xargs(1) USER COMMANDS xargs(1)
NAME
xargs - construct argument list(s) and execute command
SYNOPSIS
xargs [ flags ] [ 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 flags specified.
command, which may be a shell file, is searched for, using
one's $PATH. If command is omitted, /usr/bin/echo is used.
Arguments read in from standard input are defined to be con-
tiguous strings of characters delimited by one or more
blanks, tabs, or new-lines; empty lines are always dis-
carded. Blanks and tabs may be embedded as part of an argu-
ment 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
(\) escapes the next character.
Each argument list is constructed starting with the
initial-arguments, followed by some number of arguments read
from standard input (Exception: see -i flag). Flags -i, -l,
and -n determine how arguments are selected for each command
invocation. When none of these flags are coded, the
initial-arguments are followed by arguments read continu-
ously from standard input until an internal buffer is full,
and then command is executed with the accumulated args.
This process is repeated until there are no more args. When
there are flag conflicts (e.g., -l vs. -n), the last flag
has precedence. Valid flags are:
-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 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
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xargs(1) USER COMMANDS xargs(1)
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 are 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 argu-
ments 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) executes 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 log-
ical EOF string if -e is not coded. The
value -e with no eofstr coded turns off the
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xargs(1) USER COMMANDS xargs(1)
logical EOF string capability (underbar is
taken literally). xargs reads standard input
until either end-of-file or the logical EOF
string is encountered.
xargs terminates 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.
EXAMPLES
The following examples moves 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 example combines 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 example executes diff"(1)" with successive
pairs of arguments originally typed as shell arguments:
echo $* | xargs -n2 diff
SEE ALSO
sh(1).
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