Save php code in database

Hi,

I am a newbie in codeigniter and web development in general. I am developing a blog, and I am saving the posts ocntant in the database. The problem comes when the post content has links with php variables inside it: 

Code:

<a href='<?=base_url()?>/blog/post-lug'>text in link</a>

I wonder which is the best practice to save posts with this kind of links inside it. One optoin would be to go one by one and hard-code them. But, what if i still don't know the base_url?

(maybe a very stupid and basic question, but I can't find a solution)

Thank you in advance!