General :: Use A Global Variable To Apply A Condition Within A Script

I'm trying to use a global variable to apply a condition within a script.

The idea is to use this variable set to e.g. 1 or 2 to run a different part of the script accordingly. I can set the global variable with e.g.

Code:
export WL0=1

run my part of script, increment it by 1 with e.g.

Code:
WL0=$((WL0+1))

but if I re-run the script my WL0 is still set to 1!

I've also tried to add an

export $WL0 at the very end of my script (after the math) but this doesn't change the global variable apparently.