Aggregating Lines from a CSV who lines match a particular field and save those matches based on that matching field name

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Dog, Table, 12:30, Mercury,abcdef
Dog, Chair, 5:30, Mercury,abcdef
...
Pig, Door, 3:30, Earth, 123
Pig, Door, 3:30, Earth, 45678943985
Goat, Couch, 8:45, Mars, 9876

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{Dog.txt}
Dog, Table, 12:30, Mercury,abcdef
...

{Goat.txt}
Goat, Couch, 8:45, Mars, 9876

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#!/usr/bin/perl -w
use strict;
...

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