def for core

Signature

> def {flags} (def_name) (params) (block)

Flags

• --env: Keep the environment defined inside the command.
• --wrapped: Treat unknown flags and arguments as strings (requires ...rest-like parameter in signature).

Parameters

• def_name: The command name to define.
• params: The command parameters, a comma-separated list inside [].
• block: The body of the command, a list of instructions inside {}.

Input/output types:

Examples

Define a command and run it.

> def say-hi [] { echo 'hi' }; say-hi
hi

Define a command and run it with parameter(s).

> def say-sth [sth: string] { echo $sth }; say-sth hi
hi

Set environment variable by call a custom command.

> def --env foo [] { $env.BAR = "BAZ" }; foo; $env.BAR
BAZ

cd affects the environment, so '--env' is required to change directory from within a command.

> def --env gohome [] { cd ~ }; gohome; $env.PWD == ('~' | path expand)
true

Define a custom wrapper for an external command.

> def --wrapped my-echo [...rest] { ^echo ...$rest }; my-echo -e 'spam\tspam'
spamspam

Define a custom command with a type signature. Passing a non-int value will result in an error.

> def only_int []: int -> int { $in }; 42 | only_int
42

Notes

This command is a parser keyword. For details, check: https://www.nushell.sh/book/thinking_in_nu.html