xargs(1)

xargs -- construct argument list(s) and execute command

Synopsis

xargs [flags] [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 flags specified.

command, which may be a shell file, is searched for, using one's $PATH. 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 new-lines; empty lines are always discarded. Blanks and tabs may 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.

Each argument list is constructed starting with the initial-arguments, followed by some number of arguments read from standard input (Exception: see -i flag). Flags -i, -l, and -n determine how arguments are selected for each command invocation. When none of these flags are coded, the initial-arguments are followed by arguments read continuously from standard input until an internal buffer is full, and then command is executed with the accumulated args. This process is repeated until there are no more args. When there are flag conflicts (for example, -l and -n), the last flag has precedence. Valid flags are:

-lnumber: command is executed for each non-empty 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 new-line unless the last character of the line is a blank or a tab; a trailing blank or tab signals continuation through the next non-empty line. If number is omitted, 1 is assumed. Option -x is forced. The -L option is preferred; it is the same as the -l option except that it requires an option argument.
-L number: command is executed for each non-empty 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 new-line unless the last character of the line is a blank or a tab; a trailing blank or tab signals continuation through the next non-empty line. If number is omitted, 1 is assumed. Option -x is forced. This option is the same as the -l option except that an option argument is required for compliance with XPG4.
-ireplstr: 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 five arguments in initial-arguments may each contain one or more instances of replstr. Blanks and tabs at the beginning of each line are thrown away. Constructed arguments may not grow larger than 255 characters, and option -x is also forced. {} is assumed for replstr if not specified. The -I option is preferred; it is the same as the -i option except that it requires an option argument.
-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 five arguments in initial-arguments may each contain one or more instances of replstr. Blanks and tabs at the beginning of each line are thrown away. Constructed arguments may not grow larger than 255 characters, and option -x is also forced. {} is assumed for replstr if not specified. This option is the same as the -i option except that an option argument is required for compliance with XPG4.
-nnumber: 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 characters, 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, else xargs terminates execution.
-t: Trace mode: The command and each constructed argument list are echoed to file descriptor 2 just prior to their execution.
-p: Prompt mode: The user is asked whether to execute command each invocation. Trace mode (-t) is turned on to print the command instance to be executed, followed by a ?. . . prompt. A locale-specific affirmative response executes the command; anything else, including a <Return>, skips that particular invocation of command. In the C locale, an affirmative response is a line that starts with an uppercase or lowercase y.
-x: Causes xargs to terminate if any argument list would be greater than size characters; -x is forced by the options -i and -l. When neither of the options -i, -l, or -n are coded, the total length of all arguments must be within the size limit.
-ssize: The maximum total size of each argument list is set to size characters; size must be a positive integer less than or equal to {ARG_MAX}-2048. If -s is not coded, {ARG_MAX}-2048 is taken as the default. Note that the character count for size includes one extra character for each argument and the count of characters in the command name.
-eeofstr: eofstr is taken as the logical end-of-file string. Underbar (_) is assumed for the logical EOF string if -e is not coded. The value -e with no eofstr coded turns off the logical EOF string capability (underbar is taken literally). xargs reads standard input until either end-of-file or the logical EOF string is encountered. The -E option is preferred; it is the same as the -e option except that it requires an option argument.
-E eofstr: eofstr is taken as the logical end-of-file string. Underbar (_>) is assumed for the logical EOF string if -E is not coded. The value -E with no eofstr coded turns off the logical EOF string capability (underbar is taken literally). xargs reads standard input until either end-of-file or the logical EOF string is encountered. This option is the same as the -e option except that an option argument is required for compliance with XPG4.

xargs terminates if either it receives a return code of -1 from, 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.

The xargs command terminates with exit code 127 if the utility specified on the command line could not be found; exit code 126 is returned if the utility could be found but not executed.

Examples

The following example moves 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/{}

The following example combines the output of the parenthesized commands onto one line, which is then echoed to the end of file log:

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

The user is asked which files in the current directory are to be archived and archives them into arch (1.) one at a time, or (2.) many at a time.

   1.   ls | xargs -p -l ar r arch
   2.   ls | xargs -p -l | xargs ar r arch

The following example executes diff(1) with successive pairs of arguments originally typed as command-line arguments:

   echo $ | xargs -n2 diff

This last example assumes there are no embedded spaces in the elements of the orignal argument list.

Files

/usr/lib/locale/locale/LC_MESSAGES/uxcore: language-specific message file (See LANG in environ(5).)

References

sh(1)

Notices

xargs may never be able to invoke a utility if the environment passed in to xargs comes close to using ARG_MAX}-2048 bytes.