How do I uppercase or capitalize matched text inside a Vim substitution?

Explanation

Vim's substitute command supports special case-conversion sequences in the replacement string, letting you transform matched text to upper or lower case without a separate step. These are especially useful for normalising identifiers, fixing shouting comments, or converting column values in structured text.

How it works

The following escape sequences are available in the replacement portion of :s:

• \u — uppercase the next character only
• \U — uppercase all characters from here until \E or end of replacement
• \l — lowercase the next character only
• \L — lowercase all characters from here until \E or end of replacement
• \E — explicitly end a \U or \L region

The special & in the replacement refers to the entire matched text, making it easy to transform without a capture group.

Example

Force every word on the current line to ALL CAPS:

:s/\v\w+/\U&/g

Before: hello world foo
After:  HELLO WORLD FOO

Capitalize only the first letter of each word (title case):

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

Before: the quick brown fox
After:  The Quick Brown Fox

Force everything to lowercase:

:s/\v\w+/\L&/g

Tips

• Combine \u and \L to produce Title Case while lowercasing the rest of each word: \u\L&.
• Apply across a range: '<,'>s/\v\w+/\L&/g lowercases all words in the visual selection.
• These sequences are Vim-specific and are not part of POSIX or PCRE regex.