http://en.wikipedia.org/wiki/Run-length_encoding

(RLE) is a very simple form of data compression in which runs of data (that is,
sequences in which the same data value occurs in many consecutive data
elements) are stored as a single data value and count, rather than as the
original run. This is most useful on data that contains many such runs: for
example, relatively simple graphic images such as icons, line drawings, and
animations. It is not recommended for use with files that don't have many runs
as it could potentially double the file size.

For example, consider a screen containing plain black text on a solid white
background. There will be many long runs of white pixels in the blank space,
and many short runs of black pixels within the text. Let us take a hypothetical
single scan line, with B representing a black pixel and W representing white:

    WWWWWWWWWWWWBWWWWWWWWWWWWBBBWWWWWWWWWWWWWWWWWWWWWWWWBWWWWWWWWWWWWWW

If we apply the run-length encoding (RLE) data compression algorithm to the
above hypothetical scan line, we get the following:

    12W1B12W3B24W1B14W

Interpret this as twelve W's, one B, twelve W's, three B's, etc.

While:

    WBWBWBWBWBWBWB

would be:

    1W1B1W1B1W1B1W1B1W1B1W1B1W1B

The encoding data is quite longer.

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Write a program that takes a command (encode or decode) an input file and an
output file and either encodes or decodes (to/from RLE) the file.

  perl rle.pl encode input.txt   output.txt
  perl rle.pl decode encoded.txt original.txt