Split will seperate $_ on whitespace if given no arguments,

#!/usr/bin/perl
# file:   foo.pl
# Usage:  ./foo.pl /path/to/data.d
use warnings;
use strict;

while (<>) {
    my ($foo, $bar, $baz) = split;
    # do stuff with them
}

# report results
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The empty spaceship op takes care of opening and reading files from @ARGV. If no files are given, it will read from STDIN until Ctrl-D or eof.