XARGS(1) manual page
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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] [-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]]
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.
- --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 supported.
- -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.
- --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 logically continued on the next input line. Implies
-x.
- --max-lines[=max-lines]
- -l[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.
- --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 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.
- --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
- 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.
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 dq$@dq < /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.
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.
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.
find(1)
, locate(1)
, locatedb(5)
, updatedb(1)
, fork(2)
, execvp(3)
,
Finding Files (on-line in Info, or printed)
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.
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