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xargs - build and execute command lines from standard input
xargs
[-0prtx] [-E[eof-str]] [-e[eof-str]] [--eof[=eof-str]] [--null] [-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]
[--version] [--help] [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 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.
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 happens.
- --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 space, quote marks, or backslashes. The GNU find -print0
option produces input suitable for this mode.
- --eof[=eof-str], -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 eof-str is omitted, there
is no end of file string. If this option is not given, no end of file string
is used.
- -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.
- --help
- Print a summary
of the options to xargs and exit.
- --replace[=replace-str], -i[replace-str]
- Replace
occurences 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. If replace-str is omitted, it defaults to "{}"
(like for ‘find -exec’). Implies -x and -l 1.
- --max-lines[=max-lines], -L[max-lines]
- Use at most max-lines nonblank input lines per command line; max-lines defaults
to 1 if omitted. Trailing blanks cause an input line to be logically continued
on the next input line. Implies -x.
- -l[max-lines]
- Deprecated; non-POSIX-compliant
synonym for the -L option.
- --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
command 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.
- --exit, -x
- 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; otherwise chances are that only one
exec will be done.
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.
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.
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.
find(1)
,
locate(1)
, locatedb(5)
, updatedb(1)
, Finding Files (on-line in Info, or
printed)
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 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 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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