File existence and info checks in PHP - Step-by-Step Execution

Concept Flow - File existence and info checks

Start

↓

Check if file exists

Yes↓

Get file info

↓

Display info

↓

End

No↓

Display 'File not found'

↓

End

The program first checks if a file exists. If yes, it gets and shows file details. If not, it shows a 'File not found' message.

Execution Sample

PHP

<?php
$filename = 'example.txt';
if (file_exists($filename)) {
  echo filesize($filename);
} else {
  echo 'File not found';
}
?>

This code checks if 'example.txt' exists and prints its size or a not found message.

Execution Table

Step	Action	Evaluation	Result
1	Set $filename = 'example.txt'	Assign string	$filename = 'example.txt'
2	Check file_exists('example.txt')	Returns true if file exists	true
3	Since true, call filesize('example.txt')	Returns file size in bytes	1234
4	Print file size	Output file size	1234
5	End of script	No more code	Script ends

💡 Execution stops after printing file size because file exists.

Variable Tracker

Variable	Start	After Step 1	After Step 2	After Step 3	Final
$filename	undefined	'example.txt'	'example.txt'	'example.txt'	'example.txt'
file_exists result	undefined	undefined	true	true	true
filesize result	undefined	undefined	undefined	1234	1234

Key Moments - 2 Insights

Why does the code check file_exists before calling filesize?

Because calling filesize on a non-existing file causes an error. The check prevents this by ensuring the file is there first (see step 2 and 3 in execution_table).

What happens if the file does not exist?

The else branch runs, printing 'File not found' instead of trying to get file info (not shown in this example but implied by the else block).

Visual Quiz - 3 Questions

Look at the execution_table, what is the value of $filename after step 1?

A 'example.txt'

B undefined

C 1234

D true

💡 Hint

Check the variable_tracker row for $filename at 'After Step 1'

At which step does the code decide the file exists?

A Step 1

B Step 2

C Step 3

D Step 4

💡 Hint

Look at the 'file_exists result' in variable_tracker and execution_table step 2

If the file did not exist, what would the output be?

A The file size in bytes

B An error message from filesize

C 'File not found'

D No output

💡 Hint

The else branch prints 'File not found' when file_exists returns false

Concept Snapshot

PHP file existence and info checks:
- Use file_exists('filename') to check if a file is present.
- Use filesize('filename') to get file size in bytes.
- Always check file_exists before filesize to avoid errors.
- Use if-else to handle file found or not found cases.

Full Transcript

This example shows how PHP checks if a file exists using file_exists. If the file is there, it gets the file size with filesize and prints it. If not, it prints 'File not found'. The execution table traces each step: setting the filename, checking existence, getting size, and printing. The variable tracker shows how variables change. Key moments explain why the existence check is important to avoid errors. The quiz tests understanding of variable values and flow decisions.