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XARGS(1) General Commands Manual 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 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 in‐
put. Blank lines on the standard input are ignored.
The command line for command is built up until it reaches a system-defined limit (un‐
less 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 of‐
ten problematic; filenames containing blanks and/or newlines are incorrectly pro‐
cessed by xargs. In these situations it is better to use the -0 option, which pre‐
vents such problems. When using this option you will need to ensure that the pro‐
gram 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 immedi‐
ately 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 backslash‐
es. 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 delim‐
iter may be a single character, a C-style character escape such as
, or an
octal or hexadecimal escape code. Octal and hexadecimal escape codes are un‐
derstood as for the printf command. Multibyte characters are not supported.
When processing the input, quotes and backslash are not special; every charac‐
ter 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 al‐
most always better to design your program to use --null where this is possi‐
ble.
-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; in‐
stead 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 op‐
tion 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 argu‐
ments 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).
-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 interactive 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 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 operat‐
ing 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.
The options --max-lines (-L, -l), --replace (-I, -i) and --max-args (-n) are mutually
exclusive. If some of them are specified at the same time, then xargs will generally
use the option specified last on the command line, i.e., it will reset the value of
the offending option (given before) to its default value. Additionally, xargs will
issue a warning diagnostic on stderr. The exception to this rule is that the special
max-args value 1 ('-n1') is ignored after the --replace option and its aliases -I and
-i, because it would not actually conflict.
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 effi‐
ciently 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.
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 logi‐
cal 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 in‐
stead, respectively.
The -o option is an extension to the POSIX standard for better compatibility 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 cur‐
rent system.
BUGS
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 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.
REPORTING BUGS
GNU findutils online help: <https://www.gnu.org/software/findutils/#get-help>
Report any translation bugs to <https://translationproject.org/team/>
Report any other issue via the form at the GNU Savannah bug tracker:
<https://savannah.gnu.org/bugs/?group=findutils>
General topics about the GNU findutils package are discussed at the bug-findutils
mailing list:
<https://lists.gnu.org/mailman/listinfo/bug-findutils>
COPYRIGHT
Copyright ? 1990-2021 Free Software Foundation, Inc. License GPLv3+: 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 WAR‐
RANTY, to the extent permitted by law.
SEE ALSO
find(1), kill(1), locate(1), updatedb(1), fork(2), execvp(3), locatedb(5), signal(7)
Full documentation <https://www.gnu.org/software/findutils/xargs>
or available locally via: info xargs
XARGS(1)