Welcome to the Perl CloudBook!
This is a bioinformatics course which is really about science and about programming. Our scientific focus will be genetics. For the moment, however, we are going to write in Perl the first program anyone ever writes: a program to print the phrase "Hello World!".
In the column on the right is an editable box. Below that box is the button "Run Code". In order to get you programming in Perl right away, we have done away with any installation, and put a Perl-speaking window right here in this page. When you write in Perl in the editable box, and click the run button, the code will be executed and the output presented in its own box just below the button.
» We have started the editable box with the Hello World! program already done. Try it now - click the button.
This may come as a bit of a disappointment to you, but more often than not, your code will not work. There are two sorts of not working.
First, the code might be syntactically wrong. That is, grammatically wrong. This includes spelling errors and punctuation errors. All sorts of little things. When you run your code you might get one of these errors. If you do, often there is a suggestion as to what line number the error occured, and some percentage of the time, this suggestion is not total garbage.
The second sort of error is a logical flaw. The code is syntactically correct but it doesn't do what you had hoped it would do. This is the "semantics" of the program, what it does.
» Let's make a grammatical error and see what that looks like. In the box, remove one of the quote marks ("), run again and consider carefully the error message.
Congratulations, you have made your first programming error.
» Now fix the error and modify the program so that instead of printing Hello World! it prints Hello Perlcloud!. Do that and you are done with the lesson.
This is where the discussion goes. It's a long box underneath both the other boxes.