WSL Minimal Install

wsl-minimal.ps1

#! /usr/bin/env pwsh
<#
    Notes as code for creating a minimal WSL image.
    This is not docker!
#>
#Requires -Version 7.4
Set-StrictMode -Version Latest
$ErrorActionPreference = 'Stop'

# TODO: parameterize all these hard-coded vars
$distro = 'Ubuntu'
$ldistro = $distro.ToLower()

# TODO: ver/what are synonyms; use one, presume the other
$ver = '24'
$what = 'noble'

# TODO: dynamically lookup arch
$arch = 'amd64'

# TODO: find the latest image available
$when = '20240423'

# TODO: un-hard-code this
$WSLroot = 'D:\Users\Curtis\VMs\WSL'

$OutDir = "$WSLroot\$distro\$what\minimal-$when"

# TODO: replace these Ubuntu-specific vars with any distribution such as Fedora
$imgfile = "$ldistro-$ver.04-minimal-cloudimg-$arch-root.tar.xz"
$Uri = "https://cloud-images.ubuntu.com/minimal/releases/$what/release-$when/$imgfile"

$wsldistro = "$distro$ver-minimal-$when"

function main {

    # fetch the root filesystem image
    wgetN -Uri $Uri -OutDir $OutDir

    # create WSL distro if it doesn't already exist
    $exists = wsl --list --quiet |Select-String -Pattern $wsldistro -SimpleMatch
    if ($exists) {
        Write-Host "Distribution '$wsldistro' exists. Not overwriting."
    } else {
        wsl --import "$wsldistro" "$OutDir" "$OutDir\$imgfile" --version 2
        wsl --distribution "$wsldistro" -- bash -c 'apt update && apt upgrade --yes'
    }

    wsl --list --verbose
}

function wgetN {
    param (
        [Parameter(Mandatory = $true)][string]$Uri,
        [string]$OutDir = $PWD
    )

    # $imgfile = Split-Path -Path $Uri -Leaf
    $OutFile = Join-Path -Path $OutDir -ChildPath $imgfile

    if (!(Test-Path -LiteralPath $OutFile)) {
        $resp = Invoke-WebRequest -Uri $Uri -OutFile $OutFile -PassThru
        # without -PassThru above would be a file object instead of response object with needed headers
        $lm = $resp.Headers.'Last-Modified'
        if ($lm) {
            $rtime = [DateTime]::Parse($lm).ToUniversalTime()
            (Get-Item $OutFile).LastWriteTime = $rtime
        }
        return
    }

    $head = Invoke-WebRequest -Uri $Uri -Method HEAD
    $lm = $head.Headers.'Last-Modified'
    if ($lm) {
        $rtime = [DateTime]::Parse($lm).ToUniversalTime()
        $ltime = (Get-Item $OutFile).LastWriteTime.ToUniversalTime()
        if ($rtime -gt $ltime) {
            Invoke-WebRequest -Uri $Uri -OutFile $OutFile
            (Get-Item $OutFile).LastWriteTime = $rtime
        }
    } else {
        Invoke-WebRequest -Uri $Uri -OutFile $OutFile
    }
}

main