Emacs has an interactive regex mode that shows matches as you type. To go into the mode, **M-x regexp-builder**.  Type **C-c C-q** to exit the mode. Watch out for escape characters.  Emacs requires you to escape `\`, so type `\\b` for `\b` Copy the following text into emacs and then **M-x regexp-builder** ``` Lots of Grey things 50 shades of Grey Earl Grey Tea Lady Grey Graybeard the pirate Greyhound buses "You're looking grey," he said. "That's the greyest greyhound I ever saw," said Earl Grey. Grey1: Dark Gray Grey35: Mid grey Grey44: Battleship grey Grey100: The colour of TV tuned to a dead channel ``` In regexp-builder, type - **Grey** to find all the Greys - **Gray** to find all the Grays - **Gr\[ae\]y** to find all the Greys and Grays - **\\\\bGray\\\\b** to find Gray on its on and not part of another word - **^Gray** to find lines beginning with Gray - **grey$** to find lines ending in grey - **grey\\\\(hound\\\\)?** to find all appearances of grey and greyhound - **grey\[0-9\]** to find all the shades of grey ending with a digit - **grey\[0-9\]\\\\{2\\\\}** to find all the shades of grey with exactly two digits Follow the link for some [[Regexp Exercises]] to try out Read more about Regexps at the [Emacs Wiki](http://www.emacswiki.org/emacs/RegularExpression)