MrChat,
The following code is a starting point. You need to modify it accordingly to your given situation (how to handle files of difference number of lines, duplicates, or preserving order for instance).

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

open(FILE1, '<', 'file1.txt') or die $!;
open(FILE2, '<', 'file2.txt') or die $!;
open(FILE3, '>', 'file3.txt') or die $!;

my %hash;
while ( <FILE1> ) {
    chomp;
    my $val = <FILE2>;
    chomp $val;
    $hash{ $_ } = $val;
}
print FILE3 "$_ = $hash{ $_ }\n" for keys %hash;
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