my $data = do { local (@ARGV, $/) = $filename; <> };

##</code><code>##

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

    my $file = shift
        or die "Usage: $0 file2 < another-file";
    my $file_contents = do { local (@ARGV, $/) = $file; <> };
    my $nets = join "|", map {chomp;$_} $file_contents;

    /$nets/
        or print
      while <STDIN>;