$ grep -n ^ /path/to/file | less
— by Janos
on Nov. 9, 2011, 11:05 p.m.
In some systems you might have to use egrep instead of grep.
$ cat -n /path/to/file | less
— by openiduser28
on Feb. 13, 2012, 5:14 p.m.
cat -n will number all lines of a file.
It will add some white spaces as padding.