标准解决方案:

 expr $d1 - $d2

您也可以这样做:

echo $(( d1 - d2 ))

，但是请注意，这会将07视为八进制数字！ (因此07与7相同，但010与10不同).

but beware that this will treat 07 as an octal number! (so 07 is the same as 7, but 010 is different than 10).