ctrl u 1/2 up
ctrl d 1/2 down
ctrl e one line down
ctrl y one line up
ctrl b 往上一页 back的意思是回去的意思，所谓回上一页
ctrl f 往下一页 foward是back的反方向，故f下一页
zt move current line to the top of the screen
zb move current line to the bottom of the screen
zz move current line to the middle of the screen