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What is this for?

Making cross platform scripts that have 0 install steps / instructions

  • The user does not need to install Curl/Node/Deno, nor anything else
  • The script does not need to “target” an OS; it is a single script, the same file for all OS’s
  • The script is not a binary and is not compiled/mangled; it is readable/editable JavaScript
  • The script will not touch anything installed by the user (no pollution/side-effects)
  • The script will auto-download a specific version of Deno to an isolated folder, and then run itself using that exact version of Deno to ensure consistent/reproducable behavior.
  • Any Deno.land module can be imported/used, no need to reinvent the wheel or bundle code.

This is possible because of some rare builtin tools that allow for a single file to be valid bash, and valid powershell, AND valid JavaScript (based on this StackOverflow answer Is it possible to write one script that runs in bash/shell and PowerShell?)

How do I make an installer script?

  1. Write a Deno script, lets call it install.js
console.log("Hello World")
  1. Install the cli helper (guillotine) to make your script portable
deno install -Af https://deno.land/x/deno_guillotine@0.0.9/main/deno-guillotine.js
  1. Use it to make your script portable
deno-guillotine ./install.js
# if you have a particular version of deno you want to use, include it as the second argument
deno-guillotine ./install.js 1.33.1
  1. Profit

  • Two files will have been generated, which I’ll explain in a moment. More importantly though, typing ./install in the command line will now try an execute the script (even on Windows)

    • On Linux/Mac and other half-decent operating systems supported by Deno (incuding Arm Linux) there is no catch.
    • On Windows there is one catch; a fresh Windows install will block execution of all powershell scripts by default.
      Set-ExecutionPolicy unrestricted will need to be run in an admin terminal before powershell scripts can be executed. After that, it follows the same process as the other operating systems (downloads the specific version of Deno if needed, and executes itself using that version).

  • Two files are generated, but one is just a symlink to the other. And we can get away with a single file (with some compromises):

    • Technically install.ps1 is the only file needed. Typing ./install.ps1 on any OS will execute correctly.
      However, I find the .ps1 ugly. And the .ps1 is only needed for Windows. The other file (the symlink) is what makes it possible to do ./install on all systems:
      • On Windows, if the file is called ./install.ps1 then typing ./install in the command line naturally execute it (no change needed).
      • On Linux/Mac we can make a ./install file that is just a relative symlink to install.ps1. Volia, typing ./install now executes the ./install.ps1 file.
    • If you don’t care about Windows supoort, delete the non-ps1 file (the symlink), and then just rename the .ps1 file so that it doesn’t have a .ps1.

How can something be valid Powershell, Bash, and Deno all at the same time?

I wrote out an explaination here that covers the basics, and it was fairly straightforward to add support for JavaScript on top of Bash/Powershell. In particular, I just took the offical Deno install script and compressed it to fit inline at the top of a file.