Unlike Windows, Linux doesn't use extensions to control function. So a perl script can be .pl, .c, .sql or nothing at all. What is important is that the script have permission to execute (see man chmod if you need help here) and that the first line point to the perl interpreter. So you will usually see the first line have something like:
That indicates that the script needs to be interpreted by perl. Now if you want to use extensions so that you know what the file is, go ahead. It just doesn't make any difference to how the program is run. The same will go for SQLPlus. I can't imagine that it gives a hoot what extenstion the file has as long as the contents are SQL.
When exiting sql to use perl do I use similar tags to php such as
You're going to have to do some serious reading here. Usually I do things the other way around, I have a perl program running that then executes SQL code. I'm not sure that SQLplus has the ability to escape, run a perl program, then return to running SQL, however I may be wrong about that.