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 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. 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 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 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.
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 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 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, 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{}. 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 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 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 existing command to terminate before starting
another.
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 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).
-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 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 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, respectively. 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.
SEE ALSO
find(1), locate(1), locatedb(5), updatedb(1), fork(2), execvp(3), kill(1), signal(7), The full documentation for xargs is maintained as a Texinfo manual. If the info and xargs programs are properly installed at your site, the command info xargs should give you access to the complete manual.
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 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.
XARGS(1)
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