shell 加法问题?

littlecivic

bash 1,2,3 都可以
实在无法理解 2 sum=$(( sum + $i)) 和 3 sum=$(( sum + i))
高手帮忙

1.
echo "56516"|sed 's/[0-9]/&\n/g'|grep -v "^$" | { while read i;do sum=$(( $sum + $i));done;echo $sum;}

2.
echo "56516"|sed 's/[0-9]/&\n/g'|grep -v "^$" | { while read i;do sum=$(( sum + $i));done;echo $sum;}

3.
echo "56516"|sed 's/[0-9]/&\n/g'|grep -v "^$" | { while read i;do sum=$(( sum + i));done;echo $sum;}

关阴月飞

这有啥不能理解的，$(()) 里面使用变量时，可以忽略掉$，$可有可无。

Shell_HAT

龟腚
记住就行了

littlecivic

谢谢各位大侠,有空行的时候,还是有点不同的.

1. 会抱错, sum + : syntax error: operand expected (error token is "+ ")
echo "56516"|sed 's/[0-9]/&\n/g' |{ while read i;do sum=$(( sum + $i));done;echo "$sum";}

2. 没有问题
echo "56516"|sed 's/[0-9]/&\n/g' |{ while read i;do sum=$(( sum + i));done;echo "$sum";}


可能,用 i 的时候bash 自动跳过空行?
$i 会计算空行?

jason680

回复 5# littlecivic

learn it(shell script) and use it with right way and remember the (shell script) rule ...
or you can learn other language. ex: C, java, php, awk, sed, perl, python, tcl, ruby, ...
http://www.tiobe.com/index.php/content/paperinfo/tpci/index.html

ex:
   var=value    # right way
   var = value  # wrong way

if [a=3]; then ... fi        # wrong way
if [ a = 3 ]; then ... fi    # right way

to learn it with sometime some space are right way, sometime are wrong way.

zhaopingzi

回复 6# jason680


    和汉语一样不严谨