nix-repl

nix-repl is a simple read–eval–print loop (REPL) for the Nix package manager.

Installation

Assuming you have Nix installed, just do

$ git clone https://github.com/edolstra/nix-repl.git
$ cd nix-repl
$ nix-env -f . -i nix-repl

Example

Here is a typical nix-repl session:

$ nix-repl
Welcome to Nix version 1.6pre3215_2c1ecf8. Type :? for help.

nix-repl> 3 * 4
12

nix-repl> :l <nixpkgs>
Added 3337 variables.

nix-repl> lib.range 1 5
[ 1 2 3 4 5 ]

nix-repl> :a lib
Added 299 variables.

nix-repl> range 1 5
[ 1 2 3 4 5 ]

nix-repl> xs = range 1 5

nix-repl> map (x: x * x) xs
[ 1 4 9 16 25 ]

nix-repl> :l <nixos>
Added 7 variables.

nix-repl> config.services.dhcpd
{ configFile = null; enable = false; extraConfig = ""; interfaces = [ ... ]; machines = [ ... ]; }

nix-repl> :p config.services.dhcpd
{ configFile = null; enable = false; extraConfig = ""; interfaces = [ "eth0" ]; machines = [ ]; }

nix-repl> config.fileSystems
{ "/" = { ... }; "/boot" = { ... }; }

nix-repl> mapAttrsToList (n: v: v.device) config.fileSystems
[ "/dev/disk/by-label/nixos" "/dev/disk/by-label/boot" ]

nix-repl> :b libjson
these derivations will be built:
  /nix/store/h910xqb36pysxcxkayb1zkr1zcvvk1zy-libjson_7.6.1.zip.drv
  /nix/store/iv0rdx08di0fg704zyxklkvdz6i96lm8-libjson-7.6.1.drv
...
this derivation produced the following outputs:
  out -> /nix/store/ys6bvgfia81rjwqxjlgkwnx6jhsml8h9-libjson-7.6.1

nix-repl> :t makeFontsConf
a function

nix-repl> :b makeFontsConf { fontDirectories = [ "${freefont_ttf}/share/fonts/truetype" ]; }
...
this derivation produced the following outputs:
  out -> /nix/store/jkw848xj0gkbhmvxi0hwpnhzn2716v3c-fonts.conf

nix-repl> :s pan
# Builds dependencies of the ‘pan’ derivation, then starts a shell
# in which the environment variables of the derivation are set

[nix-shell:/tmp/nix-repl]$ echo $src
/nix/store/0ibx15r02nnkwiclmfbpzrzjm2y204fh-pan-0.139.tar.bz2

[nix-shell:/tmp/nix-repl]$ exit

nix-repl>

Tab completion works on variables in scope and on attribute sets. For example:

$ nix-repl  '<nixpkgs>' '<nixos>'
Welcome to Nix version 1.6pre3215_2c1ecf8. Type :? for help.

nix-repl> thunder<TAB> => thunderbird

nix-repl> <TAB>
Display all 3634 possibilities? (y or n)

nix-repl> lib<TAB>
Display all 291 possibilities? (y or n)

nix-repl> xorg.libX<TAB>
xorg.libXdamage  xorg.libXdmcp

nix-repl> config.networking.use<TAB>
config.networking.useDHCP   config.networking.usePredictableInterfaceNames