xargs - build and execute command lines from standard input


   xargs  [-0prtx]  [-E  eof-str] [-e[eof-str]] [--eof[=eof-str]] [--null]
   [-d delimiter] [--delimiter delimiter]  [-I  replace-str]  [-i[replace-
   str]]    [--replace[=replace-str]]   [-l[max-lines]]   [-L   max-lines]
   [--max-lines[=max-lines]] [-n max-args] [--max-args=max-args] [-s  max-
   chars]  [--max-chars=max-chars]  [-P max-procs] [--max-procs=max-procs]
   [--process-slot-var=name]    [--interactive]    [--verbose]    [--exit]
   [--no-run-if-empty]   [--arg-file=file]   [--show-limits]   [--version]
   [--help] [command [initial-arguments]]


   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.


   -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

   -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

   -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

   -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

          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).

   -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

          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.

          Print the version number of xargs and exit.


   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.

   xargs sh -c 'emacs "$@" < /dev/tty' emacs

   Launches the minimum number of copies of Emacs needed,  one  after  the
   other, to edit the files listed on xargs' standard input.  This example
   achieves the same effect as BSD's -o option, but in a more flexible and
   portable way.


   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 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.


   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.


   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

   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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