flushing a filehandle in PurePerl

dragonchild has asked for the wisdom of the Perl Monks concerning the following question:

I know that usage of IO::Handle provides the flush() method, so you can do $fh->flush(); whenever you want. However, as far as I can tell, flush() is implemented within IO.xs as fflush(). There doesn't seem to be a PurePerl way to just flush a filehandle.

I would love to proven wrong, though.

Update: I am proven wrong. Shows that you should treat SoPW as a teddy bear, hit Preview instead of Update, and wait 10 minutes. (Could this be a feature request?)

sub flush {
    my $fh = shift;

    my $old_fh = select $fh;
    local $|++;
    print $fh q{};
    select $old_fh;
    return 1;
}
[download]

My criteria for good software:

Does it work?
Can someone else come in, make a change, and be reasonably certain no bugs were introduced?

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Re: flushing a filehandle in PurePerl
by ikegami (Patriarch) on Feb 17, 2006 at 16:48 UTC

print $fh q{}; is not needed. Turning autoflush on causes an immediate flush.
$|++ is misleading. It implies $|-- will turn off autoflush, but it doesn't always. Be clear and use $| = 1 instead.
local $|++; is a compile error. ("Can't modify postincrement (++) in local".)
My tests shows that local $|; won't do what you think on block exit. It will set the autoflush flag for whichever file handle is selected when the blocks exits. That's the wrong handle.

Use this:

sub flush {
   my $osh = select($_[0]);
   my $oaf = $|;
   $| = 1;
   $| = $oaf;
   select($osh);
   return 1;
}
[download]

Update: Added last two bullets and the code snippet.

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Re: flushing a filehandle in PurePerl
by PodMaster (Abbot) on Feb 17, 2006 at 16:07 UTC

Returns "0 but true" on success, "undef" on error.

MJD says "you can't just make shit up and expect the computer to know what you mean, retardo!"
I run a Win32 PPM repository for perl 5.6.x and 5.8.x -- I take requests (README).
** The third rule of perl club is a statement of fact: pod is sexy.

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Re: flushing a filehandle in PurePerl
by salva (Canon) on Feb 17, 2006 at 16:05 UTC

select FOO;
$| = 1;
print FOO "";
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