nix3-edit:tldr:5bc48

This command sets the EDITOR environment variable to cat and then runs the nix edit command with a modified version of the nixpkgs variable.

Here is a breakdown of the command:

1. EDITOR=cat sets the EDITOR environment variable to the value cat. The EDITOR variable is often used by command-line tools to determine the user's preferred text editor for editing files.
2. ${nixpkgs#pkg} modifies the value of the nixpkgs variable by removing the substring pkg from the beginning of the string. This is a form of parameter expansion in shell scripting, where # denotes the removal of the shortest match from the beginning of the string.
3. nix edit is a command used in the Nix package manager to open a package or derivation in an editor. By default, it uses the value of the EDITOR environment variable to determine the editor to use.
4. The modified nixpkgs variable is passed as an argument to the nix edit command, which opens the specified package or derivation in the configured editor.

So, this command effectively opens a package or derivation in an editor specified by the EDITOR environment variable, with the modified nixpkgs value.