xargs(1) — Linux manual page


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

       -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.

              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.

              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

       -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.

              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.


       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 ob‐
       tained from the project's upstream Git repository
       ⟨git://git.savannah.gnu.org/findutils.git⟩ on 2020-11-01.  (At that
       time, the date of the most recent commit that was found in the repos‐
       itory was 2020-10-25.)  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 im‐
       provements to the information in this COLOPHON (which is not part of
       the original manual page), send a mail to man-pages@man7.org


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