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       This  manual  page  is part of the POSIX Programmer's Manual.  The Linux implementation of
       this interface may differ (consult the corresponding Linux  manual  page  for  details  of
       Linux behavior), or the interface may not be implemented on Linux.

NAME

       xargs — construct argument lists and invoke utility

SYNOPSIS

       xargs [-ptx] [-E eofstr] [-I replstr|-L number|-n number]
           [-s size] [utility [argument...]]

DESCRIPTION

       The  xargs  utility  shall construct a command line consisting of the utility and argument
       operands specified followed by as many arguments read in sequence from standard  input  as
       fit  in  length  and  number constraints specified by the options. The xargs utility shall
       then invoke the constructed command line and wait for its completion. This sequence  shall
       be repeated until one of the following occurs:

        *  An end-of-file condition is detected on standard input.

        *  An  argument  consisting  of  just  the  logical end-of-file string (see the -E eofstr
           option) is  found  on  standard  input  after  double-quote  processing,  <apostrophe>
           processing,  and  <backslash>-escape processing (see next paragraph). All arguments up
           to but not including the argument consisting of just the  logical  end-of-file  string
           shall be used as arguments in constructed command lines.

        *  An invocation of a constructed command line returns an exit status of 255.

       The  application  shall  ensure  that  arguments  in  the  standard input are separated by
       unquoted <blank> characters, unescaped <blank>  characters,  or  <newline>  characters.  A
       string  of zero or more non-double-quote ('"') characters and non-<newline> characters can
       be quoted by enclosing them in double-quotes. A string of zero  or  more  non-<apostrophe>
       ('\'')  characters  and  non-<newline>  characters  can  be  quoted  by  enclosing them in
       <apostrophe> characters. Any unquoted character can be escaped  by  preceding  it  with  a
       <backslash>.   The  utility named by utility shall be executed one or more times until the
       end-of-file is reached or the logical  end-of  file  string  is  found.  The  results  are
       unspecified if the utility named by utility attempts to read from its standard input.

       The  generated  command  line  length shall be the sum of the size in bytes of the utility
       name and each argument treated as strings, including a null byte terminator  for  each  of
       these  strings.  The  xargs utility shall limit the command line length such that when the
       command line is invoked, the combined argument and environment lists (see the exec  family
       of   functions  in  the  System  Interfaces  volume  of  POSIX.1‐2017)  shall  not  exceed
       {ARG_MAX}-2048 bytes. Within this constraint, if neither the  -n  nor  the  -s  option  is
       specified, the default command line length shall be at least {LINE_MAX}.

OPTIONS

       The  xargs  utility  shall conform to the Base Definitions volume of POSIX.1‐2017, Section
       12.2, Utility Syntax Guidelines.

       The following options shall be supported:

       -E eofstr Use eofstr as the logical end-of-file string. If -E  is  not  specified,  it  is
                 unspecified whether the logical end-of-file string is the <underscore> character
                 ('_') or the end-of-file string capability is disabled. When eofstr is the  null
                 string,  the  logical  end-of-file  string  capability  shall  be  disabled  and
                 <underscore> characters shall be taken literally.

       -I replstr
                 Insert mode: utility is executed for each  logical  line  from  standard  input.
                 Arguments  in  the standard input shall be separated only by unescaped <newline>
                 characters, not by <blank> characters. Any unquoted unescaped <blank> characters
                 at  the beginning of each line shall be ignored. The resulting argument shall be
                 inserted in arguments in place of each occurrence of  replstr.   At  least  five
                 arguments  in arguments can each contain one or more instances of replstr.  Each
                 of these constructed arguments cannot grow larger than an implementation-defined
                 limit greater than or equal to 255 bytes. Option -x shall be forced on.

       -L number The  utility shall be executed for each non-empty number lines of arguments from
                 standard input. The last invocation of utility shall  be  with  fewer  lines  of
                 arguments  if  fewer  than  number  remain. A line is considered to end with the
                 first <newline> unless the last character of the line is an unescaped <blank>; a
                 trailing  unescaped  <blank>  signals  continuation  to the next non-empty line,
                 inclusive.

       -n number Invoke utility using as many standard input arguments as possible, up to  number
                 (a  positive  decimal  integer) arguments maximum. Fewer arguments shall be used
                 if:

                  *  The command line length accumulated exceeds the size  specified  by  the  -s
                     option (or {LINE_MAX} if there is no -s option).

                  *  The last iteration has fewer than number, but not zero, operands remaining.

       -p        Prompt  mode:  the  user is asked whether to execute utility at each invocation.
                 Trace mode (-t) is turned on to write  the  command  instance  to  be  executed,
                 followed  by  a  prompt  to  standard  error.  An affirmative response read from
                 /dev/tty shall execute the command; otherwise,  that  particular  invocation  of
                 utility shall be skipped.

