find(1) . -name '*.?*' -type f | rev(1) | cut(1) -d. -f1 | rev(1) | tr(1) '[:upper:]' '[:lower:]' | sort(1) | uniq(1) --count | sort(1) -rn
search for files in a directory hierarchy
find [-H] [-L] [-P] [-D debugopts] [-Olevel] [path...] [expression]
-name pattern
       Base of file name (the path with the leading directories removed) matches shell  pattern  pattern.
       The  metacharacters  (`*',  `?',  and  `[]')  match a `.' at the start of the base name (this is a
       change in findutils-4.2.2; see section STANDARDS CONFORMANCE below).  To ignore  a  directory  and
       the  files  under  it,  use  -prune;  see  an example in the description of -path.  Braces are not
       recognised as being special, despite the fact that some shells including Bash imbue braces with  a
       special  meaning  in  shell  patterns.   The  filename  matching  is performed with the use of the
       fnmatch(3) library function.   Don't forget to enclose the pattern in quotes in order  to  protect
       it from expansion by the shell.
-type c
       File is of type c:

       b      block (buffered) special

       c      character (unbuffered) special

       d      directory

       p      named pipe (FIFO)

       f      regular file

       l      symbolic link; this is never true if the -L option or the  -follow  option  is  in  effect,
              unless the symbolic link is broken.  If you want to search for symbolic links when -L is in
              effect, use -xtype.

       s      socket

       D      door (Solaris)
    A  pipeline is a sequence of one or more commands separated by one of the control operators | or |&.  The
    format for a pipeline is:

           [time [-p]] [ ! ] command [ [||&] command2 ... ]

    The standard output of command is connected  via  a  pipe  to  the  standard  input  of  command2.   This
    connection  is performed before any redirections specified by the command (see REDIRECTION below).  If |&
    is used, the standard error of command is connected to command2's standard input through the pipe; it  is
    shorthand  for  2>&1  |.   This  implicit  redirection  of  the  standard  error  is  performed after any
    redirections specified by the command.

    The return status of a pipeline is the exit status of the last command, unless  the  pipefail  option  is
    enabled.   If  pipefail  is  enabled,  the  pipeline's return status is the value of the last (rightmost)
    command to exit with a non-zero status, or zero if all commands exit successfully.  If the reserved  word
    !   precedes  a  pipeline, the exit status of that pipeline is the logical negation of the exit status as
    described above.  The shell waits for all commands in the pipeline to terminate before returning a value.

    If the time reserved word precedes a pipeline, the elapsed as well as user and system  time  consumed  by
    its execution are reported when the pipeline terminates.  The -p option changes the output format to that
    specified by POSIX.  When the shell is in posix mode, it does not recognize time as a  reserved  word  if
    the  next  token begins with a `-'.  The TIMEFORMAT variable may be set to a format string that specifies
    how the timing information should be displayed; see the description of TIMEFORMAT under  Shell  Variables

    When the shell is in posix mode, time may be followed by a newline.  In this case, the shell displays the
    total user and system time consumed by the shell and its children.  The TIMEFORMAT variable may  be  used
    to specify the format of the time information.

    Each command in a pipeline is executed as a separate process (i.e., in a subshell).
reverse lines of a file or files
remove sections from each line of files
-d, --delimiter=DELIM
       use DELIM instead of TAB for field delimiter
-f, --fields=LIST
       select only these fields;  also print any line that contains no delimiter character, unless the -s
       option is specified
translate or delete characters
tr [OPTION]... SET1 [SET2]

Translate, squeeze, and/or delete characters from standard input, writing to standard output.

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

       all characters from CHAR1 to CHAR2 in ascending order

       in SET2, copies of CHAR until length of SET1

       REPEAT copies of CHAR, REPEAT octal if starting with 0

       all letters and digits

       all letters

       all horizontal whitespace

       all control characters

       all digits

       all printable characters, not including space

       all lower case letters

       all printable characters, including space

       all punctuation characters

       all horizontal or vertical whitespace

       all upper case letters

       all hexadecimal digits

       all characters which are equivalent to CHAR
sort lines of text files
report or omit repeated lines
-c, --count
       prefix lines by the number of occurrences
-r, --reverse
       reverse the result of comparisons
-n, --numeric-sort
       compare according to string numerical value
source manpages: findrevcutrevtrsortuniqsort