Name: 學習正則表達式(Regex)--初學者速成班。 (Learn Regular Expressions (Regex) - Crash Course for Beginners)
Uploaded: 2021-01-14T10:21:50.000Z
Duration: 45 min 38 s
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hello and welcome to this course on regular expressions.

to 不定詞

Regular expressions or rejects define a search pattern that could be used to search for things in a string.

動名詞

Now this course focuses on using regular expressions in JavaScript.

However, almost everything you learn about regular expressions in this course can also apply.

If you're using regular expressions in another programming language, my name is Bo Kearns.

I will be teaching this course I'm with free Coke, camped out or GE.

In fact, this whole course is based on the free curriculum at Freak Oh camped out Warg.

It's not required to go through that curriculum to also do this course, but it could be helpful.

However, this course is designed to be stand alone.

But if you want to go through the curriculum on Freak, oh, camped out organs well, you can look in this picture where it has a row right to the regular expressions part of the curriculum, so you can see where that's at.

Regular expressions are used in programming languages to match parts of strings.

You create patterns to help you do that matching So, for instance, if you have the sentence the dog chased the cat and you want to match the word the you can use This rejects here.

You can see that there's a slash in the word the in another slash You will also notice that quote marks are not required within the regular expression.

So JavaScript has multiple ways to use Reg X is one way is to test the rejects is to use the test method.

The test method takes the rejects, applies it to a string and then returns true or false, if the pattern matches something.

So in this example, we have the string Hello world.

We have this rejects and we have my rejects.

I'm gonna do dot test and then inside the parentheses I'm gonna put my string.

So we're going to see if my string contains this rejects, which is hello.

In this case, it will be true because hello world does contain the string.

So I'm gonna change this rejects instead of search.

One thing I wanna point out is that this is case sensitive.

So if I had a lower case W, then this would not match.

But since this starts with an uppercase W, I have to make the Rejects start with an uppercase w.

Also so there's a result the Waldo Reg IX dot test.

While Waldo is hiding, it's going to return.

True because it found Waldo in this sentence.

Rejects has an or operator, which is a single pipe character.

So in this example, let's say we want to try to match for multiple words instead of just a single word.

Let's say we want to match dog, cat, bird or fish.

So what I would do here is I'm going to change this.

I'll do dog and it'll put hype, which is just a straight line up and down.

So this is going to match any of these four words dog or cat war, bird or fish?

And since one of these words is in the sentence, this test is going to return true.

So far, all the reject says we looked at matched literal strings, so the case mattered.

If it was a capital letter that's completely different from a lower case letter.

You can match both cases using what is called a flag.

So let me show you how you would do that.

Let's say we have a free code camp and we'll see it's all lower case in here, but we want a match it no matter what the case.

So we want this to also match this where there's a Capital C and another capital C.

So just after the last slash, I'm just going to put an eye.

So now when it tests the string freak Oh, camp for the rejects, which is freak Ocampa, lower case, the result will be yes, because they will match.

So far, we have just checked if a pattern exists or not within a string.

But we can also extract the actual matches that we found with the match method.

So let's see how to extract the word coding from this string.

So we'll just change this to coating and then here will use the dot match Method match and then in the parentheses.

Will passion coding Reg X and then if we just run this, we'll see in the console coating because it's logging out.

This were coating out of the sentence and into the result variable, and it got logged.

So far, we've only extracted search patterns one time.

But it is also possible to search or extract a pattern more than once using the G flag.

When it matches this, it's on Lee going to return the first Repeat just this one.

But if we add the G flag after the slash here, it's going to find every single occurrence of the word.

So it's going to return an array with three elements and each element is gonna be the word.

Where says twinkle, twinkle, little star.

I want to match the word twinkle so I'll type and twinkle right here and you'll see that the first week was capitalized.

I'm gonna have to use a flag out to use the I flag, which makes it insensitive to case.

I'm also gonna add the G flag that's gonna match every single time Twinkle appears, so you can use to flags at once on the same rejects.

Now here, for the result is going to twinkle star dot match And then I'm going to pass in the star Reggie Dex.

Okay, now we'll log this and see what happens.

You can see twinkle, twinkle The first twinkle in the console is the Capital T and the second's a lower case because it matched the 1st 1 and the 2nd 1 and returned them both.

In Reg IX, a period is a wild card character.

We have these two strings up here, and the 1st 1 has the word hum.

You'll notice that these two words start with the same two letters h u.

This will match any word that starts with the characters H.

U and then then has a final character, which could be any character.

So if we look down here, we are going to take the first string Al Hama song and match it to our rejects, its going to return home.

And then when we take our second string bear hug and match it to our rejects, its going to return hug.

Let's have some fun with regular expressions, so I want to match the word fund.

But I also want this rejects to be able to match the word run son pond, non or bun, Basically any word that ends with you in and starts with another letter, so I'll change this rejects to dot u.

So when we run our Reg X and search this sentence for something that ends with you in, it should find fun.

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學習正則表達式(Regex)--初學者速成班。 (Learn Regular Expressions (Regex) - Crash Course for Beginners)

expression

pattern

period

trick