From ffeec5f283464744fc0ba850622671eb1e91e4c7 Mon Sep 17 00:00:00 2001 From: John Chapman Date: Sun, 17 Oct 2021 15:24:22 +1100 Subject: [PATCH] Clarify that not all nix packages will use the default build phases --- doc/manual/src/command-ref/nix-shell.md | 16 ++++++++-------- 1 file changed, 8 insertions(+), 8 deletions(-) diff --git a/doc/manual/src/command-ref/nix-shell.md b/doc/manual/src/command-ref/nix-shell.md index 8bcad85e1..0bd54b955 100644 --- a/doc/manual/src/command-ref/nix-shell.md +++ b/doc/manual/src/command-ref/nix-shell.md @@ -110,18 +110,18 @@ shell in which to build it: ```console $ nix-shell '' -A pan -[nix-shell]$ unpackPhase +[nix-shell]$ eval ${unpackPhase:-unpackPhase} [nix-shell]$ cd pan-* -[nix-shell]$ configurePhase -[nix-shell]$ buildPhase +[nix-shell]$ eval ${configurePhase:-configurePhase} +[nix-shell]$ eval ${buildPhase:-buildPhase} [nix-shell]$ ./pan/gui/pan ``` -Note: Other packages may override these phases (the unpackPhase, -configurePhase, buildPhase, etc). -For those, it may be required to do something like -`eval "$configurePhase-configurePhase"` or `eval "$configurePhase"` -depending on how that package's nix files have been written. +The reason we use form `eval ${configurePhase:-configurePhase}` here is because +those packages that override these phases do so by exporting the overridden +values in the environment variable of the same name. +Here bash is being told to either evaluate the contents of 'configurePhase', +if it exists as a variable, otherwise evaluate the configurePhase function. To clear the environment first, and do some additional automatic initialisation of the interactive shell: