87% of the website using linux are using php. php is an open source programming language. although perl may be open source, php has way more support from developers.
you can also run PHP on windows system.
in the past, skeptics nay have asked, why should i learn php? today, php's popularity is enough to generate interest in learning php. php is a standard feature offered by most web hosting companies. but it is interesting to understand why so many people choose php over alternatives.

plus there are many website that offer free php support, since it is open source, many people share their knowledge, like us, at wallpaperama you can find many tutorials on PHP.