CSV file reading and writing in PHP - Mini Project: Build & Apply

CSV file reading and writing

📖 Scenario: You work in a small shop and want to keep track of your products and prices using a CSV file. You will read the CSV file, update prices, and save the changes back to the file.

🎯 Goal: Build a PHP script that reads a CSV file named products.csv, updates the prices by increasing them by 10%, and writes the updated data back to the same CSV file.

📋 What You'll Learn

Read data from a CSV file named products.csv

Store the CSV data in an array

Increase each product's price by 10%

Write the updated data back to products.csv

Use PHP built-in functions for CSV handling

💡 Why This Matters

🌍 Real World

Small shops or simple apps often use CSV files to store product lists and prices because CSV files are easy to read and edit.

💼 Career

Knowing how to read and write CSV files is useful for data import/export tasks, report generation, and simple database alternatives in PHP development.

1

Create the initial CSV file

Create a CSV file named products.csv with these exact lines:
Apple,1.00
Banana,0.50
Cherry,2.00

PHP

# Create the file products.csv with the given lines

Hint

Use file_put_contents to create and write to the CSV file.

2

Read the CSV file into an array

Read the CSV file products.csv line by line using fopen and fgetcsv, and store each row as an array inside a variable called products.

PHP

<?php
file_put_contents('products.csv', "Apple,1.00\nBanana,0.50\nCherry,2.00\n");

// Read the CSV file into the products array
# Your code here

Hint

Use fopen to open the file and fgetcsv inside a while loop to read each row.

3

Increase each product price by 10%

Use a foreach loop with variables index and product to iterate over products. Increase the price (second element) by 10% and update products[index][1] with the new price formatted to 2 decimal places.

PHP

<?php
file_put_contents('products.csv', "Apple,1.00\nBanana,0.50\nCherry,2.00\n");

$products = [];
if (($handle = fopen('products.csv', 'r')) !== false) {
    while (($data = fgetcsv($handle)) !== false) {
        $products[] = $data;
    }
    fclose($handle);
}

// Increase prices by 10%
# Your code here

Hint

Convert the price to float, multiply by 1.10, then format back to string with 2 decimals.

4

Write the updated data back to the CSV file

Open products.csv for writing using fopen with mode 'w'. Use a foreach loop to write each product array to the file using fputcsv. Close the file with fclose. Then print "Updated CSV saved." to confirm.

PHP

 $product) {
    $price = (float)$product[1];
    $new_price = $price * 1.10;
    $products[$index][1] = number_format($new_price, 2, '.', '');
}

// Write updated products back to products.csv and print confirmation
# Your code here

Hint

Use fopen with 'w' mode, fputcsv inside a loop, then fclose. Finally, print the confirmation message.

Practice

1. Which PHP function is used to read a line from a CSV file and parse it into an array?

easy

A. fgetcsv()

B. fputcsv()

C. fread()

D. fwrite()

Solution

1. Step 1: Understand CSV reading functions

   PHP provides fgetcsv() to read a line from a CSV file and convert it into an array of values.

2. Step 2: Differentiate from writing functions

   fputcsv() writes arrays to CSV files, while fread() and fwrite() handle raw file reading/writing without CSV parsing.

3. Final Answer:

   fgetcsv() -> Option A

4. Quick Check:

   Read CSV line as array = fgetcsv() [OK]

Hint: Use fgetcsv() to read CSV lines into arrays [OK]

Common Mistakes:

• Confusing fgetcsv() with fputcsv()
• Using fread() which reads raw data, not CSV parsed
• Trying to read CSV without parsing into arrays

2. Which of the following is the correct way to open a CSV file for writing in PHP?

easy

A. $file = fopen('data.csv', 'r');

B. $file = fopen('data.csv', 'rw');

C. $file = fopen('data.csv', 'w');

D. $file = fopen('data.csv', 'x');

Solution

1. Step 1: Understand fopen modes

   Mode 'w' opens a file for writing and truncates it if it exists, perfect for writing CSV files.

2. Step 2: Check other modes

   'r' is read-only, 'rw' is invalid, 'x' creates a new file but fails if it exists.

