Perl examples

You can download these examples, creating files such as "example.pl". The first line, the #! line, will need to be changed to contain the correct path for your Perl interpreter (on Windows, this only really matters for Perl scripts that will be run as CGI programs). Unix/Linux users will probably find their Perl in /usr/bin/perl, but check with the which perl command. The typical Windows install will have the Perl interpereter in C:\Perl\bin". needing a first line like #!/Perl/bin/Perl5.6.1 (your Perl version may differ). Unix/Linux users can set execute permissions on a Perl script (chmod +x example.pl) and then just "execute" a Perl file (enter the file's name as if it were a Unix command). Windows users should open a "Command Prompt" window (run cmd.exe), then check that the Perl interpreter is on their PATH. (You get the current settings for PATH with the command set PATH; if you need to add the Perl interpreter then the command will be something like set PATH=%C:\Perl\bin\;%PATH%). Once the PATH is correct you can run progams by invoking the perl interpreter, e.g. perl example.pl.

Examples include:

• Simple lists
• Hashes
• A simple regular expression tester
• Examples invoking OS functions
• Database access
• CGI examples

These fragments are:

• the example illustrating the creation of city lists from list literals (and also by misusing qw and so producing an incorrect list) and then using various forms of for loop to print list elements;
• the second fragment is the program that creates lists from lines representing a dump of a database table where one has fields with separators such as colons; this has a dimunitive data file that goes with it;
• the third fragment is the example that illustrates sorting of lists, using both the default ordering and a numeric sort function;
• the key word in context example is slightly more interesting, this also needs a data file;

These fragments are:

• the example with a play's cast list repesented as two hashes - role-to-player, player-to-role; this also illustrates some of the varied ways of initializing a hash with literal data;
• the wordcount classic Perl program (using an input FILEHANDLE to read from the films data file);

This fragment is intended to let you experiment with the definition of regular expressions patterns, testing a defined pattern with different input strings.

The directory listing example program is available. This works fine on Windows, try "C:\Perl" as a directory name.

The laboratory class management code is also included. This one will take a little setting up to get to work and is limited to Unix/Linux as it is invoking shell tasks via a system call or backticks construct.

The Perl HTTP minimal client may work and let you grab pages, but it won't find its way past a proxy server.

The drivers and datasources example lets you identify the database drivers that you have installed and then lets you find the datasources that these drivers can access. For example, on a Windows machine you should find an ODBC driver; and this should let you reach any datasource that you have defined with the ODBC data source control panel.

The E-Pal example has a simple program for adding personal records to a database of people interested in finding email-penpals, and for searching the contents of the database. Users define themselves as male, female, or "eperson", and specify the type of the desired penpal (male, female, eperson, or any). Users must also specify five interests from a list of about one hundred. The search will retrieve any records where there is an interest in common and the type preferences of both potential penpals are satisfied. The user interface is poor; as a later exercise you can rework the code as a CGI example and make use of a web page interface.

Enter command (add,search, list (interests), quit): add
Your type : MALE
Your desire : ANY
Enter five personal interests : Cars Jazz Movies Skiing Snowboarding
Your email address : Jason
Enter command (add,search, list (interests), quit): add
Your type : FEMALE
Your desire : ANY
Enter five personal interests : Aerobics ClassicalMusic Movies Painting Skiing
Your email address : Angela
Enter command (add,search, list (interests), quit): search
Your type : FEMALE
Your desire : ANY
Enter five personal interests : Aerobics ClassicalMusic Movies Painting Skiing
Contact mail joe:       Common interests:       Aerobics
Contact mail fran:      Common interests:       ClassicalMusic
Contact mail tom:       Common interests:       Aerobics
Contact mail rachel:    Common interests:       ClassicalMusic
Contact mail Jason:     Common interests:       Movies  Skiing
Contact mail Angela:    Common interests:       Aerobics        ClassicalMusic  Movies  Painting        Skiing
Enter command (add,search, list (interests), quit): quit

The database for this example is just a single table (SQL definition). The program can be made to work if you create the database, modify the program so that it uses the correct database URL, and change the user-name and password. A Microsoft Access file is available in compressed form; Windows users should be able to install it somewhere and then use the Control Panel "Data Sources" to create a datasource named "epalfinder" that references this database. (The code supplied uses a DBD-ODBC connection.)

You need to have your Apache running first. You should have got this to work earlier.

The first example is the one with the trivial form with a radio-button choice that feeds data to a program that prints nursery rhyme responses.

The form is:

<html><head><title>Test page</title></head>
<body>
<form method=post 
	action="/cgi-bin/form1.cgi">
What are you? <br />
<input type=radio name=sex value=Boy>Boy
<input type=radio name=sex value=Girl>Girl
<input type=radio name=sex value=Unsure checked>Unsure
<br />
<input type=submit>
</form></body></html>

This should be installed in the htdocs directory as form1.html.

The Perl CGI program should be installed in the cgi-bin directory a form1.cgi. (The file extension doesn't matter, so long as the file name is the same as in the HTML form. All files in the cgi-bin directory are treated as CGI scripts. Later you may want more elaborate configurations with CGI programs permitted in other directories; then the file extension, like cgi as used here, should be something that is defined as being handled as a cgi script (an AddHandler directive in httpd.conf file). The #! line will need to be edited to specify the pathname of your Perl (the code is for a Windows Apache - ActivePerl set up using their default directories).

Once both files are installed, and access permissions are set on Unix/Linux, you should be able to run this little test by pointing a browser at http://localhost/form1.html (assuming Windows Apache, for Linux you would have to specify the port as 8080).

The first version of the form handling program uses just standard Perl constructs with most of the HTML code as "here" strings. Another version uses the CGI module (this should be part of your Perl release, you shouldn't have to download and install it). In this version, the various functions defined in the CGI module are used to format headers, paragraphs and so forth. It is a matter of personal preference. I actually prefer the naive approach with the "here" strings. They make it easier for your web designer colleague to change a page layout without damaging code.

Finally, there is the epal example. This is a web-based version of the earlier DBI database example. The form page allows web users to add their details to your database or search the database for email pen-pals. The CGI processing program checks the request (possibly returning a fixed error response page) and then does the add or search operation. (Obviously, you have to edit database details if you try to set this up on your own system; the example code worked with ODBC and the Microsoft Access database used in the earlier example. The Access database does not have to be in the htdocs part of your file space. Access wouldn't withstand multiple concurrent access from many copies of the CGI program - but it is unlikely that you email pen pal site would be under that kind of load.)