       -s size   Invoke  utility  using  as  many standard input arguments as possible yielding a
                 command line length less than size (a positive  decimal  integer)  bytes.  Fewer
                 arguments shall be used if:

                  *  The total number of arguments exceeds that specified by the -n option.

                  *  The total number of lines exceeds that specified by the -L option.

                  *  End-of-file   is  encountered  on  standard  input  before  size  bytes  are
                     accumulated.

                 Values of size up to at least {LINE_MAX} bytes shall be supported, provided that
                 the constraints specified in the DESCRIPTION are met. It shall not be considered
                 an error if a  value  larger  than  that  supported  by  the  implementation  or
                 exceeding the constraints specified in the DESCRIPTION is given; xargs shall use
                 the largest value it supports within the constraints.

       -t        Enable trace mode. Each generated command line  shall  be  written  to  standard
                 error just prior to invocation.

       -x        Terminate if a constructed command line will not fit in the implied or specified
                 size (see the -s option above).

OPERANDS

       The following operands shall be supported:

       utility   The name of the utility to be invoked, found  by  search  path  using  the  PATH
                 environment  variable, described in the Base Definitions volume of POSIX.1‐2017,
                 Chapter 8, Environment Variables.  If utility is omitted, the default  shall  be
                 the  echo  utility.  If  the  utility  operand names any of the special built-in
                 utilities  in  Section  2.14,  Special  Built-In  Utilities,  the  results   are
                 undefined.

       argument  An initial option or operand for the invocation of utility.

STDIN

       The  standard  input  shall  be a text file. The results are unspecified if an end-of-file
       condition is detected immediately following an escaped <newline>.

INPUT FILES

       The file /dev/tty shall be used to read responses required by the -p option.

ENVIRONMENT VARIABLES

       The following environment variables shall affect the execution of xargs:

       LANG      Provide a default value for the internationalization variables that are unset or
                 null.   (See   the   Base  Definitions  volume  of  POSIX.1‐2017,  Section  8.2,
                 Internationalization  Variables  for  the  precedence  of   internationalization
                 variables used to determine the values of locale categories.)

       LC_ALL    If  set  to  a  non-empty  string  value,  override  the values of all the other
                 internationalization variables.

       LC_COLLATE
                 Determine the locale for the behavior of ranges, equivalence classes, and multi-
                 character collating elements used in the extended regular expression defined for
                 the yesexpr locale keyword in the LC_MESSAGES category.

       LC_CTYPE  Determine the locale for the interpretation of sequences of bytes of  text  data
                 as  characters  (for example, single-byte as opposed to multi-byte characters in
                 arguments and input files) and the behavior of character  classes  used  in  the
                 extended  regular  expression  defined  for  the  yesexpr  locale keyword in the
                 LC_MESSAGES category.

       LC_MESSAGES
                 Determine the locale used to process affirmative responses, and the locale  used
                 to  affect the format and contents of diagnostic messages and prompts written to
                 standard error.

       NLSPATH   Determine the location of message catalogs for the processing of LC_MESSAGES.

       PATH      Determine the location of utility, as described in the Base  Definitions  volume
                 of POSIX.1‐2017, Chapter 8, Environment Variables.

ASYNCHRONOUS EVENTS

       Default.

STDOUT

       Not used.

STDERR

       The standard error shall be used for diagnostic messages and the -t and -p options. If the
       -t option is specified, the utility and its constructed argument list shall be written  to
       standard  error,  as it will be invoked, prior to invocation. If -p is specified, a prompt
       of the following format shall be written (in the POSIX locale):

           "?..."

       at the end of the line of the output from -t.

OUTPUT FILES

       None.

EXTENDED DESCRIPTION

       None.

EXIT STATUS

       The following exit values shall be returned:

           0   All invocations of utility returned exit status zero.

       1‐125   A command line meeting the specified requirements could not be assembled,  one  or
               more  of the invocations of utility returned a non-zero exit status, or some other
               error occurred.

         126   The utility specified by utility was found but could not be invoked.

         127   The utility specified by utility could not be found.

CONSEQUENCES OF ERRORS

       If a command line meeting the specified requirements  cannot  be  assembled,  the  utility
       cannot  be  invoked,  an  invocation  of  the  utility  is  terminated  by a signal, or an
       invocation of the utility exits with exit status 255, the  xargs  utility  shall  write  a
       diagnostic message and exit without processing any remaining input.

       The following sections are informative.

APPLICATION USAGE

       The  255 exit status allows a utility being used by xargs to tell xargs to terminate if it
       knows no further invocations using the current data stream  will  succeed.  Thus,  utility
       should explicitly exit with an appropriate value to avoid accidentally returning with 255.

