#dos2unix emailpass.txt
#dos2unix useremailhash.txt
LC_ALL=C sort -S 4G -t : -k 1 -o emailpass2.txt emailpass.txt
LC_ALL=C sort -S 4G -t : -k 2 -o useremailhash2.txt useremailhash.txt
LC_ALL=C join -i -1 1 -2 2 -t : -o 2.1,1.2 emailpass2.txt useremailhash2.txt > matched.txt