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copied!<p>The following statement assigns empty string to <code>search</code> variable if <code>search</code> is not defined. </p> <pre><code>search = "" unless search </code></pre> <p>Had this assignment not be done, <code>Regexp.new</code> would have thrown an <code>TypeError</code> with message <code>no implicit conversion of nil into String</code>, or if search was not defined then <code>NameError</code> with message undefined local variable or method 'search'...</p> <p>In the following statement: </p> <pre><code>matched_games = games.grep(Regexp.new(search)) </code></pre> <p><code>games.grep(pattern)</code> returns an array of every element that matches the pattern. For further details please refer to <a href="http://ruby-doc.org/core-2.0/Enumerable.html#method-i-grep" rel="nofollow">grep</a>. <code>Regexp.new(search)</code> constructs a new regular expression from the supplied <code>search</code> variable which can either be a string or a regular expression pattern. Again, for further details please reference <a href="http://www.ruby-doc.org/core-2.0/Regexp.html#method-c-new" rel="nofollow">Regexp::new</a></p> <p>So say for example search is <code>""</code> (empty string), then <code>Regexp.new(search)</code> returns <code>//</code>, if search = 'Super Mario Bros.' then <code>Regexp.new(search)</code> returns <code>/Super Mario Bros./</code>.</p> <p>Now the pattern matching: </p> <pre><code># For search = "", or Regexp.new(search) = // matched_games = games.grep(Regexp.new(search)) Result: matched_games = ["Super Mario Bros.", "Contra", "Metroid", "Mega Man 2"] # For search = "Super Mario Bros.", or Regexp.new(search) = /Super Mario Bros./ matched_games = games.grep(Regexp.new(search)) Result: matched_games = ["Super Mario Bros."] # For search = "something", or Regexp.new(search) = /something/ matched_games = games.grep(Regexp.new(search)) Result: matched_games = [] </code></pre> <p>Hope this makes sense.</p>

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