nl(1): Add EXAMPLES section

Add EXAMPLES section covering flags -b[ap] -n -i -s -v

Approved by:	bcr@
Differential Revision:	Add EXAMPLES section covering flags -b[ap] -n -i -s -v

usr.bin/nl/nl.1

@@ -27,7 +27,7 @@
 .\" ARISING IN ANY WAY OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE
 .\" POSSIBILITY OF SUCH DAMAGE.
 .\"
-.Dd May 4, 2014
+.Dd June 18, 2020
 .Dt NL 1
 .Os
 .Sh NAME
@@ -230,6 +230,42 @@ as described in
 .Xr environ 7 .
 .Sh EXIT STATUS
 .Ex -std
+.Sh EXAMPLES
+Number all non-blank lines:
+.Bd -literal -offset indent
+$ echo -e "This is\\n\\n\\na simple text" | nl
+     1  This is
+
+
+     2  a simple text
+.Ed
+.Pp
+Number all lines including blank ones, with right justified line numbers with
+leading zeroes, starting at 2, with increment of 2 and a custom multi-character
+separator:
+.Bd -literal -offset indent
+$ echo -e "This\\nis\\nan\\n\\n\\nexample" | nl -ba -n rz -i2 -s "->" -v2
+000002->This
+000004->is
+000006->an
+000008->
+000010->
+000012->example
+.Ed
+.Pp
+Number lines matching regular expression for an
+.Em i
+.No followed by either
+.Em m
+.No or
+.Em n
+.Bd -literal -offset indent
+$ echo -e "This is\\na simple text\\nwith multiple\\nlines" | nl -bp'i[mn]'
+        This is
+     1  a simple text
+        with multiple
+     2  lines
+.Ed
 .Sh SEE ALSO
 .Xr jot 1 ,
 .Xr pr 1