Take a look at the HTML source in your browser. If there is more than one instance of the h parameter, cgi will return a list, not a scalar.
If this is the case, and one of the h values is not set, your list will contain an undef value. Also, you would be assigning a list to $h, a scalar, and only getting one value from the list. As there is no guarantee on the order that values for multiple instances of the same parameter will be returned from the browser, you could never be sure which value you are assigning to $h.
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Posts may use any of the Perl Monks Approved HTML tags. Currently these include the following:
<code> <a> <b> <big>
<blockquote> <br /> <dd>
<dl> <dt> <em> <font>
<h1> <h2> <h3> <h4>
<h5> <h6> <hr /> <i>
<li> <nbsp> <ol> <p>
<small> <strike> <strong>
<sub> <sup> <table>
<td> <th> <tr> <tt>
Snippets of code should be wrapped in
<code> tags not
<pre> tags. In fact, <pre>
tags should generally be avoided. If they must
be used, extreme care should be
taken to ensure that their contents do not
have long lines (<70 chars), in order to prevent
horizontal scrolling (and possible janitor
Want more info? How to link
or How to display code and escape characters
are good places to start.