Copies a file if it is different than the target

copy-diff

#!/bin/bash
# Copies a file if and only if it is different
if [ "$(diff -q "${1}" "${2}" 2>&1 | wc -l)" -gt 0 ]; then cp "${1}" "${2}"; fi

This can be used in conjunction with a LaunchAgent to copy/replace files when they have changed. I implemented this to work around an issue as described at https://forum.parallels.com/threads/sip-settings-not-preserved-anymore.347821/ where NVRAM.dat was getting removed.

An example LaunchAgent plist file would be:

<?xml version="1.0" encoding="UTF-8"?>
<!DOCTYPE plist PUBLIC "-//Apple Computer//DTD PLIST 1.0//EN" "http://www.apple.com/DTDs/PropertyList-1.0.dtd">
<plist version="1.0">
<dict>
  <key>Label</key>
  <string>com.toonetown.nvram-watcher.macOS</string>
  <key>OnDemand</key>
  <true/>
  <key>Program</key>
  <string>/usr/local/bin/copy-diff</string>
  <key>ProgramArguments</key>
  <array>
    <string>copy-diff</string>
    <string>/path/to/macOS.pvm/NVRAM.dat.working</string>
    <string>/path/to/macOS.pvm/NVRAM.dat</string>
  </array>
  <key>WatchPaths</key>
  <array>
    <string>/path/to/macOS.pvm/NVRAM.dat</string>
  </array>
</dict>
</plist>

As of Parallels 17, it appears that this bug has been fixed!