Topic 9 - Regular Expressions

Question 1

matches any single character except newline

Answer 1

.

Question 2

matches zero or more occurrence of the previous single character

Answer 2

*

Question 3

escape character

Answer 3

\

Question 4

matches the beginning of a line

Question 5

matches the end of a line

Answer 5

$

do not use $ with double quotes - problems with the shell

Question 6

-matches a single character in a set or range of characters

Answer 6

[..]

Eg: a[bc]
matches a string that has a followed by b or c
- combine […] with * to match repeated sets

Question 7

[^…]

Answer 7

matches the complement of whats inside the square brackets

Eg: [^a-zA-Z] will match a string that does not have any of the English letters

Question 8

\less-than-sign

Answer 8

matches the BEGINNING of a regular expression word

Question 9

>

Answer 9

matches the END of a regex word

Question 10

(….)

\n

Answer 10

• remembers a portion of regular expression

- recalls the remembered portion where n is a digit from 1 to 9

Question 11

X{m}

X{m,n}

Answer 11

• matches exactly m repeated of the one character regular expression X
• matches m to n repeats of X

Question 12

X{m,}

Answer 12

matches m or more repeats of X

Question 13

matches simply m or fewer repeats of X

Answer 13

X{,m}

Question 14

matches a string that has a $ before one digit

Answer 14

$\d

Question 15

matches any string that starts with The

Answer 15

^The

Question 16

matches a string that ends with end

Answer 16

end$

Question 17

Matches lines which only have the words:

The end

Answer 17

^The end$

Question 18

matches a string that has ab followed by one or more c

Answer 18

abc+

Question 19

matches a string that has ab followed by zero or more c

Answer 19

abc*

Question 20

matches a string that has ab followed by zero or one c

Answer 20

abc?

Question 21

matches a string that has ab followed by 2 c

ie: abcc

Answer 21

abc{2}

Question 22

What are the quantifier operators?

Answer 22

• ,+ ,? and {}

Question 23

matches a string that has ab followed by 2 or more c

Answer 23

abc{2,}

Question 24

matches a string that has ab followed by 2 up to 5 c

Answer 24

abc{2,5}

Question 25

matches a string that has a followed by zero or more

copies of the sequence bc

Answer 25

a(bc)*

Question 26

matches a string that has a followed by 2 up to 5
copies of the sequence bc
Eg: abcbc
abcbcbcbc

Answer 26

a(bc){2,5}

Question 27

What are the character classes?

Answer 27

\d \w \s and .

\d matches a single character that is a digit
\w matches a word character (alphanumeric character plus underscore)

\s matches a whitespace character (includes tabs and line breaks)
. matches any character

Question 28

Match a single digit

Answer 28

\d

Question 29

matches a single non-digit character

Answer 29

\D

Question 30

matches a single non-word character

Answer 30

\W

Question 31

matches a single non-space character

Answer 31

\S

Question 32

matches the same text that was

matched by the first capturing group

Answer 32

([abc])\1