You either want to construct an iterator:

sub open_record_file {
    my $filein = shift;
    my $regex = shift;


    open my $FH, "<$filein" or die "$!\n";
 
    return sub {
        my $in_block = 0;
        my $last = "}";
        my @array;
 
        while (my $line = <$FH>) {
            if ($line =~ /$regex/) {
                $in_block = 1;
            }
            if ($in_block) {
                push @array, $line;
            }
            if ($line =~ m/$last$/) {
                $in_block = 0;
                last;
            }
        }
        return (@array ? \@array : undef);
    }
}

my $next_record = open_record_file("input.txt",'DH:');

while (my $record = $next_record->()) {
#    do something with the array in $record
}
undef $next_record;
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or create a class.

Update: Fixed incorrect filehandle in the while loop. Thanks to poj.