Heads up! To view this whole video, sign in with your Courses account or enroll in your free 7-day trial. Sign In Enroll
Preview
Start a free Courses trial
to watch this video
Character repetition is one of the more powerful features of regular expressions. Learn how to match repeated characters.
Code Snippet
Here's the serial numbers used in the video for easy copy and pasting:
E4763GHC
7896TOB3P
L0003
Practice
Copy both the Match and the Exclude set of test strings from each exercise below into a Regex tester like RegEx Pal or 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:
8 pieces
7 piece
6 pieces
5 pieces
4 pieces
Exclude:
A piece
A 12345
2 )
Match:
8 pieces
7 piece
6 pieces
5 pieces
4 pieces
2 pie slices
Exclude:
A piece
A 12345
3 )
Match:
1234
5678
84753
78930
Exclude:
abcde
abcde
power
bat!
4 )
Match:
123abc
333cats
821_Plants
769___
Exclude:
454!_Minutes
12statues
Related Discussions
Have questions about this video? Start a discussion with the community and Treehouse staff.
Sign upRelated Discussions
Have questions about this video? Start a discussion with the community and Treehouse staff.
Sign up
Often when constructing
a regular expression,
0:00
you'll need a way to handle
repeating characters.
0:03
For example, say you wanted to match
several spaces at the end of a line or
0:06
numbers ten or greater.
0:11
In other words, numbers with two or
more numerical characters.
0:13
Two regex characters you'll use often
are the asterisk and the plus symbol.
0:17
These two symbols both can
match more than one character.
0:22
However while the asterisk
can match zero or
0:26
more characters,
the plus matches at least one character.
0:29
For example, say you wanted
to match toy boat or toy car.
0:34
Both start with toy but end with
a different sequence of characters.
0:38
I'll start the regex with toy and
0:43
I can put a word character to
match any character that follows.
0:46
This will match the c in car or
the b in boat, but
0:51
to match the rest of either string,
I can use an asterisk.
0:55
The asterisk is saying, I want to
match zero or more word characters.
0:59
Notice how toy is also matched,
1:04
that's because there are zero word
characters after the y in toy.
1:06
To exclude toy from the matches,
we can use a plus instead.
1:11
A word character followed by a plus
matches one or more word characters.
1:15
In other words,
1:20
we're saying there has to be at least
one word character that follows toy.
1:21
And toy is now excluded from the matches.
1:26
There are also times when you want to
specify an exact number of characters,
1:29
like three digits in
a phone's area code or
1:34
the last four digits of a serial number.
1:37
You can be specific about how many
repetitions you want to accept
1:39
by using curly braces,
you can enter the number of repetitions.
1:43
Here the example matches
three repetitions.
1:47
By placing a comma after the three,
any repetition of three or
1:50
greater will be matched.
1:55
Putting a number after the comma will
bound the number of repetitions.
1:56
In this example, repetition
between three and five will match.
2:00
Let's see these in use.
2:05
Let's clear out these toy boat examples.
2:07
Let's match a US social
security number now.
2:10
Social security numbers have nine digits
and are formatted into three groups.
2:14
The first group has three digits.
2:19
The second has two.
2:22
And the last has four.
2:24
There separated by hyphens.
2:26
I'll enter a couple numbers now.
2:29
To avoid using real social security
numbers, I'll put zeros for
2:32
the first group.
2:36
Now I'll start building up
the regular expression.
2:38
I'll enter a digit
character to begin with.
2:41
I can repeat this with a plus.
2:44
Which you can see will freely match
all the groupings of numerals below.
2:47
Let's limit this to
exactly three characters
2:52
by replacing the plus with curly
braces and putting a three inside.
2:55
Now we're matching only the three
numeral sequences the parser can find.
3:00
If I put a hyphen after,
3:05
you can see there are only two occurences
of three digits followed by a hyphen.
3:08
Now, we can specify the rest of
the pattern by putting a \d with two
3:13
repetitions, and another one with four.
3:18
Now, if I delete a digit from one of these
numbers, the pattern fails to match.
3:25
Let's how to relax the number
of repetitions will accept.
3:31
Suppose there is a serial
number we want to match
3:35
that will always be between five and
nine characters.
3:37
And those characters can be letters or
numbers.
3:41
I'll just paste a few examples I
made up that follow this pattern.
3:44
You can type your own if you want or
copy and paste from the teacher's notes.
3:49
Because we want to match letters and
numbers, I'll use the word character and
3:54
follow it with an open curly bracket.
3:59
5,9 close curly.
4:01
Now, if I erase the 3 from the end of the
last number, there are four characters.
4:07
And the serial number won't be a match.
4:13
If I add a character to the second one,
there will be 10 characters and
4:16
we'll only get a partial match.
4:20
If I then erase the nine from the regex,
4:23
any serial number five characters or
more will be matched.
4:26
I'll just type a few more characters so
4:31
you can see they will all
be included in the match.
4:33
Get some practice with these in the
exercises in the teacher's notes below.
4:37
Next, let's look at how to match
anything except a specific character.
4:41
You need to sign up for Treehouse in order to download course files.
Sign upYou need to sign up for Treehouse in order to set up Workspace
Sign up