Editing Switching case of characters

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You can change the case of text:
:Toggle case "<code>HellO</code>" to "<code>hELLo</code>" with <code>g~</code> then a movement.
:Uppercase "<code>HellO</code>" to "<code>HELLO</code>" with <code>gU</code> then a movement.
:Lowercase "<code>HellO</code>" to "<code>hello</code>" with <code>gu</code> then a movement.

Alternatively, you can visually select text then press <code>~</code> to toggle case, or <code>U</code> to convert to uppercase, or <code>u</code> to convert to lowercase.

==Examples==

; <code>~</code>
: Toggle case of the character under the cursor, or all visually-selected characters.

; <code>3~</code>
: Toggle case of the next three characters.

; <code>g~3w</code>
: Toggle case of the next three words.

; <code>g~iw</code>
: Toggle case of the current word (inner word &ndash; cursor anywhere in word).

; <code>g~$</code>
: Toggle case of all characters to end of line.

; <code>g~~</code>
: Toggle case of the current line (same as <code>V~</code>).

The above uses ~ to toggle case. In each example, you can replace ~ with u to convert to lowercase, or with U to convert to uppercase. For example:

; <code>U</code>
: Uppercase the visually-selected text.
: First press <code>v</code> or <code>V</code> then move to select text.
: If you don't select text, pressing <code>U</code> will undo all changes to the current line.

; <code>gUU</code>
: Change the current line to uppercase (same as <code>VU</code>).

; <code>gUiw</code>
: Change current word to uppercase.

; <code>u</code>
: Lowercase the visually-selected text.
: If you don't select text, pressing <code>u</code> will undo the last change.

; <code>guu</code>
: Change the current line to lowercase (same as <code>Vu</code>).

==Title case==
The <code>:s</code> substitute command can change case (see {{help|s/\u}}).

The following converts the current line to Title Case (all lowercase, except for initial uppercase letters):
<pre>
:s/\<\(\w\)\(\w*\)\>/\U\1\L\2/g
</pre>

'''Explanation''' The search pattern is <code>\<\(\w\)\(\w*\)\></code> which searches for <code>\<</code> (beginning of word), then <code>\w</code> (a word character), then <code>\w*</code> (zero or more word characters), then <code>\></code> (end of word). The <code>\(...\)</code> create subexpressions to be recalled with <code>\1</code> and <code>\2</code> in the replacement. The replacement is <code>\U\1\L\2</code> which substitutes the two subexpressions transformed: The <code>\U</code> converts the first character of what follows to uppercase, while <code>\L</code> converts all of what follows to lowercase.

This approach has shortcomings in cases where words may contain what the regular expression recognizes as non-word characters, such as an apostrophe in "<kbd>I'll</kbd>" or "<kbd>she's</kbd>". An alternative based on whitespace for word boundaries is:
<pre>
:s/\<\(\w\)\(\S*\)/\u\1\L\2/g
</pre>

Another alternative is to replace the separator with # and use <code>\v</code> (very magic) to reduce the need to escape characters.
<pre>
:s#\v(\w)(\S*)#\u\1\L\2#g
</pre>

==Twiddle case==
With the following (for example, in [[vimrc]]), you can visually select text then press <code>~</code> to convert the text to <code>UPPER CASE</code>, then to <code>lower case</code>, then to <code>Title Case</code>. Keep pressing <code>~</code> until you get the case you want.

<pre>
function! TwiddleCase(str)
  if a:str ==# toupper(a:str)
    let result = tolower(a:str)
  elseif a:str ==# tolower(a:str)
    let result = substitute(a:str,'\(\<\w\+\>\)', '\u\1', 'g')
  else
    let result = toupper(a:str)
  endif
  return result
endfunction
vnoremap ~ y:call setreg('', TwiddleCase(@"), getregtype(''))<CR>gv""Pgv
</pre>

==References==
*{{help|case}}
*{{help|'tildeop'}}

==Comments==
The following will skip single-letter words and words that aren't in uppercase. It also accounts for non-english latin characters.
<pre>
:s/\v\C<([A-ZÀ-Ý])([A-ZÀ-Ý]+)>/\u\1\L\2/g
</pre>
--Jenny [[Special:Contributions/165.2.186.10|165.2.186.10]] 19:05, April 5, 2012 (UTC)
:Nice, thanks. I added <code>\C</code> to your command above to make the search case sensitive (it won't skip lowercase words if <code>'ignorecase'</code> is set, unless <code>\C</code> is present). [[User:JohnBeckett|JohnBeckett]] 09:58, April 6, 2012 (UTC)
:
: ----thank you for helping! I'm looking for an example that will change case in a substitution for matches and then keep the original case in the remainder... something like this
:: s/\(....\)abc\(....\)DeF\(....\)/\U\1DeF\L\2def'''??'''\3/  the first match is forced to uppercase but also changes the case of the following 'abc'.  The second match is forced to lowercase as well as the following 'DeF'.... The '''??''' above would hopefully tell the replacement not to force lower case but retain the original 3rd match's case... hope that makes sense...
:thanks, Jim Lumpkin Jimlumpkin(talk) 19:45, 7 October 2020 (UTC)
----
I was given the most helpful advice to check the doco :help s\L, which indicated the end replacement is enacted with \e or \E... thanks all!  

[[User:Jimlumpkin|Jimlumpkin]] ([[User talk:Jimlumpkin|talk]]) 19:57, 8 October 2020 (UTC)