nl [man page] - number lines of files
nl [OPTION]... [FILE]...
-b, --body-numbering=STYLE
use STYLE for numbering body lines
-f, --footer-numbering=STYLE
use STYLE for numbering footer lines
-h, --header-numbering=STYLE
use STYLE for numbering header lines
$ echo -e "one\ntwo\nthree\nfour\nfive\n\nsix" > file

$ nl file
