Ruby 1.9

Setting up a sleep seems to interfere with signal handlers. The following code

 trap("CLD") do
    pid = Process.wait
    puts "Child pid #{pid}: terminated"
 end

 exec("/bin/sh -c 'echo hello'") if fork.nil?
 puts "start"
 sleep 2
 puts "done"

Outputs start/hello/done with no delay, and the trap never fires. Replace the sleep with a gets, and the signal handler gets invoked—it never writes “Child xxx terminated.”