Example
Use the --number flag to print line numbers before each line. Alternatively, -n does the same thing.
$ cat --number file
1 line 1
2 line 2
3
4 line 4
5 line 5
To skip empty lines when counting lines, use the --number-nonblank, or simply -b.
$ cat -b file
1 line 1
2 line 2
3 line 4
4 line 5
