to print a result matched with or Incomplete

show arp | inc|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