Bash if语句在不同位置使用感叹号生成不同的结果

我的第一个问题是 为什么要放 ! 在if语句前面 出现语法错误时失败 status 不是双引号。我就是这么想的 [ ! $x = "string" ] 不同于 [ $x != "string" ] ?

我的剧本如下。

#!/bin/bash

status=" "

# Comparison 1: without error
echo "-----Comparison 1-----"
if [ ! $status = "success" ]
then echo 'Error: status was not success but: ' $status
else
  echo "The status is success."
fi
echo "-----Comparison 2-----"
# Comparison 2: with error message but still shows success
if [ $status != "success" ]
then echo 'Error: status was not success but: ' $status
else
  echo "The status is success."
fi
echo "-----Comparison 3-----"
# Comparison 3: Correct result after quoting status
if [ ! "$status" == "success" ]
then echo 'Error: status was not success but: ' $status
else
  echo "The status is success."
fi
echo "-----Comparison 4-----"
# Comparison 4: Correct result after quoting status
if [ "$status" != "success" ]
then echo 'Error: status was not success but: ' $status
else
  echo "The status is success."
fi

-----Comparison 1-----
The status is success.
-----Comparison 2-----
./test2.sh: line 14: [: !=: unary operator expected
The status is success.
-----Comparison 3-----
Error: status was not success but:
-----Comparison 4-----
Error: status was not success but:

其他问题

• 为什么会产生 "The status is success." 在里面 Comparison 2 语法错误之后?if语句中的语法错误如何影响if语句的计算结果?

p、 我知道我们需要 "" $status