To further clarify, what should the output be from lines like

NINETY ALANINE one two three four five six seven
xx yy NINE one two three four five six seven
xx yy NINE one NINE three four five six seven
NINE one two three four five six seven eight nueve ten
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Also, I tend to think of a line read from a file as a single string. You seem to be referring to the non-whitespace substrings of your example strings as "strings". Do you want the non-whitespace substrings of a line containing your target string to be split out as an array or list of individual strings, or is it sufficient to simply return the whole line?

In addition to the documentation links already given, please see perlre, perlretut, and perlrequick, and Short, Self-Contained, Correct Example and maybe How to ask better questions using Test::More and sample data.