Regular Expressions

Question 1

What is a regular expression?

Answer 1

It is a language for describing strings of symbols

Question 2

How do you match characters in RegExps?

Answer 2

We use a ‘/’ at the beginning and end of the sequence of characters we want to match

Question 3

What do square brackets indicate in RegExps?

Answer 3

They indicate a set of possible single-character matches (e.g. [Ww]oodchuck means match Woodchuck or woodchuck)

Question 4

What does a dash inside a bracket imply in RegExps?

Answer 4

It means a character range - e.g. [A-Z] mean match any upper case letters

Question 5

What does a caret (^) mean when it is the first character in RegExps?

Answer 5

It means the complement of the set of characters in the range

Question 6

What are named ranges in RegExps?

Answer 6

They are some ranged patterns using backslash notation for common patterns (e.g. \d means any digit, \D means any non-digit, \w means any alphanumeric/underscore)

Question 7

What does a wildcard, ‘.’, mean in RegExps?

Answer 7

It means match any character

Question 8

How can matches be forced to be at the beginning or end of a word or line?

Answer 8

^ means start of line
$ means end of line
\b means word boundary
\B means non-word boundary

Question 9

What does a question mark mean in RegExps?

Answer 9

It means that a character is optional

Question 10

What does the Kleene star operator mean (*)?

Answer 10

It means match zero or more occurrences of the previous expression

Question 11

What does Kleene + mean in RegExps?

Answer 11

It means match 1 or more occurrences of a character

Question 12

What do braces {n} or {n, m} mean in RegExps?

Answer 12

{n} - It means to match n occurrences of the expression

{n, m} - It means to match a n to m occurrences of the expression

Question 13

What must be considered about the * and + operators?

Answer 13

They are greedy, meaning that they match as much text as possible

Question 14

What can we do to make the * and + operators non-greedy?

Answer 14

Add a question mark to the end of the operator, so use *? or +? instead

Question 15

What does the pipe ‘|’ operator do?

Answer 15

It means to match this | or this

Question 16

What does priority does the pipe operator have?

Answer 16

It has parsing priority lower than the sequence

Question 17

How do we escape a special meaning?

Answer 17

We add a backslash in order to get the actual meaning of a special character

Question 18

How do we capture groups?

Answer 18

We can use parentheses for grouping, which will match whatever is in the parentheses. It is also assigned in a register that we can then refer to later by using \ns\, where n is a number depending on the number of parentheses used

Question 19

How can we forbid a groups capture?

Answer 19

We can use the non-capturing group indicator ?: after opening the parentheses

Question 20

What are lookaround assertions?

Answer 20

It is a pattern that successfully matches something but does not consume the matched text

Question 21

What forms of lookaround are there?

Answer 21

Lookahead and Lookbehind, and we can have a negative form for both of these

Question 22

What are some limitations of Pattern Matching?

Answer 22

We get false positives, strings incorrectly matches

We get false negatives, strings that we incorrectly missed

Question 23

What should be remembered with pattern matching?

Answer 23

Law of Diminishing Returns, 80:20 rule, Pareto Principle

Question 24

When should RegExps not be used?

Answer 24

When they are too long
When there are parsers
When there are better tools to do the job
When parsing human writing
When validating some types of data
When your code will be read many times