Master PHP file_put_contents: Write Strings, Arrays, and Use Flags

In PHP we often need to write data to a file; the built‑in file_put_contents() function handles this.

Function syntax

int file_put_contents ( string $filename , mixed $data [, int $flags = 0 [, resource $context ]] )

The function accepts four parameters: the filename, the data to write, optional flags, and an optional context resource.

Writing a string to a file

Example of writing the string “Hello, world!” to test.txt:

$file = "test.txt";
$data = "Hello, world!";
file_put_contents($file, $data);

Running this creates test.txt in the current directory with the content “Hello, world!”.

Writing an array to a file

To store an array, we first convert it to a string with var_export() and then write it:

$file = "users.txt";
$data = array(
    array("name" => "John", "age" => 25),
    array("name" => "Emma", "age" => 28),
    array("name" => "Michael", "age" => 31)
);
file_put_contents($file, var_export($data, true));

The resulting users.txt contains a PHP‑style array representation of the data.

Setting flags

The third parameter $flags controls how data is written. Common flags include: FILE_USE_INCLUDE_PATH: search the include_path for the file. FILE_APPEND: append data to the end of the file instead of overwriting. LOCK_EX: acquire an exclusive lock while writing to prevent concurrent writes.

Example of appending a log entry using FILE_APPEND:

$file = "log.txt";
$data = "New log entry";
file_put_contents($file, $data, FILE_APPEND);

After execution, log.txt contains the new entry.

Context parameter

The fourth parameter is a context resource for advanced file operations; consult the PHP manual for details.

Summary

Using file_put_contents() you can easily write strings or arrays to files, customize behavior with flags, and employ a context resource for more complex scenarios.