Bash function echo2 - used to redirect STDOUT to STDERR, or to send text to STDERR directly

echo2.sh

function echo2 {
  if test -p /dev/stdin
  then
    echo "$(</dev/stdin)" 1>&2
  elif test -n $1
  then
    echo "$@" 1>&2
  else
    return 1
  fi
}

# EXAMPLE USAGES
# 1) Pipe STDOUT to the echo2 function, which redirects to STDERR
#   $ echo "Cant see me in STDOUT" | echo2 | grep should-grep-nothing-but-show-stderr-data
#   Cant see me in STDOUT
# 2) Use echo2 just as you would echo
#   $ echo2 "Cant see me in STDOUT" | grep should-grep-nothing-but-show-stderr-data
#   Cant see me in STDOUT