Regex

Question 1

Write a regular expression without the use of | which would match all of the three email addresses below:

foo@demo.net
bar.bar@test.co.uk
foobar@aqa.org

Answer 1

(([A-Za-z0-9][.])?[A-Za-z0-9][@][A-Za-z0-9][.][A-Za-z]([.][A-Za-z]*)?)

Accept other solutions which work.

Question 2

Explain the difference between lazy and greedy matching.

Answer 2

Lazy matching will attempt to match the pattern using the least amount of characters possible, stopping as soon as it has matched the pattern.

Greedy will attempt to match the pattern as much as it can, it will continue looking for more matches to the pattern even after it has matched the pattern.

Answer is correct as long as the following is stated:

Greedy means match longest possible string.

Lazy means match shortest possible string.

Question 3

What does . match in regex?

Answer 3

. will match any character except line breaks.

Question 4

What does regex stand for?

Answer 4

Regular expressions.

Question 5

What does \D match and give an example of when it could be used.

Answer 5

\D will match any character that is not a digit character (0-9).

It could be used to trim phone numbers of the extra jabber added to them when they were input by a user.
Any other example where it serves the purpose of finding non-digit characters is correct.

Question 6

Write a regular expression which matches the following:

a. b.c
d. e.f
g. h.i

but not the following:

1.2.3
x.y.z
A.B.C

Answer 6

([a-i].[a-i].[a-i])

Any other expression which work are accepted.
Emphasis on escaping the ..

Question 7

Explain the use of +.

Answer 7

Will match one or more of the preceding token. (Minimum of 1 match required)

Question 8

Which of the following would this regular expression match?

([test]{1}[0-9]*)

1) test1
2) 111
3) 90
4) test
5) 9test

Answer 8

1

4

Question 9

Write an expression which matches the following without the use of | or ..

+44 (987) 123 5555
+10 (999) 420 6860
+0 (44) 123 9999

Answer 9

(+[0-9]{1,2}\s(([0-9]{1,3}))\s[0-9]{1,3}\s[0-9]{4})

Question 10

What is tokenisation?

Answer 10

Extracting elements which constitute a format.

Question 11

What are some uses of regular expressions?

Answer 11

Password strength checker.
Basic translation engine.
Grammatical suggestion engine.
Compiler.
Spam checker.
Key word filtering/identification.