# TIL capitalising letters with regex

# Background

My regex skills have improved since I wrote [Just enough regex to get going](https://techblog.timhilton.xyz/just-enough-regex-to-get-going), though I still think it's a good starting point for a developer who is new to regex. 

In that article I wrote this:

> start simple so that you can get value from using regex in simple use cases. Learn more when you need it.

I stand by that advice, and I am still learning extra regex tips & tricks as I need them.

# Problem

I recently came across code where a code analysis auto-fix had messed up some capitalisation. There were comments which had begun with a capitalised acronym, but the auto-fix converted the first letter to lower-case.

```csharp
// before:
/// <summary>
/// ABCD identifier.
/// </summary>
public int AbcdId { get; set; }

// after:
/// <summary>
/// Gets or sets aBCD identifier.
/// </summary>
public int AbcdId { get; set; }
```

In the context of this codebase, ABCD is a known acronym with a specific meaning. This change begs the question whether an aBCD is somehow different from an ABCD. In my opinion the change makes the comment less useful, not more useful.

# Solution

This felt like something which could be fixed easily with a regex find & replace, but I didn't know if regex could capitalise a lowercase letter. Happily, it can!

The find pattern is the string "Gets or sets ", then a single lowercase letter, then a single uppercase letter.

```
Gets or sets ([a-z])([A-Z])
```

The replace pattern uses `\u` to uppercase the following character, which is the captured lowercase letter in this case.

```
Gets or sets \u$1$2
```

As always there's probably a caveat that not all regex engines support the same features and syntax, so I can't promise this works globally, but it worked for me.