bash 质数脚本检查器
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Prime Number Script Checker
提问by Randy Teer
I am new to scripting. The script below checks if a number inputted is a prime number or divisible by 2. Why is the third line from the bottom needed (i=expr $i + 1). I commented that line out to see what the script would do and it hangs the script up. Please advise.
我是脚本新手。下面的脚本检查输入的数字是否为质数或可被 2 整除。为什么需要从底部算起的第三行 (i= expr $i + 1)。我注释掉了那行，看看脚本会做什么，它会挂起脚本。请指教。
#! /bin/bash
echo -n "Enter a number: "
read num
i=2
while [ $i -lt $num ]
do
if [ `expr $num % $i` -eq 0 ]
then
echo "$num is not a prime number"
echo "Since it is divisible by $i"
exit
fi
i=`expr $i + 1`
done
echo "$num is a prime number "
回答by chepner
If you don't increment i, then the test [ $i -lt $num ]will never be false, assuming istarts out less than num.
如果您不增加i，则[ $i -lt $num ]假设i开始时小于，则测试永远不会为假num。
