
172 by the operating system, xargs' choice of buffer size and the -s
173 option. Pipe the input from /dev/null (and perhaps specify
174 --no-run-if-empty) if you don't want xargs to do anything.
175 -t, --verbose
177 Print the command line on the standard error output before exe‐
178 cuting it.
179 -x, --exit
181 Exit if the size (see the -s option) is exceeded.
182 --help Print a summary of the options to xargs and exit.
184 --version
186 Print the version number of xargs and exit.
187
189 find /tmp -name core -type f -print | xargs /bin/rm -f
190 Find files named core in or below the directory /tmp and delete them.
192 Note that this will work incorrectly if there are any filenames con‐
193 taining newlines or spaces.
194 find /tmp -name core -type f -print0 | xargs -0 /bin/rm -f
196 Find files named core in or below the directory /tmp and delete them,
198 processing filenames in such a way that file or directory names con‐
199 taining spaces or newlines are correctly handled.
200 find /tmp -depth -name core -type f -delete
203 Find files named core in or below the directory /tmp and delete them,
205 but more efficiently than in the previous example (because we avoid the
206 need to use fork(2) and exec(2) to launch rm and we don't need the ex‐
207 tra xargs process).
208 cut -d: -f1 < /etc/passwd | sort | xargs echo
211 Generates a compact listing of all the users on the system.
213 xargs sh -c 'emacs "$@" < /dev/tty' emacs
216 Launches the minimum number of copies of Emacs needed, one after the
218 other, to edit the files listed on xargs' standard input. This example
219 achieves the same effect as BSD's -o option, but in a more flexible and
220 portable way.
221
226 xargs exits with the following status:
227 0 if it succeeds
228 123 if any invocation of the command exited with status 1-125
229 124 if the command exited with status 255
230 125 if the command is killed by a signal
231 126 if the command cannot be run
232 127 if the command is not found
233 1 if some other error occurred.
234 Exit codes greater than 128 are used by the shell to indicate that a
236 program died due to a fatal signal.
237
239 As of GNU xargs version 4.2.9, the default behaviour of xargs is not to
240 have a logical end-of-file marker. POSIX (IEEE Std 1003.1, 2004 Edi‐
241 tion) allows this.
242 The -l and -i options appear in the 1997 version of the POSIX standard,
244 but do not appear in the 2004 version of the standard. Therefore you
245 should use -L and -I instead, respectively.
246 The POSIX standard allows implementations to have a limit on the size
248 of arguments to the exec functions. This limit could be as low as 4096
249 bytes including the size of the environment. For scripts to be porta‐
250 ble, they must not rely on a larger value. However, I know of no im‐
251 plementation whose actual limit is that small. The --show-limits op‐
252 tion can be used to discover the actual limits in force on the current
253 system.
254
258 find(1), locate(1), locatedb(5), updatedb(1), fork(2), execvp(3),
259 kill(1), signal(7),
260 The full documentation for xargs is maintained as a Texinfo manual.
262 If the info and xargs programs are properly installed at your site, the
263 command info xargs should give you access to the complete manual.
264
267 The -L option is incompatible with the -I option, but perhaps should
268 not be.
269 It is not possible for xargs to be used securely, since there will al‐
271 ways be a time gap between the production of the list of input files
272 and their use in the commands that xargs issues. If other users have
273 access to the system, they can manipulate the filesystem during this
274 time window to force the action of the commands xargs runs to apply to
275 files that you didn't intend. For a more detailed discussion of this
276 and related problems, please refer to the ``Security Considerations''
277 chapter in the findutils Texinfo documentation. The -execdir option of
278 find can often be used as a more secure alternative.
279 When you use the -I option, each line read from the input is buffered
281 internally. This means that there is an upper limit on the length of
282 input line that xargs will accept when used with the -I option. To
283 work around this limitation, you can use the -s option to increase the
284 amount of buffer space that xargs uses, and you can also use an extra
285 invocation of xargs to ensure that very long lines do not occur. For
286 example:
287 somecommand | xargs -s 50000 echo | xargs -I '{}' -s 100000 rm '{}'
289 Here, the first invocation of xargs has no input line length limit be‐
291 cause it doesn't use the -i option. The second invocation of xargs
292 does have such a limit, but we have ensured that the it never encoun‐
293 ters a line which is longer than it can handle. This is not an ideal
294 solution. Instead, the -i option should not impose a line length lim‐
295 it, which is why this discussion appears in the BUGS section. The
296 problem doesn't occur with the output of find(1) because it emits just
297 one filename per line.
298 The best way to report a bug is to use the form at http://savan‐
300 nah.gnu.org/bugs/?group=findutils. The reason for this is that you
301 will then be able to track progress in fixing the problem. Other com‐
302 ments about xargs(1) and about the findutils package in general can be
303 sent to the bug-findutils mailing list. To join the list, send email
304 to bug-findutils-request@gnu.org.
305 XARGS(1)