<p>I want to create a regexp in Emacs that matches exactly 3 digits.   For example, I want to match the following:</p>

<pre><code>123
345
789
</code></pre>

<p>But not</p>

<pre><code>1234
12
12 23
</code></pre>

<p>If I use <code>[0-9]+</code> I match any single string of digits.   I thought <code>[0-9]{3}</code> would work, but when tested in re-builder it doesn't match anything.</p>

It's pretty simple:
```
```
[0-9][0-9][0-9]
```
```