UNIX to DOS (adding CRs)
sed -e 's/$/\r/' inputfile > outputfile
DOS to UNIX (removing CRs)
sed -e 's/\r$//' inputfile > outputfile
Convert to DOS
perl -pe 's/\r\n|\n|\r/\r\n/g' inputfile > outputfile
Convert to UNIX
This one works for Mac.
perl -pe 's/\r\n|\n|\r/\n/g' inputfile > outputfile
Convert to old Mac
perl -pe 's/\r\n|\n|\r/\r/g' inputfile > outputfile