On Fri, Jun 01, 2012 at 08:52:04AM -0500, Travis wrote:
> With that in mind, I'm still seeing strange behavior when I do this,
> where it looks to me like I'm closing and then immediately assigning
> STDIN:
>
> my $null_in_fh;
> open($null_in_fh, '<', '/dev/null') or die;
> close *STDIN; # this appears to mess things up, even with the
> following assignment
> *STDIN = $null_in_fh;
Keep in mind that STDIN is a perl filehandle, not a file descriptor.
When you close it, you close the filehandle and its underlying
descriptor. Then you assign another filehandle to STDIN, which has its
own descriptor.
Try this:
strace perl -e '
open($null, "</dev/null");
close *STDIN;
*STDIN = $null;
<STDIN>;
'
you'll see that it is doing something like:
open("/dev/null", O_RDONLY) = 3
close(0) = 0
read(3, "", 8192) = 0
The final read comes from the new descriptor, and we never re-opened
descriptor 0. You are basically just pointing the name STDIN to a new
handle, not doing anything with the underlying descriptor.
> Because, if I just do this
> open(STDIN, '<', '/dev/null') or die;
> even after the close and/or assignment, then all appears okay.
Yeah, this is the right way to re-open a descriptor in perl, because
open() does the magic to dup2 the newly opened descriptor onto STDIN's
descriptor.
> Thanks for your comments.
No problem. Glad it is working now.
-Peff
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