Ruby String#tr allows you to replace characters or patterns in strings:
irb(main):001:0> "I love coffee".tr("love", "😍")
=> "I 😍😍😍😍 c😍ff😍😍"
Compare with #gsub:
irb(main):001:0> "I love coffee".gsub("love", "😍")
=> "I 😍 coffee"
If your pattern arg to gsub is only one character consider using #tr, but beware of multi-length from_str arg to #tr