xargs

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 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
       -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.

       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 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
       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 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.

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 WARRANTY, 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)