The expression `with E1; E2' evaluates to E2 with all bindings in
the attribute set E1 substituted. E.g.,
with {x = 123;}; x
evaluates to 123. That is, the attribute set E1 is in scope in E2.
This is particularly useful when importing files containing lots
definitions. E.g., instead of
let {
inherit (import ./foo.nix) a b c d e f;
body = ... a ... f ...;
}
we can now say
with import ./foo.nix;
... a ... f ...
I.e., we don't have to say what variables should be brought into scope.
more common than the latter (which exists only on Linux and
FreeBSD). We don't really care about dropping the saved IDs since
there apparently is no way to quiry them in any case, so it can't
influence the build (unlike the effective IDs which are checked by
Perl for instance).
unreachable paths that haven't been used for N hours. For instance,
`nix-collect-garbage --min-age 168' only deletes paths that haven't
been accessed in the last week.
This is useful for instance in the build farm where many derivations
can be shared between consecutive builds, and we wouldn't want a
garbage collect to throw them all away. We could of course register
them as roots, but then we'd to unregister them at some point, which
would be a pain to manage. The `--min-age' flag gives us a sort of
MRU caching scheme.
BUG: this really shouldn't be in gc.cc since that violates
mechanism/policy separation.
doesn't just print the set of paths that should be deleted. So
there is no more need to pipe the result into `nix-store --delete'
(which doesn't even exist anymore).
* Builder output is written to standard error by default.
* The option `-B' is gone.
* The option `-Q' suppresses builder output.
The result of this is that most Nix invocations shouldn't need any
flags w.r.t. logging.
