‘--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.
'... another level of indirection not shown in the figure above ...'
but in the 'user-environments.png' figure there is '~/.nix-profile'.
the figure was updated with the commit: f982df3 on Mar 16, 2005.
Let's not just improve the error message itself, but also the behaviour
to actually work around the ntfs-3g symlink bug. If the readlink() call
returns a smaller size than the stat() call, this really isn't a problem
even if the symlink target really has changed between the calls.
So if stat() reports the size for the absolute path, it's most likely
that the relative path is smaller and thus it should also work for file
system bugs as mentioned in 93002d69fc58c2b71e2dfad202139230c630c53a.
Signed-off-by: aszlig <aszlig@redmoonstudios.org>
Tested-by: John Ericson <Ericson2314@Yahoo.com>
A message like "error: reading symbolic link `...' : Success" really is
quite confusing, so let's not indicate "success" but rather point out
the real issue.
We could also limit the check of this to just check for non-negative
values, but this would introduce a race condition between stat() and
readlink() if the link target changes between those two calls, thus
leading to a buffer overflow vulnerability.
Reported by @Ericson2314 on IRC. Happened due to a possible ntfs-3g bug
where a relative symlink returned the absolute path (st_)size in stat()
while readlink() returned the relative size.
Signed-off-by: aszlig <aszlig@redmoonstudios.org>
Tested-by: John Ericson <Ericson2314@Yahoo.com>
