int popen (string command, string mode)
Opens a pipe to a process executed by forking the command given by command.
Returns a file pointer identical to that returned by fopen(), except that it is unidirectional (may only be used for reading or writing) and must be closed with pclose(). This pointer may be used with fgets(), fgetss(), and fputs().
If an error occurs, returns false.
$fp = popen ("/bin/ls", "r");
See also pclose().