Ruby Sub vs. Gsub

A little Ruby distinction I had not seen (or remembered seeing) before.

In Ruby, both String#sub and String#gsub are methods used for string substitution, but they have a subtle difference:

String#sub: This method performs a substitution based on a regular expression pattern, replacing only the first occurrence that matches the pattern.

str = "hello world"
new_str = str.sub(/o/, "a")
puts new_str

Output: hella world

String#gsub: This method also performs a substitution based on a regular expression pattern, but it replaces all occurrences that match the pattern within the string.

str = "hello world"
new_str = str.gsub(/o/, "a")
puts new_str

Output: hella warld

Hat tip to ChatGPT, who answered this question for me.