forked from extern/nushell
17 lines
1.3 KiB
Markdown
17 lines
1.3 KiB
Markdown
# Nu-Engine
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Nu-engine handles most of the core logic of nushell. For example, engine handles:
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- Passing of data between commands
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- Evaluating a commands return values
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- Loading of user configurations
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## Top level introduction
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The following topics shall give the reader a top level understanding how various topics are handled in nushell.
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### How are environment variables handled?
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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).
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Nushell handles environment variables and their lifetime the following:
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- At startup all existing environment variables are read and put into `Scope`. (Nushell reads existing environment variables platform independent by asking the `Host`. They will most likely come from `std::env::*`)
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- Envs can also be loaded from config files. Each loaded config produces a new `ScopeFrame` with the envs of the loaded config.
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- Nu-Script files and internal commands read and write env variables from / to the `Scope`. External scripts and binaries can't interact with the `Scope`. Therefore all env variables are read from the `Scope` and put into the external binaries environment-variables-memory area.
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