A PowerShell script for downloading all of the images posted in a subreddit.

SubredditImageDownloader.ps1

param (
  [Parameter(Mandatory = $true)] [string]$Subreddit
)

$ErrorActionPreference = 'Continue'

$UserAgent = "Mozilla/4.0 (compatible; MSIE 6.0; Windows NT 5.1; FSL 7.0.6.01001)"

$StartingDirectory = Get-Location

function getFilename([string]$url) {
  $uri = New-Object -TypeName Uri -ArgumentList $url
  return $uri.Segments[$uri.Segments.Length - 1]
}

function deleteIfJunk([string]$filename) {
  $hash = (Get-FileHash $filename -Algorithm MD5).Hash
  if ($hash -eq "D835884373F4D6C8F24742CEABE74946") {
    Write-Host "Deleting junk file $filename."
    Remove-Item $filename
  }
}

function download([string]$url) {
  Write-Host "Downloading $url..."

  $filename = getFilename($url)

  if (Test-Path $filename) {
    Write-Host "$filename already exists. Skipping."
    return
  }

  try {
    Invoke-WebRequest -Uri $url -OutFile $filename -UserAgent $UserAgent -ErrorAction Continue
    deleteIfJunk($filename)
  }
  catch {
    Write-Host $_.Exception.Message
  }
}

function getJson([string]$jsonUrl) {
  Write-Host "Fetching JSON from $jsonUrl"

  $json = ""
  $success = $false
  do {
    try {
      $json = Invoke-WebRequest $jsonUrl | ConvertFrom-Json
      $success = $true
    }
    catch {
      Write-Error $_.Exception.Message
    }
  } while (-not $success)
  return $json
}

function downloadImages($json) {
  $json.data.children.data | Where-Object { $_.post_hint -eq "image" } | ForEach-Object { download $_.url }
  $after = $json.data.after
  if (-Not [string]::IsNullOrWhiteSpace($after)) {
    $json = getJson("https://www.reddit.com/r/$Subreddit/.json?after=$after")
    downloadImages($json)
  }
}

function getVideoDownloaderExecutableName() {
  $videoDownloaders = @('yt-dlp','youtube-dl')

  foreach ($videoDownloader in $videoDownloaders) {
    if (Get-Command $videoDownloader -ErrorAction SilentlyContinue) { 
      return $videoDownloader
    }
  }

  return $null
}

function downloadVideos($json) {
  $videoDownloader = getVideoDownloaderExecutableName

  if ([string]::IsNullOrWhiteSpace($videoDownloader)) {
    Write-Error "Could not find video downloader. Video downloading disabled."
    return
  }

  $json.data.children.data | Where-Object { $_.post_hint -eq "hosted:video" } | ForEach-Object { & $videoDownloader $_.url }
  $after = $json.data.after
  if (-Not [string]::IsNullOrWhiteSpace($after)) {
    $json = getJson("https://www.reddit.com/r/$Subreddit/.json?after=$after")
    downloadVideos($json)
  }
}

try {
  $Subreddit = $Subreddit -replace "[\/\\\.]",""

  if (Test-Path $Subreddit) {
    $response = Read-Host -Prompt ('Directory {0} already exists. Continue?' -f $Subreddit)
    $response = $response.ToLower()
    if (-not ($response.Equals("y") -or $response.Equals("yes"))) {
      exit
    }
  } else {
    mkdir $Subreddit | out-null
  }

  Set-Location -Path $Subreddit

  $json = getJson("https://www.reddit.com/r/$Subreddit/.json")

  downloadImages($json)

  downloadVideos($json)

  Write-Host -BackgroundColor Green -ForegroundColor White "We processed all the JSON!"
}
finally {
  Set-Location $StartingDirectory
}