Your Ruby snippet is slower for two reasons: - IO.foreach is lazy, but then you call `Array#grep` on it which allocate a huge Array - `grep` populate the "

Your Ruby snippet is slower for two reasons: - IO.foreach is lazy, but then you call `Array#grep` on it which allocate a huge Array - `grep` populate the "last_match" object, `String#match?` is much faster. Try rifraf's snippet: https://news.ycombinator.com/item?id=24597067 https://news.ycombinator.com/item?id=24597067, it should be as fast as Python.