LXXX. Program Execution functions
    Those functions provides means to executes commands on the
    system itself, and means secure such commands. Those functions
    are also closely related to the 
    backtick operator.
   
- Spis treści
 - 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
    
 - system -- Execute an external program and display output
 - shell_exec -- 
     Execute command via shell and return complete output as string