Level 4: Extraction and cleanup · Exercise 57 of 88 · Free

File extensions

A regex exercise from Regexdrill. Solve it with a pattern box with live highlighting in your browser, checked against hidden test strings, and it is checked the moment you submit.

The task

Each line is a file name or a path. Capture the extension in group 1: the letters and digits after the last period, at the very end of the line. Lines that do not end in a period followed by letters or digits give no match.

What this exercise teaches

\.([A-Za-z0-9]+)$ works backwards from the end: the $ fixes the extension to the end of the line and the class keeps periods and slashes out of it. Without the $, the first period wins and archive.tar.gz gives tar.

A hint if you get stuck

Anchor the pattern to the end of the line with $. A class of letters and digits cannot contain another period, so the match has to start at the last one.