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Writing with file_put_contents()

PHP course · Intermediate · Lesson 71/115

Learn to write a string to a file with file_put_contents().

Writing files with file_put_contents()

To write a string to a file you use the file_put_contents() function. It takes two arguments: the file path and the content to write.

For example, file_put_contents('log.txt', 'Hello'); writes 'Hello' into log.txt. If the file does not exist it is created; if it exists its content is overwritten.

The function returns the number of bytes written. If it returns false, the write failed.

Appending with the FILE_APPEND flag

If you want to add new content to the end of the file instead of overwriting it, pass the FILE_APPEND flag as the third argument.

For example, file_put_contents('log.txt', 'New entry' . PHP_EOL, FILE_APPEND); appends the line 'New entry' to log.txt. The existing content is preserved. PHP_EOL is the end-of-line character (\n on Linux).

This pattern is very useful for log files: each new entry is appended to the end, old entries are kept.

Exercise Write the file and read it back

Use file_put_contents() to write the string 'Entry added' to log.txt. Then read the file with file_get_contents() and print it with echo. Use __DIR__ in the path argument of both functions.

Show example solution 
First write file_put_contents(__DIR__ . '/log.txt', 'Entry added'); then echo file_get_contents(__DIR__ . '/log.txt');.
Example solution:
<?php
// Write to the file
file_put_contents(__DIR__ . '/log.txt', 'Entry added');

// Read and print
echo file_get_contents(__DIR__ . '/log.txt');

Test yourself

  1. If file_put_contents('a.txt', 'x') is called and a.txt already exists, what happens?

    • The file is replaced with 'x' (overwritten)
    • 'x' is appended to the end of the file
    • PHP throws an error and leaves the file untouched
    • The content 'xx' is written instead of 'x'
    Show answer

    The file is replaced with 'x' (overwritten) — Correct. file_put_contents() overwrites the file by default; the old content is lost.

  2. Append the entry to the file

    file_put_contents('log.txt', $msg . PHP_EOL, ____);
    Show answer 
    file_put_contents('log.txt', $msg . PHP_EOL, FILE_APPEND);

  3. Match file_put_contents concepts

    file_put_contents()
    Writes a string to a file
    First argument
    Is the file path
    Second argument
    Is the content to write
    FILE_APPEND
    Appends to the end

All lessons in Intermediate

1 Classes

  1. Defining a class
  2. Defining properties
  3. Defining methods
  4. In-class access with $this
  5. Instantiating with new
  6. Summary - Classes

2 Constructor

  1. The __construct method
  2. Passing parameters to the constructor
  3. Initializing properties
  4. Class type declaration
  5. The __destruct method
  6. Summary - Constructor

3 Inheritance

  1. Inheritance with extends
  2. Accessing parent with parent::
  3. Method override
  4. protected property and method
  5. Inheritance chain
  6. Summary - Inheritance

4 Project: Utility library

  1. Project: Utility library
  2. Class skeleton
  3. Adding methods
  4. Using with file inclusion
  5. Project final - Library

5 Visibility

  1. public access
  2. protected access
  3. private access
  4. Encapsulation
  5. Getter and setter methods
  6. Summary - Visibility

6 Static members

  1. static property
  2. static method
  3. In-class access with self::
  4. Late static binding with static::
  5. static vs instance
  6. Summary - Static members

7 Class constants

  1. Class constants with const
  2. Accessing constants
  3. Class name with ::class
  4. Class constants vs static
  5. Constant use cases
  6. Summary - Class constants

8 Project: Quiz app

  1. Project: Quiz app
  2. Designing a question class
  3. Checking answers
  4. Computing the score
  5. Project final - Quiz app

9 Interfaces

  1. Defining interfaces
  2. Implementing with implements
  3. Multiple interfaces
  4. Polymorphism
  5. interface vs abstract
  6. Summary - Interfaces

10 Abstract classes

  1. Defining abstract classes
  2. abstract methods
  3. Abstract class inheritance
  4. Template method pattern
  5. Constructor and abstract
  6. Summary - Abstract classes

11 Traits

  1. Defining traits
  2. Using traits with use
  3. Multiple traits
  4. Resolving method conflicts
  5. Trait vs inheritance
  6. Summary - Traits

12 Project: Blog app

  1. Project: Blog app
  2. Creating a post class
  3. Adding posts with a form
  4. Displaying the post list
  5. Project final - Blog

13 File handling

  1. Reading with file_get_contents()
  2. Writing with file_put_contents()
  3. Opening files with fopen()
  4. fwrite() and fread()
  5. Closing files with fclose()
  6. Summary - File handling

14 File upload

  1. The $_FILES superglobal
  2. move_uploaded_file()
  3. Validating file type
  4. File size limit
  5. Upload error handling
  6. Summary - File upload

15 Sessions

  1. Starting a session with session_start()
  2. Storing data with $_SESSION
  3. Reading from a session
  4. unset() and session_destroy()
  5. Login/logout logic
  6. Summary - Sessions

16 Cookies

  1. Creating cookies with setcookie()
  2. Reading cookies with $_COOKIE
  3. Cookie expiration
  4. Deleting cookies
  5. Session vs cookie
  6. Summary - Cookies

17 Project: Contact form

  1. Project: Contact form
  2. Form skeleton
  3. Validating data
  4. Integrating file upload
  5. Project final - Contact form

18 Error handling

  1. The try/catch block
  2. Throwing exceptions with throw
  3. The Exception class
  4. error_reporting configuration
  5. Custom exception classes
  6. Summary - Error handling

19 Date and time

  1. Formatting dates with date()
  2. Timestamps with time()
  3. Parsing dates with strtotime()
  4. The DateTime class
  5. DateInterval and DatePeriod
  6. Summary - Date and time

20 Intermediate final

  1. Challenge - OOP app
  2. Challenge - File and session
  3. Challenge - Multi-step registration form
  4. Challenge - Error handling
  5. Challenge - Mini API