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NAME | SYNOPSIS | DESCRIPTION | OPTIONS | EXAMPLES | EXIT STATUS | STANDARDS CONFORMANCE | HISTORY | BUGS | REPORTING BUGS | COPYRIGHT | SEE ALSO | COLOPHON |
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XARGS(1) General Commands Manual XARGS(1)
xargs - build and execute command lines from standard input
xargs [options] [command [initial-arguments]]
This manual page documents the GNU version of xargs. xargs reads
items from the standard input, delimited by blanks (which can be
protected with double or single quotes or a backslash) or new‐
lines, and executes the command (default is echo) one or more
times with any initial-arguments followed by items read from
standard input. Blank lines on the standard input are ignored.
The command line for command is built up until it reaches a sys‐
tem-defined limit (unless the -n and -L options are used). The
specified command will be invoked as many times as necessary to
use up the list of input items. In general, there will be many
fewer invocations of command than there were items in the input.
This will normally have significant performance benefits. Some
commands can usefully be executed in parallel too; see the -P op‐
tion.
Because Unix filenames can contain blanks and newlines, this de‐
fault behaviour is often problematic; filenames containing blanks
and/or newlines are incorrectly processed by xargs. In these
situations it is better to use the -0 option, which prevents such
problems. When using this option you will need to ensure that
the program which produces the input for xargs also uses a null
character as a separator. If that program is GNU find for exam‐
ple, the -print0 option does this for you.
If any invocation of the command exits with a status of 255,
xargs will stop immediately without reading any further input.
An error message is issued on stderr when this happens.
-0, --null
Input items are terminated by a null character instead of
by whitespace, and the quotes and backslash are not spe‐
cial (every character is taken literally). Disables the
end-of-file string, which is treated like any other argu‐
ment. Useful when input items might contain white space,
quote marks, or backslashes. The GNU find (and from Issue
8, POSIX) -print0 option produces input suitable for this
mode.
-a file, --arg-file=file
Read items from file instead of standard input. If you
use this option, stdin remains unchanged when commands are
run. Otherwise, stdin is redirected from /dev/null.
--delimiter=delim, -d delim
Input items are terminated by the specified character.
The specified delimiter may be a single character, a C-
style character escape such as \n, or an octal or hexadec‐
imal escape code. Octal and hexadecimal escape codes are
understood as for the printf command. Multibyte charac‐
ters are not supported. When processing the input, quotes
and backslash are not special; every character in the in‐
put is taken literally. The -d option disables any end-
of-file string, which is treated like any other argument.
You can use this option when the input consists of simply
newline-separated items, although it is almost always bet‐
ter to design your program to use --null where this is
possible.
-E eof-str
Set the end-of-file string to eof-str. If the end-of-file
string occurs as a line of input, the rest of the input is
ignored. If neither -E nor -e is used, no end-of-file
string is used.
-e[eof-str], --eof[=eof-str]
This option is a synonym for the -E option. Use -E in‐
stead, because it is POSIX compliant while this option is
not. If eof-str is omitted, there is no end-of-file
string. If neither -E nor -e is used, no end-of-file
string is used.
-I replace-str
Replace occurrences of replace-str in the initial-argu‐
ments with names read from standard input. Also, unquoted
blanks do not terminate input items; instead the separator
is the newline character. Implies -x and -L 1.
-i[replace-str], --replace[=replace-str]
This option is a synonym for -Ireplace-str if replace-str
is specified. If the replace-str argument is missing, the
effect is the same as -I{}. The -i option is deprecated;
use -I instead.
-L max-lines
Use at most max-lines nonblank input lines per command
line. Trailing blanks cause an input line to be logically
continued on the next input line. Implies -x.
-l[max-lines], --max-lines[=max-lines]
Synonym for the -L option. Unlike -L, the max-lines argu‐
ment is optional. If max-lines is not specified, it de‐
faults to one. The -l option is deprecated since the
POSIX standard specifies -L instead.
-n max-args, --max-args=max-args
Use at most max-args arguments per command line. Fewer
than max-args arguments will be used if the size (see the
-s option) is exceeded, unless the -x option is given, in
which case xargs will exit.
-P max-procs, --max-procs=max-procs
Run up to max-procs processes at a time; the default is 1.
