string = 'This is a 30-character string.'
if string =~ /([0-9]+)-character/ and $1.to_i == string.length
  "Yes, there are #$1 characters in that string."
end

match = Regexp.compile('([0-9]+)-character').match(string)
if match && match[1].to_i == string.length
  "Yes, there are #{match[1]} characters in that string."
end

string = "123"
case string
when /^[a-zA-Z]+$/
  "Letters"
when /^[0-9]+$/
  "Numbers"
else
  "Mixed"
end

/something/
Regexp.new("something")
Regexp.compile("something")
%r{something}
/something/mxi
Regexp.new('something', 
           Regexp::EXTENDED + Regexp::IGNORECASE + Regexp::MULTILINE)
%r{something}mxi
case_insensitive = /mangy/i
case_insensitive =~ "I'm mangy!"

case_insensitive =~ "Mangy Jones, at your service."

multiline = /a.b/m
multiline =~ "banana\nbanana"

/a.b/ =~ "banana\nbanana"

/a\nb/ =~ "banana\nbanana"

extended = %r{ \ was # Match " was"
               \s    # Match one whitespace character
                a    # Match "a" }xi
extended =~ "What was Alfred doing here?"

extended =~ "My, that was a yummy mango."

extended =~ "It was\n\n\na fool's errand"