OK, so you can now say "Hello" to the world. You are a programmer at last. Now we want to introduce some interactivity!
We want to ask a question on a web page and give an appropriate response. We do this by passing parameters.
The easiest way to pass parameters to a cgi program is with a form. (form tutorial) When you create a form, each field on the form has a name and an associated value, which is whatever you type into the field.
<FORM METHOD="POST" ACTION="/tutorial-scripts/form1.cgi">
What is your favourite colour: <INPUT NAME="colour">
<INPUT TYPE="submit">
</FORM>
which looks like this:
What is your favourite colour:
|
When you click on the submit button, the browser passes those name=value pairs to the cgi program specified in the form in an encoded format. For example, if you entered "red", the form would return colour=red
The CGI.pm module
The CGI Perl module (CGI.pm) provides a simple way to create Perl CGI programs. You can use the CGI module to take care of the HTTP protocol requirements, and to extract the parameters of these name=value pairs.
To include the CGI module in your program just add the following line near the top:
use CGI qw(:cgi);
To extract a value from a form, use the param() function. From the previous example param("colour") returns the value "red"
Have a good look at the CGI code and you will know what is going on.
Passing a Parameter to CGI.pm
This is a simple program passing one parameter to the CGI.pm module.
In the form shown below, the text field is called "myname".
What is your name: |
The cgi program calls the CGI.pm module to extract the "myname" parameter from the form and load it into a variable called $who. It then generates an HTML page which prints the contents of this variable.
Things to note
To use the CGI Perl module, insert the line use CGI qw(:cgi); at the top.
Use the param() function to extract the value of the textfield.
Passing Multiple Parameters to CGI.pm
This is a more advanced program as it passes multiple parameters to the CGI.pm module.
In the form shown below, the text fields are called "name", "phone" and "food".
The fields "name" and "phone" contain just one value each, but "food" can contain many values. The cgi program assumes all parameters could contain multiple values. It loops through all the parameters putting their contents in an array called "@values" and prints a nicely HTML formatted line of the name=value pairs, separating the values with commas.
Things to note
When using Multi-Choice fields, you must place the values into an array.
So we are getting a little bit more complex. Analyse the code and you will see what is happening. Stick with it and do not worry too much about multi-choice fields as this is only an optional extra.
Ok, ready for the next step...
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