在Shell If语句中使用BC会抛出预期的整数表达式

Question

我尝试在Raspberry Pi2上设置一点3bit CPU Meter，发现正常的Shell不喜欢浮动后，偶然发现了“ BC”

工作了几个小时后，我的脚本可以工作了，但是CPU使用率很高，因为控制台总是写“期望的整数表达式”

我真的不知道该如何解决这个问题，或者为什么这个错误甚至持续存在，脚本仍然可以正常工作，但是它会重击我的CPU周期...

您可以看看我的脚本，也许可以向我解释为什么会引发此错误？

while :
do
sleep 0.5
var=$(egrep -o '([0-9]{1})\.[0-9]{2}' /proc/loadavg | head -1 )
c005=0.05
c10=1.0
c05=0.5
c006=0.06

if [ "$(echo "if (${var} < ${c005}) 1" | bc)" -eq 1 ] ; then
    gpio write 0 0  
    gpio write 2 0
    gpio write 3 0

elif [ "$(echo "if (${var} > ${c10}) 1" | bc)" -eq 1 ] ; then
    gpio write 0 1 
    gpio write 2 1 
    gpio write 3 1

elif [ "$(echo "if (${var} > ${c05}) 1" | bc)" -eq 1 ] ; then
    gpio write 0 1 
    gpio write 2 1 
    gpio write 3 0

elif [ "$(echo "if (${var} > ${c006}) 1" | bc)" -eq 1 ] ; then
    gpio write 0 1 
    gpio write 2 0 
    gpio write 3 0

else
    gpio write 0 0  
    gpio write 2 0
    gpio write 3 0

fi
done

错误：

./cpu.proc: line 20: [: : integer expression expected
./cpu.proc: line 10: [: : integer expression expected
./cpu.proc: line 15: [: : integer expression expected
./cpu.proc: line 20: [: : integer expression expected
./cpu.proc: line 10: [: : integer expression expected
./cpu.proc: line 15: [: : integer expression expected
./cpu.proc: line 20: [: : integer expression expected
./cpu.proc: line 10: [: : integer expression expected
./cpu.proc: line 15: [: : integer expression expected
./cpu.proc: line 20: [: : integer expression expected
./cpu.proc: line 10: [: : integer expression expected
./cpu.proc: line 15: [: : integer expression expected
./cpu.proc: line 20: [: : integer expression expected
./cpu.proc: line 10: [: : integer expression expected
./cpu.proc: line 15: [: : integer expression expected
./cpu.proc: line 20: [: : integer expression expected
./cpu.proc: line 10: [: : integer expression expected
./cpu.proc: line 15: [: : integer expression expected
./cpu.proc: line 20: [: : integer expression expected
./cpu.proc: line 10: [: : integer expression expected
./cpu.proc: line 15: [: : integer expression expected

感谢所有花时间研究此问题的人。

最好的祝愿！

Answer 1

如果if语句成功，则bc打印1 ，但是如果失败，则不打印任何内容。 bash抱怨""不是整数。

if [ "$(echo "${var} < ${c005}" | bc)" -eq 1 ] ; then

您可以只将关系表达式传递给bc 。 它自然会根据<运算符的结果打印1或0 。

Answer 2

gpio mode 0 out;
gpio mode 2 out;
gpio mode 3 out;
while :
do
sleep 1.2
var=$(egrep -o '([0-9]{1})\.[0-9]{2}' /proc/loadavg | head -1 )
c005=0.05
c10=1.0
c05=0.5
c006=0.06

if [ "$(echo "if(${var} < ${c005}) 1" | bc)" == "1" ] ; then
    gpio write 0 0  
    gpio write 2 0
    gpio write 3 0

elif [ "$(echo "if (${var} > ${c10}) 1" | bc)" == "1" ] ; then
gpio write 0 1 
gpio write 2 1 
gpio write 3 1
elif [ "$(echo "if (${var} > ${c05}) 1" | bc)" == "1" ] ; then
gpio write 0 1 
gpio write 2 1 
gpio write 3 0
elif [ "$(echo "if (${var} > ${c006}) 1" | bc)" == "1" ] ; then
gpio write 0 1 
gpio write 2 0 
gpio write 3 0


else
gpio write 0 0  
gpio write 2 0
gpio write 3 0

fi
done