bash脚本编程和bc [英] Bash Scripting and bc

问题描述

我试图写一个bash脚本，我需要做一些浮点运算。基本上我想要做这样的事情：

I'm trying to write a bash script and I needed to do some floating point math. Basically I want to do something like this:

NUM=$(echo "scale=25;$1/10" | bc)
if [ $? -ne 0 ]
then
echo bad
fi

我遇到的问题是$？倾向于保持从回波程序的输出，而不是公元前呼叫。有没有一种方法，我从BC程序的输出保存到一个变量？

The problem I'm running into is $? tends to hold the output from the echo program and not the bc call. Is there a way I save the output from the bc program into a variable?

编辑：

感谢您的快速回复。下面是看问题的另一种方式。说我修改剧本一点点，所以它看起来是这样的：

Thanks for the quick replies. Here's another way of looking at the problem. Say I modified the script a little bit so it looks like this:

#!/bin/bash
NUM=$(echo "scale=25;$1/10" | bc)
if [ $? -ne 0 ]
then
echo bad
exit
fi
echo "$NUM"

当用户输入一个正常的浮点值，它工作正常：

When the user inputs a normal floating point value, it works fine:

bash script.sh 1.0

输出：

.1000000000000000000000000

然而，当用户输入一个不正确的值，则脚本不能恢复

However, when the user enters an incorrect value, the script can't recover:

bash script.sh 1.0a

输出：

(standard_in) 1: parse error

我想要做的就是它优雅地退出。

What I'm trying to do is get it to exit gracefully.

推荐答案

我看不出有什么毛病。 $ NUM应该握住你的 BC 命令结果

I don't see anything wrong. $NUM is supposed to hold your bc command results

请参阅：

NUM=$(echo "scale=25;$1/10" | bc)
echo "\$? is $?"
echo "NUM is $NUM"

输出

$ ./shell.sh 10
$? is 0
NUM is 1.0000000000000000000000000

另一种方法是用awk

another way is to use awk

NUM=$(awk -vinput="$1" 'BEGIN{printf "%.25f", input/10 }')
echo "\$? is $?"
echo "NUM is $NUM"

另一种方法，就是做的$ 1传递给 BC 前的检查。例如：

shopt -s extglob
input="$1"
case "$input" in
 +([0-9.]))
     IFS="."; set -- $input
     if [ $# -ne 2 ];then
        echo "bad decimal"
     else
        NUM=$(echo "scale=25;$1/10" | bc  )
        echo "$NUM"
     fi
esac

您不必从检查 $？ BC 了

you don't have to check for $? from bc anymore

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