Detect if stdout is redirected to a pipe (not to a file, character device, terminal, or socket)?

Question

Ideally, this would be scriptable in shell, but Perl or Python would be fine. C code could be helpful, but probably fails cost/benefit.

I recognize that redirection to a

Answer 1

The stat command works on MacOS X and (with some finessing of variant implementations) other Linux/Unix variants as well, so it is a solution for me:

FORMOPT=
TYPEFORM=
stat() {
  if [ -z "$FORMOPT" ]; then
    if /usr/bin/stat --version >/dev/null 2>&1; then
      FORMOPT=--format
      TYPEFORM=%F
    else
      FORMOPT=-f
      TYPEFORM=%HT
    fi
  fi
  case $1 in
    type) FORMARG="$FORMOPT $TYPEFORM" ; shift ;;
  esac
  /usr/bin/stat -L $FORMARG "$@"
}

exec 9>&1
case `stat type /dev/fd/9` in
  [Ff]ifo*) echo stdout is a pipe ;;
  *) echo stdout is not a pipe ;;
esac