Perl Programming/First programs

A first taste of Perl

Here's a simple program written in Perl to get us started:

#!/usr/bin/perl

# Outputs Hello World to the screen.
 
print "Hello World!\n";

Let's take a look at this program line by line:

• #!/usr/bin/perl

On Unix systems this tells the Operating System to execute this file with the program located at /usr/bin/perl. This is the default Unix location for the perl interpreter, on Windows #!C:\Perl\bin\perl.exe or #!C:\strawberry\perl\bin\perl.exe (depending on whether ActivePerl or Strawberry Perl was installed) should be used instead.

Shebang: A line at the start of a file, beginning with #!, that gives instructions to the operating system.

• # Outputs ...

This line is a comment - it is ignored by the perl interpreter, but is very useful. It helps you to debug and maintain your code, and explain it to other programmers.

Comment: A line of plain text ignored by the interpreter in a file of code.

• print "Hello World!\n";

The print instruction writes whatever follows it to the screen. The \n at the end of the string puts a new line to the screen. The semicolon at the end of the line tells the perl interpreter that the instruction is finished; you must put a semicolon at the end of every instruction in Perl code.

String: A sequence of characters used as data by a program.

Exercises

Change the program so it says hello to you. Change the program so that after greeting you, it asks how you are doing, on the next line. The output should look like this: Hello your_name! How are you? Experiment with the \n character, what happens when you take it away? What happens, if you put two in a row? Remember: If you add another print instruction you will need to put a semicolon after it.