Script execution and memory reset in PHP - Step-by-Step Execution

Concept Flow - Script execution and memory reset

Start script execution

↓

Execute code line by line

↓

Variables stored in memory

↓

End of script reached

↓

Memory cleared, variables reset

↓

Script execution ends

PHP runs the script from top to bottom, storing variables in memory during execution. When the script ends, all memory is cleared and variables reset.

Execution Sample

PHP

<?php
$a = 5;
echo $a;
?>

This script sets a variable $a to 5, prints it, then ends, clearing memory.

Execution Table

Step	Action	Variable State	Output
1	Start script execution	No variables
2	Assign $a = 5	$a = 5
3	Print $a	$a = 5	5
4	End of script	$a = 5 (about to clear)
5	Memory cleared	No variables

💡 Script ends, PHP clears all variables from memory

Variable Tracker

Variable	Start	After Step 2	After Step 3	After Step 5
$a	undefined	5	5	undefined

Key Moments - 2 Insights

Why does $a become undefined after the script ends?

Because PHP clears all variables from memory when the script finishes, as shown in execution_table step 5.

Does the value of $a persist between different script runs?

No, each script run starts fresh with no variables, as shown in execution_table step 1 and 5.

Visual Quiz - 3 Questions

Look at the execution_table, what is the value of $a after step 2?

A undefined

B 0

C 5

D null

💡 Hint

Check the 'Variable State' column at step 2 in execution_table

At which step does the script output the value 5?

A Step 1

B Step 3

C Step 2

D Step 5

💡 Hint

Look at the 'Output' column in execution_table

If the script had another line after step 3 that changed $a to 10, what would be $a's value at step 4?

A 10

B 5

C undefined

D null

💡 Hint

Variable changes persist until script ends, see variable_tracker pattern

Concept Snapshot

PHP script runs top to bottom.
Variables exist only during execution.
At script end, all variables are cleared.
Each run starts with fresh memory.
Output happens during execution only.

Full Transcript

This visual trace shows how a PHP script executes line by line. First, the script starts with no variables in memory. Then, the variable $a is assigned the value 5. Next, the script prints the value of $a, which outputs 5. After the script reaches the end, PHP clears all variables from memory, resetting $a to undefined. This means each time the script runs, it starts fresh with no leftover data from before. Understanding this helps beginners know why variables do not keep their values between script runs.