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Groups

3:27 with Alena Holligan

Grouping characters allow you to apply modifications to multiple characters the way you have learned to do with single characters.

Teacher's Notes
Questions?
Video Transcript
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Google URLs

google.com
google.net
google.org

Practice

Copy both the Match and the Exclude set of test strings from each exercise below into 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.

1 )

Match:

img_01.jpg
img_02.png
img_03.gif
img_04.png
img_05.gif
img_06.jpg

Exclude:

mov_01.avi

2 )

Match:

projector
protractor
proctor

Exclude:

prospector

3 )

Match:

img_sm_01.jpg
img_01.jpg
img_sm_02.jpg
img_02.jpg
img_sm_03.jpg
img_03.jpg
img_sm_04.png
img_04.png

Exclude:

img.gif

4 )

Match:

www.github.com
github.com
www.teamtreehouse.com
teamtreehouse.com
api.github.com

Exclude:

jsfiddle.net
www.jsfiddle.net

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Most of the regex wildcards I've shown you are used to match single characters. 0:00

But what if you want to match groups of characters? 0:05

You can use parentheses to group parts of an expression together. 0:08

Let's look at how we can use grouping to avoid the repetition 0:13

in the regular expression from the last video. 0:17

If I put the three alternate expressions into a group,. 0:21

Like so, we can separate that part from the part of the expression that 0:32

matches the same characters space boat. 0:37

Now the grouped part of the expression can be thought of as one unit. 0:41

It matches one of the three possible substrings, toy, sail, or tug. 0:45

The test string still has to end with space boat to be matched though. 0:52

Here's a similar challenge, write an expression to match 0:57

google.com and google.net, but not google.org. 1:03

You can copy those three test strings from the teacher's notes. 1:08

Pause the video and give it a try, and then I'll show you how I did it. 1:16

Each string begins the same way, namely, google dot. 1:22

I'll start by typing that. 1:28

Then I can group com pipe net within parentheses. 1:30

That will match only the top two strings. 1:40

One thing to note though. 1:43

While this expression works for 1:44

these strings, that dot could get us into trouble. 1:45

Remember, it's a wildcard character, so it would match the dollar sign also. 1:49

If we want to specify that it only matches a dot, 1:56

we can add a backslash before the dot. 2:00

Now this backslash dot is considered by the parser to be a literal dot character. 2:07

You may have also wrapped the dot in square braces, which would also work. 2:13

Using a backslash is a little more concise though, so 2:18

I wanted to make sure that you knew about it. 2:22

Grouping lets us treat more complex patterns, like letters. 2:25

In other words, we can make them optional with a question mark or 2:30

allow repetitions with a plus or star, for example. 2:35

Let's add the string www.google.com. 2:39

To include this entire string in our match, 2:45

we could type www slash dot. 2:50

But putting a question mark after the dot will only make the dot optional. 2:54

In other words, wwwgoogle.com with no dot is a match. 3:00

We want everything before it to be optional as well, not just the dot. 3:08

If I group this pattern, the whole group becomes optional. 3:15

Try a few of the exercises in the teacher's notes for 3:21

more practice with groups. 3:24

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