#! perl -slw
use strict;
use constant NFILES => 10;

my @fhs;
open $fhs[ $_ ], '>', 'output.' . $_
    or die $!
    for 0 .. NFILES - 1;

my $iFhs = 0;

while( <> ) {
    for my $word ( split '\W+' ) {
        print { $fhs[ $iFhs ] } $word;
        ++$iFhs;
        $iFhs %= NFILES ;
    }
}

close $_ for @fhs;