Regular Expressions

Question 1

RegEx matches for

/[wW]oodchuck/

Answer 1

Woodchuck
woodchuck

Question 2

RegEx matches for

/[abc]/

Answer 2

‘a’, ‘b’, or ‘c’

Question 3

RegEx matches for

/[1234567890]/

Answer 3

any digit

Question 4

RegEx matches for

/[A-Z]/

Answer 4

An upper case letter

Question 5

RegEx matches for

/[a-z]/

Answer 5

A lower case letter

Question 6

RegEx matches for

/[0-9]/

Answer 6

A single digit

Question 7

RegEx matches for

/[^A-Z]/

Answer 7

Not an upper case letter

Question 8

RegEx matches for

/[^Ss]/

Answer 8

Neither ‘S’ nor ‘s’

Question 9

RegEx matches for

/[^.]/

Answer 9

not a period

Question 10

RegEx matches for

/[e^]/

Answer 10

either ‘e’ or ‘^’

Question 11

RegEx matches for

/a^b/

Answer 11

the pattern ‘a^b’

Question 12

RegEx matches for

/woodchucks?/

Answer 12

woodchuck or woodchucks

Question 13

RegEx matches for

/colou?r/

Answer 13

color or colour

Question 14

RegEx matches for

/beg.n/

Answer 14

any character between beg and n

Question 15

RegEx matches for

Answer 15

start of a line

Question 16

The three uses of the caret ^

Answer 16

• to matcht the start of a line
• to indicate a negation inside of square brackets
• just to mean a caret

Question 17

RegEx matches for

$

Answer 17

end of line

Question 18

RegEx matches for

\b

Answer 18

word boundary

Question 19

RegEx matches for

\B

Answer 19

non-word boundary

Question 20

Kleene *

“cleany star”

Answer 20

Zero or more occurrences of the immediately previous character or regular expression.

Question 21

Kleene +

Answer 21

One or more occurrences of the immediately preceding character or regular expression.

Question 22

Wildcard expression

.

Answer 22

Matches any single character (except a carriage return)

Question 23

Anchors

Answer 23

Special characters that anchor regular expressions to particular places in a string.

The most common anchors are the caret ^ and the dollar sign $.

^ matches the start of a line.
$ matches the end of a line
\b matches a word boundary
\B matches a non-word boundary

Question 24

Disjunction

Answer 24

the pipe symbol |

/cat|dog/ matches either cat or dog

Question 25

Precendence

Answer 25

Use parentheses ( and ) Enclosing a pattern in paretheses makes it act like a single character for the purposes of neighbouring operators like the pipe | and the Kleene*

Question 26

Operator precedence hierarchy

Answer 26

Parenthesis `()` Counters `*` `+` `?` `{}` Sequences and anchors `the` `^my` `end$` Disjunction **I** | In that order.

Question 27

# RegEx matches for \d

Answer 27

Any digit

Question 28

# RegEx matches for \D

Answer 28

Any non-digit

Question 29

# RegEx matches for \w

Answer 29

Any alphanumeric / underscore

Question 30

# RegEx matches for \W

Answer 30

A non-alphanumeric

Question 31

# RegEx matches for \s

Answer 31

Whitespace (space, tab)

Question 32

# RegEx matches for \S

Answer 32

Non-whitespace

Question 33

# RegEx matches for *

Answer 33

zero or more occurrences of the previous char or expression

Question 34

# RegEx matches for +

Answer 34

one or more occurrences of the previous char or expression

Question 35

# RegEx matches for ?

Answer 35

exactly zero or one occurrence of the previous char or expression

Question 36

# RegEx matches for {n}

Answer 36

*n* occurrences of the previous char or expression

Question 37

# RegEx matches for {n,m}

Answer 37

From *n* to *m* occurrences of the previous char or expression.

Question 38

# RegEx matches for {n,}

Answer 38

At least *n* occurrences of the previous char or expression.

Question 39

# RegEx matches for {,m}

Answer 39

up to *m* occurrences of the previous char or expression

Question 40

newline

Answer 40

\n

Question 41

tab

Answer 41

\t

Question 42

# RegEx matches for \*

Answer 42

An asterisk "*"

Question 43

# RegEx matches for \.

Answer 43

A period "."

Question 44

# RegEx matches for \?

Answer 44

A question mark

Question 45

# RegEx matches for \n

Answer 45

a newline

Question 46

# RegEx matches for \t

Answer 46

a tab

Question 47

Capture group

Answer 47

The use of parentheses to store a pattern in memory is called a **capture group**. Every time a capture group is used (i.e., parentheses surround a pattern), the resulting match is stored in a numbered **register**. If you match two different sets of parentheses, \2 means whatever matched the *second* capture group.

Question 48

non-capturing group

Answer 48

We might want to use parenthesis for grouping, but don't want to capture the resulting pattern in a register. In that case, we use a non-capturing group, which is specified by putting the commands ?: after the open paren, in the form `(?: pattern )`

Question 49

lookahead assertions

Answer 49

The operator `(?= pattern)` is true if `pattern` occurs, but is zero-width, i.e. the match pointer doesn't advance. The operator `(?! pattern)` only returns true if a pattern does not match, but again is zero-width and doesn't advance the curosor.