ABORT_ON_COMMAND_ERROR = false

Shell. +=
   run_foo(argv) =
      foo | grep 5.

   test_close(argv) =
      fail = false
      awk(b, $(stdin))
      case $'close[(][)]: Bad file descriptor'
         eprintln($"!!: $0")
         fail = true
         export
      default
         eprintln($"OK: $0")
      if $(fail)
         eprintln($"Test failed!")
         exit 1

(( echo Starting; run_foo; echo Done  ) |& test_close) || exit 5
