  echo     PID  . 
 id2    ($0)  PID   . 
 echo ,       .

Bourne Again Shell    $!  PID  , -
   .     sleep  -
 ,      echo   $!:

$ sleep 60 S

8376
$ echo $!

8376

$?   

    (  ),   -
   .       
 .  $?     .

        false 
   .    true  -
   .      Is -
 ,   :

$ Is es

es
$ echo $?


$ Is xxx

Is: xxx: No such file or directory     (    )

$ echo $?

2

 ,   ,    
  exit (  ),    .
       exit  ,   
       .  
     ,    exit:

$ cat es

echo      7.

exit 7

$ es

     7.

$ echo $?

7

$ echo $?



  es  ,      -
  exit,     7   
   .   echo     -
 es.   echo       echo.
   ,     echo   .

 9.  II: Bourne Again Shell                                            321