xargs(1)

NAME

xargs — construct argument lists and execute command

SYNOPSIS

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

DESCRIPTION

xargs combines the fixed initial-arguments with arguments read from standard input to execute the specified command one or more times. The number of arguments read for each command invocation and the manner in which they are combined are determined by the options specified.

command, which can be a shell file, is searched for, using the $PATH environment variable. If command is omitted, /usr/bin/echo is used.

Arguments read in from standard input are defined to be contiguous strings of characters delimited by one or more blanks, tabs, or newlines; empty lines are always discarded. Spaces and tabs can be embedded as part of an argument if escaped or quoted. Characters enclosed in quotes (single or double) are taken literally, and the delimiting quotes are removed. Outside of quoted strings, a backslash (\) escapes the next character.

The amount of memory available for the execution of command is limited by the system parameter ARG_MAX. By default, the size of the argument list is limited to LINE_MAX bytes. See limits(5) and sysconf(2) for a description of these system parameters and how their values can be determined. To increase the available argument list space, use the -s option.

Each argument list is constructed starting with the initial-arguments, followed by some number of arguments read from standard input (exception: see -i or -I option). The -i, -I, -l, -L, and -n options determine how arguments are selected for each command invocation. When none of these options is specified, the initial-arguments are followed by arguments read continuously from standard input until an internal buffer is full, then command is executed with the accumulated args. This process is repeated until there are no more args. When there are option conflicts (such as -l or -L versus -n), the last option has precedence.

Options

The option values are:

-L number: command is executed for each nonempty number lines of arguments from standard input. The last invocation of command will 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 a blank or a tab; a trailing blank/tab signals continuation through the next nonempty line. The -L, -l, and -n options are mutually exclusive. The last one specified takes effect.
-l [number]: This option is equivalent to the -L option. 1 is assumed if number is omitted or is given as the empty string ("" ). Option -x is forced.
-I replstr: Insert mode: command is executed for each line from standard input, taking the entire line as a single arg, inserting it in initial-arguments for each occurrence of replstr. A maximum of 5 arguments in initial-arguments can each contain one or more instances of replstr. Blanks and tabs at the beginning of each line are discarded. Constructed arguments must not grow larger than 255 bytes, and option -x is also forced. The -I and -i options are mutually exclusive. The last one specified takes effect.
-i [repstr]: This option is equivalent to the -I option. {} is assumed if replstr is omitted or is given as the empty string ("" ).
-n number: Execute command using as many standard input arguments as possible, up to number arguments maximum. Fewer arguments are used if their total size is greater than size bytes, and for the last invocation if there are fewer than number arguments remaining. If option -x is also coded, each number arguments must fit in the size limitation or xargs terminates execution.
-s size: The maximum total size of each argument list is set to size bytes; size must be a positive integer less than LINE_MAX (see limits(5), sysconf(2)). If -s is not coded, LINE_MAX is taken as the default. Note that the bytes count for size includes one extra bytes for each argument and the count of bytes in the command name.
-t: Trace mode: The command and each constructed argument list are echoed to standard error just prior to their execution.
-p: Prompt mode: The user is asked whether to execute command prior to each invocation. Trace mode (-t) is turned on to print the command instance to be executed, followed by a ?... prompt. An affirmative reply (by default, an affirmative reply is y optionally followed by anything) executes the command; anything else, including pressing Return, skips that particular invocation of command.
-x: Causes xargs to terminate if any argument list would be greater than size bytes. -x is forced by the options -i, -I, -l, and -L. When none of the options -i, -I, -l, -L, or -n is coded, the total length of all arguments must be within the size limit.
-e [eofstr]: eofstr is taken as the logical end-of-file string. Underscore (_) is assumed for the logical EOF string if neither -e nor -E is used. The value -e with eofstr given as the empty string ( "" ) turns off the logical EOF string capability (underscore is taken literally). xargs 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 (_) character. Equivalent to the -e option above.

xargs terminates if it receives a return code of -1 from command or if it cannot execute command. When command is a shell program, it should explicitly exit (see sh(1)) with an appropriate value to avoid accidentally returning with -1.

RETURN VALUE

xargs exits with one of the following values:

0: All invocations of command completed successfully.
1 to 125: One or more invocations of command did not complete successfully.
126: The command specified was found but could not be invoked.
127: The command specified could not be found.

EXTERNAL INFLUENCES

Environment Variables

LC_CTYPE determines the space characters and the interpretation of text as single- and/or multibyte characters.

LC_MESSAGES determines the language in which messages are displayed, and the local language equivalent of an affirmative reply when the -p prompt option is specified.

If LC_CTYPE or LC_MESSAGES is not specified in the environment or is set to the empty string, the value of LANG is used as a default for each unspecified or empty variable. If LANG is not specified or is set to the empty string, a default of "C" (see lang(5)) is used instead of LANG.

If any internationalization variable contains an invalid setting, xargs behaves as if all internationalization variables are set to "C". See environ(5).

International Code Set Support

Single- and multibyte character code sets are supported.

EXAMPLES

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

ls $1 | xargs -i -t mv $1/{} $2/{} 

Combine the output of the parenthesized commands onto one line, then echo to the end of file log:

(logname; date; echo $0 $*) | xargs >>log 

Ask the user which files in the current directory are to be archived then archive them into arch one at a time:

ls | xargs -p -l ar r arch 

or many at a time:

ls | xargs -p -l | xargs ar r arch 

Execute diff (see diff(1)) with successive pairs of arguments originally typed as shell arguments:

echo $* | xargs -n2 diff 

STANDARDS CONFORMANCE

xargs: SVID2, SVID3, XPG2, XPG3, XPG4, POSIX.2