What are "steps" in RegexBuddy?

Question

RegexBuddy on the tab "Debug" shows how regular expressions are executed step by step. But what exactly that steps mean? What operations are behind every step?

Answer 1

The steps count is basically how many times the current position in the input was changed, which is a very good indicator of performance.

The "current position" may be at any character or between characters (including before and after the entire input).

Simplifying it, regex engines process the input by moving the current position along the input and evaluating whether the regex matches at that position. They also keep track of the position in the regex the match is up to.

I don't want to turn this answer into a regex tutorial, but... regex engines always consume as much of the input as possible while still matching. To give a simple example, given the input "12345" and the regex .*1.*, the regex engine will first apply .* consuming all input leaving the position at the end of the input, fail to match a 1, then back track by "uncomsuming" one character at a time until it finds a 1, then continue. You can see that this would take 9 steps just to process the initial .*.

By contrast, if the regex was [^1]*1.*, the regex will match the "1" in just one step.