Updating Pages Automatically

Have a need to change a file on your web site on a daily or monthly basis? This month Mr. Lerner tells us how to do it.
Using Databases

One additional method for publishing material on the Internet regularly is using databases. Rather than relying on file names keyed with particular dates, we can create a table that establishes a correspondence between file names and dates. We can then write a CGI program to retrieve the current file or a program meant to be run via cron to create a symbolic link to the current file.

Another option is to store the files inside of the database. However, if we were to do that, we would also have to make it possible for the site's editors and designers to store, retrieve and edit the information inside the database. For our purposes, we will assume the files exist on the server's file system, and we are trying to point to them rather than store their contents in a different way. These examples were tested under Red Hat 5.1, Perl 5.004_04, the database interface (DBI) libraries for Perl, and MySQL, a mostly free relational database system available from http://www.mysql.com/.

Before we can do anything else, we have to create a table to hold the information. The table will be relatively simple, containing only file names and dates. We will assume that each article can be published on only one date, but that each date can contain multiple articles, which makes our table creation command look like the following:

 date    DATE NOT NULL);

In the above, we define filename as a 100-character text field, which must be filled in (NOT NULL) and cannot be the same as any other file name (PRIMARY KEY). If we try to insert the same file name on two different dates, the database will stop us. By contrast, because we want to allow more than one file on a given date, the date field (which has a type of DATE) is defined as NOT NULL, meaning that we must indicate a date with each file name.

In order to add a file to our database, we can use the following SQL command:

INSERT INTO Articles (filename, date)
VALUES ("foobar.html", "1998-06-05");

If you are using MySQL, you must put quotation marks around the date, or the default date of 0000-00-00 will be inserted.

In addition to the confirmation message (1 row affected) we receive upon submitting the above query, we can check the contents of the table:

mysql> SELECT * FROM Articles;
| filename    | date       |
| foobar.html | 1998-06-05 |
1 row in set (0.08 sec)

Entering information into a database using raw SQL is inefficient, prone to errors and unhelpful for users who are unfamiliar or encomfortable with SQL. Listing 7 contains an HTML form that can be used to enter new articles into the database, using the program in Listing 8.

Finally, we will need a version of today.pl that retrieves the file for today. A CGI version of the program is in Listing 9; rewriting it such that it uses cron should be fairly straightforward. A more sophisticated version of the program would even check to see if the named file exists, searching backward.

Publishing regular articles on the Web is far less complicated than publishing a daily or weekly newspaper, but still involves a bit of planning and programming. In addition, no matter what method you choose, you will still have to make some trade-offs between performance and flexibility. Nevertheless, creating a page that changes each day and provides access to the site's archives is not especially difficult and can provide enough variety to draw people.

All listings referred to in this article are available by anonymous download in the file ftp://ftp.linuxjournal.com/pub/lj/listings/issue53/3060.tgz.

Reuven M. Lerner (reuven@netvision.net.il) s an Internet and Web consultant living in Haifa, Israel, who has been using the Web since early 1993. In his spare time, he cooks, reads and volunteers with educational projects in his community.