3. Final Answer:

   $file = fopen('data.csv', 'w'); -> Option C

4. Quick Check:

   Open file for writing = 'w' mode [OK]

Hint: Use 'w' mode in fopen() to write files [OK]

Common Mistakes:

• Using 'r' mode when intending to write
• Using invalid mode 'rw'
• Using 'x' which fails if file exists

3. What will be the output of the following PHP code snippet?

$file = fopen('data.csv', 'r');
$data = fgetcsv($file);
fclose($file);
print_r($data);

Assuming the first line of data.csv is:
John,Doe,30

medium

A. Array ( [0] => John [1] => Doe [2] => 30 )

B. John,Doe,30

C. Array ( [0] => 'John,Doe,30' )

D. Error: Cannot read file

Solution

1. Step 1: Understand fgetcsv() output

   fgetcsv() reads one CSV line and returns an array splitting values by commas.

2. Step 2: Analyze given CSV line

   The line 'John,Doe,30' splits into array elements: 'John', 'Doe', and '30'.

3. Final Answer:

   Array ( [0] => John [1] => Doe [2] => 30 ) -> Option A

4. Quick Check:

   fgetcsv() splits CSV line into array [OK]

Hint: fgetcsv() returns array of CSV fields from one line [OK]

Common Mistakes:

• Expecting a string instead of an array
• Assuming fgetcsv returns raw line string
• Not closing the file after reading

4. Identify the error in the following PHP code that writes data to a CSV file:

$file = fopen('output.csv', 'r');
fputcsv($file, ['Alice', 'Smith', 25]);
fclose($file);

medium

A. Array syntax is incorrect

B. fputcsv() cannot write arrays

C. Missing fclose() call

D. File opened in read mode instead of write mode

Solution

1. Step 1: Check fopen mode

   The file is opened with 'r' (read) mode, which does not allow writing.

2. Step 2: Understand fputcsv requirements

   fputcsv() requires the file to be opened in write ('w') or append ('a') mode to write data.

3. Final Answer:

   File opened in read mode instead of write mode -> Option D

4. Quick Check:

   Open file in write mode before writing [OK]

Hint: Open file with 'w' or 'a' before writing CSV [OK]

Common Mistakes:

• Opening file in 'r' mode when writing
• Forgetting to close the file
• Misunderstanding fputcsv() input

5. You want to read a CSV file and write only rows where the third column is greater than 50 to a new CSV file. Which code snippet correctly implements this?

hard

A. $in = fopen('input.csv', 'w');
$out = fopen('output.csv', 'r');
while (($row = fgetcsv($in)) !== false) {
if ($row[2] > 50) {
fputcsv($out, $row);
}
}
fclose($in);
fclose($out);

B. $in = fopen('input.csv', 'r');
$out = fopen('output.csv', 'w');
while (($row = fgetcsv($in)) !== false) {
if ($row[2] > 50) {
fputcsv($out, $row);
}
}
fclose($in);
fclose($out);

C. $in = fopen('input.csv', 'r');
$out = fopen('output.csv', 'w');
while (($row = fgetcsv($out)) !== false) {
if ($row[2] > 50) {
fputcsv($in, $row);
}
}
fclose($in);
fclose($out);

D. $in = fopen('input.csv', 'r');
$out = fopen('output.csv', 'w');
while (($row = fgets($in)) !== false) {
if ($row[2] > 50) {
fputcsv($out, $row);
}
}
fclose($in);
fclose($out);

Solution

1. Step 1: Open input file for reading and output file for writing

   Use 'r' mode for reading input and 'w' mode for writing output.

2. Step 2: Read each CSV row with fgetcsv() from input and check third column

   Use fgetcsv($in) to read rows, then check if $row[2] > 50.

3. Step 3: Write qualifying rows to output with fputcsv()

   If condition passes, write row to output file using fputcsv($out, $row).

4. Final Answer:

   Code snippet B correctly reads, filters, and writes CSV rows -> Option B

5. Quick Check:

   Read with fgetcsv(), filter by column, write with fputcsv() [OK]

Hint: Read with fgetcsv(), filter rows, write with fputcsv() [OK]

Common Mistakes:

• Opening files with wrong modes
• Using fgets() instead of fgetcsv() for CSV reading
• Mixing input and output file handles