XARGS(1) General Commands Manual XARGS(1)
NAME
xargs – construct argument list(s) and execute utility
SYNOPSIS
xargs [-0oprt] [-E eofstr] [-I replstr [-R replacements] [-S replsize]]
[-J replstr] [-L number] [-n number [-x]] [-P maxprocs] [-s size]
[utility [argument ...]]
DESCRIPTION
The xargs utility reads space, tab, newline and end-of-file delimited
strings from the standard input and executes utility with the strings as
arguments.
Any arguments specified on the command line are given to utility upon
each invocation, followed by some number of the arguments read from the
standard input of xargs. This is repeated until standard input is
exhausted.
Spaces, tabs and newlines may be embedded in arguments using single
(`` ' '') or double (``"'') quotes or backslashes (``\''). Single quotes
escape all non-single quote characters, excluding newlines, up to the
matching single quote. Double quotes escape all non-double quote
characters, excluding newlines, up to the matching double quote. Any
single character, including newlines, may be escaped by a backslash.
The options are as follows:
-0, --null
Change xargs to expect NUL (``\0'') characters as separators,
instead of spaces and newlines. This is expected to be used in
concert with the -print0 function in find(1).
-E eofstr
Use eofstr as a logical EOF marker.
-I replstr
Execute utility for each input line, replacing one or more
occurrences of replstr in up to replacements (or 5 if no -R flag
is specified) arguments to utility with the entire line of input.
The resulting arguments, after replacement is done, will not be
allowed to grow beyond replsize (or 255 if no -S flag is
specified) bytes; this is implemented by concatenating as much of
the argument containing replstr as possible, to the constructed
arguments to utility, up to replsize bytes. The size limit does
not apply to arguments to utility which do not contain replstr,
and furthermore, no replacement will be done on utility itself.
Implies -x.
-J replstr
If this option is specified, xargs will use the data read from
standard input to replace the first occurrence of replstr instead
of appending that data after all other arguments. This option
will not affect how many arguments will be read from input (-n),
or the size of the command(s) xargs will generate (-s). The
option just moves where those arguments will be placed in the
command(s) that are executed. The replstr must show up as a
distinct argument to xargs. It will not be recognized if, for
instance, it is in the middle of a quoted string. Furthermore,
only the first occurrence of the replstr will be replaced. For
example, the following command will copy the list of files and
directories which start with an uppercase letter in the current
directory to destdir:
/bin/ls -1d [A-Z]* | xargs -J % cp -Rp % destdir
-L number
Call utility for every number lines read. If EOF is reached and
fewer lines have been read than number then utility will be
called with the available lines.
-n number, --max-args=number
Set the maximum number of arguments taken from standard input for
each invocation of utility. An invocation of utility will use
less than number standard input arguments if the number of bytes
accumulated (see the -s option) exceeds the specified size or
there are fewer than number arguments remaining for the last
invocation of utility. The current default value for number is
5000.
-o Reopen stdin as /dev/tty in the child process before executing
the command. This is useful if you want xargs to run an
interactive application.
-P maxprocs, --max-procs=maxprocs
Parallel mode: run at most maxprocs invocations of utility at
once. If maxprocs is set to 0, xargs will run as many processes
as possible.
-p, --interactive
Echo each command to be executed and ask the user whether it
should be executed. An affirmative response, ‘y’ in the POSIX
locale, causes the command to be executed, any other response
causes it to be skipped. No commands are executed if the process
is not attached to a terminal.
-r, --no-run-if-empty
Compatibility with GNU xargs. The GNU version of xargs runs the
utility argument at least once, even if xargs input is empty, and
it supports a -r option to inhibit this behavior. The FreeBSD
version of xargs does not run the utility argument on empty
input, but it supports the -r option for command-line
compatibility with GNU xargs, but the -r option does nothing in
the FreeBSD version of xargs.
-R replacements
Specify the maximum number of arguments that -I will do
replacement in. If replacements is negative, the number of
arguments in which to replace is unbounded.
-S replsize
Specify the amount of space (in bytes) that -I can use for
replacements. The default for replsize is 255.
-s size, --max-chars=size
Set the maximum number of bytes for the command line length
provided to utility. The sum of the length of the utility name,
the arguments passed to utility (including NULL terminators) and
the current environment will be less than or equal to this
number. The current default value for size is ARG_MAX - 4096.
-t, --verbose
Echo the command to be executed to standard error immediately
before it is executed.
-x, --exit
Force xargs to terminate immediately if a command line containing
number arguments will not fit in the specified (or default)
command line length.
If utility is omitted, echo(1) is used.
Undefined behavior may occur if utility reads from the standard input.
If a command line cannot be assembled, or cannot be invoked, or if an
invocation of utility is terminated by a signal, or an invocation of
utility exits with a value of 255, the xargs utility stops processing
input and exits after all invocations of utility finish processing.
LEGACY DESCRIPTION
In legacy mode, the -L option treats all newlines as end-of-line,
regardless of whether the line is empty or ends with a space. In
addition, the -L and -n options are not mutually-exclusive.
For more information about legacy mode, see compat(5).
EXIT STATUS
The xargs utility exits with a value of 0 if no error occurs. If utility
cannot be found, xargs exits with a value of 127, otherwise if utility
cannot be executed, xargs exits with a value of 126. If any other error
occurs, xargs exits with a value of 1.
EXAMPLES
Create a 3x3 matrix with numbers from 1 to 9. Every echo(1) instance
receives three lines as arguments:
$ seq 1 9 | xargs -L3 echo
1 2 3
4 5 6
7 8 9
Duplicate every line from standard input:
$ echo -e "one\ntwo\nthree" | xargs -I % echo % %
one one
two two
three three
Execute at most 2 concurrent instances of find(1) every one of them using
one of the directories from the standard input:
ls -d /usr/local /opt | xargs -J % -P2 -n1 find % -name file
SEE ALSO
echo(1), find(1), execvp(3), compat(5)
STANDARDS
The xargs utility is expected to be IEEE Std 1003.2 (“POSIX.2”)
compliant. The -J, -o, -P, -R and -S options are non-standard FreeBSD
extensions which may not be available on other operating systems.
HISTORY
The xargs utility appeared in PWB UNIX.
BUGS
If utility attempts to invoke another command such that the number of
arguments or the size of the environment is increased, it risks execvp(3)
failing with E2BIG.
The xargs utility does not take multibyte characters into account when
performing string comparisons for the -I and -J options, which may lead
to incorrect results in some locales.
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