       Note  that  since  input  is  parsed  as lines, <blank> characters separate arguments, and
       <backslash>, <apostrophe>, and double-quote characters are used for quoting, if  xargs  is
       used  to  bundle  the  output  of  commands like find dir -print or ls into commands to be
       executed, unexpected results are likely if any filenames contain  <blank>,  <newline>,  or
       quoting  characters.  This can be solved by using find to call a script that converts each
       file found into a quoted string that is then piped to xargs,  but  in  most  cases  it  is
       preferable  just to have find do the argument aggregation itself by using -exec with a '+'
       terminator instead of ';'.  Note that the quoting rules used by xargs are not the same  as
       in  the  shell. They were not made consistent here because existing applications depend on
       the current rules. An easy (but inefficient) method that can be used  to  transform  input
       consisting  of one argument per line into a quoted form that xargs interprets correctly is
       to precede each non-<newline> character with a <backslash>.  More  efficient  alternatives
       are shown in Example 2 and Example 5 below.

       On  implementations  with  a  large  value  for {ARG_MAX}, xargs may produce command lines
       longer than {LINE_MAX}.  For invocation of utilities, this is not a problem. If  xargs  is
       being  used  to  create  a text file, users should explicitly set the maximum command line
       length with the -s option.

       The command, env, nice, nohup, time, and xargs utilities have been specified to  use  exit
       code  127  if  an  error  occurs  so that applications can distinguish ``failure to find a
       utility'' from ``invoked utility exited with an error  indication''.  The  value  127  was
       chosen because it is not commonly used for other meanings; most utilities use small values
       for ``normal error conditions'' and the values above 128 can be confused with  termination
       due  to receipt of a signal. The value 126 was chosen in a similar manner to indicate that
       the utility could be found,  but  not  invoked.  Some  scripts  produce  meaningful  error
       messages differentiating the 126 and 127 cases. The distinction between exit codes 126 and
       127 is based on KornShell practice that uses 127 when all attempts  to  exec  the  utility
       fail  with [ENOENT], and uses 126 when any attempt to exec the utility fails for any other
       reason.

EXAMPLES

        1. The following command combines the output of the  parenthesized  commands  (minus  the
           <apostrophe>  characters)  onto  one  line, which is then appended to the file log. It
           assumes that the expansion of "$0$*" does not include any  <apostrophe>  or  <newline>
           characters.

               (logname; date; printf "'%s'\n$0 $*") | xargs -E "" >>log

        2. The following command invokes diff with successive pairs of arguments originally typed
           as command line arguments. It assumes there are no embedded  <newline>  characters  in
           the elements of the original argument list.

               printf "%s\n$@" | sed 's/[^[:alnum:]]/\\&/g' |
                   xargs -E "" -n 2 -x diff

        3. In  the  following  commands,  the  user is asked which files in the current directory
           (excluding dotfiles) are to be archived. The files are archived into arch; a, one at a
           time  or  b,  many  at  a time. The commands assume that no filenames contain <blank>,
           <newline>, <backslash>, <apostrophe>, or double-quote characters.

               a. ls | xargs -E "" -p -L 1 ar -r arch

               b. ls | xargs -E "" -p -L 1 | xargs -E "" ar -r arch

        4. The following command invokes command1 one or  more  times  with  multiple  arguments,
           stopping if an invocation of command1 has a non-zero exit status.

               xargs -E "" sh -c 'command1 "$@" || exit 255' sh < xargs_input

        5. On  XSI-conformant systems, the following command moves all files from directory $1 to
           directory $2, and echoes each move  command  just  before  doing  it.  It  assumes  no
           filenames  contain  <newline>  characters  and  that  neither  $1  nor $2 contains the
           sequence "{}".

               ls -A "$1" | sed -e 's/"/"\\""/g' -e 's/.*/"&"/' |
                   xargs -E "" -I {} -t mv "$1"/{} "$2"/{}

RATIONALE

       The xargs utility was usually found only in System V-based systems; BSD  systems  included
       an  apply  utility that provided functionality similar to xargs -n number.  The SVID lists
       xargs as a software development extension. This volume of POSIX.1‐2017 does not share  the
       view that it is used only for development, and therefore it is not optional.

       The  classic  application  of the xargs utility is in conjunction with the find utility to
       reduce the number of processes launched by a simplistic use of the find -exec combination.
       The  xargs  utility  is also used to enforce an upper limit on memory required to launch a
       process. With this basis in mind, this volume of POSIX.1‐2017 selected  only  the  minimal
       features required.

