A regular expression wildcard matches more than one character in a string. 0:00 While we've been using character sets to match one than one character, 0:05 there are shorter ways to match some of these cases. 0:09 For example, instead of using 0 through 0:12 9 to match any numeral, use the \d. 0:17 The backslash is found often in regular expressions, but 0:22 its meaning can differ, according to where it's used. 0:25 Usually it's a way to say that the character that follows has a special 0:29 meaning. 0:33 In this case, it means that the d Isn't the letter d, 0:33 but a special instruction to match a numeral. 0:38 And even though there are two characters there, a backslash and 0:43 a d, the parser treats this as a single character. 0:48 To match all alphanumeric characters as well as an underscore, use \w. 0:52 This can be handy for matching what's known as word characters. 1:00 The reason underscore is included is that it's often used to space words 1:05 out that can't actually have a space character in them. 1:10 For example, some file systems won't let you use spaces in file names, 1:13 so it's become common practice to use underscores instead. 1:19 To match whitespace characters, you can use \s. 1:23 In addition to the space, this wildcard includes other kinds 1:28 of whitespace, a tab and a few kinds of line returns. 1:33 If you want to know more about these special characters, 1:37 check the Teacher's Notes. 1:40 But for now, just think of the \s as a way to match whitespace, 1:41 such as spaces, tabs, and new lines. 1:47 Also, the period or dot matches any character. 1:50 Let's try some of these out. 1:55 Let's use a digit character shorthand in place of the first set, \d. 1:58 Now any digit will be matched, but we lost the match we had for the letter a. 2:06 We could match that by using a word shorthand, like this. 2:12 Now any letter or digit will match. 2:18 I'll change this first line to use a capital A, and it still matches. 2:22 Note that an underscore will also match. 2:28 Often when you're composing regex, you'll want to control what you include though. 2:33 While the shorthand will often work, you might find yourself going with 2:39 something more limiting, like we had before. 2:43 We'll use \da, but we'll put these in a character set. 2:48 Now the top string is no longer matched because it's an underscore. 2:55 But if I change it back to an a, the first two lines are matched. 2:59 I'll replace this space with a \s. 3:03 Now notice, if I add an 8 and then a space, 3:08 and then change the second space to a tab, 3:13 the string still matches. 3:18 I'll add a 3 to the next line, And 3:21 instead of a space, I'll create a new line by typing Enter. 3:26 See how the color carries over? 3:31 So these two lines are one match now. 3:33 Let's use the dot. 3:36 I'll replace the s with a dot. 3:38 All the same matches are still there because the dot will 3:43 match any character at all. 3:46 Let's change one of these s's to be an exclamation point, for example. 3:48 It's a match, or maybe a dollar sign. 3:56 As you can see, the dot is a powerful character in regex. 4:00 You'll see it used in a lot of examples around the web. 4:04 Remember that the question mark matches zero or one character. 4:07 In other words, the character is optional. 4:12 I'll show you another example where you might use this in a new tab. 4:16 You could use the question mark to match both the American and 4:23 the British spellings of the word, like color. 4:27 Check the notes for some additional practice. 4:41 In the next video, I'll show you how to match repeating characters. 4:44