HTACCESS : RegEx match replace for URL

Question

I want the htaccess Redirect 301 to do the following using regex:

http://example.com/folder/abc_123_123.htm

to

http://example.com/abc-123-123.shtml

The 3 objectives of new URL are

• delete /folder/

• replace all _ with -

• replace htm with shtml

Answer 1

RewriteEngine On
RewriteBase /
RewriteRule ^folder/([a-z]+)_(\d+)_(\d+)\.htm$ http://example.com/$1-$2-$3.shtml [L,R=301]

Answer 2

Best I'm aware, your point #2 cannot be done without a RewriteMap, which requires some pesky configuration, or multiple rules.

This implementation should be generic and work for any number of underscores, but it's expensive in that it might trigger many redirect (in fact, potentially enough to fire redirect errors in browsers if you've tons of underscores in your paths):

RewriteBase /
RewriteRule ^(folder/[^_]*)_(.*\.html?)$ /$1-$2 [L,R=301]
RewriteRule ^folder/(*+)\.html?$ /$1.shtml [L,R=301]

Alternatives include enumerating use-cases as needed, or (better, I suspect) rewriting the request to a perl or php script and doing the regexp_replace + redirect 301 from there.

RewriteBase /
RewriteRule ^folder/(*+)\.html?$ /folder/redirect.php [L,QSA]