makeWrapper is required to extend the PATH of lesspipe to have file available at runtime:

file is mentioned as required program in lesspipe, so this should be fine: https://github.com/wofr06/lesspipe

Thank you for help. Using "--pure" with nix-shell also uncovered dependency on tput from ncurses, which I added.

I still need help though: while it works now, lesspipe.sh tries to print helpful error message referencing to itself and ends up printing something like:

$ ./result/bin/lesspipe.sh 
LESSOPEN="|/nix/store/b910wzmz5xqfv0i9xapwls8ira5vi0kh-lesspipe-1.82/bin/.lesspipe.sh-wrapped %s"
export LESSOPEN

It should instead refer to the unwrapped version of itself. What is the typical way to handle it? One way I can see right now is to do patching of the lesspipe.sh itself to replace references to 'file' with references to '${file}/bin/file' instead of the wrapProgram step. That seems somewhat fragile. Is there any other canonical way?

Since it seems to be only used there https://github.com/wofr06/lesspipe/blob/lesspipe/lesspipe.sh#L50,
you could create a simple patch that replaces file and tput there with the help of substituteAll: https://github.com/NixOS/nixpkgs/blob/master/pkgs/development/tools/flatpak-builder/default.nix#L78 https://github.com/NixOS/nixpkgs/blob/master/pkgs/development/tools/flatpak-builder/fix-paths.patch

This is more robust on updates then just using sed.

I'm happy with the result now, thank you.

What are the procedures for getting a change into current release branch by the way? I'd like to try it for this change just to see how that works.

# branch of from the release branch
$ git checkout release-18.03
# create a new local branch based on that
$ git checkout -b less-pipe-backport
# cherry pick the commits that were merged in nixpkgs master
$ git cherry-pick -x <commits-from-master...>
# upload to your own nixpkgs fork
$ git push origin less-pipe-backport

and then open a pull request for your less-pipe-backport branch.

Ah ok, no special procedures then. Thanks again.