I'd look at $login and $quotedLogin. When perl encounters that warning at some point later in an elsif ladder, it'll report it as happening on the line where the if starts it all, even if it's much later.

Updated with an example:

my $def1 = 'true';
my $def2 = 'foo';
my $def3 = 'blue';
my $undef1;

if ( $def1 =~ /X/ ) {   # <-- problem reported here
    print 'not here';
}
elsif ( $def2 =~ /Y/ ) {
    print 'not here either';
}
elsif ( $undef1 =~ /$def3/ ) { # <-- problem exists here
    print 'oh noes';
}
else {
    print "happiness ensues\n";
}
[download]