When redirecting a file, close the descriptor it's opened on immediat…

…ely.

gold/open-fds.sh showed that we had two copies of it open, which doesn't
make sense and isn't the behavior other shells have.

This might fix some bugs running debootstrap, but I haven't verified it
(issue #62).

gold/open-fds: Show descriptor state inside both redirects and
pipelines.

core/process.py

@@ -124,7 +124,10 @@ def _ApplyRedirect(self, r, waiter):
      if not self._PushDup(target_fd, r.fd):
        ok = False

      self._PushClose(target_fd)
      os.close(target_fd)  # We already made a copy of it.
      # I don't think we need to close(0) because it will be restored from its
      # saved position (10), which closes it.
      #self._PushClose(r.fd)

    elif r.tag == redirect_e.DescRedirect:
      if r.op_id == Id.Redir_GreatAnd:  # 1>&2
@@ -139,7 +142,9 @@ def _ApplyRedirect(self, r, waiter):
        raise NotImplementedError

    elif r.tag == redirect_e.HereRedirect:
      # NOTE: Do these descriptors have to be moved out of the range 0-9?
      read_fd, write_fd = os.pipe()

      if not self._PushDup(read_fd, r.fd):  # stdin is now the pipe
        ok = False
      self._PushClose(read_fd)

gold/open-fds.sh

@@ -9,22 +9,45 @@
# POSIX I guess.

# count FDs greater than 10.  0-9 are reserved for scripts.
count_fds() {
count_func() {
  local count=0
  local reserved=0
  {
    for path in /proc/$$/fd/*; do
      echo $path
      count=$((count + 1))
      if test $(basename $path) -lt 10; then
        reserved=$((reserved + 1))
      fi
    done

    echo "$count FDs open; $reserved are RESERVED (0-9)"
  local pid=$$

  # Uncomment this to show the FD table of the pipeline process!  The parent
  # doesn't change!

  #local pid=$BASHPID

  for path in /proc/$pid/fd/*; do
    echo $path
    count=$((count + 1))
    local fd=$(basename $path) 
    if test $fd -gt 2 && test $fd -lt 10; then
      reserved=$((reserved + 1))
    fi
  done

  ls -l /proc/$pid/fd

  echo "$count FDs open; $reserved are RESERVED (3-9)"
}

# What does it look like inside a redirect?  _tmp/err.txt must be open.
count_redir() {
  {
    count_func
  } 2> _tmp/err.txt
}

count_pipeline() {
  count_func | cat
}

# https://stackoverflow.com/questions/2493642/how-does-a-linux-unix-bash-script-know-its-own-pid
pid() {
  echo $$ $BASHPID | cat 
}

"$@"