Delve into Perl, a popular text processing language. Gain insights into loops, strings, and arrays, progressing to complex data structures and packages. No prior knowledge required.

alpine2.tar.gz

Perl is one of the most popular text processing languages in the world. It allows you to create extremely efficient text parsers for all sorts of applications.

This interactive course will help you get up to speed on Perl, starting off with basic concepts like loops, strings, and arrays. You'll build your way up to more complex topics like data structures and packages.

No background knowledge is needed. Anyone willing to understand the principles and syntax of Perl to use it in the future will find this course useful.

Learn Perl from Scratch

# What is a `for` loop?

It’s like a [while](https://www.educative.io/courses/learn-perl-from-scratch/while-loop) loop, but the initialization and the increment or decrement statements are included within the syntax.



## Syntax
A `for` loop is set up like this:

### Explanation
* **Initialization** - Initialize the variable that will be used as the loop control variable.
* **Condition** - The body of the loop only executes when the condition is "true".
* **Increment/Decrement** - How the variable changes every time the loop runs.

## Example

Here's an example of how the `for` loop works:

for ($i = 0; $i < 10; $i++){
  print "value of i is: $i\n";
} 

### Explanation
Let's take a look at the illustration below to understand the code above more clearly.


**What does the above `for` loop do?**

* Prior to the first iteration, it sets the value of `i` to "0". 

* Next, it tests (like a `while` loop) if `i` is less than "10". 

* If the above condition is true, the body of the loop is run and the program will print the value stored in the variable  `i`.

* Next, the terminal cursor moves down to the next line. 

* After the one iteration of the loop is finished, `i` is incremented (by "1"), as specified in the update statement, and the condition is tested again.

So, this loop will run a total of 10 times, printing the value of variable `i` each time. 

> The **variable** used in `for` loops is generally an **integer** variable named `i`, `j`, or `k`.

The loop in the above example can also be written as:

$i=0;

for (; $i < 10; $i++){  #initialization can also be done outside loop
  print "value of i is: $i\n";
} 

Similarly, another method to write it is as follows:

$i=0;

for (; $i < 10;){  #initialization can also be done outside loop. Note the semicolon is compulsory
  print "value of i is: $i \n";
  $i++; #the increment of loop control variable can also be done separately
}

# Nested `for` loops

It is possible to **nest** `for` loops. Nesting means including one `for` loop in another​ `for` loop. 

The syntax for nested `for` loops is as follows:

for (initialization ; testing ; updating ) {
   for (initialization ; testing ; updating) {
      //body
   }
   //body
} 

## Example

Let's take a look at an example code to understand nesting of `for` loops better.

$input = 5;
print "How many missiles will you fire?\n";
print "I will fire: $input missiles\n";

for ($i = 0; $i < $input; $i++) {  # outer for loop
  for ($j = 3; $j > 0; $j--) {  # inner for loop
    print "$j  ";
  }

  $temp = $i+1;
  print "Missile $temp has launched.\n";
}

print "All missiles have been launched.\n";

### Explanation

For a single value of the variable `i` in the outer loop, the inner for loop will iterate over all its values. In this example, the inner loop will iterate over the variable `j` from 3 to 1. The variable `i` will be incremented, and the outer loop will be repeated, resulting in complete execution of the inner loop again.

Let's look at the illustration below, which will help us visualize and understand this concept more clearly.​ 

In this lesson, let's understand the concepts and implementation of for loops and nested for loops in Perl.

Getting Started

Variables

Operators

Conditional Statements

Loops

Subroutines

Strings

Arrays

Packages

Conclusion

For Loop