if ($var ne '')

##</code><code>##

echo "foo" | perl -MCGI=param,-debug -le'defined param("foo") and print "defined!"'
# doesn't print defined! ??

echo "foo=" | perl -MCGI=param,-debug -le'defined param("foo") and print "defined!"'
echo "foo&" | perl -MCGI=param,-debug -le'defined param("foo") and print "defined!"'
echo "&foo" | perl -MCGI=param,-debug -le'defined param("foo") and print "defined!"'
# these all print defined!