$ abc
bash: abc: command not found           (  )

   ,      (    
 ,  ),    

$ def

bash: ./def: Permission denied.         (  .)

  

      ,    -
,    .  (process)     (,
 ""  9).      -
  ,       .   -
,        .  , 
  ,   (sleep).   
      (""),  -
     .

      ,   
  ,    ,      
  .        ,
    ,   .  
   .



chsh:   . ,     , -
,          
        GUI-.   
     .     (bash,
tcsh  zsh)   RETURN;     , 
       . 
 ,  ,     exit,   
 .       
  (   ),        -
 .      ,   exit 
 ,      .      
.

       ,  -
 chsh:    chsh.        -
    ,     (/bin/bash,
/bin/tcsh  /bin/zsh).

    

  (standard output)   ,    
, , .  ()  "",   -
,       (. 7.3).   
  ,      .    ,

226  II.   Red Hat Linux