do 'stat.pl';

is just like

    eval `cat stat.pl`;

except that it's more efficient, more concise, keeps track of the current filename for error messages, and searches all the -I libraries if the file isn't in the current directory (see also the @INC array in Predefined Names). It's the same, however, in that it does reparse the file every time you call it, so you probably don't want to do this inside a loop.

Note that inclusion of library modules is better done with the use() and require() operators, which also do error checking and raise an exception if there's a problem.