tr - translate character codes

     tr [-cds] [string1] [string2]


     -c   Complement the set of characters in string1

     -d   Delete all characters specified in string1

     -s   Squeeze all runs of characters in string1 to one character


     tr 'A-Z' 'a-z' <x >y
                         # Convert upper case to lower case

     tr -d '0123456789' <f1 >f2
                         # Delete all digits from f1


     Tr performs simple character translation.  When  no  flag  is  specified,
     each  character  in string1 is mapped onto the corresponding character in
     string2 .

     There are two types of tr out there,  one  that  requires  [  and  ]  for
     character classes, and one that does not.  Here is what the example above
     would look like for a tr that needs the brackets:

          tr '[A-Z]' '[a-z]' <x >y

     Use [ and ] if you want to be portable, because a tr  that  doesn't  need
     them will still accept the syntax and mindlessly translate [ into [ and ]
     into ].