$ perl -Mstrict -Mwarnings -E '
open my $inFH, q{<}, \ <<EOD or die $!;
hello 1234 5698 7458
hi 1457 7459 6214
good_day 1458
hi 1258 3658 
good_morning 4758
hi 1453
EOD

my @lines;
my %counts;

while ( <$inFH> )
{
    my $first = ( split )[ 0 ];
    $counts{ $first } ++;
    push @lines, [ $_, \ $counts{ $first } ];
}

print for
   map  { $_->[ 0 ] }
   grep { ${ $_->[ 1 ] } == 1 }
   @lines;'
hello 1234 5698 7458
good_day 1458
good_morning 4758
$