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 protect-
       ed 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 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 mes-
       sage 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 charac-
              ter  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 es-
              cape such as 
, or an octal or hexadecimal escape code.  Octal and hexadecimal escape codes are understood as for the  printf  com-
              mand.   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  ter-
              minate 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  ex-
              ceeded, 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 termi-
              nate 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  gen-
              eral,  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 op-
              tion.  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

       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 con-
       taining 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 con-
       taining 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 cur-
       rent 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.

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 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 the 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 http://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.

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