Or even better:

my @tops;
open my $inputFileHandle, '<', $filename or die "could not open '$file
+name', because the OS said: $!";
while ( <$inputFileHandle> )
{
    if ( m/^top \- (\d{2}:\d{2}:\d{2})/ )
    {
        push @tops, $1;
    }
}
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