So with the code underneath I am trying to match FirstName, LastName and Email in both FILE and QR to extract the BirthDate that way and paste it into FILE.

This question would not be here if it worked... Apparently $firstname, $lastname and $email need to be defined in the sub fetchBD. But if you look at the main piece of code, these 3 are defined by the time this sub gets called, so I don't understand why this is an issue.

I am not used to using subroutines, so it just might be a bad choice to throw them in, it just seemed to me that is would be the easiest way of doing what I'm supposed to do. Definitely feel free to disagree here and all tips are welcome.

2 notes that are less important:

1. use of index() and substr() are to my knowledge the safest way to fetch a specific string if it is surrounded by a known constant, any tips on easier / cleaner-looking ways are of course welcome.

2. the use of a triple 'if'-block seems to me the safest way to make sure all 3 strings are matched from the same FILE and from the same QR-line. Again, any tips on easier / cleaner-looking ways are of course welcome.

use strict; # because we should
use warnings; # because we should
use autodie; # die if problem reading or writing a file

my $base = 'D:/Some/Specific/Folder';

open (QR, '<', $oldqr);

for my $file (glob qq($base/ToUpload/Staging/*)) {
    open FILE,'+<',$file;
    binmode (FILE);
    while (my $line = <FILE>){
        my $firstname = getFN();
        my $lastname = getLN();
        my $email = getEM();
        if ($line =~ /<birthdate>/) {
            my $bdate = fetchBD();
            print FILE '      <birthdate>'.$bdate.'</birthdate>';
        }
    }
}

close QR;

sub fetchBD {
    while (my $line = <QR>){
        my $fns = index($line,'FirstName');
        $fns += 10;
        my $fne = index($line,'    LastName');
        my $fnl = $fne - $fns;
        my $fn = substr($line,$fns,$fnl);
        my $lns = index($line,'LastName');
        $lns += 10;
        my $lne = index($line,'    Email');
        my $lnl = $lne - $lns;
        my $ln = substr($line,$lns,$lnl);
        my $ems = index($line,'    Email    ');
        $ems += 7;
        my $eme = index($line,'    BirthDate');
        my $eml = $eme - $ems;
        my $em = substr($line,$ems,$eml);

        if ($fn = $firstname) {
            if ($ln = $lastname) {
                if ($em = $email) {
                    my $bdates = index($line,'    BirthDate    ');
                    $bdates += 11;
                    my $bdate = substr($line,$bdates,10);

                    return $bdate;
                }
            }
        }
    }
}

sub getFN{
    while (my $line = <FILE>){
        if ($line =~ /<firstname>/) {
            my $fnse = index($line,'<firstname>');
            $fnse += 11;
            my $fnen = index($line,'</firstname>');
            my $fnlo = $fnen - $fnse;
            my $firstname = substr($line,$fnse,$fnlo);

            return $firstname;
        }
    }
}

sub getLN{
    while (my $line = <FILE>){
        if ($line =~ /<name>/) {
            my $lnse = index($line,'<name>');
            $lnse += 6;
            my $lnen = index($line,'</name>');
            my $lnlo = $lnen - $lnse;
            my $lastname = substr($line,$lnse,$lnlo);

            return $lastname;
        }
    }
}

sub getEM{
    while (my $line = <FILE>){
        if ($line =~ /<email>/) {
            my $emse = index($line,'<email>');
            $emse += 7;
            my $emen = index($line,'</email>');
            my $emlo = $emen - $emse;
            my $email = substr($line,$emse,$emlo);

            return $email;
        }
    }
}
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I am sure I'm missing something crucial here, but I'm having a hard time to keeping track of what I'm actually doing with this code.