Here is what I've tried:

#!/agl/tools/perl/bin/perl

if($ENV{'REQUEST_METHOD'} eq 'GET') {
   $query=$ENV{'QUERY_STRING'}
   }
elsif($ENV{'REQUEST_METHOD'} eq 'POST') {
   sysread(STDIN,$query,$ENV{'CONTENT_LENGTH'})
   }
else { die 'Unsupported method: $ENV{'REQUEST_METHOD'}' }

# Now $query consists a string with pairs name=value which 
# are sticked '&'

$query =~ s/&/\n/g;

open(FILE, '/home/testuser3:choicebug.txt') or die 'Cannot open file: 
+$!';
print FILE $query;
close FILE;
[download]

_{edited by ybiC: <code> tags enclosing code sample}