XARGS(1) User Commands XARGS(1)


NAME


xargs - construct argument lists and invoke utility

SYNOPSIS


xargs [-t] [-0] [-p] [-e[eofstr]] [-E eofstr]
[-I replstr] [-i[replstr]] [-L number] [-l[number]]
[-n number [-x]] [-P maxprocs] [-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:

-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:

o The command line length accumulated exceeds the
size specified by the -s option (or {LINE_MAX}
if there is no -s option), or

o 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.


-P maxprocs
Invokes utility using at most maxprocs (a positive decimal
integer) parallel child processes. If maxprocs is zero,
then the system will set a large upper bound to try and
run as many processes as possible.


-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:

o The total number of arguments exceeds that
specified by the -n option, or

o The total number of lines exceeds that
specified by the -L option, or

o 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).


-0
Null separator mode. Instead of using white space or new lines to
delimit arguments, zero bytes are used. This is suitable for use
with the -print0 argument to find(1).


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 |
+--------------------+-----------------+
|CSI | Enabled |
+--------------------+-----------------+
|Interface Stability | Standard |
+--------------------+-----------------+

SEE ALSO


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


September 13, 2018 XARGS(1)