xargs(1) — Linux manual page

NAME | SYNOPSIS | DESCRIPTION | OPTIONS | EXAMPLES | EXIT STATUS | STANDARDS CONFORMANCE | SEE ALSO | COPYRIGHT | BUGS | COLOPHON

XARGS(1)                 General Commands Manual                XARGS(1)

NAME         top

       xargs - build and execute command lines from standard input

SYNOPSIS         top

       xargs [options] [command [initial-arguments]]

DESCRIPTION         top

       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         top

       -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).

       -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 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         top

       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.

EXIT STATUS         top

       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         top

       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 -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 current system.

SEE ALSO         top

       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         top

       Copyright © 1990-2020 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 WARRANTY, to the extent permitted by law.

BUGS         top

       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 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
       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 general can be sent to the bug-findutils
       mailing list.  To join the list, send email to
       bug-findutils-request@gnu.org.

COLOPHON         top

       This page is part of the findutils (find utilities) project.
       Information about the project can be found at 
       ⟨http://www.gnu.org/software/findutils/⟩.  If you have a bug
       report for this manual page, see
       ⟨https://savannah.gnu.org/bugs/?group=findutils⟩.  This page was
       obtained from the project's upstream Git repository
       ⟨git://git.savannah.gnu.org/findutils.git⟩ on 2020-12-18.  (At
       that time, the date of the most recent commit that was found in
       the repository was 2020-12-02.)  If you discover any rendering
       problems in this HTML version of the page, or you believe there
       is a better or more up-to-date source for the page, or you have
       corrections or improvements to the information in this COLOPHON
       (which is not part of the original manual page), send a mail to
       man-pages@man7.org

                                                                XARGS(1)

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