echo "Your error message here" >&2
This is a normal echo (which goes to stdout), however the >&2 (which is shorthand for 1>&2), means 'mix the stdout to the stderr'. 1 is stdout, and 2 is stderr here.
This is a normal echo (which goes to stdout), however the >&2 (which is shorthand for 1>&2), means 'mix the stdout to the stderr'. 1 is stdout, and 2 is stderr here.