Bash 脚本和 bc
声明：本页面是StackOverFlow热门问题的中英对照翻译，遵循CC BY-SA 4.0协议，如果您需要使用它，必须同样遵循CC BY-SA许可，注明原文地址和作者信息，同时你必须将它归于原作者（不是我）：StackOverFlow
原文地址: http://stackoverflow.com/questions/2331936/
Warning: these are provided under cc-by-sa 4.0 license. You are free to use/share it, But you must attribute it to the original authors (not me):
StackOverFlow
Bash Scripting and bc
提问by LandonSchropp
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:
我正在尝试编写一个 bash 脚本，我需要做一些浮点数学运算。基本上我想做这样的事情：
NUM=$(echo "scale=25;/10" | bc)
if [ $? -ne 0 ]
then
echo bad
fi
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?
我遇到的问题是 $? 倾向于保存 echo 程序的输出而不是 bc 调用。有没有办法将 bc 程序的输出保存到变量中？
EDIT:
编辑：
Thanks for the quick replies. Here's another way of looking at the problem. Say I modified the script a little bit so it looks like this:
感谢您的快速回复。这是看待问题的另一种方式。假设我稍微修改了脚本，使其看起来像这样：
#!/bin/bash
NUM=$(echo "scale=25;/10" | bc)
if [ $? -ne 0 ]
then
echo bad
exit
fi
echo "$NUM"
When the user inputs a normal floating point value, it works fine:
当用户输入一个普通的浮点值时，它工作正常：
bash script.sh 1.0
output:
输出：
.1000000000000000000000000
However, when the user enters an incorrect value, the script can't recover:
但是，当用户输入错误值时，脚本无法恢复：
bash script.sh 1.0a
output:
输出：
(standard_in) 1: parse error
What I'm trying to do is get it to exit gracefully.
我要做的是让它优雅地退出。
采纳答案by ghostdog74
I don't see anything wrong. $NUM is supposed to hold your bccommand results
我看不出有什么不对。$NUM 应该保存您的bc命令结果
see:
看：
NUM=$(echo "scale=25;/10" | bc)
echo "$? is $?"
echo "NUM is $NUM"
output
输出
$ ./shell.sh 10
$? is 0
NUM is 1.0000000000000000000000000
another way is to use awk
另一种方法是使用 awk
NUM=$(awk -vinput="" 'BEGIN{printf "%.25f", input/10 }')
echo "$? is $?"
echo "NUM is $NUM"
The other way, is to do the check of "$1" before you pass to bc. eg
另一种方法是在传递给bc. 例如
shopt -s extglob
input=""
case "$input" in
+([0-9.]))
IFS="."; set -- $input
if [ $# -ne 2 ];then
echo "bad decimal"
else
NUM=$(echo "scale=25;/10" | bc )
echo "$NUM"
fi
esac
you don't have to check for $?from bcanymore
你不必检查$?从bc再
回答by Paused until further notice.
For GNU bc, an error similar to "(standard_in) 1: syntax error" will be output on stderr. You can capture this in your variable and check for it.
对于 GNU bc，将在 stderr 上输出类似于“(standard_in) 1: syntax error”的错误。您可以在变量中捕获它并检查它。
#!/bin/bash
NUM=$(echo "scale=25;/10" | bc 2>&1)
if [[ $NUM =~ error || $? -ne 0 ]]
then
echo bad
exit
fi
echo "$NUM"
回答by stefanB
Are you after the result of calculation from bc (which you store in NUM) or the status return from the system call?
你是在追求 bc 的计算结果（你存储在 NUM 中）还是系统调用的状态返回？
As I said you have the result of calculation in $NUM:
正如我所说，您的计算结果为$NUM：
#bctest.sh
NUM=$(echo "scale=25;/10" | bc)
if [ $? -ne 0 ]
then
echo bad
fi
echo "result: ", $NUM
Test:
测试：
bash ./bctest.sh 15
result: , 1.5000000000000000000000000
