infile=r_mini_20120503.txt
filesize=1234567890 # manual set
skip=0
chunk=8000000000
bs=1000000000
count=8
part=1

while [ $skip -lt $filesize ] ; do
    dd if=$infile of=$infile.$part bs=$bs count=$count skip=$skip
    skip=[[ $skip + $chunk ]]
    part=[[ $part + 1 ]]
done

正如我所写,未经测试.