tr

    tr [options] [string1 [string2]]

Copy standard input to standard output, performing substitution of characters from string1 to string2 or deletion of characters in string1. Some older System V systems require that string1 and string2 be enclosed in square brackets. (This is true of Solaris's /usr/bin/tr, for example.) Most other versions do not have this requirement. POSIX-compliant versions do not have this requirement either.