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Beginning and Ending of Strings2:01 with Joel Kraft
It's important to be able to specify that a regular expression starts matching at the beginning of a string and match all the way to the end. Learn more in this video.
Copy both the Match and the Exclude set of test strings from each exercise below into a Regex tester like regexpal or regex101. Using what you've learned so far, create a regular expression that will match all of the strings in the Match set and exclude the ones in the Exclude set.
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Notice this string I typed in the last video, wwwgoogle.com. 0:00 Even though we've grouped the www dot together, 0:06 the regex is still finding a partial match in this test string. 0:09 As you can see, it does this by starting to match the pattern, 0:14 later in the string, at the fourth character. 0:18 We can see the opposite problem by typing another test string, 0:20 with extra characters at the end. 0:24 If we're trying to match Google.com, neither of these strings are valid. 0:28 We can tell the parser to only consider these a match if the entire string 0:33 fits our pattern, and to reject partial matches like these. 0:37 You will see these characters often in regex's. 0:42 They are very useful in ensuring, 0:45 you are only matching at the beginning or ending of a string. 0:47 While other regex characters have represented characters and 0:51 strings, these only represent location. 0:54 As I mentioned in the first video, 0:59 make sure you have this checked, match at line breaks. 1:01 This lets us treat each line as a separate test string rather than one block. 1:05 To tell the parser to only start matching at the beginning of test strings 1:10 I'll put a caret at the beginning of the regex. 1:15 You see, that excluded wwwgoogle.com because 1:19 if www is present, it must be followed by a dot. 1:24 Now to specify the string must end with net or 1:29 com, with only one m, I'll put a dollar sign at the end of the expression. 1:32 Now all of the valid strings are matched. 1:38 You'll probably use a carat and dollar sign often in your regular expressions to 1:41 eliminate strings that contain the pattern you're matching, but 1:46 as a whole would be considered invalid. 1:49 Find some additional practice in the teacher's notes below. 1:53 Next, let's start using everything we've learned in a real project. 1:56
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