#!/usr/bin/perl
use strict;
use warnings;

my $i = 0;
my @out_files;
foreach ( qw( op0 op1 op2 op3 ) ) {
    unless ( open $out_files[ $i ], '>', $_ ) {
        die "Cannot open $_ for writing: $!\n";
    }
    $i++;
}

while ( <> ) {
    foreach my $out ( @out_files ) {
        print $out $_;
    }
}