tr - translate or delete characters

• tr always reads stdin and writes stdout

• tr from_chars to_chars
  

• tr abc def
  Each a becomes d, each b becomes e and each c becomes f

• tr a-z A-Z
  Convert to upper case

• tr -d abc
  Deletes all a's, b's and c's

• tr -s ' ' ' '
  Convert strings of spaces to single spaces