Periodically update homebrew once a week.

README.md

Simply add this to ~/Library/LaunchAgents/homebrew.mxcl.update.plist and run launchctl load ~/Library/LaunchAgents/homebrew.mxcl.update.plist.

homebrew.mxcl.update.plist

<?xml version="1.0" encoding="UTF-8"?>
<!DOCTYPE plist PUBLIC "-//Apple//DTD PLIST 1.0//EN" "http://www.apple.com/DTDs/PropertyList-1.0.dtd">
<plist version="1.0">
  <dict>
    <key>Label</key>
    <string>homebrew.mxcl.update</string>
    <key>ProgramArguments</key>
    <array>
      <string>brew</string>
      <string>update</string>
    </array>
    <key>StartCalendarInterval</key>
    <dict>
      <key>Minute</key>
      <integer>0</integer>
      <key>Hour</key>
      <integer>3</integer>
      <key>Weekday</key>
      <integer>1</integer>
    </dict>
    <key>StartInterval</key>
    <integer>604800</integer>
  </dict>
</plist>