sed search and add some sting

Question

 ======KVM 虚拟化手册======
=====简介=====
=====安装和配置kvm虚拟化=====
====检查是否支持KVM====
====安装kvm虚拟化平台====
====配置nested virtualization====
==== 配置网络====
====重启系统并检查相关配置====
=====virsh创建 & 安装虚拟机=====
====通过VNC进行安装====
=====REFERENCE=====

1. The lines which begin with"=" and end with "="

2. add - at the end of the left "=", like:

   ===== - REFERENCE=====
   

How can I do ? thks ...

Answer 1

sed '/^=.*=$/ s/=\+/& - /' file

The first bit is "for each line that starts and ends with =".
The second bit is "replace the first sequence of = with: itself space dash space".