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Would that do what you want?
perl -anF'[/._=":]' -e 'print "@F[2,3,4,7,8,17,20,21,27,30]\n"' file.txt

Could you please state, in English, the logic determining which words are to be discarded and which words are to be printed?

It isn't at all clear to me why your desired output excludes "world",...