Scoping zsh variables

By default in zsh, if you define a local myVariable it will be available to the whole script running it.

Any of those variables defined in your .zshrc will also be visible in your terminal. This can create weird bugs when you accidentally defined a variable with the same name as another zsh script.

Note that those are not environment variables. Even if you can read them from your zsh terminal, they are not accessible from other tools. To explicitly make them available as environment variables, you need to export them.

If you define a variable inside a function, it stays scoped to that function, though. Also, anonymous functions are run as soon as they are defined, and discarded afterwards.

Using those two features, we can define our variables without them being available in the terminal global scope.

I find it a best practice to wrap any of my sourced zsh scripts in a function () { } block, like this:

local one=1
function () {
  local two=2
  export THREE=3
}

one is accessible in the whole .zsh script, including inside of the function, and even during your whole terminal session (you can echo $one). Other, non-zsh, scripts won't be able to read it though.

two is accessible only in the body of the function, and is scoped there and won't be accessible from outside. It's perfect for small variables you need to simplify your code but don't need laying around.

THREE is an environment variable, that can be used in the terminal (echo $THREE) as well as in any other script you're running from the terminal. It's useful if you need to set some global flags or editing global settings (like the $PATH variable).

Tags : #zsh

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