Ok, I admit this is (very) basic but currently it make my head spin fast 
I have some variable like this (note: i dont want array even with array maybe it will be much simpler and easier, consider it's a flaw from the beginnning of design)
$key1="value1"
$key2="value2"
$key3="value3"
$key4="value4"
$key5="value5"
$key6="value6"
if $key1 = "" then set $condition = false and doesn't need to check other key anymore
if $key1<>"" and FileExists($key1) then $condition = true and pls check another key
if $key2<>"" and FileExists($key2) then $condition = true and pls check another key, but if $key2<>"" but NOT FileExists($key2) then $condition=false and do not need to check another key anymore.
if $key3<>"" and FileExists($key3) then $condition = true and pls check another key, but if $key3<>"" but NOT FileExists($key3) then $condition=false and do not need to check another key anymore.
<do that above until key6>
If NOT $condition then
...
EndIf
Thank you!