Named variables for regex captures
Inline instead of top-of-scope variable declarations
Lexical instead of global filehandles
3-argument open
File::Spec and File::Basename instead of string manipulation on file names
Only checks target directory existence once instead of over and over
No LABELs
Does not slurp the whole log file into memory
No nested output loop
30% (30 lines) shorter

(I almost didn’t publish this because of CC-BY.)