How to add line numbers to file being edited in vi?

Question

I have some text and I use :number in command mode to get number in each line and besides this I also want to have this number at saved output. What method/command can I use to achieve this?

Answer 1

Use the power of Unix utilities with the power of vi filtering. There are several utilities that number text files: nl(1), but also cat(1) (assuming it supports the non-POSIX -n option). When you are in vi, run this command to filter the whole file through cat -n:

:%!cat -n

You could also use

:%!nl

but note that nl by default does not number empty lines, while cat does. To number all lines with nl, use

:%!nl -b a

Answer 2

You can use this vim tip:

%s/^/\=printf('%-4d', line('.'))

Answer 3

Use the command nl.

i.e.

nl <in.txt > out.txt