bash 检查一个数字是否在 shell 中
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/17960817/
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
Check if a number is even in shell
提问by rabotalius
I need to check if a number is even.
我需要检查一个数字是否是偶数。
Here's what I've tried.
这是我尝试过的。
newY="281"
eCheck=$(( $newY % 2 ))
echo $newY
echo $eCheck
while [ $eCheck -eq 0 ]; do
newY=$((newY-1))
eCheck=$(( $newY % 2 ))
echo $newY
done
...
returns eCheck = 1how can it be? 281/2 = 140.5
……回来eCheck = 1怎么可能？281/2 = 140.5
i've also tried using bc, but it went into an infinite loop eCheck=$(echo "scale=1;$newY%2" | bc)
我也试过使用bc，但它进入了无限循环eCheck=$(echo "scale=1;$newY%2" | bc)
回答by jderefinko
Nici is right, "%" is the modulo, and gives you the remainder of the division.
Nici 是对的，“%”是模数，并为您提供除法的余数。
Your script can be simplified as follows :
您的脚本可以简化如下：
if [[ $((var % 2)) -eq 0 ]];
then echo "$var is even";
else echo "$var is odd";
fi
回答by blackSmith
You can do a simple :
你可以做一个简单的：
eCheck=$(( $newY & 1 ))
to utilize the bitwise operators in bash.
在 bash 中使用按位运算符。
回答by rici
The %operator computes the remainder. So 281 % 2is 1, because 281divided by 2is 140with a remainder of 1.
该%运算符计算余数。所以，281 % 2是1的，因为281除以2就是140用剩余1。
回答by Devaashish Sharma
#!/usr/bin/env bash
[[ $( expr % 2 ) -eq 0 ]] && echo "Even Number" || echo "Odd Number"
回答by Jeff N
You are so close! Think of it like this. There are only two possible answers for Y in the expression
你离得那么近！像这样想。表达式中 Y 只有两个可能的答案
Y = X % 2
for ALL values of X. What are they? Play with a few values of X to see if you can come up with the values for Y.
对于 X 的所有值。它们是什么？试玩几个 X 值，看看你是否能想出 Y 的值。
Next, is there anything you can determine about what the value of Y says about the value of X? That is, can you use the value of Y to answer the problem you are trying to solve?
接下来，您是否可以确定 Y 的值对 X 值的影响？也就是说，你能不能用 Y 的值来回答你试图解决的问题？
回答by OM Prakash Singh
As you mention you are checking even for single no, So there is no need to use a loop. Here is my bit of code.
正如您所提到的，您甚至在检查单个否，因此无需使用循环。这是我的代码。
read -p "Enter a number: " num
if [ $((num%2)) -eq 0 ]
then
echo "Entered Number is even:"
else
echo "Entered Number is odd:"
fi
回答by codeforester
Since this question is tagged as Bash, the right way to check if a number is even in Bash is:
由于此问题被标记为 Bash，因此在 Bash 中检查数字是否为偶数的正确方法是：
if ((num%2 == 0)); then
echo "The number is even"
fi
or, more even shorter:
或者，更短：
if ((num % 2)); then
echo "The number is even"
fi
We don't need to use [[ ... ]]in this case.
[[ ... ]]在这种情况下我们不需要使用。
See also:
也可以看看：
- Difference between Bash operators double vs single brackets and (((on Unix & Linux Stack Exchange)
- How do I check whether a variable has an even numeric value?
- Bash 运算符双括号和单括号之间的区别和 ((（在 Unix 和 Linux Stack Exchange 上）
- 如何检查变量是否具有偶数值？
回答by Harpreet Khanduja
#!bin/bash
echo "Type the input integer, followed by [Enter]:"
read x
if [ $((x%2)) -eq 0 ]; then
echo "$x is even"
else
echo "$x is odd"
fi
Yes "%" is modulo, it gives you the remainder like others have mentioned
回答by Saurabh
This can be done using expr
这可以使用 expr 来完成
evenCheck=$(expr $newY % 2)
if [ $evenCheck = 0 ] ;
then echo "number is even";
else echo "number is odd";
fi
done
