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Updated: Wednesday, July 27, 2022
 
 

xargs (1g)

Name

xargs - build and execute command lines from standard input

Synopsis

xargs [options] [command [initial-arguments]]

Description

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 echo) one or more times with any  initial-argu-
       ments  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.

       The  options  --max-lines  (-L,  -l), --replace (-I, -i) and --max-args
       (-n) are mutually exclusive. If some of them are specified at the  same
       time,  then  xargs  will generally use the option specified last on the
       command line, i.e., it will reset the value  of  the  offending  option
       (given  before) to its default value.  Additionally, xargs will issue a
       warning diagnostic on stderr.  The exception to this rule is  that  the
       special  max-args value 1 ('-n1') is ignored after the --replace option
       and its aliases -I and -i, because it would not actually conflict.


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.

BUGS
       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 it never encounters a
       line which is longer than it can handle.   This is not an  ideal  solu-
       tion.   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.

REPORTING BUGS
       GNU   findutils   online   help:   <https://www.gnu.org/software/findu-
       tils/#get-help>
       Report any translation bugs to <https://translationproject.org/team/>

       Report any other issue via the form at the GNU Savannah bug tracker:
              <https://savannah.gnu.org/bugs/?group=findutils>
       General  topics  about  the  GNU findutils package are discussed at the
       bug-findutils mailing list:
              <https://lists.gnu.org/mailman/listinfo/bug-findutils>

COPYRIGHT
       Copyright (C) 1990-2022 Free Software Foundation, Inc.  License GPLv3+:
       GNU GPL version 3 or later <https://gnu.org/licenses/gpl.html>.
       This  is  free  software:  you  are free to change and redistribute it.
       There is NO WARRANTY, to the extent permitted by law.


ATTRIBUTES
       See attributes(7) for descriptions of the following attributes:


       +---------------+--------------------+
       |ATTRIBUTE TYPE |  ATTRIBUTE VALUE   |
       +---------------+--------------------+
       |Availability   | file/gnu-findutils |
       +---------------+--------------------+
       |Stability      | Uncommitted        |
       +---------------+--------------------+

SEE ALSO
       find(1), kill(1), locate(1), updatedb(1),  fork(2),  execvp(3),  locat-
       edb(5), signal(7)

       Full documentation <https://www.gnu.org/software/findutils/xargs>
       or available locally via: info xargs



NOTES
       Source  code  for open source software components in Oracle Solaris can
       be found at https://www.oracle.com/downloads/opensource/solaris-source-
       code-downloads.html.

       This software was built from source available at https://github.com/or-
       acle/solaris-userland.  The original community  source  was  downloaded
       from  http://ftp.gnu.org/gnu/findutils/findutils-4.9.0.tar.xz.

       Further information about this software can be found on the open source
       community website at https://www.gnu.org/software/findutils.



                                                                      XARGS(1)