Question

What is the regular expression to get the position of the last separator character before a certain pattern?

For example, I have a string as follows

some value;some other value;some special XYZ value;some more special XYZ value

Here, the separator character is semicolon (“;”) and the pattern I am looking for is any string that contains “XYZ”.

The correct answer is this case is position 28, which is the last occurence of the separator character (“;”) before an element containing the match pattern (“XYZ”).

What would the regular expression look like?

Answer 1

;(?=[^;]*XYZ)

matches a semicolon that’s followed by XYZ within the same segment of the string.

Use it once to find the first occurrence. If you use it repeatedly, you’ll find the following occurrences, too.