bash 检查文件是否可读并存在于一个 if 条件中：if [[ -r -f "/file.png" ]]
声明：本页面是StackOverFlow热门问题的中英对照翻译，遵循CC BY-SA 4.0协议，如果您需要使用它，必须同样遵循CC BY-SA许可，注明原文地址和作者信息，同时你必须将它归于原作者（不是我）：StackOverFlow
原文地址: http://stackoverflow.com/questions/4653829/
Warning: these are provided under cc-by-sa 4.0 license. You are free to use/share it, But you must attribute it to the original authors (not me):
StackOverFlow
Checking if a file is readable and exists in one if condition: if [[ -r -f "/file.png" ]]
提问by Mint
I was writing an if statement which checked if a file is readable and exists by doing the following:
我正在编写一个 if 语句，通过执行以下操作来检查文件是否可读和存在：
if [[ -r "$upFN" && -f "$upFN" ]]; then
....
fi
Then I thought, surly you can make this smaller, something maybe like this:
然后我想，当然你可以把它变小，可能是这样的：
if [[ -r -f "$upFN" ]]; then
....
fi
But this doesn't work, it returns errors:
但这不起作用，它返回错误：
./ftp.sh: line 72: syntax error in conditional expression
./ftp.sh: line 72: syntax error near `"$upFN"'
./ftp.sh: line 72: `if [[ -r -f "$upFN" ]]; then'
回答by D.Shawley
AFAICT, there is no way to combine them further. As a portability note, [[ expr ]]is less portable than [ expr ]or test expr. The C-style &&and ||are only included in bash so you might want to consider using the POSIX syntax of -afor andand -ofor or. Personally, I prefer using test exprsince it is very explicit. Many shells (bash included) include a builtin for it so you do not have to worry about process creation overhead.
AFAICT，没有办法将它们进一步结合起来。作为便携性说明，[[ expr ]]不如[ expr ]或便携test expr。C 风格的&&and||仅包含在 bash 中，因此您可能需要考虑使用-afor and和-ofor or的 POSIX 语法。就个人而言，我更喜欢使用，test expr因为它非常明确。许多 shell（包括 bash）都包含一个内置函数，因此您不必担心进程创建开销。
In any case, I would rewrite your test as:
无论如何，我会将您的测试重写为：
if test -r "$upFN" -a -f "$upFN"
then
...
fi
That syntax will work in traditional Bourne shell, Korn shell, and Bash. You can use the [syntax portably just as well.
该语法适用于传统的 Bourne shell、Korn shell 和 Bash。您也可以[便携地使用该语法。
回答by Rob Kennedy
Is there ever a case where a file would be readable but it doesn'texist? Don't bother checking for existence when readability will tell you all you need.
是否有文件可读但不存在的情况？当可读性会告诉你所有你需要的时候，不要费心检查是否存在。
