xargs(1) (User Environment Utilities) 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 contiguous
strings of characters delimited by one or more blanks, tabs, or new-
lines; 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
(\) 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 continuously 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 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
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xargs(1) (User Environment Utilities) xargs(1)
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 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) 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 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.
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.
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xargs(1) (User Environment Utilities) xargs(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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