   , ,     ,
 , ,    .   -
      .    -
 ,       .  
         export
(.  "export:    "    ).

  

         , -
    ().    
    exec ("execute"  ).   
fork,  exec    ( ). 
   , ,  --
,  exec  ,      -
   .     -
,  exec  .    exec -
   ,     . 
   ,      , -
        .

   ,       ,  
    ,       -
 bash,      .  
 bash   ,      
whoson:

$ bash whoson

  bash   ,  ,  
  whoson   (     ). 
   bash       whoson,  , -
     -   .

        bash,   -
   ,        -
  .      -
   ,      .  , 
  ,          ( 
   ,         ).
  bash     ,    -
,       , ,    ,
  bash (   ),     , -
 .

sh    Bourne Shell.   Bourne Shell -
  sh.  sh   bash,     Bourne Shell.
    /bin/bash,        bash.
  bash  sh  bash    -
   Bourne Shell (    ).

 9.  II: Bourne Again Shell 299