Re: Buffered output/Forked processes

[Reini Urban <rurban at x-ray dot at>]

Nuno Leitao schrieb:
>   I have a Perl script which looks like:
>
>   open( VMSTAT, "vmstat 5|" );
>   VMSTAT->autoflush( 1 );
>   while( <VMSTAT>) {
>      print $_;
>   }
>
>   Now, under Linux and other UNIX OS's this works fine, and "print $_" will
> print the vmstat output every 5 seconds since the output from vmstat is not
> buffered. Under Cygwin however, it seems vmstat will always buffer its
> stdout with the undesirable effect that lines come in batches as the output
> buffer gets full and is flushed by the Cygwin C libraries.
>
>   Is there a way to go around this without having to patch and recompile
> vmstat or other binaries I might want to use in this way ?

basic perl question, not cygwin related.
$ perldoc -q buffer
$ perldoc -f select

cygwin perl doesn't honor $| ? not true.
Because you told VMSTAT not to buffer.
But you shold have told it to STDOUT.

open( VMSTAT, "vmstat 5|" );
VMSTAT->autoflush( 1 );
$| = 1; # STDOUT is selected so STDOUT will get unbuffered.
while( <VMSTAT>) {
    print $_;
}


--
Reini Urban
http://xarch.tu-graz.ac.at/home/rurban/

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