while( <DATA> ) {
    chomp;
    if( is_empty($_) ) {
        print "$.: ---\n" if is_empty($_);
    }
    else {
        print "$.: $_\n";
    }
    goto JUMP if $. == 4;
}

sub is_empty {
    return ! length $_[0];
}


BEGIN { print "Beginning execution.\n" }

JUMP: { print "Look, found the JUMP block.\n"; }

__DATA__
First line

Third line
Fourth line
Fifth line