How do I change the case of matched text in a substitute?

Explanation

Vim provides case-conversion atoms in substitute replacements: \u uppercases the next character, \l lowercases it, \U uppercases until \e, and \L lowercases until \e.

How it works

• \u — uppercase the next character
• \l — lowercase the next character
• \U — uppercase all following characters until \e
• \L — lowercase all following characters until \e
• \e — end case conversion

Example

Capitalize first letter of every word:

:%s/\(\w\+\)/\u\1/g

Before: hello world → After: Hello World

Convert to uppercase:

:%s/error/\U&/g

Before: error → After: ERROR

Tips

• & refers to the whole match
• \u\U combines: first character behavior then rest
• These only work in the replacement part of :s
• Combine with capture groups for precise transformations