Linux中如何执行数学运算?

$[ operation ]

$1nbsp;var1=$[2 + 5]  $1nbsp;echo $var1  7  $1nbsp;var2=$[$var1 * 2]  $1nbsp;echo $var2  14  $ 

$ cat test.sh  #!/bin/bash  var1=10  var2=5  var3=3  var4=$[$var1 * ($var2 - $var3)]  echo The final result is $var4  $  

$chmod u+x test.sh  $./test.sh  The final result is 20  $

$bc -q  3.44 / 5  0  scale=3  3.44 / 5  .688  quit  $

var=$(echo "options; expression" | bc)

$ cat test.sh  #!/bin/bash  var1=$(echo " scale=3; 3.44 / 5" | bc)  echo The answer is $var1  $

$./test.sh  The answer is .688  $