String comparison inside a update_by_query api script

[djoobbani (Daryoush)]

I am performing a Update_by_query api and inside its script i need to do string comparison
of two different parameteres, similar to how u would do it with intgers:
So, i need to do something like this with string:
string str1 "ABC";
string str2 "abc";
if (str1 > str2)
OR
if (str1 < str2)
and so on.
I keep getting elastic: Error 400 (Bad Request): failed to execute script [type=illegal_argument_exception] when i use > or < characters? Please advice! Thanks!