. 7.2.   

         , 
     (   , ,   ,
 )      (   /bin) , 
  Is    .       -
         ,  -
     .     , 
 ,      (shell variable) PATH.  
 PATH    "PATH:    "  9. 
   which  whereis   "which, whereis:  "
 5.

      ,2    
:

  ,             -
  -       PATH.   bash 
    PATH   (.):

$ =$:.

          PATH
; .  "PATH  "   9.

 7,  I: Bourne Again Shell 225