Notepad++ Capitalize Every First Letter of Every Word
Background
According to Notepad++ specification (see Substitutions section), there are three operators that can be useful when turning substrings uppercase:
\u
Causes next character to output in uppercase\U
Causes next characters to be output in uppercase, until a\Eis found.\E
Puts an end to forced case mode initiated by\Lor\U.
Thus, you can either match a substring and turn its first character uppercase with \u to capitalize it, or match a character and use \U/\E.
Note that Unicode characters won't be turned uppercase, only ASCII letters are affected.
BOW (Beginning of Word) Bug in Notepad++
Note that currently (in Notepad++ v.6.8.8) the beginning of word does not work for some reason. A common solution that works with most engines (use it in Sublime Text and it will match) does not work:
\b(\w)
This regex matches all word characters irrespective of their position in the string.
I logged a bug Word boundary issue with a generic subpattern next to it #1404.
Solution #1 (for the current Notepad++ v.6.8.8)
The first solution can be using the \w+ and replace with \u$0 (no need using any capturing groups). Though this does not mean we only match the characters at the beginning of a word, the pattern will just match chunks of word characters ([a-zA-Z0-9_] + all Unicode letters/digits) and will turn the first character uppercase.
Solution #2 (for the current Notepad++ v.6.8.8)
The second solution can be implemented with special boundaries defined with lookbehinds:
(?:(?<=^)|(?<=\W))\w
And replace with \U$0\E.
The regex (?:(?<=^)|(?<=\W))\w matches an alphanumeric only at the beginning of a line ((?<=^)) or after a non-word character ((?<=\W)).
The replacement - \U$0\E - contains a \U flag that starts turning letters uppercase and \E is a flag that tells Notepad++ to stop converting case.
Edge case
In case you have hyphenated words, like well-known, and you only want the first part to be capitalized, you can use [\w-]+ with \u$0 replacement. It will also keep strings like -v or --help intact.
A simpler regex that worked for me:
Find: (\w+)
Replace: \u$0