passing variable between decks

I'm using Perl to generate dynamic WML, however, I'm not able to pass variables between different subroutines.

This is part of the code in one of the subroutines:

print <<END_of_wml;
Content-type: text/vnd.wap.wml
...
<center>
<p>Please enter a course code:</p>
<input name="course_code" size="9"/><br/>
<anchor>Submit<br/>
<go href="wml.cgi" method="post">
<postfield name="action" value="check_course"/>
<postfield name="abc" value="$course_code"/>
</go>
</anchor>
...

In another subroutine, I tried to display $abc:

print <<END_of_wml;
Content-type: text/vnd.wap.wml
...
<wml>
<card id="test" title="check">
abc = $abc
</card>
</wml>
END_of_wml

The the content of $abc is blank. I also tried \$abc, but still...

What did I do wrong?

oli