Okay...had a few minutes, so I threw a simple bash script together.
Just put the following into a file named compare.sh, in the same directories as your 2 files:
#!/bin/bash
file1=$1
file2=$2
cat $file1 | while read i
do
grep -x "$i" $file2
done
Go to your terminal (bash shell), and cd into the directory where these files reside. Run it:
sh compare.sh list1 list2
(where list1 and list2 are the names of your files)
It'll spit out the COMMON lines only.
Gary