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 diffENVIRONMENT 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)