Execution Operators
PHP supports one execution operator: backticks (``). Note that
these are not single-quotes! PHP will attempt to execute the
contents of the backticks as a shell command; the output will be
returned (i.e., it won't simply be dumped to output; it can be
assigned to a variable). Use of the backtick operator is identical
to
shell_exec(). 

Note: The backtick operator is disabled when safe mode is enabled or shell_exec() is disabled.
See also the manual section on Program Execution functions, popen() proc_open(), andUsing PHP from the commandline.



