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nix-super/src/nix/repl.md
Alexander Bantyev 33926ed1e7
nix repl: add :log 
Add a :log command that shows logs for a derivation.

Closes https://github.com/NixOS/nix/issues/3504

Co-authored-by: Taeer Bar-Yam <taeer@bar-yam.me>
2021-12-06 16:52:50 +03:00

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R""(

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; hello > $out"

nix-repl> :b drv
this derivation produced the following outputs:
  out -> /nix/store/0njwbgwmkwls0w5dv9mpc1pq5fj39q0l-hello

nix-repl> builtins.readFile drv
"Hello, world!\n"

nix-repl> :log drv
Hello, world!

Description

This command provides an interactive environment for evaluating Nix expressions. (REPL stands for 'read–eval–print 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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