simple web counter

fred has asked for the wisdom of the Perl Monks concerning the following question:

I'm attempting to add a very simple hit counter to my web page. The source is from the mouse book, CGI Programming with Perl by Scott Guelich, et al (O'Reilly & Associates, Inc).

It seemed like a fairly safe project. Unfortunately, the code always returns 1. I've double checked permissions, and am pretty sure they are correct. Any help on correcting this would be appreciated.

The prototype web page is simple. The CGI output is called via SSI with the statement <!--#include virtual="/cgi-bin/counter.cgi">.

The CGI code is almost straight from the book, with a correction made on the DBM file path and the USE statement listed in the errata.

#!/usr/bin/perl -wT

#use strict;
use Fcntl qw( :DEFAULT :flock );
use DB_File;

use constant COUNT_FILE => "/home/httpd/data/count.dbm";

my %count;
my $url = $ENV{DOCUMENT_URI};
local *DBM;

print "Content-type: text/plain\n\n";

if (my $db = tie %count, "DB_File", COUNT_FILE, O_RDWR | O_CREAT) {
        my $fd = $db->fd;
        open DBM, "+<&=$fd" or die "Could not dup DBM for lock: $!";
        flock DBM, LOCK_EX;
        undef $db;
        $count{$url} = 0 unless exists $count{$url};
        my $num_hits = ++$count{$url};
        untie %count;
        close DBM;
        print "$num_hits\n";
} else {
        print "[Error processing counter data]\n";
}
[download]

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Re: simple web counter by merlyn (Sage) on Sep 15, 2000 at 10:40 UTC
That code doesn't work in real life, in spite of the fact that it was in an Animal Book. You can't flock a tied DBM, because some I/O has already happened before the flock is obtained, and not re-triggered once you have a flock. You need to use a sentinel file before you tie and open. Super search here for `sentinel`, since I've mentioned it once or twice before. {grin} -- Randal L. Schwartz, Perl hacker	[reply]
RE: Re: simple web counter by runrig (Abbot) on Sep 16, 2000 at 00:02 UTC
There is a DB_File::Lock module. Am I missing something?	[reply]
Re: simple web counter by extremely (Priest) on Sep 15, 2000 at 08:17 UTC
I don't know why it doesn't work but I can give you a few things to test. Change the following line so it has a "4" where the "0" is. Does it always return 5 now? That would smell like a DB problem. Probably permissions. `$count{$url} = 0 unless exists $count{$url};` Also, are you sure that your ENVironment contains DOCUMENT_URI? Always having a "" for that could be a problem. Minor nit, why is "use strict;" turned off? What error made you do that? Is that or any other error in your webserver logs? -- $you = new YOU; honk() if $you->love(perl)	[reply] [d/l]
Re^2: simple web counter by Anonymous Monk on Mar 18, 2017 at 13:56 UTC
Even i tried this code from the same book . Following is my code #!/usr/bin/perl use strict; use Fcntl qw (LOCK_EX); use Fcntl; use DB_File; use constant COUNT_FILE => "count.dbm"; my %count; my $num_hits; my $url = $ENV{REQUEST_URI}; local *DBM; print "Content-type : text/plain\n\n"; my $db = tie %count , "DB_File" , COUNT_FILE , O_RDWR \| O_CREAT; if( $db ) { my $fd = $db->fd; open DBM , "+<&=$fd" or die "Count not dump DBM for lock: $!"; flock DBM,LOCK_EX; undef $db; $count{$url} = 0 unless exists $count{$url}; $num_hits = ++$count{$url}; untie %count; close DBM; print "$num_hits\n"; }else{ print "[Error processing counter data]\n"; } [download] Following are my observations when run the code from my terminal it updates the count and prints root@inll11325816l:/usr/lib/cgi-bin# perl counter.cgi Content-type : text/plain 11 root@inll11325816l:/usr/lib/cgi-bin# vi counter.cgi root@inll11325816l:/usr/lib/cgi-bin# perl counter.cgi Content-type : text/plain 12 root@inll11325816l:/usr/lib/cgi-bin# vi counter.cgi root@inll11325816l:/usr/lib/cgi-bin# perl counter.cgi Content-type : text/plain 13 root@inll11325816l:/usr/lib/cgi-bin# perl counter.cgi Content-type : text/plain 14 When i run from the Browser it just exits from the if loop and prints the statement in the else block I have another question also here , why there is no check for the URI we are accessing here , wht if the DOCUMENT_URI or REQUEST_URI ( in my case has a different .html file that is been accessed Can anyone please help here ?	[reply] [d/l]
Re^3: simple web counter by poj (Abbot) on Mar 18, 2017 at 14:23 UTC
Add absolute `/path/folder/` that is writeable by the webserver. For example `/tmp/` `use constant COUNT_FILE => "/tmp/count.dbm";` poj	[reply] [d/l] [select]