Re: -e and permission denied

[victor]

On Friday, October 4, 2013 5:10:43 AM UTC+4, Eduardo A. Bustamante López wrote:
> If you are using -e to test if a file is readable, then you're asking
> 
> the wrong question. If you want to know if a file is readable, use
> 
> the -r test.
> 
> 
> 
> if [ -r some/file ]; then
> 
>   ... do something with file that involves reading it ..
> 
> fi
> 
> 
> 
> Regarding the 'permission denied' errors, that's an *operating
> 
> system* issue. The operating system is (on purpose) not letting you
> 
> know if that file exists or not, because, if you don't have the
> 
> permission to check it, then you shouldn't get that information!
> 
> That's the whole point of having permissions on directories, to avoid
> 
> handling the list of files to users that don't have the permissions.
> 
> 
> 
> So, at the end, if the file exists or not, you as a user cannot know,
> 
> because it might, but you don't have permission to see it. So, don't
> 
> expect bash to circumvent O/S security mechanisms.
> 
> 
> 
> Better yet, most sane commands return a proper exit code when there
> 
> was an error. So, if you try to read the file, but the command
> 
> couldn't read it, then the command should return an error exit code,
> 
> and you can test things like this:
> 
> 
> 
> if program some/file; then
> 
>   everything went fine
> 
> else
> 
>   something went wrong...
> 
> fi
> 
> 
> 
> -- 
> 
> Eduardo A. Bustamante López

> If you are using -e to test if a file is readable
no, I am not

> The operating system is (on purpose) not letting you know if that file exists 
> or not
OS is not lying about file existence. It returns "permission denied" error, 
which means file may or may not exist.

> Better yet, most sane commands return a proper exit code when there was an 
> error

Whole issues was that -e behaviour is not properly documented  ("-e True if 
file exists." is simply not true),
so user won't know that he/she needs to use right command and right logic.

example of better documentation:
http://pubs.opengroup.org/onlinepubs/9699919799/utilities/test.html
"True if pathname resolves to an existing directory entry. False if pathname 
cannot be resolved."