If max-procs is 0, xargs will run as many processes as
possible at a time. Use the -n option or the -L option
with -P; otherwise chances are that only one exec will be
done. While xargs is running, you can send its process a
SIGUSR1 signal to increase the number of commands to run
simultaneously, or a SIGUSR2 to decrease the number. You
cannot increase it above an implementation-defined limit
(which is shown with --show-limits). You cannot decrease
it below 1. xargs never terminates its commands; when
asked to decrease, it merely waits for more than one ex‐
isting command to terminate before starting another.
xargs always waits for all child processes to exit before
exiting itself (but see BUGS).
If you do not use the -P option, xargs will not handle the
SIGUSR1 and SIGUSR2 signals, meaning that they will termi‐
nate the program (unless they were blocked in the parent
process before xargs was started).
Please note that it is up to the called processes to prop‐
erly manage parallel access to shared resources. For ex‐
ample, if more than one of them tries to print to stdout,
the output will be produced in an indeterminate order (and
very likely mixed up) unless the processes collaborate in
some way to prevent this. Using some kind of locking
scheme is one way to prevent such problems. In general,
using a locking scheme will help ensure correct output but
reduce performance. If you don't want to tolerate the
performance difference, simply arrange for each process to
produce a separate output file (or otherwise use separate
resources).
-o, --open-tty
Reopen stdin as /dev/tty in the child process before exe‐
cuting the command. This is useful if you want xargs to
run an interactive application.
-p, --interactive
Prompt the user about whether to run each command line and
read a line from the terminal. Only run the command line
if the response starts with `y' or `Y'. Implies -t.
--process-slot-var=name
Set the environment variable name to a unique value in
each running child process. Values are reused once child
processes exit. This can be used in a rudimentary load
distribution scheme, for example.
-r, --no-run-if-empty
If the standard input does not contain any nonblanks, do
not run the command. Normally, the command is run once
even if there is no input. This option is a GNU exten‐
sion.
-s max-chars, --max-chars=max-chars
Use at most max-chars characters per command line, includ‐
ing the command and initial-arguments and the terminating
nulls at the ends of the argument strings. The largest
allowed value is system-dependent, and is calculated as
the argument length limit for exec, less the size of your
environment, less 2048 bytes of headroom. If this value
is more than 128 KiB, 128 KiB is used as the default val‐
ue; otherwise, the default value is the maximum. 1 KiB is
1024 bytes. xargs automatically adapts to tighter con‐
straints.
--show-limits
Display the limits on the command-line length which are
imposed by the operating system, xargs' choice of buffer
size and the -s option. Pipe the input from /dev/null
(and perhaps specify --no-run-if-empty) if you don't want
xargs to do anything.
-t, --verbose
Print the command line on the standard error output before
executing it.
-x, --exit
Exit if the size (see the -s option) is exceeded.
-- Delimit the option list. Later arguments, if any, are
treated as operands even if they begin with -. For exam‐
ple, xargs -- --help runs the command --help (found in
PATH) instead of printing the usage text, and xargs --
--mycommand runs the command --mycommand instead of re‐
jecting this as unrecognized option.
--help Print a summary of the options to xargs and exit.
--version
Print the version number of xargs and exit.
The options --max-lines (-L, -l), --replace (-I, -i) and --max-
args (-n) are mutually exclusive. If some of them are specified
at the same time, then xargs will generally use the option speci‐
fied last on the command line, i.e., it will reset the value of
the offending option (given before) to its default value. Addi‐
tionally, xargs will issue a warning diagnostic on stderr. The
exception to this rule is that the special max-args value 1
('-n1') is ignored after the --replace option and its aliases -I
and -i, because it would not actually conflict.
find /tmp -name core -type f -print | xargs /bin/rm -f
Find files named core in or below the directory /tmp and delete
them. Note that this will work incorrectly if there are any
filenames containing newlines or spaces.
find /tmp -name core -type f -print0 | xargs -0 /bin/rm -f
Find files named core in or below the directory /tmp and delete
them, processing filenames in such a way that file or directory
names containing spaces or newlines are correctly handled.
find /tmp -depth -name core -type f -delete
Find files named core in or below the directory /tmp and delete
them, but more efficiently than in the previous example (because
we avoid the need to use fork(2) and exec(2) to launch rm and we
don't need the extra xargs process).
cut -d: -f1 < /etc/passwd | sort | xargs echo
Generates a compact listing of all the users on the system.
xargs exits with the following status:
0 if it succeeds
123 if any invocation of the command exited with status
1–125
124 if the command exited with status 255
125 if the command is killed by a signal
126 if the command cannot be run
127 if the command is not found
1 if some other error occurred.
Exit codes greater than 128 are used by the shell to indicate
that a program died due to a fatal signal.
