#! perl -slw
use strict;
use threads;

my $pid = open IN, '-|',  qq[ 
perl -E"\$t=time; say ~~localtime, select'','','',.0001 while time() < \$t + $ARGV[0]" 
] or die $!;

async {
    eval {
        local $SIG{ ALRM } = sub {
            kill -9, $pid;
            warn 'timeout';
        };
        alarm 5;
        waitpid $pid, 0;
        alarm 0;
    };
}->detach;

while( <IN> ){
   print;
}

__END__
c:\test>junk 4 >junk.log

c:\test>dir junk.log
08/06/2010  17:58        13,703,760 junk.log

c:\test>junk 6 >junk.log
timeout at C:\test\junk.pl line 13.

c:\test>dir junk.log
08/06/2010  17:58        22,759,264 junk.log