when you call shift it increments $ARGV[0] to $ARGV[1] to $ARGV[2] and so on for each shift used.

No, shift removes the first element of @ARGV on each call, returning the element it removed.

/(\d)\s*(\d)\s*(\d)\s*(\w*)/

Note that this will also match a line as simple as "123", or really anything that has three consecutive digits, since that's the only thing this regex requires. I would strongly recommend using \s+, \d+, and \w+, and anchoring the regex to the beginning and end of the string with ^ resp. $.

As long as that does not corrupt your data set it should be fine (and i am sure it is fine)

Sorry, but how can you be sure? Some file formats require \t as a column separator.

Update: Expanded the last quote and highlighted the part I was reacting to.