tr/SEARCHLIST/REPLACEMENTLIST/cdsr
y/SEARCHLIST/REPLACEMENTLIST/cdsr

...

Options:

    c Complement the SEARCHLIST.
    d Delete found but unreplaced characters.
    s Squash duplicate replaced characters.
    r Return the modified string and leave the original string
    untouched.

If the /c modifier is specified, the SEARCHLIST character set is complemented.
If the /d modifier is specified, any characters specified by SEARCHLIST not
found in REPLACEMENTLIST are deleted. (Note that this is slightly more flexible
than the behavior of some tr programs, which delete anything they find in the
SEARCHLIST, period.) If the /s modifier is specified, sequences of characters
that were transliterated to the same character are squashed down to a single
instance of the character.

If the /d modifier is used, the REPLACEMENTLIST is always interpreted exactly as
specified.