Explain the difference between unset() and null and unlike()

You asked about unset(), null, and unlink() in PHP. Let’s go careful step by step because they are often confused.

1️⃣ unset()

• Purpose: Removes a variable or array element from memory.
• Effect: After unset($var), $var no longer exists.
• Usage Example:

$var = "Hello";
unset($var);

var_dump($var); // ❌ Notice: Undefined variable

• Important: unset() does not delete files or database entries; only variables in PHP memory.

2️⃣ null

• Purpose: Represents a variable with no value.
• Effect: Variable still exists, but its value is empty/undefined.
• Usage Example:

$var = "Hello";
$var = null;

var_dump($var); // NULL

• Difference from unset():
  • null → variable exists but has no value.
  • unset() → variable does not exist anymore.

3️⃣ unlink()

• Purpose: Deletes a file from the filesystem.
• Usage Example:

$file = "example.txt";
unlink($file); // Deletes example.txt from server

• Important: unlink() has nothing to do with variables. It operates on files.

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