Perl is a very tried and true language, it 's been around since the late eighties, but PHP is maturing very quickly.
The biggest advantage of PHP over Perl is that PHP was designed for scripting for the web where Perl was designed to do a lot more and can because of this get very complicated. The flexibility / complexity of Perl makes it easier to write code that another author / coder has a hard time reading. PHP has a less confusing and stricter format without losing flexibility. PHP is easier to integrate into existing HTML than Perl. PHP has pretty much all the 'good' functionality of Perl: constructs, syntax and so on, without making it as complicated as Perl can be. Perl is a very tried and true language, it's been around since the late eighties, but PHP is maturing very quickly.