For Mac OS X, run `brew update` every hour. Copy this file to ~/Library/LaunchAgents/git.bachue.brewupdate.plist to install.

git.bachue.brewupdate.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>git.bachue.brewupdate</string>
	<key>ProcessType</key>
	<string>Background</string>
	<key>EnvironmentVariables</key>
	<dict>
		<key>TERM</key>
		<string>ansi</string>
	</dict>
	<key>ProgramArguments</key>
	<array>
		<string>/usr/local/bin/brew</string>
		<string>update</string>
	</array>
    <key>StartInterval</key>
    <integer>3600</integer>
    <key>RunAtLoad</key>
    <true/>
</dict>
</plist>