nu-cmd-lang 0.112.2

Nushell's core language commands
Documentation 
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use nu_engine::command_prelude::*;
use nu_protocol::engine::CommandType;

#[derive(Clone)]
pub struct Def;

impl Command for Def {
    fn name(&self) -> &str {
        "def"
    }

    fn description(&self) -> &str {
        "Define a custom command."
    }

    fn signature(&self) -> nu_protocol::Signature {
        Signature::build("def")
            .input_output_types(vec![(Type::Nothing, Type::Nothing)])
            .required("def_name", SyntaxShape::String, "The command name to define.")
            .required("params", SyntaxShape::Signature, "The command parameters, a comma-separated list inside [].")
            .required("block", SyntaxShape::Closure(None), "The body of the command, a list of instructions inside {}.")
            .switch("env", "Keep the environment defined inside the command.", None)
            .switch("wrapped", "Treat unknown flags and arguments as strings (requires ...rest-like parameter in signature).", None)
            .category(Category::Core)
    }

    fn extra_description(&self) -> &str {
        "This command is a parser keyword. For details, check:
  https://www.nushell.sh/book/thinking_in_nu.html"
    }

    fn command_type(&self) -> CommandType {
        CommandType::Keyword
    }

    fn run(
        &self,
        _engine_state: &EngineState,
        _stack: &mut Stack,
        _call: &Call,
        _input: PipelineData,
    ) -> Result<PipelineData, ShellError> {
        Ok(PipelineData::empty())
    }

    fn examples(&self) -> Vec<Example<'_>> {
        vec![
            Example {
                description: "Define a command and run it.",
                example: "def say-hi [] { echo 'hi' }; say-hi",
                result: Some(Value::test_string("hi")),
            },
            Example {
                description: "Define a command and run it with parameter(s).",
                example: "def say-sth [sth: string] { echo $sth }; say-sth hi",
                result: Some(Value::test_string("hi")),
            },
            Example {
                description: "Set environment variable by call a custom command.",
                example: r#"def --env foo [] { $env.BAR = "BAZ" }; foo; $env.BAR"#,
                result: Some(Value::test_string("BAZ")),
            },
            Example {
                description: "cd affects the environment, so '--env' is required to change directory from within a command.",
                example: "def --env gohome [] { cd ~ }; gohome; $env.PWD == ('~' | path expand)",
                result: Some(Value::test_string("true")),
            },
            Example {
                description: "Define a custom wrapper for an external command.",
                example: r#"def --wrapped my-echo [...rest] { ^echo ...$rest }; my-echo -e 'spam\tspam'"#,
                result: Some(Value::test_string("spam\tspam")),
            },
            Example {
                description: "Define a custom command with a type signature. Passing a non-int value will result in an error.",
                example: "def only_int []: int -> int { $in }; 42 | only_int",
                result: Some(Value::test_int(42)),
            },
        ]
    }
}