Mac OS Catalina: “invalid active developer path” error

After upgrading to Catalina, I encountered the error below. Seems Xcode was no longer available.

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

Try the following in your terminal; otherwise, head to and download Xcode manually.

xcode-select --install

How to add environment variables in Mac OS X

Adding here for reference (tried this in Mac OS X Mojave):

# To set an environment variable, enter the following command:
launchctl setenv variable "value"

# To find out if an environment variable is set, use the following command:
launchctl getenv variable

# To clear an environment variable, use the following command:
launchctl unsetenv variable

Git: Command to fix corrupted repository

I occasionally get fatal, such as:

error: cannot lock ref 'refs/remotes/origin/AB-123': is at dffbe642f088781a5e485227927e141ddb73443a but expected e377921a6d00f4d4c0463774990e03343683177e

Rebasing doesn’t work, but if you do the following it will resolve it:

git gc --prune=now

This guarantees to remove all git garbage.

NOTE: Make sure all your code has been committed before doing this.