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

Explanation

Vim's substitute command supports special case modifiers in the replacement string that let you change the case of captured text on the fly. This is powerful for reformatting identifiers, fixing capitalization, or transforming data without multiple steps.

How it works

• \u — uppercase the next character
• \U — uppercase all following characters (until \e or \E)
• \l — lowercase the next character
• \L — lowercase all following characters (until \e or \E)
• \e or \E — end case modification

These go in the replacement part of :s and apply to whatever follows them, including backreferences like \1.

Example

Capitalize the first letter of every word on a line:

Before: hello world foo bar
After:  Hello World Foo Bar

:s/\<\(\w\)/\u\1/g

Convert an entire match to uppercase:

Before: status: ok
After:  status: OK

:s/ok/\U&/

Tips

• Combine \U and \e to uppercase only part of the replacement: \U\1\e_\2
• Use & in the replacement to refer to the entire match
• Works with :%s for file-wide transformations