php execution operator

PHP supports an execution operator: backtick (``). Note that this is not a single quote! PHP will attempt to execute what is enclosed in backticks as a shell command, and return its output information (i.e., it can be assigned to a variable rather than simply discarded to standard output). The effect of using the backtick operator "`" is the same as the function shell_exec().

Note:

The backtick operator is invalid when safe mode is activated or shell_exec() is turned off.

Note:

Unlike some other languages, backticks cannot be used in double-quoted strings.