5-2-shell：数值处理--加减乘除

一、整数

加减乘除

echo `expr 2 + 1`
echo `expr 2 - 1`
echo `expr 2 * 1`
echo `expr 2 / 1`

比较

-eq  等于,如:if [ "$a" -eq "$b" ]   
-ne  不等于,如:if [ "$a" -ne "$b" ]   
-gt  大于,如:if [ "$a" -gt "$b" ]   
-ge  大于等于,如:if [ "$a" -ge "$b" ]   
-lt   小于,如:if [ "$a" -lt "$b" ]   
-le  小于等于,如:if [ "$a" -le "$b" ]   
<   小于(需要双括号),如:(("$a" < "$b"))   
<=  小于等于(需要双括号),如:(("$a" <= "$b"))   
>   大于(需要双括号),如:(("$a" > "$b"))   
>=  大于等于(需要双括号),如:(("$a" >= "$b"))   

二、浮点数-bc

使用awk或者bc计算

加减乘除

精度丢失
echo "0.2+2.5"|bc
echo "0.2-2.5"|bc
echo "0.2*2.5"|bc    --结果.5
echo "2.5/0.2"|bc    --结果12

比较

if [ $(echo '5.2 > 2'|bc) = 1 ]
then 
    echo "test"
fi

差值比较

a=5.2
b=2
if [ `echo "$a - $b > 1"|bc` = 1 ]
then 
    echo "test greater"
fi

if [ `echo "$a - $b == 3.2"|bc` = 1 ]
then 
    echo "test equal"
fi

二、浮点数-awk

使用awk或者bc计算

加减乘除

完整计算
a=5.2
b=2
echo "$a $b" | awk '{printf("%0.3f
",$1+$2)}'
echo "$a $b" | awk '{printf("%0.3f
",$1-$2)}'
echo "$a $b" | awk '{printf("%0.3f
",$1×$2)}'
echo "$a $b" | awk '{printf("%0.3f
",$1/$2)}'

比较

a=5.2
b=2
if [ $(echo "$a $b" | awk '{printf("%d
",$1<$2)}') = 1 ]
then 
    echo "test"
fi

差值比较

a=5.2
b=2
if [ `echo "$a $b" | awk '{printf("%d
",$1<$2)}'` = 1 ] 
then 
    echo "test greater" 
fi 
if [ `echo "$a - $b == 3.2"|bc` = 1 ] 
then 
     echo "test equal" 
fi