Text File Compare Using diff and grep

Make sure both input files are sorted and UPPERCASE

Lines only in file1.txt

diff -d -i -w file1.txt file2.txt | grep "^[<]" > file1-only.txt

Lines only in file2.txt

diff -d -i -w file1.txt file2.txt | grep "^[>]" > file2-only.txt

Lines common in both files

diff -u -d -i -w file1.txt file2.txt | grep -v "^[-+]" > both-files.txt