shell编程中如何使用浮点运算？

用bc或awk
$a=3.4 b=345.3
echo "scale=4;$a*$b/2"|bc
587.0100
$echo $a*$b/2|bc -l
587.01000000000000000000
$awk 'BEGIN{printf '$a'*'$b'/2}'
587.01