Add space after commas only if it doesn't already?

Question

Is there a way to add a space after commas in a string only if it doesn\'t exist.

Example:

word word,word,word,

Would end up as

Answer 1

Add missing space:

 "word word,word,word,".gsub(/,(?=\w)/, ', ') # "word word, word, word,"

and removing the last unnecessary comma if necessary

"word word,word,word,".gsub(/,(?=\w)/, ', ').sub(/,\Z/, '') # "word word, word, word"