Question

Write a CGl script that prints the squares of the integers from 1 to 10 on separate lines.

Short answer

Create a CGI script using Perl to print squares of numbers 1 to 10 with HTML formatting.

Step-by-step solution

Define the CGI Script

Start by defining the CGI script using Perl. A cgi-bin script typically begins with the shebang line to indicate the interpreter. Add `#!/usr/bin/perl` at the top of your file.

Include Necessary Libraries

Include the CGI library for creating CGI scripts. Add the following line right after your shebang: `use CGI qw(:standard);`.

Start the HTML Document

Begin your HTML document using the CGI module's functions. Add the following lines to start: `print header();` `print start_html("Squares of Integers");`

Iterate Over Integers from 1 to 10

Use a loop to iterate over the integers from 1 to 10. The `for` loop in Perl can be used as: `for (my $i = 1; $i <= 10; $i++)`.

Calculate and Print Squares

Within the loop, compute the square of each integer and print it. Use Perl's print statement: `print "\(i squared is " . (\)i**2) . "
";` to output each square on a new line.

End the HTML Document

Finish the CGI script by closing the HTML document appropriately with: `print end_html();`.

Make the Script Executable

Ensure the script file has executable permissions. Use the command `chmod +x scriptname.cgi` from the terminal.

Key concepts

Perl Programming

Perl is a high-level programming language that's well-suited for text processing, system administration, and web development through CGI scripts. It stands out for its strong ability to handle regular expressions and its flexibility in managing various data formats.

When programming in Perl for CGI scripts, you start with the shebang line `#!/usr/bin/perl`, which specifies that Perl should execute the script. Following this, it's common to import necessary libraries such as `CGI.pm`, which provides functions to handle form data and output HTTP headers. In Perl, you can use simple syntax to perform powerful actions, like reading files or handling exceptions. This makes it an excellent choice for creating dynamic web applications on the server side.

HTML Document Structure

The structure of an HTML document is crucial in ensuring that web browsers display content correctly. In CGI scripts, the structure is dynamically generated using functions provided by libraries like `CGI.pm`. The basic HTML elements include a `` and a ``, with content often placed within the body to display on the browser.

In the context of a Perl CGI script, you start by printing the HTTP header using `print header();` to indicate that an HTML document follows. Next, the `print start_html("Title")` function is used to begin the document, setting up the ``, ``, and `` tags. Closing the document involves calling `print end_html();`, which ensures all HTML tags are properly closed. This dynamically manages the output for the browser, making the script's output appear like any manually written HTML document.

File Permissions

File permissions are an essential aspect when working with CGI scripts. Permissions control who can read, write, or execute a file, impacting its security and accessibility. For CGI scripts, you need to ensure that the web server has the right permissions to execute the script.

Typically, CGI scripts are stored in a `cgi-bin` directory on the server. To run the script, you use the command `chmod +x scriptname.cgi`, which provides the necessary execute permission. This command changes the script's permissions to make it executable by the user. Understanding how permissions work, and regularly checking them, ensures your scripts run smoothly without encountering permission errors.

Loop Constructs

Loop constructs in Perl are fundamental for executing repeated actions, such as processing lists or performing an operation on multiple elements. A commonly used loop construct in Perl is the `for` loop, which provides an efficient way to iterate over a range of values.

In our example CGI script, the `for` loop `for (my $i = 1; $i <= 10; $i++)` is used to iterate through numbers 1 to 10. Inside the loop, you can perform various operations, like calculating the square of each integer. By using `print "i squared is " . ( i**2) . "
";`, each square is computed and displayed on a new line of the HTML document. Loop constructs simplify code readability and maintainability, especially when the same logic needs to be applied to multiple data elements.