The mod_setenvif module allows you to set environment variables according to whether different aspects of the request match regular expressions you specify. These environment variables can be used by other parts of the server to make decisions about actions to be taken. The SetEnvIf directive defines [...]

The stat command can be use to check file status ( like file properties on Windows platform) or check the file system status on Linux. It comes from GNU Coreutils package. (function(d, s, id) { var js, fjs = d.getElementsByTagName(s)[0]; if (d.getElementById(id)) return; js = d.createElement(s); [...]