/regex/

Components for patterns

- Range

a-z matches an lower case letters from a to z
0-5 matches any number from 0 to 5

[] Match exactly one of the objects inside these brackets

[a] matches the letter a
[abc] matches a single letter which can be a, b or c
[a-z] matches any single lower case letter of the alphabet.

() Groups different matches for return purposes

See examples below.

{} Multiplier for repeated copies of pattern defined before it

[a]{2} matches two consecutive lower case letter a: aa
[a]{1,3} matches at least one and up to three lower case letter a, aa, aaa

+ Match at least one, or more, of the pattern defined before it

a+ will match consecutive a's a, aa, aaa, and so on

? Match zero or one of the pattern defined before it

Pattern may or may not be present but can only be matched one time.
[a-z]? matches empty string or any single lower case letter.

* Match zero or more of the pattern defined before it

Wildcard for pattern that may or may not be present.
[a-z]* matches empty string or string of lower case letters.

. Matches any character except newline \n

a. Matches a two character string starting with a and ending with anything except \n

| OR operator

a|b means either a or b can be matched.
red|white|orange matches exactly one of the colors.

^ NOT operator

[^0-9] character can not contain a number
[^aA] character can not be lower case a or upper case A

\ Escapes special character that follows (overrides above behavior)

\., \\, \(, \?, \$, \^

^ Match must occur at start of string

^a First character must be lower case letter a
^[0-9] First character must be a number.

$ match must occur at end of string

a$ Last character must be lower case letter a

Precedence table

order	name	representation
1	parentheses	( )
2	multipliers	? + * {m,n} {m, n}?
3	sequence & anchors	abc ^ $
4	alternation	|

Predefined character abbreviations

abbreviation	equal to	meaning
\d	[0-9]	any single digit
\D	[^0-9]	any single character that's not a digit
\w	[a-zA-Z0-9_]	any word character
\W	[^a-zA-Z0-9_]	any non-word character
\s	[ \r\t\n\f]	any space character
\S	[^ \r\t\n\f]	any non-space character
\n	[\n]	new line

Test it

https://regexr.com/ or https://regex101.com/ work like charm ❤️