regular expression character classes and atoms

Character Classes

Character classes	Python	Rg	Vim
Word char	`\w`	same	`\w`
Space	`\s`	same	`\s`
Multiline	`re.DOTALL` / `(?s)`	`--multiline` or `(?s)`	`\_.`

Atoms	Python	Rg	Vim
zero or more	`?`	same	`?`
1 or more	`+`	same	`+`
precise number of matches	`{n,m}`	same	`{n,m}`
word boundary	`\b`	same	`< >`
multiple patterns or	`\|`	same	`\|`
non greedy	`.*?`	same	`.{-}`
line starts with	`^`	same	`^`
line ends with	`$`	same	`$`
group	`( )`	same	`( )`
back reference	`\1 \2 \3`		`\1 \2 \3`
set start of match			`\zs`
set end of match			`\ze`

Example: to match company and companies