Practical Vim, 2nd Edition

Tip 95

Perform Arithmetic on the Replacement

The replacement field needn’t be a simple string. We can evaluate a Vim script expression and then use the result as the replacement string. Thus with a single command, we can promote every HTML header tag in a document.

Suppose that we have an HTML document like this:

substitution/headings.html

<h2>Heading number 1</h2>
<h3>Number 2 heading</h3>
<h4>Another heading</h4>

We want to promote each heading, turning <h2> into <h1>, <h3> into <h2>, and so on. To put it another way, we want to subtract one from the numeral part of all HTML header tags.

We’ll harness the substitute command to do it. Here’s the general idea: we write a pattern that matches the numeral portion of HTML header tags. Then ...