in reply to Parsing in perl?

So many ways to do it!
use Modern::Perl;

say +(split ':')[0] while (<DATA>);

__DATA__
BRCA1:breast cancer 1, early onset
TNF: tumor necrosis factor
OMG:oligodendrocyte myelin glycoprotein

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CountZero

A program should be light and agile, its subroutines connected like a string of pearls. The spirit and intent of the program should be retained throughout. There should be neither too little or too much, neither needless loops nor useless variables, neither lack of structure nor overwhelming rigidity." - The Tao of Programming, 4.1 - Geoffrey James

In Section Seekers of Perl Wisdom