Add a use warnings; after your use strict. That should help with any oddities caused by your code.

Your tnsentry.txt file could be read into a hash of hashes by the looks of it to me. (See perldsc) You might take a look at some of the CPAN modules that read various text formats. Perhaps one of the Config::* modules. That might save you a bit of time having to write a parser for reading that file in. If nothing else, looking at the POD for a couple of them should give you some good ideas of how to write your own if you want or have to.

Hope that is helpful...

Update:Actually, it looks like DBD::Oracle has the ability to do what you want built right into the module. I have not worked with Oracle, but if your file is like This, the the above module looks like it will do what you want without you having to re-invent the wheel. Again, I have not worked with this, so take this with a grain of salt, or a pound...