I've installed PHP 5.4 with MacPorts, using all the ports I had on my current PHP 5.3.
I then (foolishly) ran the command sudo port select --set php php54 and received Selecting 'php54' for 'php' succeeded. 'php54' is now active.
However, I couldn't run any of my current PHP pages, receiving a 'Forbidden' error from Apache. I decided to switch back to 5.3, and ran sudo port select --set php php5 only to receive Selecting 'php5' for 'php' failed: The specified version 'php5' is not valid.. I tried the same with php53 - and got the same message.
To verify what's installed I ran port installed php* and got:
php5 @5.3.28_0+apache2+pear (active)
php5-apc @3.1.9_1 (active)
php5-curl @5.3.28_0 (active)
php5-iconv @5.3.28_0 (active)
php5-mbstring @5.3.28_0 (active)
php5-mcrypt @5.3.28_0 (active)
php5-memcache @2.2.7_0 (active)
php5-mysql @5.3.28_0+mysqlnd (active)
php5-openssl @5.3.28_0 (active)
php5-xdebug @2.2.5_0 (active)
php54 @5.4.30_0+libedit (active)
php54-apache2handler @5.4.30_0 (active)
php54-APC @3.1.13_0 (active)
php54-curl @5.4.30_0 (active)
php54-iconv @5.4.30_0 (active)
php54-mbstring @5.4.30_0 (active)
php54-mcrypt @5.4.30_0 (active)
php54-memcache @2.2.7_0 (active)
php54-mysql @5.4.30_0+mysqlnd (active)
php54-openssl @5.4.30_0 (active)
php54-xdebug @2.2.5_0 (active)
php_select @1.0_0 (active)
So, there are 2 version of PHP installed. How do I switch back to PHP 5.3? And why is running 5.4 encounters a permissions issue?
Well, I haven't been able to revert to 5.3. I ended up fixing the access rights error, and I'm currently using 5.4. Fortunately, it's backwards compatible (at least, I have not hit on anything significant yet).
Bottom line - be careful with Ports activations - there may be no (known) going back.