I have a bunch of paths and for each path I want to convert it from relative path to absolute path.

Have a look at Path::ExpandTilde. Note that the resulting path will be dependent on the system this function is being run on and the current username.

Update: Note the docs of File::Spec's rel2abs: "No checks against the filesystem are made." But if you don't mind going out to the filesystem, you can also use Cwd's abs_path.