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README.md |
Nu-Engine
Nu-engine handles most of the core logic of nushell. For example, engine handles: - Passing of data between commands - Evaluating a commands return values - Loading of user configurations
Top level introduction
The following topics shall give the reader a top level understanding how various topics are handled in nushell.
How are environment variables handled?
Environment variables (or short envs) are stored in the Scope
of the EvaluationContext
. That means that environment variables are scoped by default and we don't use std::env
to store envs (but make exceptions where convenient).
Nushell handles environment variables and their lifetime the following:
- At startup all existing environment variables are read and put into
Scope
. (Nushell reads existing environment variables platform independent by asking theHost
. They will most likely come fromstd::env::*
) - Envs can also be loaded from config files. Each loaded config produces a new
ScopeFrame
with the envs of the loaded config. - Nu-Script files and internal commands read and write env variables from / to the
Scope
. External scripts and binaries can't interact with theScope
. Therefore all env variables are read from theScope
and put into the external binaries environment-variables-memory area.