Zsh Autoloading Functions

Let's say there's a function file named foobar with following content in our fpath variable:

  foobar() {
      echo helloworld
  }

  echo bonjour

When we autoload foobar, the foobar function will be marked as undefined and have this content:

  foobar () {
      # undefined
      builtin autoload -X
  }

On the first usage of the foobar command, it'll print bonjour and its definition will be this:

  foobar () {
      echo helloworld
  }

Subsequent execution of the command will print helloworld.

My interpretation of this is that when foobar was ran for the first time, it took on the content of the entire file as definition before executing itself.

And when it executed itself, it redefined itself and performed the commands as side effects.

When it performed the commands as side effects during that execution is when we saw "bonjour" being printed, and the subsequent executions used the redefined foobar function.

Let's say the content of the function file was just a function definition:

  foobar() {
      echo helloworld
  }

On the first usage of the foobar command, it'll print "helloworld".

This doesn't really align with the process in the previous experiment though; if it took on the content of the entire file as definition and then executed itself, it would just be performing a redefinition and not printing anything.

I suspect what's happening is that Zsh realized the content was only a simple function definition, so it executed the content and executed the redefined function.

This is what the shell would do to any file when the KSH_AUTOLOAD option is set.

This experiment uses the same content as one of the experiment above, but with the KSH_AUTOLOAD option set.

Hint: You can set the KSH_AUTOLOAD option by running setopt KSH_Autoload.

  foobar() {
      echo helloworld
  }

  echo bonjour

On the first usage of the foobar command, it'll print "bonjour" and "helloworld".

Subsequent usages will only print "helloworld".

The way I interpret this is that the shell will execute the content, which includes a redefinition of the function and then execute the function again which has been redefined.

We can replicate the effects of KSH_AUTOLOAD by calling the redefined function ourselves:

  echo bonjour

  foobar() {
      echo helloworld
  }

  foobar

This is what's described in the official documentation, although they placed the initialization code at the end and don't have a call to the redefined function.