How do I insert a line above specific lines in a file using Vim or Perl?

Question

I'd like to insert the line

<hr />

above every occurrence of a header 2 line in a file - e.g., above this pattern

<h2>variable pattern here</h2>

So the above should become

<hr />
<h2>variable pattern here</h2>

How can I do this with Vim, Sed or Perl?

Answer 1

vim way:

cmd :g/<h2>/normal O<hr /> will do the job.

see it here: (I took the example from sudo_O)