XARGS
Section: User Commands (1)
Updated: 6 June 1986
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NAME
xargs - construct argument list(s) and execute command
SYNOPSIS
xargs
[ -lnumber ]
[ -ireplstr ]
[ -nnumber ]
[ -t ]
[ -p ]
[ -x ]
[ -ssize ]
[ -eeofstr ]
[ command [initial-arguments] ]
DESCRIPTION
xargs
combines the fixed
initial-arguments
with arguments read from standard input, to execute the specified
command
one or more times.
The number of arguments read for each
command
invocation, and the manner in which they are combined
are determined by the options specified.
command,
which may be a shell file,
is searched for using one's $PATH.
If
command
is omitted,
/bin/echo
is used.
Arguments read in from standard input are defined to be contiguous
strings of characters delimited by white space.
Empty lines are always discarded.
Blanks and tabs may be embedded as part of an argument if they
are escaped or quoted.
Characters enclosed in quotes (single or double) are taken literally,
and the delimiting quotes are removed. Outside of quoted strings,
a backslash
(\)
will escape the character it precedes.
Each arguments-list is constructed starting with the
initial-arguments,
followed by some number of arguments read from standard input
(Exception: see
-i
option).
Options
-i,
-l,
and
-n
determine how arguments are selected for each command invocation.
When none of these options are coded, the
initial-arguments
are followed by arguments read continuously from standard input
until an internal buffer is full, and then
command
is executed with the accumulated arguments.
This process is repeated until there are none left.
When there are option conflicts (e.g.,
-l
vs.
-n),
the last option takes precedence.
xargs
will terminate if it receives a return code of
-1,
or if it cannot execute
command.
When
command
is a shell script,
it should explicitly
exit
(see
sh(1))
with an appropriate value to avoid accidentally returning with
-1.
OPTIONS
- -lnumber
-
command
is executed for each nonempty
number
lines of arguments from standard input.
The last invocation of
command
will be with fewer lines of arguments if fewer than
number
remain.
A line is considered to end with the first new-line
unless
the last character of the line is a blank or a tab;
a trailing blank/tab signals continuation through the next non-empty line.
If
number
is omitted, 1 is assumed.
Option
-x
is forced.
- -ireplstr
-
Insert mode:
command
is executed for each line from standard input,
taking the entire line as a single arg, inserting it in
initial-arguments
for each occurrence of
replstr.
A maximum of 5 arguments in
initial-arguments
may each contain one or more instances of
replstr.
Blanks and tabs at the beginning of each line are thrown away.
Constructed arguments may not grow larger than 255 characters, and option
-x
is also forced.
{}
is assumed for
replstr
if not specified.
- -nnumber
-
Execute
command
using as many standard input arguments as possible, up to
number
arguments maximum.
Fewer arguments will be used if their total size is greater than
size
characters, and for the last invocation if there are fewer than
number
arguments remaining.
If option
-x
is also coded, each
number
arguments must fit in the
size
limitation, else
xargs
terminates execution.
- -t
-
Trace mode: The
command
and each constructed argument list are echoed to file descriptor 2
just prior to their execution.
- -p
-
Prompt mode: The user is asked whether to execute
command
each invocation. Trace mode (-t) is turned on to print the command instance to be executed,
followed by a ?... prompt.
A reply of
y
(optionally followed by anything) will execute the command; anything else, including
just a carriage return, skips that particular invocation of
command.
- -x
-
Causes
xargs
to terminate if any argument list would be greater than
size
characters;
-x
is forced by the options
-i
and
-l.
When neither of the options
-i,
-l,
or
-n
are coded, the total length of all arguments must be within the
size
limit.
- -ssize
-
The maximum total size of each argument list is set to
size
characters;
size
must be a positive integer less than or equal to 470. If
-s
is not coded, 470 is taken as the default.
Note that the character count for
size
includes one extra character for each argument and the count of characters in the command name.
- -eeofstr
-
eofstr
is taken as the logical end-of-file string.
Underbar (_) is assumed for
the logical EOF string
if -e is not coded.
The value
-e with no
eofstr
coded turns off the logical EOF string capability
(underbar is taken literally).
xargs
reads standard input until either end-of-file or the logical EOF string is encountered.
EXAMPLES
The following will move all files from directory
$1
to directory
$2,
and echo each move command just before doing it:
-
ls $1 | xargs -i -t mv $1/{} $2/{}
The following will combine the output of the parenthesized commands onto one line,
which is then echoed to the end of file log:
-
(logname; date; echo $0 $*) | xargs >>log
The user is asked which files in the current directory are to be archived
and archives them into arch (1.) one at a time, or (2.) many at a time.
-
1. ls | xargs -p -l ar r arch
2. ls | xargs -p -l | xargs ar r arch
The following will execute
diff(1)
with successive
pairs of arguments originally typed as shell arguments:
-
echo $* | xargs -n2 diff
SEE ALSO
sh(1)
Index
- NAME
-
- SYNOPSIS
-
- DESCRIPTION
-
- OPTIONS
-
- EXAMPLES
-
- SEE ALSO
-
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