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

Using negative lookahead to check no space after comma, then replace with comma and space.

print 'word word,word,word,'.gsub(/,(?![ ])/, ', ')