In USA, the phone numbers follow
a pattern. The pattern is like this:
When we ask the user to enter their
phone number, they can enter their
phone number in any of the following ways:
- 789-3459876
- 7893459876
- 786 345 9876
- 789.345.9876
The user will think that all of these
are correct ways to share the phone number.
But we want the phone number to match
a particular format.
Regular expressions can help
enforce that particular pattern.
If the user's pattern does not match
our format, then using regular expressions,
we can reject that data.
A regular expression starts with
/ and ends with /.
The following is a regular expression:
Here \d has a special meaning.
It stands for any digit.
Let's try to make use of it and the
meaning will become much clearer.
Let's say that we want to check
if a number is at least a three digit
number or not.
This is what we can do:
Ruby allows us to use =~
to check if a regular
expression is matching
with the word or not.
Let's see one more example.
This time, we want to see
if the zipcode 76981
is made up of at least five digits or not.