environment

STDOUT vs STDERR

All error messages should go to STDERR.

This makes it easier to separate normal status from actual issues.

A function to print out error messages along with other status information is recommended.

err() {
  echo "[$(date +'%Y-%m-%dT%H:%M:%S%z')]: $*" >&2
}

if ! do_something; then
  err "Unable to do_something"
  exit 1
fi