Perl Basics

You write Perl using a simple text editor, like pico or nano. Log on to a UNIX computer and use a text editor to open a file called script.pl, e.g.

nano script.pl

Perl scripts traditionally end in .pl. This isn’t a requirement, but it does make it easier to recognise the file.

Now type the following into the file;

print "Hello from Perl!\n";

Save the file. You have just written a simple Perl script! To run it, type

perl script.pl

This line uses the Perl interpreter (called perl) to read your perl script and to follow the instructions that it finds. In this case you have told Perl to print to the screen the line “Hello from Perl!”. The \n represents a return (newline). Try removing the \n, or adding multiple \n’s and rerunning the script to see what I mean.

This was a simple script, but Perl is a language designed to help you write small and simple scripts. Indeed, in my opinion Perl is the best language around for writing small and simple scripts (less than 100 lines of code).

This script has introduced three of the basic building blocks of Perl;

A string is a type of variable. A variable is a value in a script that can be changed and manipulated. Variables in Perl are identified using the dollar sign $. For example, use a text editor to write a new Perl script, called variables.pl

nano variables.pl

Type into the script the following lines (remember to include the semicolons at the end of each line!);

$a = "Hello";
$b = "from";
$c = "Perl!";

print "$a $b $c\n";

What do you think will be printed when you run this script? Run the script by typing;

perl variables.pl

Did you see what you expected? In this script we created three variables, $a, $b and $c. The line $a = "Hello"; sets the variable $a equal to the string Hello. $b is set equal to the string from while $c is set equal to Perl!.

The last line is interesting! The print command prints the string that follows it. In this case the string is equal to $a $b $c\n. However, Perl knows that $a, $b and $c are variables, so it substitutes their values into this string (so $a is replaced by its value, Hello, $b is replaced with from and $c is replaced with Perl!). Thus the print command prints the string Hello from Perl!\n to the screen.

Perl can also put numbers into variables. Create a new script (numbers.pl) and write this;

$x = 5;
$pi = 3.14159265;
$n = -6;

$n_plus_one = $n + 1;
$five_times_x = 5 * $x;
$pi_over_two = $pi / 2;

print "x equals $x. pi equals $pi. n equals $n.\n";

print "Five times x equals $five_times_x.\n";
print "pi divided by two equals $pi_over_two.\n";
print "n plus one equals $n_plus_one.\n";

What do you think will be printed to the screen when you run this script?

Run this script (perl numbers.pl). Did you see what you expected?


Compare with Python


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