Regex Cheatsheet

Regex is very powerful and available in virtually every language. Eventually I’ll write a whole post about why every engineer should know some Regex, but this post is all about common regex patterns, flags, etc—in easy-to-read table form.

First, here are some patterns similar to ones I’ve used in recent memory:

Pattern	Meaning	Example Match
\d+	match 1 or more digits	abc123def
\w+$	match 1 or more word chars before end of line	abc-123def
ab|de	match ab or de	abc123def
(?<=:)\w{4}	match exactly 4 word characters preceded by a “:”	abc:123def
(?<=\w+):	match a : preceded by 1 or more word characters	abc: 123

Now to break down the common Regex elements.

Regex Character Classes

Character	Meaning
\w	any alphanumeric character, does not match accented characters1
\W	any non-alphanumeric character
\s	whitespace (includes tabs, line breaks)
\S	not whitespace
\d	any digit (same as doing [0-9])
\D	not digits
.	match any character (except line breaks)
[ab]	match any character inside the [] (same as a|b)

Regex Anchors

Anchor	Meaning
^	the start of a line
$	the end of a line
\b	a word boundary
\B	not a word boundary

Regex Quantifiers

Quantifier	Meaning
+	match 1 or more of the preceding token
*	match 0 or more of the preceding token
{1, 2}	match 1 or 2 of the preceding token
{2}	match exactly 2 of the preceding token
{2,}	match 2 or more of the preceding token

Grouping, Lookaheads, and Lookbehinds²

Syntax	Meaning	Example Match
(abc)	match the full group abc	abc123
a|b	match a or b, | is the regex “or”	attribute
[abc]	match any of a, b, or c	attribute
[^abc]	match not a, b, or c	carbs
[a-z]	match any character in the range a-z	aBc123
(?=abc)	abc must come after your match: hi(?=abc)	hiabc
(?!abc)	abc cannot follow your match: hi(?!abc)	hi_there
(?<=abc)	abc must precede your match: (?<=abc)hi	abchi
(?<!abc)	abc cannot precede your match: (?<!abc)hi	well_hi

There is a lot more to regex, but combinations of the above classes, anchors, quantifiers, and groupings will get you very far. I recommend Regexr for a quick regex test bed and reference page, I’ve used it countless times (including while writing this post).

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Helpful Links

• An expression to match all characters, including accented ones

Notes

1. \w catches ascii word characters. Accented characters, like é, are unicode. Accented characters will also be interpreted as word boundaries (\b), so beware! For a starting point on how to handle unicode characters, try the helpful link above. ↩︎
2. This is one area where you might run into some language-specific limitations. Golang, for instance, doesn’t support lookbehind matches with non-deterministic lengths ↩︎