make the cp/mv modification more robust

make the cp/mv modification more robust

this makes it so that if the cp/mv commands are changed the in the
future, it will continue to work reliably instead of having hardcoded
indexes to modify the array.

the `#ifdef __linux__` is also removed, compilers should be smart enough
to see that PROGRESS_{CP,MV} are unused (on non-linux systems) and
optimize it out.