This is a collection of challenges for learning regex. By completing these challenges, you will learn how to use regex to parse text. Throughout this tutorial we'll be referencing the regex101.com website.
Matching an email address: /^([a-z0-9_\.-]+)@([\da-z\.-]+)\.([a-z\.]{2,6})$/
Matching a Hex Value: /^#?([a-f0-9]{6}|[a-f0-9]{3})$/
Matching a URL: /^(https?:\/\/)?([\da-z\.-]+)\.([a-z\.]{2,6})([\/\w \.-]*)*\/?$/
Matching an HTML Tag: /^<([a-z]+)([^<]+)*(?:>(.*)<\/\1>|\s+\/>)$/
The goal of each regex is to match a string of characters against a pattern. The pattern is a string of characters that defines the type of string that we want to match.
- Description:
Anchors are used to match the beginning or end of a string.
-
Syntax: The beginning of a string is marked with a ^ and the end with a $.
-
Example:
^Hello
Hello$
- Note: The beginning and end of a string are not anchored by default.
- Description:
Quantifiers are used to specify how many times a pattern should be matched.
- Syntax:
- Quantifiers:
- *: Matches zero or more times.
- +: Matches one or more times.
- ?: Matches zero or one time.
- Example:
a+
- Description:
The OR operator is used to match one of the patterns.
- Syntax:
|: Matches one of the patterns.
- Example:
a|b
- Description:
Character classes are used to match a set of characters.
- Syntax:
[]: Matches any of the characters between the brackets. [^]: Matches any character that is not between the brackets.
- Example:
[abc]
[^abc]
- Description:
Flags are used to control the behavior of the regex.
- Syntax:
i: Case insensitive. m: Multi-line. s: Dot matches all characters (including newline). u: Unicode. x: Allow comments.
- Example:
[abc]
[^abc]
- Description:
Grouping and Capturing are used to group patterns and capture parts of the string.
- Syntax:
(pattern): Matches the pattern and stores the match in a capture group. (?Ppattern): Named capture group.
- Example:
(a)
(a)b
(?:a)
(?P<name>a)
- Description:
Bracket expressions are used to match any of the characters inside the brackets.
- Syntax:
[...]
- Example:
[a-z]
[a-z0-9]
[^a-z]
- Description:
Greedy and Lazy Match are used to control the behavior of the regex.
- Syntax:
?: Lazy match. *: Greedy match.
- Example:
[a-z]+
[a-z]+?
[a-z]*
[a-z]*?
- Description:
Boundaries are used to match the beginning or end of a string.
- Syntax:
^: Match the beginning of a string. $: Match the end of a string.
- Example:
^Hello
Hello$
- Description:
Back-references are used to reference a previously matched pattern.
- Syntax:
\1: References the first capture group. \2: References the second capture group. \3: References the third capture group. \4: References the fourth capture group. \5: References the fifth capture group. \6: References the sixth capture group. \7: References the seventh capture group. \8: References the eighth capture group. \9: References the ninth capture group.
- Example:
(a)(b)
(a)(b)(c)
(a)(b)(c)(d)
(a)(b)(c)(d)(e)
(a)(b)(c)(d)(e)(f)
(a)(b)(c)(d)(e)(f)(g)
(a)(b)(c)(d)(e)(f)(g)(h)
(a)(b)(c)(d)(e)(f)(g)(h)(i)
(a)(b)(c)(d)(e)(f)(g)(h)(i)(j)
(a)(b)(c)(d)(e)(f)(g)(h)(i)(j)(k)
(a)(b)(c)(d)(e)(f)(g)(h)(i)(j)(k)(l)
(a)(b)(c)(d)(e)(f)(g)(h)(i)(j)(k)(l)(m)
(a)(b)(c)(d)(e)(f)(g)(h)(i)(j)(k)(l)(m)(n)
AS A web development student
I WANT a tutorial explaining a specific regex
SO THAT I can understand the search pattern the regex defines
GIVEN a regex tutorial
WHEN I open the tutorial
THEN I see a descriptive title and introductory paragraph explaining the purpose of the tutorial, a summary describing the regex featured in the tutorial, a table of contents linking to different sections that break down each component of the regex and explain what it does, and a section about the author with a link to the author’s GitHub profile
WHEN I click on the links in the table of contents
THEN I am taken to the corresponding sections of the tutorial
WHEN I read through each section of the tutorial
THEN I find a detailed explanation of what a specific component of the regex does
WHEN I reach the end of the tutorial
THEN I find a section about the author and a link to the author’s GitHub profile