Question

I was trying out an elementary Perl/CGI script to keep track of visitors coming to a web page. The Perl code looks like this:

#!/usr/bin/perl
#KEEPING COUNT OF VISITORS IN A FILE
use CGI':standard';
print "content-type:text/html\n\n";
#opening file in read mode
open (FILE,"<count.dat");
$cnt= <FILE>;
close(FILE);
$cnt=$cnt+1;
#opening file to write
open(FILE,">count.dat");
print FILE $cnt;
close(FILE);
print "Visitor count: $cnt";

The problem is that the web page does not increment the count of visitors on each refresh. The count remains at the initital value of $cnt , ie `1“. Any ideas where the problem lies?

Answer 1

You never test if the attempt to open the file handle works. Given a file which I had permission to read from and write to that contained a single number and nothing else, the code behaved as intended. If the file did not exist then the count would always be 1, if it was read-only then it would remain at whatever the file started at.

More general advice:

• use strict; and use warnings; (and correct code based on their complaints)
• Use the three argument call to open as per the first example in the documentation
• When you open a file always || handle_the_error_in($!);
• Don’t use a file to store data like this, you have potential race conditions.
• Get the name of the language correct