nushell/src/commands/nth.rs

use crate::commands::WholeStreamCommand;
use crate::errors::ShellError;
use crate::parser::CommandRegistry;
use crate::prelude::*;

pub struct Nth;

impl WholeStreamCommand for Nth {
    fn run(
        &self,
        args: CommandArgs,
        registry: &CommandRegistry,
    ) -> Result<OutputStream, ShellError> {
        nth(args, registry)
    }

    fn name(&self) -> &str {
        "nth"
    }

    fn signature(&self) -> Signature {
        Signature::build("nth").required("amount", SyntaxType::Literal)
    }
}

fn nth(args: CommandArgs, registry: &CommandRegistry) -> Result<OutputStream, ShellError> {
    let args = args.evaluate_once(registry)?;

    let amount = args.expect_nth(0)?.as_i64();

    let amount = match amount {
        Ok(o) => o,
        Err(_) => {
            return Err(ShellError::labeled_error(
                "Value is not a number",
                "expected integer",
                args.expect_nth(0)?.span(),
            ))
        }
    };

    Ok(OutputStream::from_input(
        args.input.values.skip(amount as u64).take(1),
    ))
}