tags: vim regex
title: VIM Regex Guide

Sources: [vimregex.com](https://vimregex.com/) [learnbyexample.github](https://learnbyexample.github.io/vim_reference/Regular-Expressions.html) [vim.fandom](https://vim.fandom.com/wiki/Regex_lookahead_and_lookbehind)

## Quantifiers
### Greedy
```
* match zero or more times
\+ match one or more times
\? match zero or one times
\= can also be used, helpful if you are searching backwards with the ? command
\{m,n} match m to n times (inclusive)
\{m,} match at least m times
\{,n} match up to n times (including 0 times)
\{n} match exactly n times
```

### Non Greedy
```
\{-}                # matches 0 or more of the preceding atom, as few as possible
\{-n,m}             # matches 1 or more of the preceding characters...
\{-n,}              # matches at lease or more of the preceding characters...
\{-,m}              # matches 1 or more of the preceding characters...
```

## Anchors, Lookahead, Lookbehind
```
\<the\>                 # matches the if surrounded by non-word chars
\<the                   # the at start of word, their but not lathe
the\>                   # the at end of word, lathe but not their
hello\zsworld\zeflibble # matched text will be world, only if hello before and flibble after
```

## Grouping
```
\(...\)            # group
\1 \2 \3 ...       # backreference to group n
~                  # previous substitute string
```
So if we replace `:s/hello/world` then `:s/pattern/~` is equivalent to `:s/pattern/world` and `:s/pattern/~_~` is equivalent to `:s/pattern/world_world`.

## Replacing
```
\U...\E            # make uppercase
\L...\E            # make lowercase
\u                 # make next char uppercase
\l                 # make next char lowercase
\r                 # split line
```

## Example
### Changing case of first character of word
To change case, use `\l`

To get from
```js
const PtkKeys = { 
  EditKeys, ViewKeys, CommandKeys, GlobalKeys,
  EditChain, ViewChain, CommandChain,
  Selector
}
```
to
```js
const ptkKeys = { 
  editKeys, viewKeys, commandKeys, globalKeys,
  editChain, viewChain, commandChain,
  selector
}
```
select lines with visual and use
```
:s/\w\+/\l&/g                      " or to do it less elegantly
:s/\(\w\+\)/\l\1/g                 " or the even uglier
:'<,'>s/\(\s\)\([A-Z]\)/\1\l\2/g
```

## Links
* [vim.fandom: Changing Case with Regular Expressions](https://vim.fandom.com/wiki/Changing_case_with_regular_expressions)