echo "Arch Linus." | tr 's' 'x'

Arch Linux.

echo "Apple_Banana" | tr 'a' 'b'

Apple_Bbnbnb

echo "Apple_Banana" | tr 'a_' 'b='

Apple=Bbnbnb

echo "Apple_Banana" | tr 'a_n' 'b=q'

Apple=Bbqbqb

echo "Apple_Banana" | tr 'a_np' 'b=qg'

Aggle=Bbqbqb

tr -c '[:print:]' '.' < /bin/bash | less

cat nani.txt

Omae
wa
mou
shindeiru

xxd nani.txt

00000000: 4f6d 6165 200a 7761 200a 6d6f 7520 0a73  Omae .wa .mou .s
00000010: 6869 6e64 6569 7275 200a                 hindeiru .

cat nani.txt | tr -d '\n'

Omae wa mou shindeiru

cat nani.txt | tr -d '\n' | xxd

00000000: 4f6d 6165 2077 6120 6d6f 7520 7368 696e  Omae wa mou shin
00000010: 6465 6972 7520                           deiru

{
  """inventory""":[
    {
      """type""":"""coal""",
      """count""": 43
    },
    {
      """type""":"""diamond""",
      """count""": 64
    },
    {
      """type""":"""lapis_lazuli""",
      """count""": 9999999
    }
  ]
}

cat blocks.json | tr -s '"'

{
  "inventory":[
    {
      "type":"coal",
      "count": 43
    },
    {
      "type":"diamond",
      "count": 64
    },
    {
      "type":"lapis_lazuli",
      "count": 9999999
    }
  ]
}

man tr

...
       [:alnum:]
              all letters and digits

       [:alpha:]
              all letters

       [:blank:]
              all horizontal whitespace

       [:cntrl:]
              all control characters
...

info tr

...
     Many historically common and even accepted uses of ranges are not
     portable.  For example, on EBCDIC hosts using the ‘A-Z’ range will
     not do what most would expect because ‘A’ through ‘Z’ are not
     contiguous as they are in ASCII.  If you can rely on a POSIX
     compliant version of ‘tr’, then the best way to work around this is
     to use character classes (see below).  Otherwise, it is most
     portable (and most ugly) to enumerate the members of the ranges.
...

info tr

...
   Currently ‘tr’ fully supports only single-byte characters.
Eventually it will support multibyte characters; when it does, the ‘-C’
option will cause it to complement the set of characters, whereas ‘-c’
will cause it to complement the set of values.  This distinction will
matter only when some values are not characters, and this is possible
only in locales using multibyte encodings when the input contains
encoding errors.
...