See perlguts for more than you probably ever want to know. Under the hood an ordinary Scalar Value (SV) can be any one or more of an integer value (IV), a double (NV), a string (PV), and another scalar (SV). Conversions are made on demand so if you use a string as a number it gets converted to a number at that stage. If you only use it as a string it stays as a string. The bottom line is that part of the beauty of Perl is that you don't have to worry about the nitty gritty.