#!/usr/bin/perl

use strict; # https://www.perlmonks.org/?node_id=11154123
use warnings;
use List::AllUtils qw( uniq_by );

open my $fh, '<', \<<END or die;
nick 5
nick 10
nick 20
john 78
erik 9
erik 12
END

my @firstofeachname = uniq_by { (split)[0] } <$fh>;

print @firstofeachname;
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Outputs:

nick 5
john 78
erik 9
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