nix-env:tldr:315f7

The nix-env -u command is used to upgrade already installed packages in your Nix package set.

Here is a breakdown of what each part of the command does:

• nix-env is the Nix package manager's command-line tool that allows managing packages in your package set.
• -u is a flag or option for the nix-env command. In this context, it stands for "upgrade". It instructs nix-env to upgrade the specified packages.

By executing nix-env -u, you are telling the nix-env command to check for available updates for the packages already installed in your package set and upgrade them if updates are found.

It's important to note that this command will only upgrade the packages that were installed using the nix-env command. If a package was installed by other means or managed by another tool, it won't be affected by this command.