How gsub works in ruby with meta characters in input

Question

I need help in understanding how the following works.

"middl'-.*$%ddlemiddlemiddlemiddlemiddlemiddlemiExcess".gsub(/[^a-zA-Z'-.]/, '')
# => "middl'-.*ddlemiddlemiddlemiddlemiddlemiddlemiExcess"

"middl'-.*$%ddlemiddlemiddlemiddlemiddlemiddlemiExcess".gsub(/[^a-zA-Z.'-]/, '')
# => "middl'-.ddlemiddlemiddlemiddlemiddlemiddlemiExcess"

When I give /[^a-zA-Z'-.]/ , then the star is not removed, but in the second example, the star is removed. Why?

I want the result after gsub to have only letters ( a-zA-Z ), period ( . ), hypen ( - ), single apostphe ( ' ) to exist. Just by changing the period position inside regular expression the output is different ?

Answer 1

In /[^a-zA-Z'-.]/ hyphen is treated as range delimiter, exactly as in AZ before. The range is:

▶ ("'"..'.').to_a
#⇒ ["'", "(", ")", "*", "+", ",", "-", "."] # note asterisk

In /[^a-zA-Z.'-]/ hyphen is the last symbol and hence it is treated as hyphen itself.