Need a reliable way to send SIGINT to a perl process on 5.8.8/windows XPpro

Maybe you're looking at the wrong place. Windows doesn't have signals, so you're dealing with an emulation. If you want reliability, maybe you should use the underlying mechanism (SetConsoleCtrlHandler) directly.

Better yet, just send the CTRL_C_EVENT to the right process. Perl sets the CREATE_NEW_PROCESS_GROUP flag when spawning an asynchronous child (according to a shallow look at relevant Perl guts), so you should be able to affect only the child you wish to kill without doing anything special in the parent.

use Win32::Console qw( CTRL_C_EVENT );

my $pid = open(my $fh_from_child, "$cmd |");

my $output  = '';
while (<$fh_from_child>) { 
   $output .= $_; 
   if ( /waiting for control c/i ) {
      Win32::Console->GenerateCtrlEvent(CTRL_C_EVENT, $pid);
   }
}

close($fh_from_child);
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By the way, here's a version where you don't have to quote and escape your arguments anymore.

use IPC::Open3     qw( open3 );
use Win32::Console qw( CTRL_C_EVENT );

my $pid = open3('<&STDIN', my $fh_from_child, '>&STDERR', 'perl', @arg
+s);

my $output  = '';
while (<$fh_from_child>) { 
   $output .= $_; 
   if ( /waiting for control c/i ) {
      Win32::Console->GenerateCtrlEvent(CTRL_C_EVENT, $pid);
   }
}

close($fh_from_child);
waitpid($pid, 0);
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