So maybe because $2 from my previous regex is undef, $tmp2 becomes undef resulting in the warning.. this makes sense.

So to fix this would the 'best' solution to wrap my code in an if block:

if($tmp2){
  if($tmp2 =~ m/'/){ 
 ...
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You shouldn't be even using $2 if the match that was supposed to give it a value failed. You must rework your script's logic so that $2 is only being used if the match that loaded it succeeded.

In fact, it's dangerous to simply assume that if $2 is undefined if the previous match failed. Such is not always the case. It's even dangerous to assume anything about $2 unless you KNOW that the previous match succeeded. Take a look at the following contrived snippet:

use strict;
use warnings;

my $string = "Hello world!";

$string =~ m/(H\w+)\s(\w+)/; # This match succeeds.

print $2, "\n";

$string =~ /(\d)(\d)/;  # This match fails.

print $2, "\n";
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And the output is:

world
world
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This tells us that $2, which gains a value during the first match, retains that value even though the second match failed. In other words, even though you gave the possibility for $2 to gain a new value in the second match, it retained the original value because the second match failed.

That means that it is unreliable to just assume $2 is going to be undef if the most recent match failed, because it could possibly be holding some value from a previous pattern match.

Go back to the drawing board with regards to your program's logic. ;)

Now in regards to how to avoid an "undefined" warning, just check for definedness before doing anything with it. Please note, this solution is a stopgap measure, and won't fix the underlying bug in your script. I am providing this only because you essentially asked how to do something only if a scalar holds a defined value:

my $tmp2 = $var;  # Because of bad logic we don't know
                  # if $var is defined, thus don't know if
                  # $tmp2 is defined.

if ( defined( $tmp2 ) and $tmp2 =~ m/regex/ ) {
    # Do your stuff.
}
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Enjoy! I hope all this helps...