#!/usr/bin/perl -T

use strict;
use warnings;
use CGI qw(:standard);

# print form
print header,
   start_html('test for blank vals'),
   start_form(-method=>'POST'),
   'Enter something (or not) ',
   textfield('value'),
   submit,
   end_form,
   hr,
;

# get val from query - empty string as default
my $value = param('value');

# remove leading and trailing space
$value =~ s/^\s+//;
$value =~ s/\s+$//;

# have to be careful ... the empty string is defined
# and zero is false, so let's check the length instead
if (length($value)) {
   print p("You entered '$value' - thanks. :)");
} else {
   print p('No value entered, please try again');
}
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jeffa

L-LL-L--L-LL-L--L-LL-L--
-R--R-RR-R--R-RR-R--R-RR
B--B--B--B--B--B--B--B--
H---H---H---H---H---H---
(the triplet paradiddle with high-hat)