XARGS - Manpage

xargs --help

Usage: xargs [OPTION]... COMMAND [INITIAL-ARGS]...
Run COMMAND with arguments INITIAL-ARGS and more arguments read from input.

Mandatory and optional arguments to long options are also
mandatory or optional for the corresponding short option.
  -0, --null                   items are separated by a null, not whitespace;
                                 disables quote and backslash processing and
                                 logical EOF processing
  -a, --arg-file=FILE          read arguments from FILE, not standard input
  -d, --delimiter=CHARACTER    items in input stream are separated by CHARACTER,
                                 not by whitespace; disables quote and backslash
                                 processing and logical EOF processing
  -E END                       set logical EOF string; if END occurs as a line
                                 of input, the rest of the input is ignored
                                 (ignored if -0 or -d was specified)
  -e, --eof[=END]              equivalent to -E END if END is specified;
                                 otherwise, there is no end-of-file string
  -I R                         same as --replace=R
  -i, --replace[=R]            replace R in INITIAL-ARGS with names read
                                 from standard input, split at newlines;
                                 if R is unspecified, assume {}
  -L, --max-lines=MAX-LINES    use at most MAX-LINES non-blank input lines per
                                 command line
  -l[MAX-LINES]                similar to -L but defaults to at most one non-
                                 blank input line if MAX-LINES is not specified
  -n, --max-args=MAX-ARGS      use at most MAX-ARGS arguments per command line
  -o, --open-tty               Reopen stdin as /dev/tty in the child process
                                 before executing the command; useful to run an
                                 interactive application.
  -P, --max-procs=MAX-PROCS    run at most MAX-PROCS processes at a time
  -p, --interactive            prompt before running commands
      --process-slot-var=VAR   set environment variable VAR in child processes
  -r, --no-run-if-empty        if there are no arguments, then do not run COMMAND;
                                 if this option is not given, COMMAND will be
                                 run at least once
  -s, --max-chars=MAX-CHARS    limit length of command line to MAX-CHARS
      --show-limits            show limits on command-line length
  -t, --verbose                print commands before executing them
  -x, --exit                   exit if the size (see -s) is exceeded
      --help                   display this help and exit
      --version                output version information and exit

Manpage

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-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  situa‐
       tions 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.  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.  Oc‐
              tal 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 possible.

       -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.

       -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 de‐
              crease 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 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 prob‐
              lems.  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).

       -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 interactive 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 response starts with `y' or `Y'.  Implies -t.

       --process-slot-var=name
              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 constraints.

       --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 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.

       --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 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.

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 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 -o option is an extension to the POSIX standard for better compatibility 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 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.

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  de‐
       tailed  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 it never en‐
       counters  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.

REPORTING BUGS
       GNU findutils online help: <https://www.gnu.org/software/findutils/#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 © 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.

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

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

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