xargs - construct argument lists and invoke utility
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...]]
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}.
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).
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.
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.
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
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).
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.
See attributes(7) for descriptions of the following attributes:
| ATTRIBUTE
TYPE |
ATTRIBUTE VALUE |
| CSI |
Enabled |
| Interface Stability |
Standard |