How to tell if you're running RHEL or Centos

osdistro.sh

#!/bin/bash

DISTROS="rhel centos darwin"

for distro in $DISTROS; do
  case $distro in
    rhel) [[ ! -L /etc/redhat-release ]] && echo "dist = $distro"
      ;;
    centos) [[ ! -L /etc/centos-release  ]] && echo "dist = $distro"
      ;;
    darwin) [[ uname == "Darwin" ]] && echo "dist = $distro"
      ;;
    *)
      echo "unknown distro"
  esac
done