G'day ghosh123,

"In the above code, what does this <<END and END mean ?"

The construct

<<END;
...
END
[download]

is called a heredoc.

Simplistically, it's just a string. In perlop, it's introduced in "Quote and Quote-like Operators" with a lot more detail in "Quote-Like Operators".

"how can I change the code which is in between that <<END and END, to insert a if-else condition for that popup_menu."

Now that you know that's a string, you probably won't be trying to do that any more. :-)

I'd suggest something along these lines:

my $popup_string;

if (some_condition()) {
    $popup_string = ...;
}
else {
    $popup_string = ...;
}

$html .= <<END;
...
<td bgcolor="#EEEEEE">$popup_string</td>
...
END
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