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XARGS(1) General Commands Manual XARGS(1)
NAME
xargs - build and execute command lines from standard input
SYNOPSIS
xargs [-0prtx] [-E eof-str] [-e[eof-str]] [--eof[=eof-str]] [--null] [-d delimiter]
[--delimiter delimiter] [-I replace-str] [-i[replace-str]] [--replace[=replace-str]]
[-l[max-lines]] [-L max-lines] [--max-lines[=max-lines]] [-n max-args] [--max-args=max-
args] [-s max-chars] [--max-chars=max-chars] [-P max-procs] [--max-procs=max-procs]
[--process-slot-var=name] [--interactive] [--verbose] [--exit] [--no-run-if-empty]
[--arg-file=file] [--show-limits] [--version] [--help] [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 back-
slash) or newlines, and executes the command (default is /bin/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 general, there will be many fewer invoca-
tions 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 containing blanks and/or newlines are incorrectly processed by
xargs. In these situations it is better to use the -0 option, which prevents such prob-
lems. 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 hap-
pens.
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). Dis-
ables the end of file string, which is treated like any other 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 re-
mains 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 hexa-
decimal escape code. Octal and hexadecimal escape codes are understood as for the
printf command. Multibyte characters are not supported. When processing the in-
put, 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 new-
line-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, 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 re-
place-str argument is missing, the effect is the same as -I{}. This option is dep-
recated; 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 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 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
decrease it below 1. xargs never terminates its commands; when asked to decrease,
it merely waits for more than one existing command to terminate before starting an-
other.
-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'. Im-
plies -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. Nor-
mally, the command is run once even if there is no input. This option is a GNU ex-
tension.
-s max-chars, --max-chars=max-chars
Use at most max-chars characters per command line, including the command and ini-
tial-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 128KiB, 128Kib is used as the default value; otherwise, the
default value is the maximum. 1KiB 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.
--help Print a summary of the options to xargs and exit.
--version
Print the version number of xargs and exit.
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 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 sh -c 'emacs "$@" < /dev/tty' emacs
Launches the minimum number of copies of Emacs needed, one after the other, to edit the
files listed on xargs' standard input. This example achieves the same effect as BSD's -o
option, but in a more flexible and portable way.
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, respec-
tively.
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 envi-
ronment. 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.
SEE ALSO
find(1), locate(1), locatedb(5), updatedb(1), fork(2), execvp(3), kill(1), signal(7),
Finding Files (on-line in Info, or printed)
BUGS
The -L option is incompatible with the -I option, but perhaps should not be.
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 dur-
ing 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 in-
crease the amount of buffer space that xargs uses, and you can also use an extra invoca-
tion 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 the 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 out-
put of find(1) because it emits just one filename per line.
The best way to report a bug is to use the form at http://savan-
nah.gnu.org/bugs/?group=findutils. The reason for this is that you will then be able to
track progress in fixing the problem. Other comments about xargs(1) and about the findu-
tils package in general can be sent to the bug-findutils mailing list. To join the list,
send email to bug-findutils-request AT gnu.org.
XARGS(1)
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