use strict;
use warnings;
use Carp qw(croak);
{
    my $input_file = "input_file.txt";
    my @lines = slurp($input_file);
    for my $line (@lines){
        my ($filename, $ligand) = split(/\t/, $line);
        open(FILE, '<', $filename) or die "Cannot open file: $!";
        while (my $line = <FILE>) {
            print $line if $line =~ /$ligand/;
        }
        close(FILE);
    }   
}

##Slurps a file into a list
sub slurp {
    my ($file) = @_;
    my (@data, @data_chomped);
    open IN, "<", $file or croak "can't open $file\n";
    @data = <IN>;
    for my $line (@data){
        chomp($line);
        push (@data_chomped, $line);
    }
    close IN;
    return (@data_chomped);
}