View source for FAQ/nixpkgs

Question: When I do an <code>import <nixpkgs> {}</code>, which ''channel'' or path gets imported.

Answer: 

Use <code>nix repl '<nixpkgs>' </code> on shell and then enter <code>path</code> in the repl to know what nixpkgs is currently being used. 

Nix tools use <code>$NIX_PATH </code> to decide which path to use in the <code> import </code> call. The first entry in that variable is typically <code> <userhome>/.nix-defexpr/channels </code>. If a user has explicitly added a channel named <code>nixpkgs</code>, then that channel is used in the <code>import <nixpkgs></code> call. Otherwise, the <code>nixpkgs=</code> named entry is used for the <code>import <nixpkgs> </code> call. 

Some tools don't fully respect <code>$NIX_PATH </code> and instead search <code>~/.nix-defexpr</code> so there might be some unexpected behavior.