Insert single successive numbers at the beginning of each line in a text file with Vim

Question

Assume I have a text file containing some strings:

string_g
string_r
string_qqwer
string_p
string_f
string_3qw
string_e
string_qw

And I need to insert increasing or decreasing numbers before the strings:

001 string_g
002 string_r
003 string_qqwer
004 string_p
005 string_f
006 string_3qw
007 string_e
008 string_qw

Just to avoid confusion:

I do not want line numbers to be displayed. I know how that works. What I want is an actual number at the beginning of each string within the text.

Is there a way to do this automatically with vim?

I can mark the beginning of each string with CTRL-V then type : to enter the execute mode, which will allow me to execute command on the selection via :'<,'> but I’m stuck there.

Answer 1

Use external unix command nl.

:'<,'>!nl -w 3 -n rz -s' '

Answer 2

With vim only (don't use external command):

let i=1 | '<,'>g/^/ s//\=printf("%03d ",i) / | let i+=1

Change let i=1 to number you want to start.