For a long time CentOS 5 users have been banging their head against their desks because CentOS 5 has only supported OpenLDAP 2.3.  While this release has been stable, it is quite long in the tooth and is missing many features that system administrator consider a 'requirement.'  Since so many packages link the ldap libraries that OpenLDAP 2.3 provides, upgrading OpenLDAP has been no easy task... until now. 

Here is a POSIX compliant regular expression for testing a hostname.  This does not support a fully quilified domain name (FQDN).  This was tested with linux grep. 

'^([[:digit:]a-zA-Z]([-[:digit:]a-zA-Z]{0,61}[[:digit:]a-zA-Z]){0,1})$'

Here is a working example:

grep -E -i -w '^([[:digit:]a-zA-Z]([-[:digit:]a-zA-Z]{0,61}[[:digit:]a-zA-Z]){0,1})$'

Here is a easy little script to get the IP of a specific interface.  It supports both IPv4 and IPv6. 

Great software dependancy checker for windows.

The official PHP project webpage.  It is also a great source of documentation.