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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.

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
  • 0:00

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

  • 0:05

    But what if you want to match groups of characters?

  • 0:08

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

  • 0:13

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

  • 0:17

    in the regular expression from the last video.

  • 0:21

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

  • 0:32

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

  • 0:37

    matches the same characters space boat.

  • 0:41

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

  • 0:45

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

  • 0:52

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

  • 0:57

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

  • 1:03

    google.com and google.net, but not google.org.

  • 1:08

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

  • 1:16

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

  • 1:22

    Each string begins the same way, namely, google dot.

  • 1:28

    I'll start by typing that.

  • 1:30

    Then I can group com pipe net within parentheses.

  • 1:40

    That will match only the top two strings.

  • 1:43

    One thing to note though.

  • 1:44

    While this expression works for

  • 1:45

    these strings, that dot could get us into trouble.

  • 1:49

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

  • 1:56

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

  • 2:00

    we can add a backslash before the dot.

  • 2:07

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

  • 2:13

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

  • 2:18

    Using a backslash is a little more concise though, so

  • 2:22

    I wanted to make sure that you knew about it.

  • 2:25

    Grouping lets us treat more complex patterns, like letters.

  • 2:30

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

  • 2:35

    allow repetitions with a plus or star, for example.

  • 2:39

    Let's add the string www.google.com.

  • 2:45

    To include this entire string in our match,

  • 2:50

    we could type www slash dot.

  • 2:54

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

  • 3:00

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

  • 3:08

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

  • 3:15

    If I group this pattern, the whole group becomes optional.

  • 3:21

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

  • 3:24

    more practice with groups.

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