[email protected]:~$ tr --help

Usage: tr [OPTION]... SET1 [SET2]

Translate, squeeze, and/or delete characters from standard input,

writing to standard output.

  -c, -C, --complement    use the complement of SET1

  -d, --delete            delete characters in SET1, do not translate

  -s, --squeeze-repeats   replace each input sequence of a repeated character

                            that is listed in SET1 with a single occurrence

                            of that character

  -t, --truncate-set1     first truncate SET1 to length of SET2

      --help     display this help and exit

      --version  output version information and exit

SETs are specified as strings of characters.  Most represent themselves.

Interpreted sequences are:

  \NNN            character with octal value NNN (1 to 3 octal digits)

  \\              backslash

  \a              audible BEL

  \b              backspace

  \f              form feed

  \n              new line

  \r              return

  \t              horizontal tab

  \v              vertical tab

  CHAR1-CHAR2     all characters from CHAR1 to CHAR2 in ascending order

  [CHAR*]         in SET2, copies of CHAR until length of SET1

  [CHAR*REPEAT]   REPEAT copies of CHAR, REPEAT octal if starting with 0

  [:alnum:]       all letters and digits

  [:alpha:]       all letters

  [:blank:]       all horizontal whitespace

  [:cntrl:]       all control characters

  [:digit:]       all digits

  [:graph:]       all printable characters, not including space

  [:lower:]       all lower case letters

  [:print:]       all printable characters, including space

  [:punct:]       all punctuation characters

  [:space:]       all horizontal or vertical whitespace

  [:upper:]       all upper case letters

  [:xdigit:]      all hexadecimal digits

  [=CHAR=]        all characters which are equivalent to CHAR

Translation occurs if -d is not given and both SET1 and SET2 appear.

-t may be used only when translating.  SET2 is extended to length of

SET1 by repeating its last character as necessary.  Excess characters

of SET2 are ignored.  Only [:lower:] and [:upper:] are guaranteed to

expand in ascending order; used in SET2 while translating, they may

only be used in pairs to specify case conversion.  -s uses SET1 if not

translating nor deleting; else squeezing uses SET2 and occurs after

translation or deletion.