How to redirect / convert any URL to lowercase?

To implement such redirect using mod_rewrite and .htaccess you need to use RewriteMap directive which cannot be placed in .htaccess -- only in server config / VirtualHost context. If you have such access:

1. Place this line inside <VirtualHost> block for your site:

RewriteMap lc int:tolower

2. Place this in your .htaccess:

RewriteCond %{REQUEST_URI} [A-Z]
RewriteRule . ${lc:%{REQUEST_URI}} [R=301,L]

This will redirect (301 Permanent Redirect) any URL that has at least 1 capital letter (Latin letters only) in path part of URL (query string is ignored) to the same but in lower case.

For example:

http://mydomain.com/myfolder-sample-URL.html
=> 
http://mydomain.com/myfolder-sample-url.html

http://mydomain.com/myfolder-sample-url.HTML
=> 
http://mydomain.com/myfolder-sample-url.html

but will do nothing for these URLs:

http://mydomain.com/myfolder-sample-url.html?say=MEOW
http://MYDOMAIN.com/myfolder-sample-url.html

If you want to restrict it to .html files only:

RewriteCond %{REQUEST_URI} [A-Z]
RewriteRule ^.+\.html$ ${lc:%{REQUEST_URI}} [NC,R=301,L]

---

Where to place: I would place it after domain name redirect rule:

RewriteEngine On

RewriteCond %{HTTP_HOST} ^domain\.com [NC]
RewriteRule (.*) http://mydomain.com/$1 [L,R=301]

RewriteCond %{REQUEST_URI} [A-Z]
RewriteRule . ${lc:%{REQUEST_URI}} [R=301,L]

# your other rules

---

I also recommend using rel="canonical" links:

<link rel="canonical" href="PROPER_URL_HERE" />

• http://www.google.com/support/webmasters/bin/answer.py?answer=139394
• http://googlewebmastercentral.blogspot.com/2009/02/specify-your-canonical.html

---

If you do not need redirect, but rather ability to serve the file regardless of the file name case (case insensitive file names), then you can use mod_spelling ( http://httpd.apache.org/docs/current/mod/mod_speling.html ) and CheckCaseOnly On directive.

Add this to the top of your .htaccess

SOURCE: Htaccess to Redirect Uppercase to Lowercase

RewriteEngine On
RewriteBase /

# If there are caps, set HASCAPS to true and skip next rule
RewriteRule [A-Z] - [E=HASCAPS:TRUE,S=1]

# Skip this entire section if no uppercase letters in requested URL
RewriteRule ![A-Z] - [S=28]

# Replace single occurance of CAP with cap, then process next Rule.
RewriteRule ^([^A]*)A(.*)$ $1a$2
RewriteRule ^([^B]*)B(.*)$ $1b$2
RewriteRule ^([^C]*)C(.*)$ $1c$2
RewriteRule ^([^D]*)D(.*)$ $1d$2
RewriteRule ^([^E]*)E(.*)$ $1e$2
RewriteRule ^([^F]*)F(.*)$ $1f$2
RewriteRule ^([^G]*)G(.*)$ $1g$2
RewriteRule ^([^H]*)H(.*)$ $1h$2
RewriteRule ^([^I]*)I(.*)$ $1i$2
RewriteRule ^([^J]*)J(.*)$ $1j$2
RewriteRule ^([^K]*)K(.*)$ $1k$2
RewriteRule ^([^L]*)L(.*)$ $1l$2
RewriteRule ^([^M]*)M(.*)$ $1m$2
RewriteRule ^([^N]*)N(.*)$ $1n$2
RewriteRule ^([^O]*)O(.*)$ $1o$2
RewriteRule ^([^P]*)P(.*)$ $1p$2
RewriteRule ^([^Q]*)Q(.*)$ $1q$2
RewriteRule ^([^R]*)R(.*)$ $1r$2
RewriteRule ^([^S]*)S(.*)$ $1s$2
RewriteRule ^([^T]*)T(.*)$ $1t$2
RewriteRule ^([^U]*)U(.*)$ $1u$2
RewriteRule ^([^V]*)V(.*)$ $1v$2
RewriteRule ^([^W]*)W(.*)$ $1w$2
RewriteRule ^([^X]*)X(.*)$ $1x$2
RewriteRule ^([^Y]*)Y(.*)$ $1y$2
RewriteRule ^([^Z]*)Z(.*)$ $1z$2

# If there are any uppercase letters, restart at very first RewriteRule in file.
RewriteRule [A-Z] - [N]

RewriteCond %{ENV:HASCAPS} TRUE
RewriteRule ^/?(.*) /$1 [R=301,L]

Alternatively your host may support mod_speling, in which if they do, you can use in the server config, virtual host, directory or within a .htaccess file, example below:

<IfModule mod_speling.c>
    CheckCaseOnly On
    CheckSpelling On
</IfModule>