       Although  the  255  exit  status  is  mostly an accident of historical implementations, it
       allows a utility being used by xargs to tell xargs to terminate if  it  knows  no  further
       invocations  using  the current data stream shall succeed. Any non-zero exit status from a
       utility falls into the 1‐125 range when xargs exits. There is  no  statement  of  how  the
       various  non-zero  utility exit status codes are accumulated by xargs.  The value could be
       the addition of all codes, their highest value, the last one received, or a  single  value
       such  as  1.  Since no algorithm is arguably better than the others, and since many of the
       standard utilities say little more (portably) than ``pass/fail'',  no  new  algorithm  was
       invented.

       Several  other xargs options were removed because simple alternatives already exist within
       this volume of POSIX.1‐2017. For example, the -i replstr option can be just as efficiently
       performed using a shell for loop. Since xargs calls an exec function with each input line,
       the -i option does not usually exploit the grouping capabilities of xargs.

       The requirement that xargs never produces command lines such that invocation of utility is
       within 2048 bytes of hitting the POSIX exec {ARG_MAX} limitations is intended to guarantee
       that the invoked utility has room to modify its environment  variables  and  command  line
       arguments  and  still  be  able to invoke another utility. Note that the minimum {ARG_MAX}
       allowed by the System Interfaces volume of POSIX.1‐2017 is  4096  bytes  and  the  minimum
       value  allowed  by  this  volume  of POSIX.1‐2017 is 2048 bytes; therefore, the 2048 bytes
       difference seems reasonable. Note, however, that xargs may  never  be  able  to  invoke  a
       utility if the environment passed in to xargs comes close to using {ARG_MAX} bytes.

       The  version  of xargs required by this volume of POSIX.1‐2017 is required to wait for the
       completion of the invoked command before invoking another command. This was  done  because
       historical  scripts  using  xargs assumed sequential execution. Implementations wanting to
       provide parallel operation of the invoked  utilities  are  encouraged  to  add  an  option
       enabling parallel invocation, but should still wait for termination of all of the children
       before xargs terminates normally.

       The -e option was omitted from the ISO POSIX‐2:1993 standard in the belief that the eofstr
       option-argument  was  recognized only when it was on a line by itself and before quote and
       escape processing were performed, and that the logical  end-of-file  processing  was  only
       enabled  if  a -e option was specified. In that case, a simple sed script could be used to
       duplicate the -e functionality. Further investigation revealed that:

        *  The logical end-of-file string was checked for  after  quote  and  escape  processing,
           making  a  sed  script  that  provided equivalent functionality much more difficult to
           write.

        *  The default was to perform logical end-of-file processing with an <underscore> as  the
           logical end-of-file string.

       To  correct  this  misunderstanding,  the  -E  eofstr  option  was adopted from the X/Open
       Portability Guide. Users should note  that  the  description  of  the  -E  option  matches
       historical  documentation  of  the  -e  option  (which  was not adopted because it did not
       support the Utility Syntax Guidelines), by saying that  if  eofstr  is  the  null  string,
       logical  end-of-file processing is disabled.  Historical implementations of xargs actually
       did not disable logical end-of-file processing; they treated a null argument found in  the
       input  as  a  logical end-of-file string. (A null string argument could be generated using
       single or double-quotes ('' or "").  Since this behavior was not documented  historically,
       it is considered to be a bug.

       The  -I,  -L, and -n options are mutually-exclusive. Some implementations use the last one
       specified if more than one is  given  on  a  command  line;  other  implementations  treat
       combinations of the options in different ways.

FUTURE DIRECTIONS

       None.

SEE ALSO

       Chapter 2, Shell Command Language, diff, echo, find

       The  Base  Definitions  volume  of POSIX.1‐2017, Chapter 8, Environment Variables, Section
       12.2, Utility Syntax Guidelines

       The System Interfaces volume of POSIX.1‐2017, exec

COPYRIGHT

       Portions of this text are reprinted and  reproduced  in  electronic  form  from  IEEE  Std
       1003.1-2017,  Standard  for  Information Technology -- Portable Operating System Interface
       (POSIX), The Open Group Base Specifications Issue 7, 2018 Edition, Copyright (C)  2018  by
       the  Institute  of  Electrical  and Electronics Engineers, Inc and The Open Group.  In the
       event of any discrepancy between this version and the original IEEE  and  The  Open  Group
       Standard,  the  original  IEEE  and  The  Open Group Standard is the referee document. The
       original Standard can be obtained online at http://www.opengroup.org/unix/online.html .

       Any typographical or formatting errors that appear in this page are most  likely  to  have
       been  introduced  during  the conversion of the source files to man page format. To report
       such errors, see https://www.kernel.org/doc/man-pages/reporting_bugs.html .