Realise a string with context

[roberth]

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Sometimes I just want to paste a string into my shell and run it.

For example

nix-repl> config.system.activationScripts.check-manual-docbook
"if [[ $(cat /nix/store/zvzbmg408jbb7x60kdwndfv68x7mlcnj-options-used-docbook) = 1 ]]; then\n  echo -e \"\\e[31mwarning\\e[0m: This configuration contains option documentation in docbook.\" \\\n          \"Support for docbook is deprecated and will be removed after NixOS 23.05.\" \\\n          \"See nix-store --read-log /nix/store/6vknjm2hbvqpwql7qp1dxhg4hbq5hs26-options.json.drv\"\nfi\n"

nix-repl> :b config.system.activationScripts.check-manual-docbook
error: expression does not evaluate to a derivation, so I can't build it

Describe the solution you'd like

In the repl, when :b evaluates its argument to a string, continue to build the string context. Maybe print the raw string? (ie not in string literal syntax)

In the cli, add a flag to build a string? An nix eval flag? A nix build flag?

e.g.

$ s=$(nix eval --raw --realise nixpkgs#hello.shellHook)
eval "$s"

or perhaps something like

$ s=$(nix build --stdout=string nixpkgs#hello.shellHook)
eval "$s"

or something like --print=raw or --print=json.

Describe alternatives you've considered

a. Keep digging through toplevel instead of building the option I wish to inspect.

b. Write ad hoc script builder in the repl. This is not the same, as the result is a bit harder to read, and the script derivation is slightly cumbersome to write.

Additional context

Priorities

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[nixos-discourse]

This issue has been mentioned on NixOS Discourse. There might be relevant details there:

https://discourse.nixos.org/t/lib-getexe-and-lib-getexe-are-not-safe/43529/16