Re: > /dev/stderr 2>&-

[Chet Ramey]

On 3/29/24 9:32 AM, Greg Wooledge wrote:
> On Fri, Mar 29, 2024 at 09:02:12PM +1100, Reuben wrote:
> > $ echo cat /dev/stderr > bug
> > $ bash bug 2>&-
> > cat /dev/stderr
>
> I don't understand what you were trying to do here.
>
> > calling bash script 2>&- on linux
> > seems to make /dev/stderr refer to script,
> > though &2 seems unaffected.
> > using 2>&- inside script does not trigger this bug.
> > i assume it is a bug and not 'historical compatibility'.
> > the bug does not seem to appear in bash on openbsd.
> > the bug does not seem to appear in dash or pdksh.
>
> As a first guess, bash was given the name of a file to read as a script,
> so it opened that file using the first available file descriptor.  Since
> you had already closed FD 2 before invoking bash, FD 2 was the first
> available, and therefore the script was opened as FD 2.

This is pretty much right. cat's behavior depends on how the OS handles
/dev/stderr. On Linux, the open succeeds and the read returns the script
data. On FreeBSD, the open succeeds and the read returns 0.


--
``The lyf so short, the craft so long to lerne.'' - Chaucer
                 ``Ars longa, vita brevis'' - Hippocrates
Chet Ramey, UTech, CWRU    chet@case.edu    http://tiswww.cwru.edu/~chet/

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