xargs



XARGS(1)                                                              XARGS(1)




NAME

       xargs - build and execute command lines from standard input


SYNOPSIS

       xargs  [-0prtx]  [-E[eof-str]] [-e[eof-str]] [--eof[=eof-str]] [--null]
       [-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]  [--interactive]  [--verbose]  [--exit]
       [--no-run-if-empty]  [--arg-file=file]  [--version]  [--help]  [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.

       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  pro-
       duces  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
       --arg-file=file, -a 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.


       --null, -0
              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.

       --eof[=eof-str], -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 eof-str is omitted, there is no end of file string.
              If this option is not given, no end of file string is used.

       -e[eof-str]
              This option is  a  synonym  for  the  ‘-E’  option.    Use  ‘-E’
              instead, because it is POSIX compliant while this option is not.

       --help Print a summary of the options to xargs and exit.

       --replace[=replace-str], -i[replace-str]
              Replace occurences 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.  If replace-str is omitted, it defaults to "{}" (like
              for ‘find -exec’).  Implies -x and -l 1.

       --max-lines[=max-lines], -L[max-lines]
              Use at most max-lines nonblank input  lines  per  command  line;
              max-lines  defaults  to  1 if omitted.  Trailing blanks cause an
              input line to be logically continued on  the  next  input  line.
              Implies -x.

       -l[max-lines]
              Deprecated; non-POSIX-compliant synonym for the -L option.

       --max-args=max-args, -n 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.

       --interactive, -p
              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.

       --no-run-if-empty, -r
              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.

       --max-chars=max-chars, -s 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 default is 131072 characters,
              not  including  the size of the environment variables (which are
              provided for separately so that it doesn’t matter if your  envi-
              ronment  variables take up more than 131072 bytes).  The operat-
              ing system places limits on the values  that  you  can  usefully
              specify,  and  if  you exceed these a warning message is printed
              and the value actually used is set to the appropriate  upper  or
              lower limit.

       --verbose, -t
              Print  the command line on the standard error output before exe-
              cuting it.

       --version
              Print the version number of xargs and exit.

       --exit, -x
              Exit if the size (see the -s option) is exceeded.

       --max-procs=max-procs, -P 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 with -P; otherwise chances  are  that
              only one exec will be done.


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
       containing spaces or newlines are correctly handled.

       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.



SEE ALSO

       find(1), locate(1), locatedb(5), updatedb(1), Finding Files (on-line in
       Info, or printed)


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 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
       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://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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