XARGS(1) XARGS(1)
NAME
xargs - build and execute command lines from standard input
SYNOPSIS
xargs [options] [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 pro-
tected 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 exe-
cuted 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 pro-
duces 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 whi-
tespace, 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. Other-
wise, stdin is redirected from /dev/null.
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--delimiter=delim, -d delim
Input items are terminated by the specified character. The
specified delimiter may be a single character, a C-style charac-
ter 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 dis-
ables any end-of-file string, which is treated like any other ar-
gument. You can use this option when the input consists of sim-
ply 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, be-
cause 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 char-
acter. 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
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XARGS(1) XARGS(1)
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 run-
ning, you can send its process a SIGUSR1 signal to increase the
number of commands to run simultaneously, or a SIGUSR2 to de-
crease 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 com-
mands; 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) un-
less the processes collaborate in some way to prevent this. Us-
ing some kind of locking scheme is one way to prevent such prob-
lems. 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 pro-
cess to produce a separate output file (or otherwise use separate
resources).
-o, --open-tty
Reopen stdin as /dev/tty in the child process before executing
the command. This is useful if you want xargs to run an interac-
tive application.
-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 run-
ning 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
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XARGS(1) XARGS(1)
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 con-
straints.
--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 exe-
cuting 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
Find files named core in or below the directory /tmp and delete them.
Note that this will work incorrectly if there are any filenames con-
taining 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 con-
taining spaces or newlines are correctly handled.
find /tmp -depth -name core -type
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 |
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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 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 stan-
dard, but do not appear in the 2004 version of the standard. There-
fore you should use -L and -I instead, respectively.
The -o option is an extension to the POSIX standard for better compa-
tibility with BSD.
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.
COPYRIGHT
Copyright c 1990-2019 Free Software Foundation, Inc. License GPLv3+:
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XARGS(1) XARGS(1)
GNU GPL version 3 or later <https://gnu.org/licenses/gpl.html>.
This is free software: you are free to change and redistribute it.
There is NO WARRANTY, to the extent permitted by law.
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 al-
ways 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
Here, the first invocation of xargs has no input line length limit be-
cause 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 en-
counters 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
https://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 gen-
eral 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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