regular expressions I still look up every time

The bits of regex syntax I forget between projects. Not a tutorial, just the reference card I wish I'd bookmarked years ago.

. matches any character except a line break

beginners overuse this one before they learn the alternatives

\d matches any digit, same as [0-9]

\w matches a word character: letters, digits, underscore

not spaces, that trips people up

\s matches whitespace: space, tab, newline

^ anchors to the start of the string (or line, with the m flag)

you will look this up again the day you actually need the m flag

$ anchors to the end of the string (or line, with m)

* means zero or more of whatever came before it

+ means one or more

i use this one more than any other, by far

? means zero or one, or makes a quantifier lazy right after it

the double meaning is the confusing part

{n,m} matches between n and m repeats of the thing before it

(...) is a capturing group, saves the match for later

(?:...) is a non-capturing group

use this when you need the grouping but not the capture, cleaner results

(?=...) is a lookahead, matches only if followed by the pattern

(?<=...) is a lookbehind, matches only if preceded by the pattern

newer browsers only, check support before you ship it

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