xargs(1)
NAME
xargs - construct argument lists and invoke utility
SYNOPSIS
xargs [-t] [-p] [ -e [eofstr]] [-E eofstr] [-I replstr] [ -i
[replstr]] [-L number] [ -l [number]] [ -n number [-x]] [-
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 will
fit in length and number constraints specified by the
options. The xargs utility then invokes the constructed com-
mand line and waits for its completion. This sequence is
repeated until an end-of-file condition is detected on stan-
dard 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
will be 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 will be 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 will limit the command line
length such that when the command line is invoked, the com-
bined argument and environment lists will not exceed
{ARG_MAX}-2048 bytes. Within this constraint, if neither the
-n nor the -s option is specified, the default command line
length will be at least {LINE_MAX}.
OPTIONS
The following options are supported:
-e[eofstr]
Uses eofstr as the logical end-of-file string. Under-
score (_) 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. The xargs utility reads standard
input until either end-of-file or the logical EOF
string is encountered.
-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 omit-
ted.
-L number
The utility is executed for each non-empty number
lines of arguments from standard input. The last invo-
cation of utility will be with fewer lines of argu-
ments if fewer than number remain. A line is con-
sidered 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 will be 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, fol-
lowed by a prompt to standard error. An affirmative
response (specific to the user's locale) read from
/dev/tty will execute the command; otherwise, that
particular invocation of utility is skipped.
-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 argu-
ments will be 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 implementa-
tion or exceeding the constraints specified in
DESCRIPTION is given. xargs will use the largest value
it supports within the constraints.
-t Enables trace mode. Each generated command line will
be written to standard error just prior to invocation.
-x Terminates if a command line containing number argu-
ments (see the -n option above) or number lines (see
the -L option above) will not fit in the implied or
specified size (see the -s option above).
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(5).) 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 will succeed. 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 exe-
cuted, unexpected results are likely if any filenames con-
tain 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 will interpret correctly is to precede each char-
acter in the string with a backslash (\).
On implementations with a large value for {ARG_MAX}, xargs
may produce command lines longer than {LINE_MAX}. For invo-
cation 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 indica-
tion." 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 will move 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 will combine 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 $*") | xargs >>log
The following command will invoke diff with successive pairs
of arguments originally typed as command line arguments
(assuming there are no embedded blank characters in the ele-
ments of the original argument list):
example% printf "%s\n" "$*" | 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 will execute with successive pairs of argu-
ments originally typed as command line arguments:
example% echo $* | xargs -n 2 diff
ENVIRONMENT VARIABLES
See environ(5) 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.
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
will write a diagnostic message and exit without processing
any remaining input.
ATTRIBUTES
See attributes(5) for descriptions of the following attri-
butes:
____________________________________________________________
| ATTRIBUTE TYPE | ATTRIBUTE VALUE |
|_____________________________|_____________________________|
| Availability | SUNWcsu |
|_____________________________|_____________________________|
| CSI | enabled |
|_____________________________|_____________________________|
| Interface Stability | Standard |
|_____________________________|_____________________________|
SEE ALSO
echo(1), shell_builtins(1), attributes(5), environ(5), stan-
dards(5)
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