Storing User Recommendations

Now we must deal with a few issues related to storing new site recommendations. When a user wants to recommend a new site for a particular category, he/she clicks the link labeled Suggest new link at the bottom of the directory page. This link is created dynamically in the print_footer subroutine (Lines 152-157). This calls the print_add_screen subroutine (Lines 99-122) which prints the form. The form is similar to the one below:

When the user completes the form and clicks the Submit Resource button, the data is sent back to the script. Assuming the form method is POST, the add_link subroutine (Lines 55-91) appends the information to $rootdir/$reldir/$new_datafile which in our case would be /www/directory/Computers/Perl/perlhoo_new.csv if the category was Computers/Perl.

File Permissions

File Locking

To solve this potential problem, add_link requests an exclusive lock on the file before it writes to it. This will ensure that data will not be lost. In Line 60, we open the data file in append mode. Then we request an exclusive lock in Line 61. We combine the form data into a CSV record in Lines 63-65 and write it to the file. The lock is released when the file handle is closed in Line 66.