cut命令
ls -l i386.pdf | grep pdf | cut -c49-52 结果输出为i386 详见:man cut
tmp.s: boot/bootsect.s tools/system
(echo -n ''SYSSIZE = (''; ls -l tools/system | grep system | cut -c23-31 | tr \012'''; echo '' +15)/16 ") > tmp.s (解释详见linux内核完全注释)
cat /boot/bootsect.s >> tmp.s