bash 的奇怪之处不是运算符
我正在尝试确定文件或目录是否不存在。我尝试了以下命令来查看文件是否存在并且它们正常工作：
if [ -a 'settings.py' ]; then echo 'exists'; fi
exists #output
if [ -a 'foo' ]; then echo 'exists'; fi #outputs nothing
但是当我尝试这样做时：
if [ ! -a 'settings.py' ]; then echo 'does not exist'; fi
does not exist #shouldn't be output since the file does exist
if [ ! -a 'foo' ]; then echo 'does not exist'; fi
does not exist
无论如何都会输出“不存在”。
I'm trying to determine if a file or directory doesn't exist. I tried the following commands to see if a file does exist and they work correctly:
if [ -a 'settings.py' ]; then echo 'exists'; fi
exists #output
if [ -a 'foo' ]; then echo 'exists'; fi #outputs nothing
But when I try this:
if [ ! -a 'settings.py' ]; then echo 'does not exist'; fi
does not exist #shouldn't be output since the file does exist
if [ ! -a 'foo' ]; then echo 'does not exist'; fi
does not exist
'does not exist' is output no matter what.
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我之前在使用
[命令时遇到过问题。我更喜欢[[变体，因为它更强大，而且根据我的经验，不太容易出现这样的“陷阱”。如果您使用
[[命令，您的测试命令可以正常工作：I've had problems with the
[command before. I prefer the[[variant since it's much more powerful and, in my experience, less prone to "gotchas" like this.If you use the
[[command, your test commands work fine:尝试使用
-e代替-a此页面位于 Linux 文档项目 说：
-a与-e效果相同。但它已被弃用，并且不鼓励使用。Try using
-ein place of-aThis page on the Linux Documentation Project says:
-ais identical in effect to-e. But it has been deprecated, and its use is discouraged.您可以使用
测试you can use
test