What is your problem ?

1. I can't open a file. open
2. I can't read lines in a file. perlop I/O Operators
3. I don't know what to do with a line. split
4. I don't know how to keep values somewhere. perldata perllol

Feel free to contact me to arrange payment...

#!/usr/bin/env perl
use Modern::Perl;

my @p;

open my $fd2, '<', 'INPUT_FILE2.TXT' or die $!;
while(<$fd2>){
    next if /#/ or ! /\w/;
    my( $p, $n ) = split;
    push @{$p[$n]}, $p;
}
close $fd2;

open my $fd1, '<', 'INPUT_FILE1.TXT' or die $!;
while(<$fd1>){
    next if /#/ or ! /\w/;
    my( $r, $n ) = split;
    say "reactant: $r, product: $_" for @{$p[$n]};
}
close $fd1;
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