How to add line numbers to range of lines in Vim?

Question

How can I add line numbers to a range of lines in a file opened in Vim? Not as in :set nu—this just displays line numbers—but actually have them be prepended to each line in the file?

Answer 1

With

:%s/^/=line('.')/

EDIT: to sum up the comments.

This command can be tweaked as much as you want.

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Let's say you want to add numbers in front of lines from a visual selection (V + move), and you want the numbering to start at 42.

:'<,'>s/^/=(line('.')-line("'<")+42)/

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If you want to add a string between the number and the old text from the line, just concatenate (with . in VimL) it to the number-expression:

:'<,'>s/^/=(line('.')-line("'<")+42).' --> '/

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If you need this to sort as text, you may want to zero pad the results, which can be done using printf for 0001, 0002 ... instead of 1, 2... eg:

:%s/^/=printf('%04d', line('.'))/

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Anyway, if you want more information, just open vim help: :h :s and follow the links (|subreplace-special|, ..., |submatch()|)