instr ( haystack , needle )
instr ( haystack , needle , start )
instr ( haystack , needle , start , caseinsensitive)

Check to see if the string needle is contained in the string haystack. If it is, then this function will return the index of starting character of the first place where needle occurs. Otherwise, this function will return 0. You may also specify an optional starting location for the search to begin start and a boolean value caseinsensitive to specify that the search will treat upper and lower case letters the same.

String indices begin at 1.

print instr("Hello", "lo")
print instr("101,222,333",",",5)

will display

4
8

0.9.6.55