This sounds suspiciously like homework only because you say that you have not been able to try it. Maybe you should have tried it before submitting it.

That being said, I will give you the benefit of the doubt. My guess is that it will not work because it should be lc($string) not lc $string or lc_$string.

Also, for readability I would do:

for ( keys %input ) 
{
    my $string = $_ . $input->param('wrapper');
    my $lcstring = $input->param('wrapper') . lc($string);
    my $ucstring = $input->param('wrapper') . uc($string);
    $report =~ s/$input->param('wrapper')$string/$input->param($_)/g;
    $report =~ s/$input->param('wrapper')$lcstring/$input->param($_)/g
+;
    $report =~ s/$input->param('wrapper')$ucstring/$input->param($_)/g
+;
}
[download]

At least it is a little clearer.

What is not clear, is why you want to do this. It looks very strange.

NOTE: This is untested, but I think it should work.

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I admit it, I am Paco.