• Regexes perform textual pattern matching
• Regexes ask:
  Does a string...
• ...contain the letters "dog" in order?
• ...not contain the letter "z"?
• ...begin with the letters "Y" or "y"?
• ...end with a question mark?
• ...contain only letters?
• ...contain only digits?

        my $string = "Did the fox jump over the dogs?";
        print "1: $string\n" if $string =~ /dog/;          # matches
        print "2: $string\n" if $string !~ /z/;            # matches
        print "3: $string\n" if $string =~ /^[Yy]/;
        print "4: $string\n" if $string =~ /\?$/;          # matches
        print "5: $string\n" if $string =~ /^[a-zA-Z]*$/;
        print "6: $string\n" if $string =~ /^\d*$/;