A small change gives the requested numerical file names: split -d1a 4 /path/to/input_file.txt subfile Still not exactly as specified since the names will be zero-padded but it keeps them sorting alphanumerically ... and that's probably better anyway.
OK, this ain't Perl but a one-liner is a one-liner.
Comment on Re^2: loop da loop chomp chomp loop chomp blurp oops