Xargs Reference

There are three major Xargs implementations: POSIX, Linux and Solaris.  Linux (GNU/FSF) implementation is the most elaborate and is a superset of two others.

Posix

The following options are supported in POSIX:

-e[eofstr]

Use eofstr as the logical end-of-file string. Underscore (_) is assumed for the logical EOF string if neither -e nor -E is used. When the -eofstr option-argument is omitted, the logical EOF string capability is disabled and underscores are taken literally. The xargs utility reads standard input until either end-of-file or the logical EOF string is encountered.

-E eofstr

Specify a logical end-of-file string to replace the default underscore. The xargs utility reads standard input until either end-of-file or the logical EOF string is encountered.

-I replstr

Insert mode: utility will be executed for each line from standard input, taking the entire line as a single argument, inserting it in arguments for each occurrence of replstr. A maximum of five arguments in arguments can each contain one or more instances of replstr. Any blank characters at the beginning of each line are ignored. Constructed arguments cannot grow larger than 255 bytes. Option -x is forced on. The -I and -i options are mutually exclusive; the last one specified takes effect.

-i[replstr]

This option is equivalent to -I replstr. The string {} is assumed for replstr if the option-argument is omitted.

-L number

The utility will be executed for each non-empty number lines of arguments from standard input. The last invocation of utility will be with fewer lines of arguments if fewer than number remain. A line is considered to end with the first newline character unless the last character of the line is a blank character; a trailing blank character signals continuation to the next non-empty line, inclusive. The -L, -l and -n options are mutually exclusive; the last one specified takes effect.

-l[number]

(The letter ell.) This option is equivalent to -L number. If number is omitted, 1 is assumed. Option -x is forced on.

-n number

Invoke utility using as many standard input arguments as possible, up to number (a positive decimal integer) arguments maximum. Fewer arguments will 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 will execute the command; otherwise, that particular invocation of utility is 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 will 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 are supported, provided that the constraints specified in the DESCRIPTION section are met. It is not considered an error if a value larger than that supported by the implementation or exceeding the constraints specified in the DESCRIPTION section is given; xargs will use the largest value it supports within the constraints.

-t

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

-x

Terminate if a command line containing number arguments (see the -n option above) or number lines (see the -L option above) will not fit in the implied or specified size (see the -s option above).

Linux

xargs - build and execute command lines from standard input

Synopsis

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] [--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 newlines 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

--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. Otherwise, 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.

--delimiter=delim, -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 better to design your program to use '--null' where this is possible. The specified delimiter may be a single character, a C-style character 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.

-Eeof-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.

--eof[=eof-str], -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. 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.

--replace[=replace-str], -i[replace-str]

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.

--max-lines[=max-lines], -l[max-lines]

Synonym for the -L option. Unlike -L, the max-lines argument is optional. If max-args is not specified, it defaults to one. The -l option is deprecated since the POSIX standard specifies -L instead.

--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 environment variables take up more than 131072 bytes). The operating 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 executing 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 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.

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.

Solaris

/usr/bin/xargs [-t] [-p] [-e [eofstr]] [-E eofstr] 
     [-I replstr] [-i [replstr]] [-L number] [-l [number]] 
     [-n number [-x]] [-s size] [utility [argument...]]

/usr/xpg6/bin/xargs [-t] [-p] [-e [eofstr]] [-E eofstr] 
     [-I replstr] [-i [replstr]] [-L number] [-l [number]] 
     [-n number [-x]] [-s size] [utility [argument...]]

Description

The xargs  utility constructs a command line consisting of the utility and argument operands specified followed by as many arguments read in sequence from standard input as will fit in length and number constraints specified by the options. The xargs  utility then invokes the constructed command line and waits for its completion. This sequence is repeated until an end-of-file condition is detected on standard input or an invocation of a constructed command line returns an exit status of 255.

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

The generated command line length will 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 will limit the command line length such that when the command line is invoked, the combined argument and environment lists will not exceed {ARG_MAX}-2048  bytes. Within this constraint, if neither the -n  nor the -s  option is specified, the default command line length will be at least {LINE_MAX}.

Options

The following options are supported:

-e[eofstr] 

Uses eofstr as the logical end-of-file string. Underscore (_) is assumed for the logical EOF  string if neither -e  nor -E  is used. When the eofstr option-argument is omitted, the logical EOF  string capability is disabled and underscores are taken literally. The xargs  utility reads standard input until either end-of-file or the logical EOF  string is encountered.

