to print a result matched with 192.168.1.120 or Incomplete
show arp | inc 192.168.1.120|Incomplete
to print a result matched with 192.168.120.x and Incomplete in a line
show arp | inc 192.168.120..*Incomplete
The above gets the first three octets. The reason for . is just for consistency. For example if you don “12” that would match “12” and “120”. However 12. would only match 12 in the third octet. Then the .* is one or more or anything. Then we have “Incomplete”. So this will match all incomplete arps on 192.168.120.0/24.