@argv = qw(/bin/echo hello world);
open(SAVOUT, '>&STDOUT') or die $!;
open(STDOUT, '+>', "/tmp/stdout.log") or die $!;
system(@argv);

print SAVOUT "before=", tell(STDOUT), "\n";
seek(STDOUT, 0, 0) or die $!;
print SAVOUT "after=", tell(STDOUT), "\n";
while (1) {
  read STDOUT, $_, 8192;
  last unless $_;
  print SAVOUT "stdout=", $_;
}
print SAVOUT "at end=", tell(STDOUT), "\n";
close STDOUT;