/regex-talk

Introduction to Regular Expressions taught with Regex Crosswords

Primary LanguageJavaScriptMIT LicenseMIT

Intro to Regex

Cheatsheet

Metacharacters

Char Purpose
\ Escaping next character
^ Start of String or Negation in Character Class
$ End of String
. Any Character (Except Newlines)
| Alternation in Groups
? Zero or One or Lazy Mode or Lookarounds & more
* Zero or More
+ One or More
{} Range Delimiters
() Group Delimiters
[] Character Class Delimiters

Note: Lazy Mode & Lookarounds are not discussed in this workshop

Repeating Characters

Pattern Description Matches
a? Zero or One 'a' '' 'a'
a* Zero or More 'a' '' 'a' 'aa' 'aaa' 'aaaa'...
a+ One or More 'a' 'a' 'aa' 'aaa' 'aaaa'...
a{3} Exactly three 'a' 'aaa'
a{2,4} Two to four 'a' 'aa' 'aaa' 'aaaa'
a{2,} Two or more 'a' 'aa' 'aaa' 'aaaa' 'aaaaa'...
a{,3} Three or fewer 'a' '' 'a' 'aa' 'aaa'

Character Class

Pattern Description Matches
[abc] One of 'a', 'b' or 'c' 'a' 'b' 'c'
[a-g] Letters between a and g 'a' 'b' 'c' 'd' 'e' 'f' 'g'
[a-c1-3] Letters a-c or number 1-3 'a' 'b' 'c' '1' '2' '3'
[ab]{2} Two of 'a' or 'b' 'aa' 'bb' 'ab' 'ba'

Shorthand Character Class

Shorthand Equivalent
[0-9] [0123456789]
\d [0-9]
\w [A-Za-z\d_]
\s [ \t\n\r]

Shorthand Negation

Shorthand Equivalent
\D [^\d]
\S [^\s]
\W [^\w]
. [^\r\n]
[\w\W] Anything

Literal Characters

Command Matches
a a
\? ?
\. .
\\ \

Groups

const reg = /(na)+/

const isTheme = str => reg.test(str)

isTheme("nanananananana Batman!")
// true

isTheme("aaaaannnnnnnnn Batman!")
// false

Backreferences

const reg = /(\w+)-\1/

const strings = ["foo-foo", "foo-bar", "bar-bar"]
strings.filter(str => reg.test(str))
// [ "foo-foo", "bar-bar" ]

Note: Backreferences are 1-indexed

Flags

Command Purpose
g Global -- find all matches (default is 1st only)
i Insensitive -- Case insensitive
m Multi-line -- ^ and $ refer to line ends
s Dotall -- . == [\w\W]