Create RAM Disk in MacOS and move some cache folders to RAM

macos_ramdisk_setup.sh

#!/bin/bash

## Read and edit this file.
## Run it once as a root.

FILE="/Library/Scripts/ramdisk.sh"

if [[ $EUID -ne 0 ]]; then
  echo "You must be a root user" 2>&1
  exit 1
else
  cat > "$FILE" << 'EOF'
#!/bin/bash

# Size at the end is * 2048 where 2048 = 1 MB, so 8388608 = 4096 MB

if ! test -e "/Volumes/RAMD"; then
  diskutil erasevolume HFS+ "RAMD" `hdiutil attach -nobrowse -nomount ram://8388608`
fi

CACHEDIR="/Volumes/RAMD/.Cache"

if test -e "/Volumes/RAMD"; then

# Create CacheDir
  mkdir -p "$CACHEDIR"

# Google Chrome Cache
  mkdir -p "$CACHEDIR/GoogleChrome/com.google.Chrome"
  mkdir -p "$CACHEDIR/GoogleChrome/Default"
  mkdir -p "$CACHEDIR/GoogleChrome/Service Worker/CacheStorage"
  mkdir -p "$CACHEDIR/GoogleChrome/Service Worker/ScriptCache"
  if [ ! -L "$HOME/Library/Caches/com.google.Chrome" ]
  then
    rm -rf "$HOME/Library/Caches/com.google.Chrome"
    ln -s "$CACHEDIR/GoogleChrome/com.google.Chrome" "$HOME/Library/Caches/com.google.Chrome"
  fi
  if [ ! -L "$HOME/Library/Caches/Google/Chrome/Default" ]
  then
    rm -rf "$HOME/Library/Caches/Google/Chrome/Default"
    ln -s "$CACHEDIR/GoogleChrome/Default" "$HOME/Library/Caches/Google/Chrome/Default"
  fi
  if [ ! -L "$HOME/Library/Application Support/Google/Chrome/Default/Service Worker/CacheStorage" ]
  then
    rm -rf "$HOME/Library/Application Support/Google/Chrome/Default/Service Worker/CacheStorage"
    ln -s "$CACHEDIR/GoogleChrome/Service Worker/CacheStorage" "$HOME/Library/Application Support/Google/Chrome/Default/Service Worker/CacheStorage"
  fi
  if [ ! -L "$HOME/Library/Application Support/Google/Chrome/Default/Service Worker/ScriptCache" ]
  then
    rm -rf "$HOME/Library/Application Support/Google/Chrome/Default/Service Worker/ScriptCache"
    ln -s "$CACHEDIR/GoogleChrome/Service Worker/ScriptCache" "$HOME/Library/Application Support/Google/Chrome/Default/Service Worker/ScriptCache"
  fi

# Chromium Cache
  mkdir -p "$CACHEDIR/Chromium/Default"
  mkdir -p "$CACHEDIR/Chromium/Service Worker/CacheStorage"
  mkdir -p "$CACHEDIR/Chromium/Service Worker/ScriptCache"
  if [ ! -L "$HOME/Library/Caches/Chromium/Default" ]
  then
    rm -rf "$HOME/Library/Caches/Chromium/Default"
    ln -s "$CACHEDIR/Chromium/Default" "$HOME/Library/Caches/Chromium/Default"
  fi
  if [ ! -L "$HOME/Library/Application Support/Chromium/Default/Service Worker/CacheStorage" ]
  then
    rm -rf "$HOME/Library/Application Support/Chromium/Default/Service Worker/CacheStorage"
    ln -s "$CACHEDIR/Chromium/Service Worker/CacheStorage" "$HOME/Library/Application Support/Chromium/Default/Service Worker/CacheStorage"
  fi
  if [ ! -L "$HOME/Library/Application Support/Chromium/Default/Service Worker/ScriptCache" ]
  then
    rm -rf "$HOME/Library/Application Support/Chromium/Default/Service Worker/ScriptCache"
    ln -s "$CACHEDIR/Chromium/Service Worker/ScriptCache" "$HOME/Library/Application Support/Chromium/Default/Service Worker/ScriptCache"
  fi

# Opera Cache
  mkdir -p "$CACHEDIR/Opera/com.operasoftware.Opera"
  if [ ! -L "$HOME/Library/Caches/com.operasoftware.Opera" ]
  then
    rm -rf "$HOME/Library/Caches/com.operasoftware.Opera"
    ln -s "$CACHEDIR/Opera/com.operasoftware.Opera" "$HOME/Library/Caches/com.operasoftware.Opera"
  fi

