Advanced (for me anyway) Regex stuff in the Ruby language that I often forget

ruby_advanced_regex_stuff.rb

ruby_regex

# Capture groups
if /(hello) (world)/ =~ "hello world"
  puts "#{$2} #{$1}" # => "world hello"
end

# Named groups
if /(?<domain>rubycademy)/ =~ 'https://www.rubycademy.com'
  puts domain # => "rubycademy"
end

# Named groups w/the match method
if projects = /(?<domain>rubycademy)/.match('https://www.rubycademy.com')
  puts projects['domain'] # => "rubycademy"
end

# Capture groups w/Back references

# the \1 refers to the first capture group which is (hello)
/(hello) \1/ =~ "hello hello" # => 0

# you can access capture groups outside of the regular expression by using back-references

# capture everything between an html/xml tag
html[/<(html)>(.+)<\/\1>/m, 2]
# the \1 back-reference to the first capture group (html)

# accessing the capture group outisde of the regex
# a regexp that is the substring to replace, it includes (http) & excludes the s ((?!s))
# the replacing string with a back-reference to the first capture group (http)
# (?!) is negative look ahead https://ruby-doc.org/core-2.7.2/Regexp.html#class-Regexp-label-Anchors
def to_https(url)
  url.gsub(/(?<scheme>http)(?!s)/, '\k<scheme>s')
end
# in the 2nd arg we use \k<label> to back-ref the named group in the pattern passed as 1st arg