我在 bash shell 中遇到一个简单程序的 expr 语法错误
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I am getting expr syntax errors in bash shell for a simple program
提问by Robo Smith
#!/bin/bash
clear
echo "Enter a number"
read a
s = 0
while [ $a -gt 0 ]
do
r = ` expr $a % 10 `
s = ` expr $s + $r `
a = ` expr $a / 10 `
done
echo "sum of digits is = $s"
This is my code guys . I am getting a bunch of expr syntax errors. I am using the bash shell. Thanks!
这是我的代码家伙。我收到一堆 expr 语法错误。我正在使用 bash shell。谢谢！
回答by paxdiablo
Your error is caused by the spaces surrounding the =in the assignments, the following replacements should work (I prefer $()to using backticks since they're much easier to nest):
您的错误是由=分配中的空格引起的，以下替换应该有效（我更喜欢$()使用反引号，因为它们更容易嵌套）：
s=0
r=$(expr $a % 10)
s=$(expr $s + $r)
a=$(expr $a / 10)
For example, s = 0(with the spaces) does not set the variable sto zero, rather it tries to run the command swith the two arguments, =and 0.
例如，s = 0（带有空格）不会将变量s设置为零，而是尝试s使用两个参数=和0.
However, it's not really necessaryto call the external expr1to do mathematical manipulation and capture the output to a variable. That's because bashitself can do this well enough withoutresorting to output capture (see ARITHMETIC EVALUATIONin the bashman page):
但是，实际上并没有必要调用外部expr1来进行数学运算并将输出捕获到变量中。这是因为bash本身就可以做到这一点不够好，而不诉诸输出捕获（见ARITHMETIC EVALUATION的bash手册页）：
#!/bin/bash
clear
read -p "Enter a number: " number
((sum = 0))
while [[ $number -gt 0 ]]; do
((sum += number % 10))
((number /= 10))
done
echo "Sum of digits is $sum"
You'll notice I've made some other minor changes which I believe enhances the readability, but you could revert back to the your original code if you wish and just use the ((expression))method rather than expr.
你会注意到我做了一些其他的小改动，我相信这些改动提高了可读性，但如果你愿意，你可以恢复到原始代码，只需使用((expression))方法而不是expr.
1If you don't mindcalling external executables, there's no need for a loop in bash, you could instead use sneakier methods:
1如果您不介意调用外部可执行文件，则不需要在 中循环bash，您可以使用更隐蔽的方法：
#!/bin/bash
clear
read -p "Enter a number: " number
echo "Sum of digits is $(grep -o . <<<$number | paste -sd+ | bc)"
But, to be brutally honest, I think I prefer the readable solution :-)
但是，老实说，我想我更喜欢可读的解决方案:-)
