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A First Perl CGI Script

Let us now look at how we write our first perl program that will be used as a CGI script.

We will learn three main things in here:

The format of Perl CGI program
How to comment Perl programs
One Perl function print -- which outputs data

Format of a Perl program

Every Perl program MUST obey the following format:

A first line consisting of:
```
#!/usr/local/bin/perl
```
The rest of the program consisting of legal Perl syntax and commands

Strictly speaking the first line is only required for running Perl programs on UNIX machines. Since that is the intended destination of most of our Perl scripts. It is a good idea to make this the first line of every perl program. What is the purpose of this first line?

The first line declaration has two purposes:

It indicates that the program is a Perl script.
It tells UNIX how to run Perl. (Do not worry too much about this last fact).
It MUST be typed exactly as above.

The first line is actually a comment (albeit a very special type of comment) Comments in Perl

It is good practice to comment all your programs (whatever the language (HTML, Perl, Pascal C) -- Comments serve you well.

In Perl comments are easy:

The # symbol indicates a comment.
The remainder of the line is regarded as a comment
DO NOT put any Perl code after a # symbol until you type a carriage return.

So a simple comment in Perl might be:

# hello.cgi - My first CGI program

Output from Perl

To output from a Perl script you use the print statement:

The print statement takes a string (delimited by "... ") argument which it outputs.
Unlike Pascal (though like C) the string argument formats output.
- You can control how the output looks from a single print statement.
- The \n character indicates that a newline is required at that point in the text.
- We will introduce further aspects of the print statement later.

For Example, The first line of our CGI script must be ``Content-Type: text/html'' and the print statement must have 2 \n characters:

One to terminate the current line, and
The second to produce the require blank line between CGI header and data.

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

Finally -- Our complete script

Recall that our Perl CGI script must output the header and HTML code and must begin with a special first line.

Our complete first program (with nice comments) is a follows:

#!/usr/local/bin/perl
# hello.cgi - My first CGI program

print "Content-Type: text/html\n\n";
# Note there is a newline between 
# this header and Data

# Simple HTML code follows

print "<html> <head>\n";
print "<title>Hello, world!</title>";
print "</head>\n";
print "<body>\n";
print "<h1>Hello, world!</h1>\n";
print "</body> </html>\n";

Next: Writing, Creating and Running Up: Beginning CGI Programming in Previous: CGI Script Output

Dave Marshall
9/28/2001