It moves runHook to a later position in the rcfile. After that we are
able to set the PS1 environment-variable for a nix-shell environment
e.g.:
# turn the color of the prompt to blue
shellHook = ''
export PS1="\n\[\033[1;34m\][\u@\h:\w]$\[\033[0m\] ";
'';
‘--run’ is like ‘--command’, except that it runs the command in a
non-interactive shell. This is important if you do things like:
$ nix-shell --command make
Hitting Ctrl-C while make is running drops you into the interactive
Nix shell, which is probably not what you want. So you can now do
$ nix-shell --run make
instead.
So you can have a script like:
#! /usr/bin/env nix-shell
#! nix-shell script.nix -i python
import prettytable
x = prettytable.PrettyTable(["Foo", "Bar"])
for i in range(1, 10): x.add_row([i, i**2])
print x
with a ‘script.nix’ in the same directory:
with import <nixpkgs> {};
runCommand "dummy" { buildInputs = [ python pythonPackages.prettytable ]; } ""
(Of course, in this particular case, using the ‘-p’ flag is more
convenient.)
This allows scripts to fetch their own dependencies via nix-shell. For
instance, here is a Haskell script that, when executed, pulls in GHC
and the HTTP package:
#! /usr/bin/env nix-shell
#! nix-shell -i runghc -p haskellPackages.ghc haskellPackages.HTTP
import Network.HTTP
main = do
resp <- Network.HTTP.simpleHTTP (getRequest "http://nixos.org/")
body <- getResponseBody resp
print (take 100 body)
Or a Perl script that pulls in Perl and some CPAN packages:
#! /usr/bin/env nix-shell
#! nix-shell -i perl -p perl perlPackages.HTMLTokeParserSimple perlPackages.LWP
use HTML::TokeParser::Simple;
my $p = HTML::TokeParser::Simple->new(url => 'http://nixos.org/');
while (my $token = $p->get_tag("a")) {
my $href = $token->get_attr("href");
print "$href\n" if $href;
}
Note that the options to nix-shell must be given on a separate line
that starts with the magic string ‘#! nix-shell’. This is because
‘env’ does not allow passing arguments to an interpreter directly.
If derivation declares multiple outputs and first (default) output
if not "out", then "nix-instantiate" calls return path with output
names appended after "!". Than suffix must be stripped before
ant path checks are done.
This allows you to easily set up a build environment containing the
specified packages from Nixpkgs. For example:
$ nix-shell -p sqlite xorg.libX11 hello
will start a shell in which the given packages are present.
The flag ‘--check’ to ‘nix-store -r’ or ‘nix-build’ will cause Nix to
redo the build of a derivation whose output paths are already valid.
If the new output differs from the original output, an error is
printed. This makes it easier to test if a build is deterministic.
(Obviously this cannot catch all sources of non-determinism, but it
catches the most common one, namely the current time.)
For example:
$ nix-build '<nixpkgs>' -A patchelf
...
$ nix-build '<nixpkgs>' -A patchelf --check
error: derivation `/nix/store/1ipvxsdnbhl1rw6siz6x92s7sc8nwkkb-patchelf-0.6' may not be deterministic: hash mismatch in output `/nix/store/4pc1dmw5xkwmc6q3gdc9i5nbjl4dkjpp-patchelf-0.6.drv'
The --check build fails if not all outputs are valid. Thus the first
call to nix-build is necessary to ensure that all outputs are valid.
The current outputs are left untouched: the new outputs are either put
in a chroot or diverted to a different location in the store using
hash rewriting.
nix-shell with the --command flag might be used non-interactively, but
if bash starts non-interactively (i.e. with stdin or stderr not a
terminal), it won't source the script given in --rcfile. However, in
that case it *will* source the script found in $BASH_ENV, so we can use
that instead.
Also, don't source ~/.bashrc in a non-interactive shell (detectable by
checking the PS1 env var)
Signed-off-by: Shea Levy <shea@shealevy.com>
Nixpkgs's stdenv setup script sets the "nullglob" option, but doing so
breaks Bash completion on NixOS (when ‘programs.bash.enableCompletion’
is set) and on Ubuntu. So clear that flag afterwards. Of course,
this may break stdenv functions in subtle ways...
Nixpkgs' stdenv disables dependency tracking by default. That makes
sense for one-time builds, but in an interactive environment we expect
repeated "make" invocations to do the right thing.
