Perl Tutorial

Fundamentals

Input and Output

Control Flow

Arrays and Lists

Hash

Scalars

Strings

Object Oriented Programming in Perl

Subroutines

Regular Expressions

File Handling

Context Sensitivity

CGI Programming

Misc

Decision Making in Perl

Decision-making is an essential part of any programming language. In Perl, decision-making structures help determine the direction in which the program's flow should move. Let's dive into these structures:

1. The `if` Statement

This evaluates a condition. If the condition is true, the block of code inside the if statement is executed.

my $number = 10;

if ($number > 5) {
    print "$number is greater than 5\n";
}

2. The `if-else` Statement

This allows you to execute one block of code if the condition is true, and another block if the condition is false.

my $number = 3;

if ($number > 5) {
    print "$number is greater than 5\n";
} else {
    print "$number is less than or equal to 5\n";
}

3. The `if-elsif-else` Statement

For situations with multiple conditions, elsif can be used:

my $number = 5;

if ($number > 10) {
    print "$number is greater than 10\n";
} elsif ($number < 5) {
    print "$number is less than 5\n";
} else {
    print "$number is between 5 and 10 (inclusive)\n";
}

4. The `unless` Statement

This is the opposite of the if statement. The code inside the unless block is executed if the condition is false.

my $number = 4;

unless ($number > 5) {
    print "$number is not greater than 5\n";
}

You can also combine unless with else:

unless ($number > 5) {
    print "$number is not greater than 5\n";
} else {
    print "$number is greater than 5\n";
}

5. The `given-when` Structure (similar to `switch-case` in other languages)

To use this structure, you'll need to include the feature pragma for versions of Perl 5.10 through 5.18. However, it's worth noting that starting from Perl 5.18, given-when is considered experimental and might produce warnings. You might want to consider using the Switch module or an if-elsif chain for a more stable solution.

use feature 'switch';

my $value = 'B';

given ($value) {
    when ('A') { print "It's A\n"; }
    when ('B') { print "It's B\n"; }
    default { print "It's neither A nor B\n"; }
}

6. Ternary Conditional Operator (`? :`)

This is a shorthand for if-else. It's useful for short evaluations.

my $number = 7;
my $result = ($number > 5) ? "$number is greater than 5" : "$number is less than or equal to 5";
print $result;

Key Points:

Understand the nature of the condition you're testing and select the most appropriate decision-making structure.
Be aware of the "truthiness" of values in Perl. The values 0, '0', '' (empty string), undef, and () (empty list) evaluate to false. Everything else is true.
Parentheses around the condition in if and unless statements are mandatory.
Remember that given-when is experimental in newer versions of Perl and might produce warnings.

By understanding and applying these decision-making structures, you can create complex logic flows tailored to your Perl application's needs.

If statements in Perl:
- Description: If statements in Perl are used for conditional execution of code based on a specified condition.
- Example Code:
```
my $value = 10;

if ($value > 5) {
    print "Value is greater than 5\n";
}
```

Perl else if and else statements:

Description: Else if statements allow you to check multiple conditions, and else is used for code that executes when none of the if or else if conditions are true.

Example Code:

my $value = 10;

if ($value > 15) {
    print "Value is greater than 15\n";
} elsif ($value > 5) {
    print "Value is greater than 5 but less than or equal to 15\n";
} else {
    print "Value is 5 or less\n";
}

Switch statements in Perl:

Description: Perl does not have a built-in switch statement, but you can achieve similar functionality using if-elsif-else constructs.

Example Code:

my $day = "Monday";

given ($day) {
    when ("Monday") { print "It's the start of the week\n"; }
    when ("Friday") { print "Weekend is near\n"; }
    default { print "Some other day\n"; }
}

Comparisons and conditions in Perl:
- Description: Perl supports various comparison operators (<, >, <=, >=, ==, !=) for evaluating conditions.
- Example Code:
```
my $x = 5;
my $y = 10;

if ($x < $y) {
    print "$x is less than $y\n";
}
```
Ternary operator in Perl:
- Description: The ternary operator (? :) allows for concise conditional expressions.
- Example Code:
```
my $value = 10;
my $result = ($value > 5) ? "Greater than 5" : "5 or less";
print "$result\n";
```
Logical operators in Perl decision-making:
- Description: Logical operators (&&, ||, !) are used for combining and negating conditions.
- Example Code:
```
my $x = 5;
my $y = 10;

if ($x > 0 && $y > 0) {
    print "Both values are positive\n";
}
```

Nested if-else in Perl:

Description: You can nest if-else statements to handle multiple levels of conditions.

Example Code:

my $x = 5;
my $y = 10;

if ($x > 0) {
    if ($y > 0) {
        print "Both values are positive\n";
    } else {
        print "\$y is not positive\n";
    }
} else {
    print "\$x is not positive\n";
}

Perl case-insensitive comparisons:

Description: Use the lc or uc functions to make comparisons case-insensitive.

Example Code:

my $string1 = "Hello";
my $string2 = "hello";

if (lc($string1) eq lc($string2)) {
    print "Strings are equal (case-insensitive)\n";
}

Decision Making in Perl

1. The if Statement

2. The if-else Statement

3. The if-elsif-else Statement

4. The unless Statement

5. The given-when Structure (similar to switch-case in other languages)

6. Ternary Conditional Operator (? :)

Key Points:

1. The `if` Statement

2. The `if-else` Statement

3. The `if-elsif-else` Statement

4. The `unless` Statement

5. The `given-when` Structure (similar to `switch-case` in other languages)

6. Ternary Conditional Operator (`? :`)