The long-standing -0 option of xargs will be included in Issue 8
of the POSIX standard.
As of GNU xargs version 4.2.9, the default behaviour of xargs is
not to have a logical end-of-file marker. POSIX (IEEE Std
1003.1, 2004 Edition) allows this.
The -l and -i options appear in the 1997 version of the POSIX
standard, but do not appear in the 2004 version of the standard.
Therefore you should use -L and -I instead, respectively.
The -o option is an extension to the POSIX standard for better
compatibility with BSD.
The POSIX standard allows implementations to have a limit on the
size of arguments to the exec functions. This limit could be as
low as 4096 bytes including the size of the environment. For
scripts to be portable, they must not rely on a larger value.
However, I know of no implementation whose actual limit is that
small. The --show-limits option can be used to discover the ac‐
tual limits in force on the current system.
In versions of xargs up to and including version 4.9.0, SIGUSR1
and SIGUSR2 would not cause xargs to terminate even if the -P op‐
tion was not used.
The xargs program was invented by Herb Gellis at Bell Labs. See
the Texinfo manual for findutils, Finding Files, for more infor‐
mation.
It is not possible for xargs to be used securely, since there
will always be a time gap between the production of the list of
input files and their use in the commands that xargs issues. If
other users have access to the system, they can manipulate the
filesystem during this time window to force the action of the
commands xargs runs to apply to files that you didn't intend.
For a more detailed discussion of this and related problems,
please refer to the ``Security Considerations'' chapter in the
findutils Texinfo documentation. The -execdir option of find can
often be used as a more secure alternative.
When you use the -I option, each line read from the input is
buffered internally. This means that there is an upper limit on
the length of input line that xargs will accept when used with
the -I option. To work around this limitation, you can use the
-s option to increase the amount of buffer space that xargs uses,
and you can also use an extra invocation of xargs to ensure that
very long lines do not occur. For example:
somecommand | xargs -s 50000 echo | xargs -I '{}' -s 100000 rm
'{}'
Here, the first invocation of xargs has no input line length lim‐
it because it doesn't use the -i option. The second invocation
of xargs does have such a limit, but we have ensured that it nev‐
er encounters a line which is longer than it can handle. This is
not an ideal solution. Instead, the -i option should not impose
a line length limit, which is why this discussion appears in the
BUGS section. The problem doesn't occur with the output of
find(1) because it emits just one filename per line.
In versions of xargs up to and including version 4.9.0, xargs -P
would exit while some of its children were still running, if one
of them exited with status 255.
GNU findutils online help: <https://www.gnu.org/software/findu‐
tils/#get-help>
Report any translation bugs to <https://translationpro‐
ject.org/team/>
Report any other issue via the form at the GNU Savannah bug
tracker:
<https://savannah.gnu.org/bugs/?group=findutils>
General topics about the GNU findutils package are discussed at
the bug-findutils mailing list:
<https://lists.gnu.org/mailman/listinfo/bug-findutils>
Copyright © 1990–2024 Free Software Foundation, Inc. License
GPLv3+: GNU GPL version 3 or later <https://gnu.org/licens‐
es/gpl.html>.
This is free software: you are free to change and redistribute
it. There is NO WARRANTY, to the extent permitted by law.
find(1), kill(1), locate(1), updatedb(1), fork(2), execvp(3),
locatedb(5), signal(7)
Full documentation <https://www.gnu.org/software/findutils/xargs>
or available locally via: info xargs
This page is part of the findutils (find utilities) project. In‐
formation about the project can be found at
⟨http://www.gnu.org/software/findutils/⟩. If you have a bug
report for this manual page, see
⟨https://savannah.gnu.org/bugs/?group=findutils⟩. This page was
obtained from the project's upstream Git repository
⟨git://git.savannah.gnu.org/findutils.git⟩ on 2024-06-14. (At
that time, the date of the most recent commit that was found in
the repository was 2024-06-03.) If you discover any rendering
problems in this HTML version of the page, or you believe there
is a better or more up-to-date source for the page, or you have
corrections or improvements to the information in this COLOPHON
(which is not part of the original manual page), send a mail to
[email protected]
XARGS(1)
Pages that refer to this page: dpkg-name(1), find(1), grep(1), locate(1), updatedb(1), lsof(8)
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HTML rendering created 2024-06-26 by Michael Kerrisk, author of The Linux Programming Interface. For details of in-depth Linux/UNIX system programming training courses that I teach, look here. Hosting by jambit GmbH. |
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