A Regular Expression, or regex, or regexp, is used to match a pattern against a string. The literal constructors are /.../ and %r{...}. The other constructor is Regexp::new. Examples:

      /dog/.match('dogwalker')
      =>#<MatchData "dog">

      /dog/ =~ ('cat')
      =>nil
    
  

Note that we can use #match or =~ to test if it matches. But =~ will return nil or the position in the string it finds the match.

Some characters have to be "escaped" with a backslash because they have specific meanings in a regexp. Those characters are:

      { => \{
      } => \}
      ( => \(
      ) => \)
      [ etc.
      ]
      .
      ?
      +
      *
      Example:
      /1 \+ 2/.match('1 + 2')
      =>#<MatchData "1 + 2">
    
  

You can interpolate the match criteria like so:

      name = "Majd"
      /#{name}/.match("Hey, Majd")
      =>#<MatchData "Majd">
    
  

The following are different ways to check different criteria. Note the characters used:

      /[aeiou]/ => brackets check individual
          characters listed without commas
      /[0-9a-d]/ => hyphen checks a range
      /[^a-d]/ => caret checks if NOT in range

    
  

I think that's good for now. I haven't used these, so I don't want to add examples I don't yet understand. I may come back and add more to this, since I think it might be easier for me to read than RubyDocs (who am I kidding? RubyDocs is great!) In any event, I hope you enjoyed my little demo on RegExp.