xargs(1)



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-de-
       fined  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 new-
       lines 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.  Other-
              wise, 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 charac-
              ter 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; ev-
              ery 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 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  ig-
              nored.   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, be-
              cause  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  implemen-
              tation-defined  limit  (which is shown with --show-limits).  You
              cannot decrease it below 1.  xargs  never  terminates  its  com-
              mands; 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 sep-
              arate 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 inter-
              active 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 re-
              sponse starts with `y' or `Y'.  Implies -t.

       --process-slot-var=name
              Set the environment variable name to a unique value in each run-
              ning  child process.  Values are reused once child processes ex-
              it.  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 sys-
              tem-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  con-
              straints.

       --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  exe-
              cuting 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 ex-
       tra 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  Edi-
       tion) 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 compati-
       bility 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  porta-
       ble,  they  must not rely on a larger value.  However, I know of no im-
       plementation whose actual limit is that small.  The  --show-limits  op-
       tion  can be used to discover the actual limits in force on the current
       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  al-
       ways  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  be-
       cause  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  encoun-
       ters  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  lim-
       it,  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://savan-
       nah.gnu.org/bugs/?group=findutils.  The reason for  this  is  that  you
       will then be able to track progress in fixing the problem.   Other com-
       ments 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.

                                                                      XARGS(1)

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