This seems like an incredibly long winded, risky and inefficient way to install bun.

I've never actually (knowingly) run Bun before, but decided to give it a try - below is my terminal session to get it running (on macOS):

    $ nix-shell -p bun
    
    [nix-shell:~]$ bun
    Bun is a fast JavaScript runtime, package manager, bundler, and test
    runner. (1.3.5+1e86cebd7)
    
    Usage: bun <command> [...flags] [...args]
    
    Commands:
      run       ./my-script.ts       Execute a file with Bun
                lint                 Run a package.json script
    ... (rest of output trimmed)...

(Edited to wrap a long preformatted line)