巴什if语句来检查。如果字符串等几个字符串常量之一 [英] Bash If-statement to check If string is equal to one of several string literals

问题描述

我需要确保的说法我bash脚本或者是 - ，0或+（不含引号）

I need to ensure that the argument to my bash script is either "-", "0", or "+" (without quotes).

所以，我做了如下声明如果：

So, I made the following If statement:

LEVEL=$1
if [ "$LEVEL" -ne "-" ] && [ "$LEVEL" -ne "0" ] && [ "$LEVEL" -ne "+" ]
then
     echo "The value of LEVEL must be either -, 0, or +!"
     exit 1
fi

但它给我的错误 [： - ：整数EX pression有望，指的是用if语句条件的行

But it's giving me the error [: -: integer expression expected, referring to the line with the If-statement conditions.

我一直在试图很多不同的语法（例如，双单VS括号，报价VS非引用变量和字符串），但我不明白。

I've been trying lots of different syntaxes (e.g., double vs single brackets, quoting vs non-quoting the variables and string literals), but I can't figure it out.

推荐答案

传统的方法，与POSIX兼容的SH，而不是利用bash化，是使用情况语句：

The conventional approach, compatible with POSIX sh rather than leveraging bashisms, is to use the case statement:

case $level in
   -|0|+)
     echo "Got it!" ;;
   *)
     echo "Not a valid value" ;;
esac

这是说，如果你想使用测试，你可以做到这一点：

That said, if you wanted to use test, you could do that too:

if [ "$LEVEL" != "-" ] && [ "$LEVEL" != "0" ] && [ "$LEVEL" != "+" ]; then
  ...
fi

！= 是否定的字符串比较操作符和 = （不是 == ）与POSIX兼容的正匹配之一。 （猛砸扩展POSIX支持 == 的测试，但使采用这种扩展将让你陷入困境的习惯，如果你尝试写code为一个纯粹的POSIX后壳）。

!= is the negating string comparison operator, and = (not ==) is the POSIX-compatible positive-matching one. (Bash extends POSIX to support == in test, but making a habit of using this extension will get you into trouble if you try to write code for a pure POSIX shell later).

在一个评论，一个跟进的问题是问，是否一组可能的字符可以从变量中读取方面。一般情况下，是的，尽管也有一些注意事项：

In a comment, a follow-up question was asked, in terms of whether the set of possible characters could be read from a variable. In general, yes, though there are some caveats:

possible_levels='-0+'
possible_levels_pattern="[${possible_levels}]"
if [[ $value = $possible_levels_pattern ]]; then
  echo "value contains a valid level"
fi

......或者，真正给你，你要问什么，可以的方式，是完全安全的：

...or, to really give you exactly what you're asking for, in a manner that's entirely safe:

possible_levels=' - 0 +'
read -a possible_levels_array <<<"$possible_levels"
check_level() {
  local possible_level
  local value=$1
  for possible_level in "${possible_levels_array[@]}"; do
    [[ $value = "$possible_level" ]] && return 0
  done
  return 1
}

if check_level "$value"; then
  echo "$value is a valid level"
else
  echo "$value is not a valid level"
fi

显然，这是一个大量的工作，而在一般情况下，只是硬编码比较适当的时候（可能没有安全的丢失）会麻烦您节省了试图让事情更通用比他们真正需要的人。

Obviously, this is a lot of work, and in general, just hardcoding the comparisons when appropriate (and possible without a loss of safety) will save you trouble over trying to make things more generic than they truly need to be.

现在，如果我们能够在变量作为关联数组传递，而不需要支持愚蠢的空格分隔列表的东西，这使得它更短：

Now, if we could pass in the variable as an associative array, without needing to support the silly space-separated-list thing, that makes it much shorter:

declare -A possible_levels=( [-]=1 [+]=1 [0]=1 )
if [[ ${possible_levels[$value]} ]]; then
  echo "valid level"
else
  echo "invalid level"
fi

这篇关于巴什if语句来检查。如果字符串等几个字符串常量之一的文章就介绍到这了，希望我们推荐的答案对大家有所帮助，也希望大家多多支持IT屋！