I recently run into this problem, after updating my macOS version to Catalina.

Trying to update Hugo via Homebrew triggered this error:

xcrun: error: invalid active developer path (/Library/Developer/CommandLineTools), missing xcrun at: /Library/Developer/CommandLineTools/usr/bin/xcrun

The command was successfully completed, but we don’t want errors, right?

Here’s what I did to solve it.

In the terminal, I ran:

xcode-select --install

This triggered a dialog box in macOS:

After clicking Install and accepting the terms, the download started:

After the installation finished:

I closed the terminal window and opened a new one.

Problem solved.