Regular Expressions

Question 1

What does the regex operator ^ signify?

Answer 1

The ^ operator signifies the start of a line or string. It is used to match a pattern only if it appears at the beginning.

Question 2

What does the regex operator $ signify?

Answer 2

The $ operator signifies the end of a line or string. It is used to match a pattern only if it appears at the end.

Question 3

What does the regex operator . signify?

Answer 3

The . operator matches any single character except a newline. It acts as a wildcard in regex.

Question 4

What does the regex operator * signify?

Answer 4

The * operator matches zero or more occurrences of the preceding character or group. For example, a* matches ‘’, ‘a’, ‘aa’, etc.

Question 5

What is the function of the regex operator *?

Answer 5

The * operator matches zero or more occurrences of the preceding character or group. It allows for repetition, including none at all.

Question 6

What does the regex operator + signify?

Answer 6

The + operator matches one or more occurrences of the preceding character or group. For example, a+ matches ‘a’, ‘aa’, ‘aaa’, etc.

Question 7

What does the regex operator ? signify?

Answer 7

The ? operator matches zero or one occurrence of the preceding character or group. For example, colou?r matches both ‘color’ and ‘colour’.

Question 8

What does the regex operator [] signify?

Answer 8

Square brackets [] define a character set and match any one character within the set. For example, [abc] matches ‘a’, ‘b’, or ‘c’.

Question 9

What does the regex operator [^ ] do?

Answer 9

The [^ ] operator defines a negated character set and matches any character not in the set. For example, [^abc] matches any character except ‘a’, ‘b’, or ‘c’.

Question 10

What does the regex operator | signify?

Answer 10

The | operator acts as an OR condition and matches either pattern on its sides. For example, cat|dog matches ‘cat’ or ‘dog’.

Question 11

What does the regex operator () signify?

Answer 11

Parentheses () are used for grouping patterns. They allow regex operators to act on the entire group as a unit.

Question 12

What does the regex operator \d signify?

Answer 12

The \d operator matches any digit (0–9). It is equivalent to the character set [0-9].

Question 13

What does the regex operator \D signify?

Answer 13

The \D operator matches any non-digit character. It is equivalent to the negated set [^0-9].

Question 14

What does the regex operator \w signify?

Answer 14

The \w operator matches any word character (alphanumeric and underscore). It is equivalent to [a-zA-Z0-9_].

Question 15

What does the regex operator \W signify?

Answer 15

The \W operator matches any non-word character. It is equivalent to the negated set [^a-zA-Z0-9_].

Question 16

What does the regex operator \s signify?

Answer 16

The \s operator matches any whitespace character, such as spaces, tabs, or newlines.

Question 17

What does the regex operator \S signify?

Answer 17

The \S operator matches any non-whitespace character.

Question 18

What does the regex operator {n} signify?

Answer 18

The {n} operator matches exactly ‘n’ occurrences of the preceding character or group. For example, a{3} matches ‘aaa’.

Question 19

What does the regex operator {n,} signify?

Answer 19

The {n,} operator matches ‘n’ or more occurrences of the preceding character or group. For example, a{2,} matches ‘aa’, ‘aaa’, etc.

Question 20

What does the regex operator {n,m} signify?

Answer 20

The {n,m} operator matches between ‘n’ and ‘m’ occurrences of the preceding character or group. For example, a{2,4} matches ‘aa’, ‘aaa’, or ‘aaaa’.

Question 21

What does the regex operator \ signify?

Answer 21

The \ operator escapes special characters, allowing them to be treated as literals. For example, \* matches the ‘*’ character instead of treating it as a regex operator.

Question 22

What does the regex operator \b signify?

Answer 22

The \b operator matches a word boundary, ensuring the match occurs at the start or end of a word.

Question 23

What does the regex operator \B signify?

Answer 23

The \B operator matches a non-word boundary, ensuring the match occurs within a word.

Question 24

What does the regex operator (?=…) signify?

Answer 24

The (?=…) operator is a positive lookahead, ensuring that a certain pattern follows the current position without consuming characters.

