a=1.1
b=2.2
做计算：
echo "$a*$b" | bc
echo "$a/$b" | bc
echo "$a+$b" | bc
echo "$a-$b" | bc
echo "$a%$b" | bc
echo "$a^$b" | bc
做比较:
echo "$a>$b" | bc #成立为1
b.awk命令a=1.1
b=2.2
做计算：
echo $a $b | awk '{printf("%fn",$1*$2)}'
做比较:
echo $a $b | awk '{if($1>$2) {printf("%fn",$1)} else {printf("%fn",$2)}}'
