lix/src/nix/repl.md
2020-12-21 13:32:28 +01:00

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Examples

  • Display all special commands within the REPL:

    # nix repl
    nix-repl> :?
    
  • Evaluate some simple Nix expressions:

    # nix repl
    
    nix-repl> 1 + 2
    3
    
    nix-repl> map (x: x * 2) [1 2 3]
    [ 2 4 6 ]
    
  • Interact with Nixpkgs in the REPL:

    # nix repl '<nixpkgs>'
    
    Loading '<nixpkgs>'...
    Added 12428 variables.
    
    nix-repl> emacs.name
    "emacs-27.1"
    
    nix-repl> emacs.drvPath
    "/nix/store/lp0sjrhgg03y2n0l10n70rg0k7hhyz0l-emacs-27.1.drv"
    
    nix-repl> drv = runCommand "hello" { buildInputs = [ hello ]; } "hello > $out"
    
    nix-repl> :b x
    this derivation produced the following outputs:
      out -> /nix/store/0njwbgwmkwls0w5dv9mpc1pq5fj39q0l-hello
    
    nix-repl> builtins.readFile drv
    "Hello, world!\n"
    

Description

This command provides an interactive environment for evaluating Nix expressions. (REPL stands for 'readevalprint loop'.)

On startup, it loads the Nix expressions named files and adds them into the lexical scope. You can load addition files using the :l <filename> command, or reload all files using :r.

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