-E  eofstr

In /usr/bin/args:

Specifies a logical end-of-file string to replace the default underscore. The xargs  utility reads standard input until either end-of-file or the logical EOF  string is encountered. The eofstr cannot be a null string.

In /usr/xpg6/bin/args: 

Specifies a logical end-of-file string to replace the default underscore. The xargs  utility reads standard input until either end-of-file or the logical EOF  string is encountered. When eofstr  is a null string, the logical end-of-file string capability is disabled and underscore characters are taken literally.

-I  replstr

Insert mode. utility is executed for each line from standard input, taking the entire line as a single argument, inserting it in argument s for each occurrence of replstr. A maximum of five arguments in arguments can each contain one or more instances of replstr. Any blank characters at the beginning of each line are ignored. Constructed arguments cannot grow larger than 255 bytes. Option -x  is forced on. The -I  and -i  options are mutually exclusive; the last one specified takes effect.

-i[replstr] 

This option is equivalent to -I  replstr. The string { }  is assumed for replstr if the option-argument is omitted.

-L  number

The utility is executed for each non-empty number lines of arguments from standard input. The last invocation of utility will be with fewer lines of arguments if fewer than number remain. A line is considered to end with the first newline character unless the last character of the line is a blank character; a trailing blank character signals continuation to the next non-empty line, inclusive. The -L, -l, and -n  options are mutually exclusive; the last one specified takes effect.

-l[number] 

(The letter ell.) This option is equivalent to -L  number. If number is omitted, 1  is assumed. Option -x  is forced on.

-n  number

Invokes utility using as many standard input arguments as possible, up to number (a positive decimal integer) arguments maximum. Fewer arguments will 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), or
• 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 (specific to the user's locale) read from /dev/tty  will execute the command; otherwise, that particular invocation of utility is skipped.

-s  size

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

• The total number of arguments exceeds that specified by the -n  option, or
• The total number of lines exceeds that specified by the -L  option, or
• End of file is encountered on standard input before size bytes are accumulated.

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

-t 

Enables trace mode. Each generated command line will be written to standard error just prior to invocation.

-x 

Terminates if a command line containing number arguments (see the -n  option above) or number lines (see the -L  option above) will not fit in the implied or specified size (see the -s  option above).

Operands

The following operands are supported:

utility

The name of the utility to be invoked, found by search path using the PATH  environment variable. (ee environ(5).) If utility is omitted, the default is the echo(1) utility. If the utility operand names any of the special built-in utilities in shell_builtins(1), the results are undefined.

argument

An initial option or operand for the invocation of utility.

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.

Notice that input is parsed as lines. Blank characters separate arguments. If xargs  is used to bundle output of commands like find  dir -print  or ls  into commands to be executed, unexpected results are likely if any filenames contain any blank characters or newline characters. This can be fixed by using find  to call a script that converts each file found into a quoted string that is then piped to xargs. Notice 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 and the shell syntax is not fully compatible with it. An easy rule that can be used to transform any string into a quoted form that xargs  will interpret correctly is to precede each character in the string with a backslash (\).

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 xargs  utility returns exit status 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.

Examples

---

Example 1 Using the xargs command




The following will move all files from directory $1  to directory $2, and echo each move command just before doing it:

example% ls $1 | xargs -I {} -t mv $1/{} $2/{}

The following command will combine the output of the parenthesised commands onto one line, which is then written to the end of file log:

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

The following command will invoke diff  with successive pairs of arguments originally typed as command line arguments (assuming there are no embedded blank characters in the elements of the original argument list):

example% printf "%s\n" "$*" | xargs -n 2 -x diff

The user is asked which files in the current directory are to be archived. The files are archived into arch  ;  a, one at a time, or b, many at a time:

example% ls | xargs -p -L 1 ar -r arch ls | xargs -p -L 1 | xargs ar -r arch

The following will execute with successive pairs of arguments originally typed as command line arguments:

example% echo $* | xargs -n 2 diff

---

Environment Variables

See environ(5) for descriptions of the following environment variables that affect the execution of xargs: LANG, LC_ALL, LC_COLLATE, LC_CTYPE, LC_MESSAGES, and NLSPATH.

PATH 

Determine the location of utility.

Exit Status

The following exit values are returned:

0 

All invocations of utility returned exit status 0.

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.

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 will write a diagnostic message and exit without proce

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