CGI Programming with Perl

CGI Programming with `Perl`

CGI linkage

The connection between the HTML document displayed by the browser and a CGI program on the server

Where are CGI Perl programs stored?

How does the server recognizes them as Perl programs?

CGI programs reside in a specific subdirectory,cgi-bin/, on the server
- The cgi-bin/ at personal.utulsa.edu is a subdirectory of public_html/
- CGI programs are invoked by the server, their access protection must be set to allow this
```
chmod a+rx cgi-bin
```

The server can be set to recognize requested file by it's extension

If a CGI program has been compiled, the server can invoke the executable code directly

The Perl system must be invoked on every Perl CGI program

Add a special line to the beginning of the program

This line specifies that Perl must be run and the location of perl
```
#!/usr/bin/perl -w
```
- The #! specifies that the program whose address follows must be run on the rest of the file
- The path, /usr/bin/perl, to the perl system can change from system to system
- The flag, -w, used on the perl system, indicates to the compiler to produce warnings for potential errors
- For compiled versions of Perl consider

A call to a CGI program is done through a link in an HTML document

<a href="cgi-bin/reply.pl">
Click here to run the CGI program, reply.pl 
</a>

If the cgi-bin directory is not a subdirectory of public_html a full path (absolute URL) must be specified

The CGI program can be on any Web server on the internet!!

<!DOCTYPE HTML PUBLIC "-//W3C//DTD XHTML 1.0 strict//EN"
"http://www.w3.org/TR/xhtml1/dtd/xhtml1-strict.dtd">

<!-- reply.html
     A trivial document to call a simple CGI Perl program
     -->

<html> 
<head> 
<title> HTML to call the CGI-Perl program reply.pl
</title>
</head> 
<body>
<p>
This is our first CGI-Perl example
<br /><br />
<a href="http://personal.utulsa.edu/~diaz/cgi-bin/reply.pl">
Click here to run the CGI program, <tt>reply.pl</tt>
</a>
</p>
</body> 
</html>

The CGI program, reply.html, should simply return a greeting to the browser
The CGI program connects to the client through standard output

In Perl the print function is used by CGI programs to communicate with the client

If the response is going through the header, the CGI program supplies the first line of the header

The remainder is added by the server before being sent to the client

The first line specifies the format of the response as MIME content type
- HTML a the response type is specified with text/html

The line following the one-line header must be blank

It indicates the end of the HTTP header

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

The rest of the program will generate the required HTML tags
#!/usr/bin/perl -w # reply.pl - a CGI program that returns a greeting to the user print "Content-type: text/html \n\n", "<html><head> \n", "<title>reply.pl example </title></head> \n", "<body> \n", "<h1> Greetings from your Web server! <h1> \n", "</body></html> \n";

reply.html at www.ens.utulsa.edu

reply.html at personal.utulsa.edu/~diaz