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Updated: Thursday, June 13, 2019
 
 

xargs(1)

Name

xargs - construct argument lists and invoke utility

Synopsis

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 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 are 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 is 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 limits the command line length such that when the command line is invoked, the combined argument and environment lists can not exceed {ARG_MAX}−2048 bytes. Within this constraint, if neither the –n nor the –s option is specified, the default command line length is at least {LINE_MAX}.

Options

The following options are supported:

–0

Input items are terminated by a null character instead of by white space or a NEWLINE, and the quotes and backslash are not special, that is, every character is taken literally. The end of file string is also disabled and is treated like any other argument. This is useful when input items might contain white space, quote marks, or backslashes. The find –print0 option produces input suitable for this mode.

–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

Specifies a logical end-of-file string to replace the default underscore. xargs 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 is 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 are 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 executes 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 are 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 specified. xargs uses the largest value it supports within the constraints.

–t

Enables trace mode. Each generated command line is 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) does 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(7).) 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 succeeds. 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 interprets correctly is to precede each character in the string with a backslash (\ ).

On implementations with a large value for {ARG_MAX}, xargs can 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 example moves 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 combines 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 invokes 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 executes with successive pairs of arguments originally typed as command line arguments:

example% echo $* | xargs -n 2 diff

Environment Variables

See environ(7) 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.

Affirmative responses are processed using the extended regular expression defined for the yesexpr keyword in the LC_MESSAGES category of the user's locale. The locale specified in the LC_COLLATE category defines the behavior of ranges, equivalence classes, and multi-character collating elements used in the expression defined for yesexpr. The locale specified in LC_CTYPE determines the locale for interpretation of sequences of bytes of text data a characters, the behavior of character classes used in the expression defined for the yesexpr. See locale(7).

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 writes a diagnostic message and exit without processing any remaining input.

Attributes

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

ATTRIBUTE TYPE
ATTRIBUTE VALUE
Availability
system/core-os
CSI
Enabled
Interface Stability
Committed
Standard

See Also

echo(1), shell_builtins(1), attributes(7), environ(7), standards(7)