XARGS(1) XARGS(1)
xargs - construct argument list(s) and execute command
xargs [options] [ command [initial-arguments] ]
xargs constructs a command line consisting of the command and initial-
arguments 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. xargs 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.
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 one or more blanks, tabs, or newlines;
empty lines are always discarded. Blanks and tabs may be embedded
as part of an argument if 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
next character.
The generated command line length will be the sum of the size in bytes of
the command name and each argument treated as strings, including a null
byte terminator for each of these strings. The xargs command will limit
the command line length such that when the command line is invoked, the
combined 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.
-Lnumber command is executed for each non-empty 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 nonempty
line.
-l[number]
Same as -L, except: 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
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XARGS(1) XARGS(1)
line are ignored. Constructed arguments may not grow larger
than what the kernel ncargs value allows (the default as
shipped is 20480), including room for pointers. This may be
further reduced, depending on environment size and other
arguments), and option -x is forced.
-i[replstr]
Same as -I except that {} is assumed for replstr if omitted.
The -I and -i options are mutually exclusive; the last one
specified takes effect.
-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. In any case, a maximum of 1024 arguments
will be passed per command invocation. This is further reduced
by any extra command arguments given on the xargs command line.
If option -x is also coded, each number arguments must fit in
the size limitation, else xargs terminates execution. The -L,
-l and -n options are mutually exclusive; the last one
specified takes effect.
-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 Invoke command using as many standard input arguments as
possible yielding a command line length less than size (a
positive decimal integer) bytes. Fewer arguments will be used
if the total number of arguments (lines) exceeds that specified
by the -n (-L) option or end of file is encountered on standard
input before size bytes are accumulated. The maximum size
depends partly on the size of the environment, but is limited
to a maximum of the kernel value of ncargs (the default as
shipped is 20480), including room for pointers. If -s is not
coded, the maximum is taken as the default.
-Eeofstr Specify 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.
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XARGS(1) XARGS(1)
-e[eofstr]
Same as -E except that the option -e with no eofstr coded turns
off the logical EOF string capability (underbar is taken
literally).
Note: The -e, -i and -l take optional option-arguments that cannot be
separate arguments.
xargs will terminate if either it receives a return code of -1 from, or
if it cannot execute, command. When command is a shell program, it
should explicitly exit (see sh(1)) with an appropriate value to avoid
accidentally returning with -1.
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/{}
or
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
xargs exits with 0 when all invocations of command returned exit status
zero. xargs exits with 126 when the command specified was found but
could not be invoked. xargs exits with 127 when the command specified
could not be found.
sh(1).
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