vimwiki

Regex

Flag

Flag are modifier that change the output of a regex expression.
Place the flag after the second /: /expression/flag

flag	name	action	input
g	global	select in all	/\W+.com /g
m	multiline	select in all line	/\W+.com /g
i	case-insensitive	select case insensitively	/\W+.com /i

Basics expression

string used in example: bar bor. boo bir

• [] is a character class. It always match one character.

key	action	example	output	case sensitive
.	select all !char!	/./g	bar bor. boo bir
[]	alternative char	/b[aoi]r/g	bar bor bir
[^]	exclude char	/b[^o]r/g	bar bir
[a-z]	letter range	/b[i-z]	bor bir	yes
[0-9]	number range
[a-z0-9]	number or letter range
\	escape character	/ ./g	.

Note: to match - as a character instead the bracket, put it in first or last (the order does not matter): [-a-z] match - and a to z

key	action	example	output
^	select matching start of line	/^[0-9]/g	select all digit at the start of a line
$	select matching end of line	/html$/g	select all html expr that are in the end of a line
\w	select letter,number and underscore	/ \w /g	a b 1 2 _ …
\W	except letter,number and underscore	/ \w /g	. : ! ? … (space too)
\d	select only digit	/ \d /g	1 2 …
\D	except digit	/ \D /g	a b …
\s	only space	/ \s /g	’ ‘
\S	except space	/ \S /g	you get it
\b	is boundary	/ \bvim /g	select vim alone but not vim in neovim
\B	is not boundary	/ \Bvim /g	select vim in neovim but not just vim

Quantifiers

• Asterisk *: after a character, indicate that this character may either: not appear at all, or appear once or more side by side.
• Plus +: after a character, indicate that this character may appear either once or more side by side

input	regex	output
br ber beer	/be*r/g	br ber beer
br ber beer	/be+r/g	ber beer

* and + are greedy quantifiers. To make them non greedy use a ? after them : .*?

• Question mark ?: after a char, indicate that it is optional.

input	regex	output
color colour	/colou?r/g	color colour

• Curly braces {}: after a char, indicate the number of time it can appear. - {n}: only n times - {n,}: minimum n times - {n,x}: between n and x times

input	regex	output
ber beer beeer beeeer	/be{2}r/g	beer
ber beer beeer beeeer	/be{2,}r/g	beer beeer beeeer
ber beer beeer beeeer	/be{2,3}r/g	beer beeer

Grouping

• Group expression with the parentheses ()

input	regex	output
ha haa haaa haa	/(haa)/g	group the 2 occurence of haa
ha haa haaa haa	/(haa)-\1/g	the group is given the reference \1

• (?:expression): denote a non-capturing group

In nvim, group by escaping the parentheses \(group\), use the group with \1 \2 ... Example: %/s/’(a)’/\1/g -> replace 'a' with just a

Alternation

• Pip |: specifies that an expression can be in different expression.

input	regex	output
rat cat dog	/cat｜`dog/g	cat dog
rat cat dog	/(c｜r)at｜`dog/g	rat cat dog

Note: the | in the table is not a pipe, because it make the table bug

Lookahead/lookbehind

Need to use the flag -P to use them

• Positive lookahead: expression1(?=expression): select expression1 if followed by expression in lookahead

• Negative lookahead: expression1(?!expression): select expression1 if not followed by expression in lookahead

• Positive lookbehind: (?<=expression)expression1: select expression1 if preceded with expression in lookbehind
• Negative lookbehind: (?<!expression)expression1: select expression1 if not preceded with expression in lookbehind

name	input	regex	output
Positive lookahead	Date: 4 aug 3PM	/ \d+(?=PM)/g	3
Negative lookahead	Date: 4 aug 3PM	/ \d+(?!PM)/g	4
Positive lookbehind	Code: 109 price: $5	/ (?<=$)\d+/g	5
Negative lookbehind	Code: 109 price: $5	/ (?<!$)\d+/g	109

In nvim, the syntax is different, If we want to select text, depending on the ‘look’ word:

	Lookbehind	lookahead
positive	(look)\@<=text	(look)\@=text
negative	(look)\@<!text	(look)\@!text

A simpler version in nvim is to use \zs for positive lookbehind and \ze for positive lookahead (there is no negative version). T

	Lookbehind	lookahead
positive	look\zstext	text\zelook

Other

Usage with grep

Use -P use perl regex style.

grep -P "regexhere \d+" file.txt

Vim

Use \v before the regex to use perl regex style.

/\v\d+

For \b word boundary use < and > :

/\v<vim>

The non greedy equivalent of * and + are : {-} and {-1,}