Provided by standard library.
FIND searches for a partial string within a string.
The input variable STR1 and STR2 are type STRING, the return value of the function is type STRING.
FIND(STR1, STR2) means: Find the position of the first character where STR2 appears in STR1 for the first time. If STR2 is not found in STR1, then OUT:=0.
Example in Function Block Diagram
Example in Structured Text
arINT1 := FIND ('abcdef','de');
String functions are not "thread safe": When using tasks, string functions may only be used in a single task. If the same function is used in different tasks, there is a danger of overwriting.