Manual: xargs
XARGS(1) General Commands Manual XARGS(1)
NAME
xargs - build and execute command lines from standard input
SYNOPSIS
xargs [options] [command [initial-arguments]]
DESCRIPTION
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 newlines, 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 system-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 gen‐
eral, 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 option.
Because Unix filenames can contain blanks and newlines, this default behaviour is often problematic; filenames con‐
taining 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 example, 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.
OPTIONS
-0, --null
Input items are terminated by a null character instead of by whitespace, and the quotes and backslash are not
special (every character is taken literally). Disables the end-of-file string, which is treated like any oth‐
er argument. Useful when input items might contain white space, quote marks, or backslashes. The GNU find
-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 hexadecimal escape code. Octal and hexadecimal escape
codes are understood as for the printf command. Multibyte characters are not supported. When processing the
input, quotes and backslash are not special; every character in the input 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 better 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 instead, 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-arguments with names read from standard input. Also, un‐
quoted 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 miss‐
ing, 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 logi‐
cally 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 argument is optional. If max-lines is not specified, it
defaults 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 process‐
es as possible at a time. Use the -n option or the -L option with -P; otherwise chances are that only one ex‐
ec 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 imple‐
mentation-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 existing command to termi‐
nate 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
terminate 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 properly manage parallel access to shared resources. For
example, 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 en‐
sure 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 executing 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 com‐
mand 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 extension.
-s max-chars, --max-chars=max-chars
Use at most max-chars characters per command line, including the command and initial-arguments and the termi‐
nating nulls at the ends of the argument strings. The largest allowed value is system-dependent, and is cal‐
culated 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 value; otherwise, the default value is the
maximum. 1 KiB is 1024 bytes. xargs automatically adapts to tighter constraints.
--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 ex‐
ample, xargs -- --help runs the command --help (found in PATH) instead of printing the usage text, and xargs
-- --mycommand runs the command --mycommand instead of rejecting 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 specified last on the command line, i.e., it
will reset the value of the offending option (given before) to its default value. Additionally, xargs will issue a
warning diagnostic on stderr. The exception to this rule is that the special max-args value 1 ('-n1') is ignored af‐
ter the --replace option and its aliases -I and -i, because it would not actually conflict.
EXAMPLES
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 exam‐
ple (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.
EXIT STATUS
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.
STANDARDS CONFORMANCE
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 actual 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 option was not used.
HISTORY
The xargs program was invented by Herb Gellis at Bell Labs. See the Texinfo manual for findutils, Finding Files, for
more information.
BUGS
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 ``Se‐
curity 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 limita‐
tion, 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 limit because it doesn't use the -i option. The second
invocation of xargs does have such a limit, but we have ensured that it never 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.
REPORTING BUGS
GNU findutils online help:
Report any translation bugs to
Report any other issue via the form at the GNU Savannah bug tracker:
General topics about the GNU findutils package are discussed at the bug-findutils mailing list:
COPYRIGHT
Copyright © 1990–2024 Free Software Foundation, Inc. License GPLv3+: GNU GPL version 3 or later .
This is free software: you are free to change and redistribute it. There is NO WARRANTY, to the extent permitted by
law.
SEE ALSO
find(1), kill(1), locate(1), updatedb(1), fork(2), execvp(3), locatedb(5), signal(7)
Full documentation
or available locally via: info xargs
XARGS(1)