Regular expressions

A regular expression (regex for short) allow developers to match strings against a pattern, extract submatch information, or simply test if the string conforms to that pattern.

Usually such patterns are used by string-searching algorithms for “find” or “find and replace” operations on strings, or for input validation. - Wiki

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🚩 The Basics: Characters & Anchors

Symbol	Description	Example
.	Wildcard: Matches any single character except newline.	b.t matches bat, bet, bit.
^	Start: Matches the beginning of a line.	^Hello matches “Hello world”.
$	End: Matches the end of a line.	bye$ matches “See ya, bye”.
\	Escape: Lets you search for special characters like . or *.	\.com matches “.com”.
` | `	OR: Matches the pattern on the left or the right.

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🔢 Quantifiers: “How many?”

• * : 0 or more (The “greedy” one).
• + : 1 or more (At least one must exist).
• ? : 0 or 1 (Makes the character optional).
• {n} : Exactly n times (e.g., \d{3} matches 3 digits).
• {n,m} : Between n and m times.

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📦 Character Classes & Shorthand

Shorthand	Meaning	Equivalent To
\d	Any Digit	[0-9]
\D	Any Non-digit	[^0-9]
\w	Any Word character	[a-zA-Z0-9_]
\W	Any Non-word character	(symbols, spaces, etc.)
\s	Any Whitespace	(space, tab, newline)
[abc]	Set: Matches any char in brackets	a, b, or c
[^abc]	Negated Set: Matches anything except…	Everything but a, b, or c

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Frequently Used Resources

• Regex One - Learning Tutorial
  • Sketch Engine - Regex - it’s like regexone, but fewer hints
• Regex 101 - Expression Generator & Validation Testing
• Account Required Execute Program - Regex Courses

Games

• Regex Crossword
• Regex Golf
• Regexle - REgex Hexagon Puzzles

Examples in the Wild

• Wordle in bash by huytd