I still get those particular operators confused.

Top tip: since you know that you fall victim to this (which is more than half the battle), don't write them as $mac2 = '' which is plausible, but instead like '' = $mac2 which is not. The latter is trapped at compile time. Then when you see the compiler errors you can replace the offending expression with the correct '' eq $mac2. Always put the literal value on the left side of the operator to prevent it being a plausible assignment. HTH.

(Edited for typo)