use strict;
use warnings;
use Tie::File;

# usage: perl script.pl [file1] [file2] [...]

foreach my $file (grep { -f } @ARGV) {

    tie my @file, 'Tie::File', $file
      or die "Can't tie into file $file: $!";

    my $regex = qr/\sSIL\s*\z/;

    foreach my $i (reverse 0 .. $#file) {
        if ($file[$i] =~ /$regex/) {
            1 while ($file[--$i] =~ /$regex/);
            print "$file[$i + 1]\n";
            $#file = $i + 1;
            last;
        }
    }

    untie @file;
}