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A regular expression wildcard matches
more than one character in a string.

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While we've been using character sets
to match one than one character,

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there are shorter ways to
match some of these cases.

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For example, instead of using 0 through

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9 to match any numeral, use the \d.

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The backslash is found often
in regular expressions, but

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its meaning can differ,
according to where it's used.

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Usually it's a way to say that
the character that follows has a special

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meaning.

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In this case,
it means that the d Isn't the letter d,

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but a special instruction
to match a numeral.

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And even though there are two
characters there, a backslash and

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a d, the parser treats this
as a single character.

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To match all alphanumeric characters
as well as an underscore, use \w.

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This can be handy for
matching what's known as word characters.

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The reason underscore is included is
that it's often used to space words

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out that can't actually have
a space character in them.

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For example, some file systems won't
let you use spaces in file names,

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so it's become common practice
to use underscores instead.

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To match whitespace characters,
you can use \s.

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In addition to the space,
this wildcard includes other kinds

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of whitespace, a tab and
a few kinds of line returns.

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If you want to know more about
these special characters,

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check the Teacher's Notes.

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But for now, just think of the \s
as a way to match whitespace,

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such as spaces, tabs, and new lines.

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Also, the period or
dot matches any character.

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Let's try some of these out.

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Let's use a digit character shorthand
in place of the first set, \d.

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Now any digit will be matched, but
we lost the match we had for the letter a.

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We could match that by using
a word shorthand, like this.

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Now any letter or digit will match.

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I'll change this first line to use
a capital A, and it still matches.

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Note that an underscore will also match.

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Often when you're composing regex, you'll
want to control what you include though.

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While the shorthand will often work,
you might find yourself going with

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something more limiting,
like we had before.

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We'll use \da, but
we'll put these in a character set.

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Now the top string is no longer
matched because it's an underscore.

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But if I change it back to an a,
the first two lines are matched.

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I'll replace this space with a \s.

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Now notice, if I add an 8 and
then a space,

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and then change the second space to a tab,

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the string still matches.

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I'll add a 3 to the next line, And

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instead of a space,
I'll create a new line by typing Enter.

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See how the color carries over?

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So these two lines are one match now.

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Let's use the dot.

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I'll replace the s with a dot.

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All the same matches are still
there because the dot will

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match any character at all.

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Let's change one of these s's to be
an exclamation point, for example.

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It's a match, or maybe a dollar sign.

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As you can see,
the dot is a powerful character in regex.

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You'll see it used in a lot
of examples around the web.

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Remember that the question mark
matches zero or one character.

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In other words, the character is optional.

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I'll show you another example where
you might use this in a new tab.

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You could use the question mark
to match both the American and

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the British spellings of the word,
like color.

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Check the notes for
some additional practice.

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In the next video, I'll show you
how to match repeating characters.