Ok, I asked this earlier in the CB, but I think it was to hard to explain there, so im posting this nice question for your viewing pleasure. :) The main reason I post this question to you is not for sheer enjoyment, But to find other ways to do the same thing.

Anyway, let me start off by posting example code:

And the code:

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);
[download]

here is some sample data:

file1.txt

123
456
789
[download]

file2.txt

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
[download]

Output:

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
[download]

Thanks for the tips btw :)

What I am trying to do is take each string from file1.txt, and match it in file2.txt which populates @original. Once that is done I loop through @original and compare it back against file2.txt but this time I am comparing the right side of the split to the current line in file2.txt Then a final push to @gottem, just incase I need to use this list somewhere else.

This will allow me to catch all lines that match with 'string 1' or 'string 2' in file2.txt, because those are what I am going for, but there is no way to get the whole string out of file2.txt without some kind of moderate algorithm.

Like I said, I really would love to see some other ways to do this.

If you have any questions on need me to try to clarify/explain it more, just let me know. EDIT: It seems there is indeed an error in the output, there are some additional 'string 2's in there after 'string 5'. I am not sure how they got in there but hopefully you still see my idea, and can expand the horizon :D

I will tinker with it a little more and try to get the correct output, sorry for any confusion.

EDIT: Updated the post with sample data and output is expected.

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