But I want to avoid writing the whole path for destination directory and source directory each time I run the program. Is there a clever way to use the alias definitions in bash when calling my "dircopy"-program ?
(Example: dircopy $src $dst - or something similar...)
You could use environment variables. In C/C++ you can access your environment either by the envp to main or through the getenv call. For getenv you might do something similar to the following pseudocode:
for arg in argv:
if arg == '$':
char * variable = getenv(arg[1..-1])
You'd obviously need to add error checking to that but it should convey the process clear enough.