I'm assuming the second example (p1.sh file2 file1) should output cc as there is no line with just c in file1. If so, then:

#!/bin/bash



cat "$1" | while read m  

do

    grep "$m" "$2"

done | sort -u

example:

$ cat f1

a

b

bb

b

cc

$ cat f2

aa

ab

bc

c

$ ./p1.sh f1 f2

aa

ab

bc

$ ./p1.sh f2 f1

cc