User Commands 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] [--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
backslash) or newlines, and executes the command (default is
/bin/echo) one or more times with any initial-arguments fol-
lowed by items read from standard input. Blank lines on the
standard input are ignored.
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 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 hap-
pens.
OPTIONS
--arg-file=file, -a 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.
--null, -0
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 other
argument. Useful when input items might contain white
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space, quote marks, or backslashes. The GNU find
-print0 option produces input suitable for this mode.
--delimiter=delim, -d delim
Input items are terminated by the specified character.
Quotes and backslash are not special; every character
in the input is taken literally. Disables the end-of-
file string, which is treated like any other argument.
This can be used 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. 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 sup-
ported.
-Eeof-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.
--eof[=eof-str], -e[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.
--help
Print a summary of the options to xargs and exit.
-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.
--replace[=replace-str], -i[replace-str]
This option is a synonym for -Ireplace-str if replace-
str is specified, and for -I{} otherwise. This 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.
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--max-lines[=max-lines], -l[max-lines]
Synonym for the -L option. Unlike -L, the max-lines
argument is optional. If max-args is not specified, it
defaults to one. The -l option is deprecated since the
POSIX standard specifies -L instead.
--max-args=max-args, -n 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.
--interactive, -p
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.
--no-run-if-empty, -r
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.
--max-chars=max-chars, -s max-chars
Use at most max-chars characters per command line,
including the command and initial-arguments and the
terminating nulls at the ends of the argument strings.
The default is 131072 characters, not including the
size of the environment variables (which are provided
for separately so that it doesn't matter if your
environment variables take up more than 131072 bytes).
The operating system places limits on the values that
you can usefully specify, and if you exceed these a
warning message is printed and the value actually used
is set to the appropriate upper or lower limit.
--verbose, -t
Print the command line on the standard error output
before executing it.
--version
Print the version number of xargs and exit.
--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.
--exit, -x
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Exit if the size (see the -s option) is exceeded.
--max-procs=max-procs, -P 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 with -P; oth-
erwise chances are that only one exec will be done.
EXAMPLES
find /tmp -name core -type 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
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.
cut -d: -f1 < /etc/passwd
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 indi-
cate 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
(IE 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.
SEE ALSO
find(1), locate(1), locatedb(5), updatedb(1), Finding Files
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(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 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 discus-
sion 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 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
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 sec-
tion. The problem doesn't occur with the output 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:/savannah.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 findutils package in general can be sent to the
bug-findutils mailing list. To join the list, send email to
bug-findutils-request@gnu.org.
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