# Safari Cache
  mkdir -p "$CACHEDIR/Safari/com.apple.Safari"
  mkdir -p "$CACHEDIR/Safari/com.apple.Safari.SafeBrowsing"
  if [ ! -L "$HOME/Library/Caches/com.apple.Safari" ]
  then
    rm -rf "$HOME/Library/Caches/com.apple.Safari"
    ln -s "$CACHEDIR/Safari/com.apple.Safari" "$HOME/Library/Caches/com.apple.Safari"
  fi
  if [ ! -L "$HOME/Library/Caches/com.apple.Safari.SafeBrowsing" ]
  then
    rm -rf "$HOME/Library/Caches/com.apple.Safari.SafeBrowsing"
    ln -s "$CACHEDIR/Safari/com.apple.Safari.SafeBrowsing" "$HOME/Library/Caches/com.apple.Safari.SafeBrowsing"
  fi

# Apple Music Cache
  mkdir -p "$CACHEDIR/com.apple.Music"
  if [ ! -L "$HOME/Library/Caches/com.apple.Music" ]
  then
    rm -rf "$HOME/Library/Caches/com.apple.Music"
    ln -s "$CACHEDIR/com.apple.Music" "$HOME/Library/Caches/com.apple.Music"
  fi

# Spotify Cache
  mkdir -p "$CACHEDIR/Spotify/com.spotify.client"
  mkdir -p "$CACHEDIR/Spotify/PersistentCache"
  if [ ! -L "$HOME/Library/Caches/com.spotify.client" ]
  then
    rm -rf "$HOME/Library/Caches/com.spotify.client"
    ln -s "$CACHEDIR/Spotify/com.spotify.client" "$HOME/Library/Caches/com.spotify.client"
  fi
  if [ ! -L "$HOME/Library/Application Support/Spotify/PersistentCache" ]
  then
    rm -rf "$HOME/Library/Application Support/Spotify/PersistentCache"
    ln -s "$CACHEDIR/Spotify/PersistentCache" "$HOME/Library/Application Support/Spotify/PersistentCache"
  fi

# VSCodium Cache
  mkdir -p "$CACHEDIR/VSCodium/Cache"
  mkdir -p "$CACHEDIR/VSCodium/CachedData"
  if [ ! -L "$HOME/Library/Application Support/VSCodium/Cache" ]
  then
    rm -rf "$HOME/Library/Application Support/VSCodium/Cache"
    ln -s "$CACHEDIR/VSCodium/Cache" "$HOME/Library/Application Support/VSCodium/Cache"
  fi
  if [ ! -L "$HOME/Library/Application Support/VSCodium/CachedData" ]
  then
    rm -rf "$HOME/Library/Application Support/VSCodium/CachedData"
    ln -s "$CACHEDIR/VSCodium/CachedData" "$HOME/Library/Application Support/VSCodium/CachedData"
  fi

# JetBrains Products Cache & Logs
  mkdir -p "$CACHEDIR/JetBrains/Caches"
  if [ ! -L "$HOME/Library/Caches/JetBrains" ]
  then
    rm -rf "$HOME/Library/Caches/JetBrains"
    ln -s "$CACHEDIR/JetBrains/Caches" "$HOME/Library/Caches/JetBrains"
  fi
  mkdir -p "$CACHEDIR/JetBrains/Logs"
  if [ ! -L "$HOME/Library/Logs/JetBrains" ]
  then
    rm -rf "$HOME/Library/Logs/JetBrains"
    ln -s "$CACHEDIR/JetBrains/Logs" "$HOME/Library/Logs/JetBrains"
  fi

# /usr/bin/chflags hidden "/Volumes/RAMD" #Hide RAMD volume
fi

unset CACHEDIR

EOF

fi

if [ -f "$FILE" ]; then
  sudo defaults write com.apple.loginwindow LoginHook "$FILE"
fi

chmod a+x $FILE

unset FILE

google chrome/ safari cache doesn't seem to move to RAMD per my testing

Yes, that seems to be the case that this is no longer working for Chrome/Safari. According to this Japanese here it is because of the sandboxing around Safari and Chrome are now even more strong so that they even block symlinks going out of the sandbox allowed paths. And symlinks leading to a Ramdisk under /Volumes folder are blocked (if the google translation of his site is correct). So he created two separat Ramdisks (one for Chrome and one for Safari) directly at paths where the caches are placed.
${HOME}/Library/Caches/Google
${HOME}/Library/Containers/com.apple.Safari/Data/Library/

I just tired the script for Safari 16 only (I comment out the Chrome part in the script since I don't use Chrome) and according to FSMonitor it seems to work.

Here is the Japanese website with the article and the bash script:
https://sakura.lazycat.info/archives/1018.html