On 8/23/16 5:00 PM, Helmut Karlowski wrote:
> Now extending Pierre's example:
>
> exec 3>tb.err
> echo 3>&1 > >(echo 1 1>&3)
> echo +++++
> cat tb.err
> echo -----
> echo 3>&1 > >(echo 11 1>&3)
> echo +++++
> cat tb.err
> echo -----
> echo > >(echo 2 1>&3) 3>&1
> echo +++++
> echo -----
> cat tb.err
> echo > >(echo 3 1>&3)
> echo +++++
> cat tb.err
> echo -----
> wait
>
> I get in bash:
Strange. I get
+++++
1
-----
+++++
11
-----
+++++
-----
2
+++++
2
3
-----
on Mac OS X and RHEL 6. I'm not sure why the last redirection (the one
with just process substitution and not 3>&1) doesn't cause the file to
be truncated, or the file pointer to be adjusted, but the trace is the
same in all cases.
>
> 1
>
> in ksh93 (where > >() does not work anyway, at least on cygwin):
This doesn't work on any ksh93, whether /dev/fd and process substitution
are available or not.
> in zsh (sometimes, sometimes it prints nothing):
I speculate that this has to do with something that zsh does to force
appending, whether that's lseek or something else, other than the fact
that zsh doesn't seem to use /dev/fd at all (I think it just straight
uses pipes). Bash doesn't do anything special with tb.err after opening
it, just manipulates the file descriptors with dup2 and fcntl.
Chet
--
``The lyf so short, the craft so long to lerne.'' - Chaucer
``Ars longa, vita brevis'' - Hippocrates
Chet Ramey, UTech, CWRU c...@case.edu http://cnswww.cns.cwru.edu/~chet/
