SSIS How to get part of a string by separator

Question

I need an SSIS expression to get the left part of a string before the separator, and then put the new string in a new column. I checked in derived column, it seems no such e

Answer 1

if SUBSTRING length param returns -1 then it results in error, "The length -1 is not valid for function "SUBSTRING". The length parameter cannot be negative. Change the length parameter to zero or a positive value."