From mboxrd@z Thu Jan  1 00:00:00 1970
From: ludo@gnu.org (Ludovic =?utf-8?Q?Court=C3=A8s?=)
Subject: Re: Toward 0.2
Date: Wed, 20 Feb 2013 12:28:27 +0100
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References: <877gm7f01v.fsf@gnu.org> <87obfigz7g.fsf@karetnikov.org>
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In-Reply-To: <87fw0rom1n.fsf@karetnikov.org> (Nikita Karetnikov's message of
	"Tue, 19 Feb 2013 19:39:17 -0500")
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To: Nikita Karetnikov <nikita@karetnikov.org>
Cc: bug-guix@gnu.org

Nikita Karetnikov <nikita@karetnikov.org> skribis:

>>  wrapProgram $out/bin/guile-snarf --prefix PATH : "${gawk}/bin"
>
> How can I get the output of a package?

With the recently-added =E2=80=98package-output=E2=80=99 (singular):

--8<---------------cut here---------------start------------->8---
scheme@(guile-user)> (package-output s binutils "out")
$2 =3D "/nix/store/bfh5c2a4is27jdmc811fp6g0jfac7fiw-binutils-2.22"
scheme@(guile-user)> (package-output s binutils "lib")
$3 =3D "/nix/store/n29brzqlhjkzww51labk9anx493gl4d3-binutils-2.22-lib"
--8<---------------cut here---------------end--------------->8---

Under the hood it calls =E2=80=98package-derivation=E2=80=99, which does th=
e actual
output path computation.

>>   #!/bin/sh
>>   export PATH=3D"/nix/store/...-gawk/bin:$PATH"
>>   exec ./.guile-snarf-real "$@"
>
> Should it be saved as 'guile-snarf'?  And I have to use rename(2),
> right?

You first rename the wrapped program, then create the wrapper as above,
and finally chmod it so that it=E2=80=99s executable.

> What should I use to handle prefixes (e.g., a keyword, a simple
> argument)?  Should they be case insensitive?

Good question.  The thing is that sometimes you want to affect several
environment variables.  Maybe something like:

  (define* (wrap-program file #:rest variables)
     ...)

Where each rest argument has a form like this:

  ("PATH" ":" prefix ("/nix/.../foo/bin" "/nix/.../bar/bin"))

Instead of =E2=80=98prefix=E2=80=99, users could ask for =E2=80=98prefix=E2=
=80=99 (prepend to the search
path) or =E2=80=98=3D=E2=80=99 (set the search path to exactly that value.)

WDYT?

Ludo=E2=80=99.