/dev/null:  

 /dev/null    (data sink),   
   (bit bucket).  /dev/null    , -
     .     :

$ echo ", " > /dev/null

$

   /dev/null   .    
cat     messages,      
:

$ Is -I messages

-rw-r--r--   1 alex     pubs        25315 Oct 24 10:55 messages
$ cat /dev/null > messages
$ Is -1 messages

-rw-r--r--   1 alex     pubs            0 Oct 24 11:02 messages



   (pipe)      -
      .  ( -
 " " (pipeline))    ,   -
      ,      
    .     -
    .    -
 (|).   ,    
:

  [] |   []

      ,     :

  [] > temp
  [] < temp
rm temp

        -
  _    temp.   
   _   .   
 temp.       ,     ,
       .

        Linux,  
    ,    ,   
.      ,   
   . ,  tr ("translate"  ) -
      .      
 :

tr ! 2

 7.  I: Bourne Again Shell 233