Not sure I understand - if you only have 3-4 packages you can just search for them specifically in the long list?

Even if you have 50 or 100s of packages, bash makes it pretty doable

comm -12 <(sort -u file1.txt) <(sort -u file2.txt) > common.txt

Should spit out only the packages appearing in both lists (done by memory so may not be 100%)