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XARGS


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NAME

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]
[--show-limits]
[--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.


-E eof-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-lines

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 largest allowed value is system-dependent,
and is calculated as the argument length limit for exec, less the size
of your environment, less 2048 bytes of headroom. If this value is
more than 128KiB, 128Kib is used as the default value; otherwise, the
default value is the maximum. 1KiB is 1024 bytes.



–verbose



-t

Print the command line on the standard error output before executing
it.

–version


Print the version number of
xargs

and exit.

–show-limits


Display the limits on the command-line length which are imposed by the
operating system,
xargs

choice of buffer size and the
-s

option. Pipe the input from
/dev/null

(and perhaps specify
–no-run-if-empty)

if you don’t want
xargs

to do anything.



–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.


find /tmp -depth -name core -type f -delete

Find files named
core

in or below the directory
/tmp

and delete them, but more efficiently than in the previous example
(because we avoid the need to use
fork(2)

and
exec(2)

to launch
rm

and we don’t need the extra
xargs

process).



cut -d: -f1 < /etc/passwd | sort | xargs echo

Generates a compact listing of all the users on the system.



xargs sh -c ‘emacs "[email protected]" < /dev/tty’ emacs

Launches the minimum number of copies of Emacs needed, one after the
other, to edit the files listed on
xargs

standard input. This example achieves the same effect as BSD’s
-o

option, but in a more flexible and portable way.




 

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.
 

STANDARDS CONFORMANCE

As of GNU xargs version 4.2.9, the default behaviour of
xargs

is not to have a logical end-of-file marker. POSIX (IEEE Std 1003.1,
2004 Edition) allows this.

The -l and -i options appear in the 1997 version of the POSIX
standard, but do not appear in the 2004 version of the standard.
Therefore you should use -L and -I instead, respectively.

The POSIX standard allows implementations to have a limit on the size
of arguments to the
exec

functions. This limit could be as low as 4096 bytes including the size of the
environment. For scripts to be portable, they must not rely on a
larger value. However, I know of no implementation whose actual limit
is that small. The
–show-limits

option can be used to discover the actual limits in force on the
current system.



 

SEE ALSO

find(1), locate(1), locatedb(5), updatedb(1),
fork(2), execvp(3),
Finding Files (on-line in Info, or printed)
 

BUGS

The
-L

option is incompatible with the
-I

option, but perhaps should not be.

It is not possible for
xargs

to be used securely, since there will always be a time gap between the
production of the list of input files and their use in the commands
that
xargs

issues. If other users have access to the system, they can manipulate
the filesystem during this time window to force the action of the
commands
xargs

runs to apply to files that you didn’t intend. For a more detailed
discussion of this and related problems, please refer to the
“Security Considerations” chapter in the findutils Texinfo
documentation. The
-execdir

option of
find

can often be used as a more secure alternative.


When you use the
-I

option, each line read from the input is buffered
internally. This means that there is an upper limit on the length
of input line that
xargs

will accept when used with the
-I

option. To work around this
limitation, you can use the
-s

option to increase the amount of
buffer space that
xargs

uses, and you can also use an extra invocation of
xargs

to ensure that very long lines do not occur.
For example:

somecommand | xargs -s 50000 echo | xargs -I ‘{}’ -s 100000 rm ‘{}’

Here, the first invocation of
xargs

has no input line length limit
because it doesn’t use the
-i

option. The second invocation of
xargs

does have such a limit, but we have ensured that the it never encounters
a line which is longer than it can handle. This is not an ideal
solution. Instead, the
-i

option should not impose a line length
limit, which is why this discussion appears in the BUGS section.
The problem doesn’t occur with the output of
find(1)

because it emits just one filename per line.

The best way to report a bug is to use the form at
http://savannah.gnu.org/bugs/?group=findutils.
The reason for this is that you will then be able to track progress in
fixing the problem. Other comments about xargs(1) and about
the findutils package in general can be sent to the
bug-findutils

mailing list. To join the list, send email to
[email protected].



 

Index



NAME

SYNOPSIS

DESCRIPTION

OPTIONS

EXAMPLES

EXIT STATUS

STANDARDS CONFORMANCE

SEE ALSO

BUGS



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