add Searching for Substrings recipe to Regular Expressions

Author: phlipper

chapters/regular_expressions/searching-for-substrings.md

@@ -0,0 +1,63 @@
+---
+layout: recipe
+title: Searching for substrings
+chapter: Regular Expressions
+---
+## Problem
+
+You need to search for a substring, and return either the starting position of the match or the matching value itself.
+
+## Solution
+
+There are several ways to accomplish this using regular expressions. Some methods are called on a `RegExp` pattern or object and some are called on `String` objects.
+
+### `RegExp` objects
+
+The first way is to call the `test` method on a `RegExp` pattern or object. The `test` method returns a boolean value:
+
+{% highlight coffeescript %}
+match = /sample/.test("Sample text")
+# => false
+
+match = /sample/i.test("Sample text")
+# => true
+{% endhighlight %}
+
+The next way to is to call the `exec` method on a `RegExp` pattern or object. The `exec` method returns an array an array with the match information or `null`:
+
+{% highlight coffeescript %}
+match = /s(amp)le/i.exec "Sample text"
+# => [ 'Sample', 'amp', index: 0, input: 'Sample text' ]
+
+match = /s(amp)le/.exec "Sample text"
+# => null
+{% endhighlight %}
+
+### `String` objects
+
+The `match` method matches a given string with the `RegExp`. With 'g' flag returns an array containing the matches, without 'g' flag returns just the first match or if no match is found returns `null`.
+
+{% highlight coffeescript %}
+"Watch out for the rock!".match(/r?or?/g)
+# => [ 'o', 'or', 'ro' ]
+
+"Watch out for the rock!".match(/r?or?/)
+# => [ 'o', index: 6, input: 'Watch out for the rock!' ]
+
+"Watch out for the rock!".match(/ror/)
+# => null
+{% endhighlight %}
+
+The `search` method matches `RegExp` with string and returns the index of the beginning of the match if found, -1 if not.
+
+{% highlight coffeescript %}
+"Watch out for the rock!".search /for/
+# => 10
+
+"Watch out for the rock!".search /rof/
+# => -1
+{% endhighlight %}
+
+## Discussion
+
+Regular Expressions are a powerful way to test and match substrings.

wanted-recipes.md

@@ -84,9 +84,6 @@ foo 1, 2, 3
 
 ## Regular Expressions
 
-* Searching for substrings # "foo bar baz".match(/ba./) # => [ 'bar', index: 4, input: 'foo bar baz' ]
-* Searching for substrings # "foo bar baz".search(/ba./) # => 4
-
 ## Networking
 
 * Streaming HTTP server