Context#
When you use rez-env to create a resolved environment, you are actually creating something called a context. A context is a store of information including:
The initial package request list;
The resolve (the list of variants that were chosen);
A graph which shows the resolve visually.
The context does not store copies of the packages it resolved to; rather, it stores a kind of handle for each, which gives enough information to know where to fetch the full package definition and contents from.
Contexts themselves are quite small, and are stored in JSON format in a file
with the extension rxt. When you use rez-env, it actually creates a temporary
context file on disk, which is removed when the shell is exited:
$ rez-env foo bah
You are now in a rez-configured environment.
resolved by ajohns@14jun01.methodstudios.com, on Wed Oct 22 12:44:00 2014,
using Rez v2.0.rc1.10
requested packages:
foo
bah
resolved packages:
eek-2.6 /packages/inhouse/eek/2.6
foo-1.2 /packages/inhouse/foo/1.2
bah-4 /packages/inhouse/bah/4
> $ echo $REZ_RXT_FILE
/tmp/rez_context_0tMS4U/context.rxt
Baking Resolves#
You can use the rez-env --output flag to write a resolved context directly
to file, rather than invoking a subshell:
$ rez-env foo bah --output test.rxt
Later, you can read the context back again, to reconstruct the same environment:
$ rez-env --input test.rxt
You are now in a rez-configured environment.
resolved by ajohns@14jun01.methodstudios.com, on Wed Oct 22 12:44:00 2014,
using Rez v2.0.rc1.10
requested packages:
foo
bah
resolved packages:
eek-2.6 /packages/inhouse/eek/2.6
foo-1.2 /packages/inhouse/foo/1.2
bah-4 /packages/inhouse/bah/4
> $ █
Contexts do not store a copy of the environment that is configured (that is, the
environment variables exported, for example). A context just stores the resolved
list of packages that need to be applied in order to configure the environment.
When you load a context via rez-env --input, each of the packages’ commands
sections are interpreted once more.
You can think of package commands like fragments of a wrapper script which
configures an environment. By creating a context, you are creating a list of
script fragments which, when run in serial, produce the target environment. So,
if your package added a path to $PATH which included a reference to $USER
for example, this would work correctly even if Joe created the rxt file, and
Jill read it because the commands are reinterpreted when Jill loads the context.
The rez-context Tool#
The rez-context tool inspects context files. When you’re within a resolved subshell, rez-context inspects the current context, unless one is specified explicitly. For example, we can inspect the context created in the previous example, without actually being within it:
$ rez-context test.rxt
resolved by ajohns@14jun01.methodstudios.com, on Wed Oct 22 12:44:00 2014,
using Rez v2.0.rc1.10
requested packages:
foo
bah
resolved packages:
eek-2.6 /packages/inhouse/eek/2.6
foo-1.2 /packages/inhouse/foo/1.2
bah-4 /packages/inhouse/bah/4