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We've relied on `clap` for building our cli app bootstrapping that figures out the positionals, flags, and other convenient facilities. Nu has been capable of solving this problem for quite some time. Given this and much more reasons (including the build time caused by `clap`) we start here working with our own. |
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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
ScopeFramewith 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 theScopeand put into the external binaries environment-variables-memory area.