Notepad++ is a free (as in “free speech” and also as in “free beer”) source code editor and Notepad replacement that supports several languages. Basically all Windows devs and power users should have it installed since it is small, fast and supports all kinds of neat tricks.
Quote from Wikipedia “A regular expression, regex or regexp (sometimes called a rational expression) is, in theoretical computer science and formal language theory, a sequence of characters that define a search pattern.”
How to combo Notepad++ and Regular expression
With Notepad++ you can use regexp e.g. in search patterns. So just open Search -> Find… and change Search Mode to Regular expression. Then input your pattern to Find what : field.
Find any number (e.g. 1023 or 7) ___
Find any of following: 909, 919, 929, 939, 949 or 959 ___
Find all words that only contain lowercase letters between a-z and have at least 5 chars ___
Find all words that only contain lowercase letters between a-z and have exactly 5 chars
Find also has nice Count button that you can use to count matches.