REQUEST_URI RewriteCond Syntax - regex

Question

I am sure I am doing something silly here, but I can't seem to figure out what it is.
I can't understand why the RewriteCond for the {REQUEST_URI} isn't evaluating to true and thus preventing the RewriteRule from firing. Instead, given the following url, the rule fires and the user is always taken to https://www.diffsite.com.
Any help would really be appreciated - and thanks in advance.
url:
http://www.regularsite.com/page-name/
.htaccess code:
# Use PHP5.4 as default
AddHandler application/x-httpd-php54 .php
# BEGIN WordPress
<IfModule mod_rewrite.c>
RewriteEngine On
RewriteBase /
RewriteCond %{HTTP_USER_AGENT} (iphone|ipod|android|symbian|windows\phone|blackberry|iemobile|opera\ mobile|palmos|webos|googlebot-mobile) [NC]
RewriteCond %{REQUEST_URI} !^page-name/ [NC]
RewriteRule ^(.*)$ https://www.diffsite.com/ [L,R=302]
RewriteRule ^index\.php$ - [L]
RewriteCond %{REQUEST_FILENAME} !-f
RewriteCond %{REQUEST_FILENAME} !-d
RewriteRule . /index.php [L]
</IfModule>
# END WordPress

Answer 1

%{REQUEST_URI} always matches a URI that starts with leading forward slash / so this will work for you:
RewriteCond %{REQUEST_URI} !^/page-name/ [NC]
However in your rule RewriteCond %{REQUEST_URI} is not even needed as you can do this negation in RewriteRule itself:
RewriteCond %{HTTP_USER_AGENT} (iphone|ipod|android|symbian|windows\phone|blackberry|iemobile|opera\ mobile|palmos|webos|googlebot-mobile) [NC]
RewriteRule !^page-name/ https://www.diffsite.com/ [NC,L,R=302]
Not that inside .htaccess leading slash is not matched in RewriteRule.