Function to check if a package managed by homebrew is installed

brew::is_installed

brew::is_installed() {
  local failcount
  failcount=0
  if ! command -v brew >/dev/null 2>&1; then
    printf -- '%s\n' "This script requires brew on a mac.  This wasn't found..." >&2
    exit 1
  fi
  for brew_pkg in ${*:?Package unspecified}; do
    if brew list | grep -w "${brew_pkg}" >/dev/null 2>&1; then
      printf -- '%s\n' "${brew_pkg} appears to be installed"
    else
      printf -- '%s\n' "${brew_pkg} is not installed"
      (( failcount++ ))
    fi
  done
  (( failcount > 0 )) && return 1
}