System program execution

escapeshellarg - Escape a string to be used as a shell argument
escapeshellcmd - Escape shell metacharacters
exec - Execute an external program
passthru - Execute an external program and display raw output
proc_close - Close a process opened by <function>proc_open</function> and return the exit code of that process
proc_get_status - Get information about a process opened by <function>proc_open</function>
proc_nice - Change the priority of the current process
proc_open - Execute a command and open file pointers for input/output
proc_terminate - Kills a process opened by proc_open
shell_exec - Execute command via shell and return the complete output as a string
system - Execute an external program and display the output