Andy Chase

I'm a big fan of regular expressions - there's no better way to tweak many multiple instances of an HTML tag or attribute, or change a variable name across a bunch of PHP scripts.

Perl sets the standard, but Emacs also provides regex support quite nicely - the only thing is keeping the subtle differences straight. I'm committing this to the site so that I don't have to keep searching hundreds of Emacs mailing list archives the next time I forget.

When specifying a group or character class in an Emacs, you have to escape the container characters. Take the following Perl regex:

/foo (.*?) bar/

This will match any string that has the words 'foo' and 'bar' and extract the string between them. This is how to format it in Emacs:

foo \(.*?\) bar

If you want to use a backrefence in a regex find/replace, use the format

\n

where n is the matched group you want to substitute. So say you have a buffer containing

foo bat bar

and you did a search for

foo \(.*?\) bar

and replaced it with

foo bar \1

The contents of the buffer will now read

foo bar bat.

Read the Emacs manual page on regexps for more details.