How to read every 3 lines in perl?

Question

Sorry for the bad English

I have a txt file like this:

id: 1
name: a
sex: m
id: 2
name: b
sex: f

so I would like to read every 3 lines

Answer 1

The following does what you ask:

my @recs;
while (!eof()) {
   my %rec;
   for (1..3) {
      chomp( my $line = <> );
      my ($key, $val) = split(/:\s*/, $line, 2);
      $rec{$key} = $val;
   }

   push @recs, \%rec;
}

And so does the following:

my @recs;
my $rec;
while (<>) {
   chomp;
   my ($key, $val) = split(/:\s*/, $_, 2);
   if ($. % 3 == 1) {
      $rec = {};
      push @recs, $rec;
   }

   $rec->{$key} = $val;
}

However, I think it would be best to rely on records starting with the id key-value.

my @recs;
my $rec;
while (<>) {
   chomp;
   my ($key, $val) = split(/:\s*/, $_, 2)
   if ($key eq 'id') {
      $rec = {};
      push @recs, $rec;
   }

   $rec->{$key} = $val;
}