I have a file with one column . How do I load this into a hash with one column .

Marshall already gave an example of a complete solution here. The only problem with Marshall's code is that it depends on Inline::Files to support the example.

You want to do more general file I/O. Please see Files and I/O in perlintro and some of the articles in the Input and Output section of the Monastery's Tutorials. After you take a look at these, please come back if you have any more questions.