use warnings;
use strict;

my $f1 = 'file1.txt';
my $f2 = 'file2.txt';

my @original;
my @gottem;

open( my $file1, '<', $f1 );

while ( my $line1 = (<$file1>) ) {
    next if ( $line1 =~ /^#/ );
    chomp($line1);

    open( my $file2, '<', $f2 );

    while ( my $line2 = (<$file2>) ) {
        next if ( $line2 =~ /^#/ );
        chomp($line2);
        my ( $leftside, $rightside ) = split( /\s/, $line2, 2 );
        if ( $line1 =~ $leftside ) {
            push( @original, $rightside );
        }
    }
}

# print "$_\n" for(@original);

for (@original) {
    open( my $file_2, '<', $f2 );
    while ( my $line_2 = (<$file_2>) ) {
        my ( $first, $last ) = split( /\s/, $line_2, 2 );
        if ( $last =~ $_ ) {
            push( @gottem, $line_2 );
        }
    }
}

print $_ for (@gottem);

##</code><code>##

123
456
789

##</code><code>##

123 string 1
111 string 1
script should skip this line
222 string 1
333 string 1
456 string 2
444 string 2
it should skip this line as well
555 string 2
666 string 2
789 string 3
777 string 3
also skipping this line too
888 string 3
999 string 3

##</code><code>##

123 string 1
111 string 1
222 string 1
333 string 1
456 string 2
444 string 2
555 string 2
666 string 2
789 string 3
777 string 3
888 string 3
999 string 3