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Linux 2.6 - man page for xargs (linux section 1)

XARGS(1)										 XARGS(1)

       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]
       [--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 back-
       slash) 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  newlines are incorrectly processed by
       xargs.  In these situations it is better to use the -0 option, which prevents  such  prob-
       lems.   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  hap-

       -a file
	      Read  items from file instead of standard input.	If you use this option, stdin re-
	      mains unchanged when  commands  are  run.   Otherwise,  stdin  is  redirected  from

       -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).   Dis-
	      ables  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.

       -d delim
	      Input  items  are  terminated by the specified character.  Quotes and backslash are
	      not special; every character in the input is taken literally.  Disables the end-of-
	      file  string,  which is treated like any other argument.	This can be used when the
	      input consists of simply newline-separated items, although it is almost always bet-
	      ter to design your program to use --null where this is possible.	The specified de-
	      limiter may be a single character, a C-style character escape such as \n, or an oc-
	      tal  or hexadecimal escape code.	Octal and hexadecimal escape codes are understood
	      as for the printf command.   Multibyte characters are not supported.

       -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.

	      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.

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

       -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.

	      This option is a synonym for -Ireplace-str if replace-str  is  specified,  and  for
	      -I{} otherwise.  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.

	      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
	      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     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'.  Im-
	      plies -t.

       -r     If the standard input does not contain any nonblanks, do not run the command.  Nor-
	      mally, the command is run once even if there is no input.  This option is a GNU ex-

       -s max-chars
	      Use at most max-chars characters per command line, including the command	and  ini-
	      tial-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.

       -t     Print the command line on the standard error output before executing it.

	      Print the version number of xargs and exit.

	      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

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

       -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.

       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

       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,  respec-

       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  envi-
       ronment.   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), Finding Files (on-line
       in Info, or printed)

       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 dur-
       ing 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 in-
       crease  the  amount of buffer space that xargs uses, and you can also use an extra invoca-
       tion 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  out-
       put 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 comments about xargs(1) and about the findu-
       tils 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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