Question 25

What does the regex operator (?!…) signify?

Answer 25

The (?!…) operator is a negative lookahead, ensuring that a certain pattern does not follow the current position without consuming characters.

Question 26

What does the regex operator (?<=…) signify?

Answer 26

The (?<=…) operator is a positive lookbehind, ensuring that a certain pattern precedes the current position without consuming characters.

Question 27

What does the regex operator (?<!…) signify?

Answer 27

The (?<!…) operator is a negative lookbehind, ensuring that a certain pattern does not precede the current position without consuming characters.

Question 28

^hello

Answer 28

Matches any string that starts with ‘hello’. For example, it will match ‘hello world’ but not ‘a hello world’.

Question 29

.*

Answer 29

Matches zero or more of any character except newline. This can match an empty string, ‘abc’, or even ‘hello123’.

Question 30

\d{3}-\d{2}-\d{4}

Answer 30

Matches a Social Security number format, such as ‘123-45-6789’. It consists of three digits, a dash, two digits, another dash, and four digits.

Question 31

[A-Za-z]+

Answer 31

Matches one or more uppercase or lowercase letters. For example, it will match ‘Hello’ and ‘abc’ but not ‘123’.

Question 32

colou?r

Answer 32

Matches both ‘color’ and ‘colour’. The ‘?’ means the preceding character ‘u’ is optional.

Question 33

\bword\b

Answer 33

Matches the word ‘word’ as a whole word only. It won’t match ‘sword’ or ‘wording’ but will match ‘word’.

Question 34

\d+.?\d*

Answer 34

Matches integers or decimals. For example, it matches ‘123’, ‘45.67’, or ‘89.’.

Question 35

(cat|dog)

Answer 35

Matches either ‘cat’ or ‘dog’. The ‘|’ acts as an OR operator between the two options.

Question 36

^[a-z0-9_-]{3,16}$

Answer 36

Matches usernames 3 to 16 characters long, allowing lowercase letters, numbers, underscores, and hyphens. It enforces both the length and allowed characters.

Question 37

\w+@\w+.\w+

Answer 37

Matches simple email addresses such as ‘example@mail.com’. It requires a word, an ‘@’, another word, a ‘.’, and a final word.

Question 38

\s{2,}

Answer 38

Matches two or more whitespace characters in a row. Useful for finding excessive spaces.

Question 39

(?i)hello

Answer 39

Matches ‘hello’ in a case-insensitive way. It will match ‘HELLO’, ‘hello’, or ‘HeLLo’.

Question 40

[0-9]{4,}-[A-Z]{2}

Answer 40

Matches a pattern like ‘1234-AB’ where four or more digits are followed by a dash and two uppercase letters.

Question 41

(https?|ftp)://[^\s/$.?#].[^\s]*

Answer 41

Matches URLs that start with ‘http’, ‘https’, or ‘ftp’, such as ‘https://example.com’.

Question 42

^.{8,}$

Answer 42

Matches any string that is at least 8 characters long. The ‘.’ matches any character, and ‘{8,}’ enforces the minimum length.

Question 43

^[^@]+@[^@]+.[a-zA-Z]{2,}$

Answer 43

Matches valid email addresses by ensuring there is no ‘@’ at the start, no ‘@’ immediately before the domain, and the domain has at least two letters.

Question 44

([A-Z][a-z]*){2,}

Answer 44

Matches strings with at least two capitalized words, such as ‘JohnDoe’ or ‘JaneSmith’.

Question 45

([01]?\d|2[0-3]):[0-5]\d

Answer 45

Matches valid 24-hour time formats, such as ‘23:59’, ‘5:30’, or ‘00:00’.

Question 46

(?<=$)\d+(.\d{2})?

Answer 46

Matches monetary values preceded by a ‘$’ symbol, such as ‘$100’ or ‘$99.99’. It uses a positive lookbehind.

Question 47

^[A-Fa-f0-9]{6}$

Answer 47

Matches valid hexadecimal color codes, such as ‘FFAACC’ or ‘abcdef’.