测试零或正整数

Question 1

常见的习惯用法是检查变量的值是否仅由数字组成。对于较新的 bash shell，您可以使用=~正则表达式：

zero_or_positive_integer(){
    for i in "$@"; do
        if [[ "$i" =~ ^[0-9]+$ ]]; then
            echo "YES $i is either 0 or a positive integer"
        else
            echo "NO $i is neither 0 nor a positive integer"
        fi
    done
}

结果是：

$ zero_or_positive_integer foo -2 1.5 0 12
NO foo is neither 0 nor a positive integer
NO -2 is neither 0 nor a positive integer
NO 1.5 is neither 0 nor a positive integer
YES 0 is either 0 or a positive integer
YES 12 is either 0 or a positive integer

Answer

常见的习惯用法是检查变量的值是否仅由数字组成。对于较新的 bash shell，您可以使用=~正则表达式：

zero_or_positive_integer(){
    for i in "$@"; do
        if [[ "$i" =~ ^[0-9]+$ ]]; then
            echo "YES $i is either 0 or a positive integer"
        else
            echo "NO $i is neither 0 nor a positive integer"
        fi
    done
}

结果是：

$ zero_or_positive_integer foo -2 1.5 0 12
NO foo is neither 0 nor a positive integer
NO -2 is neither 0 nor a positive integer
NO 1.5 is neither 0 nor a positive integer
YES 0 is either 0 or a positive integer
YES 12 is either 0 or a positive integer

Question 2

要进行测试，通常使用[or[[运算符。[是命令的同义词test（不是 Bash 的一部分）

$ help [
[: [ arg... ]
    Evaluate conditional expression.
    
    This is a synonym for the "test" builtin, but the last argument must
    be a literal `]', to match the opening `['.

$ man test
[...]
       INTEGER1 -eq INTEGER2
              INTEGER1 is equal to INTEGER2
       INTEGER1 -ge INTEGER2
              INTEGER1 is greater than or equal to INTEGER2
[...]

所以看起来你可以写（不要忘记空格——[只是一个内置程序，所以将其参数分开）

if [ "$var" -eq 0 ]; then
  echo "Zero"
elif [ "$var" -gt 0 ]; then
  echo "Positive"
fi

请注意，如果$var不是整数，则会导致错误。我们假设$var已经是某个整数了。

如果您不确定这$var是一个整数，我不知道这是一个很好的测试，所以这里有一些使用正则表达式的代码：

if [[ "$var" =~ ^[1-9][0-9]+$ ]]; then
  echo "Positive"
elif [[ "$var" = 0 ]]; then
  echo "Zero"
else
  echo "Other"
fi

Answer