search for: 4_field2ndtry_0000

Dear all, I would like to search in a string for the second occurrence of a symbol and replace the symbol after it For example my strings look like sta_+1+0_field2ndtry_0000$01.cfg I want to find the digit that comes after the second +, in that case is zero and then over a loop create the strings below sta_+1+0_field2ndtry_0000$01.cfg sta_+1+1_field2ndtry_0000$01.cfg