How do I zero-pad or reformat numbers during a substitution using printf in Vim?

Explanation

Combining Vim's \= expression substitution with the printf() function lets you apply arbitrary formatting to matched text. This is particularly useful for zero-padding numbers so they sort lexicographically — for example, normalizing file1, file2, file10 into file001, file002, file010.

How it works

• \d\+ matches one or more digits
• \= tells Vim the replacement is a Vimscript expression
• printf('%03d', submatch(0)) formats the matched digits: %03d means an integer padded with leading zeros to at least 3 digits
• submatch(0) returns the full match (equivalent to & in a plain replacement)

Example

Given:

file1.txt file2.txt file10.txt

After :%s/\d\+/\=printf('%03d', submatch(0))/g:

file001.txt file002.txt file010.txt

Tips

• Use '%05d' for five-digit padding, or '%04d' for four.
• printf() follows C-style format specifiers: %s for strings, %f for floats, %x for hex.
• Combine with capture groups via submatch(1), submatch(2) etc. for more complex transformations.
• To convert to uppercase while reformatting: \=printf('%s', toupper(submatch(0)))