use strict;
use warnings;

for (0..2) {
    my $line1 = do { local $/ = "\n\n"; <DATA> };
    print "got a line1: \"$line1\"\n" if(defined($line1));
    my  $line2 = do { local $/ = "paragraph"; <DATA> };
    print "got a line2: \"$line2\"\n" if(defined($line2));
}
__DATA__
This is a paragraph
with two lines.

This is another paragraph
with two lines.

This is a third paragraph.
This paragraph
has three lines.