All these languages (Perl, Java, Python ...) started out as means of writing scripts — short programs for analyzing data, moving files around, and so on — long before the Web was conceived. Once you have been to the trouble of downloading, compiling, installing, and learning a particular language, it’s annoying not to be able to use it for odd jobs around the computer. At first sight, PHP seems disqualified because we have seen it built into HTML pages, but from Version 4.3 it is also capable of executing scripts from the command line. See http://www.php.net/manual/en/features.commandline.php.