Intro to Regex 🔍

Quick Intro to Regular Expressions

Regular expressions (aka Regex) define patterns for matching, extracting, and/or transforming data. They are available for use in many major programming languages (Python, R, Java, Javascript, etc.).

Essentials

• Character set [abc] = Matches any single character (in this case a, b, or c is matched)
• Optional element via a? = Matches 0 or 1 occurrences (0 or 1 of the a character for example)
• Range [0–9] = Matches any single character in inclusive range (includes numbers in a range)
• (Kleene) Star/Asterisk * =Matches 0 or more occurrences
• Plus sign + = Matches 1 or more occurrences
• Dot . = Matches any character (except line breaks)
• Escape Character \= Take next character literally (no special meaning)
• Alternation |= Boolean “or”
• Exact quantifiers via {n} {a, b} {a,} = Match a number of something or range of something
• Capturing group (a) = Group multiple tokens and can be used for backreference

Here are some character classes and info on anchors which may be useful to quickly build an expression:

• \w\d\s word, digit, whitespace character
• \W\D\S non-word, non-digit, non-whitespace character
• [abc] a b or c
• [^abc] any character other than a b or c
• [a-g] any char between a and g (inclusive)
• ^abc start of string
• abc$ end of string
• xyz\b word boundary
• xyz\B not word boundary

Resources

Interactive learning here

RegexOne - Learn Regular Expressions - Lesson 1: An Introduction, and the ABCs

Read this book chapter here

Regular Expressions :: Eloquent JavaScript

Practice via crossword game here

Regex Crossword