Re: Bash handling of ENOENT on missing files and directories

[Jonny Grant]

Hello Greg!

On 29/08/17 16:21, Greg Wooledge wrote:
> On Tue, Aug 29, 2017 at 03:40:54PM +0300, Jonny Grant wrote:
> > (B) is good, but (A) and (C) are problematic below.
> >
> > A)
> > $ cd missingdir
> > bash: cd: missingdir: No such file or directory
>
> How is this a problem?  It seems completely clear to me.  It tells
> you what program generated the error, what the program was trying to
> do, what argument was given, and what the result was.
>
> The wording is taken directly from perror() and related library calls,
> as translated for your locale.

Yes, it's a known limitation of POSIX that it uses a shared error code 
for both files and directors, ENOENT. Which without programmers handling 
and checking the stat() flags, means the error isn't completely clear in 
the case where a file or dir does exist.

Software the deals with files, can very easily report "No such file", a 
lot of GNU software does. Bash should also lead by example in this area! 
Why not incorporate this suggestion quickly?

$ objdump -d missing.elf
objdump: 'missing.elf': No such file

$ objdump -d mydir
objdump: Warning: 'mydir' is not an ordinary file


Likewise, software that deals with directories, or in the case of "cd" 
in bash, trying to change directory, can very easily report "No such 
directory"


eg another example:
$ objdump -d docs
objdump: Warning: 'docs' is not an ordinary file

> wooledg:~$ grep -r 'No such file' /usr/include
> /usr/include/asm-generic/errno-base.h:#define   ENOENT           2      /* No 
> such file or directory */
> /usr/include/rpcsvc/nfs_prot.x: NFSERR_NOENT=2,         /* No such file or 
> directory */
>
> The magic phrase "No such file or directory" tells the aware reader
> that some system call failed with errno set to ENOENT.
>
> > C)
> > $ ./main
> > -bash: ./main: No such file or directory
>
> Again, I'm not seeing the problem.

I don't think executing a directory ever works. So this could easily be 
clearer.

I imagine we have spoken already for longer about this, than it would 
have been to fix it.

Regards, Jonny