WP_Filesystem example

WP_Custom_Writer.php

class WP_Custom_Writer {

	/**
	 * Stores the initialized WordPress filesystem.
	 *
	 * @access private
	 * @var WP_Filesystem
	 */
	private $file_system;


	/**
	 * Class constructor.
	 *
	 * @global WP_Filesystem_Base $wp_filesystem
	 * @access public
	 */
	public function __construct() {

		// Start initiating filesystem.
		global $wp_filesystem;
		$url = wp_nonce_url( admin_url( 'tools.php?page=your_page'), 'your_text_domain' );

		// Get filesystem credentials needed for WP_Filesystem.
		$creds = request_filesystem_credentials( $url, '', false, false, null );
		if ( false === $creds ) {
			_e( 'Credentials are required to save the file.', 'your_text_domain' );
			exit();
		}

		// Get the upload directory.
		$wp_upload_dir = wp_upload_dir();

		// When credentials are obtained, check to make sure they work.
		if ( ! WP_Filesystem( $creds, $wp_upload_dir['basedir'] ) ) {
			// Request_filesystem_credentials a second time, but this time with the $error flag set.
			request_filesystem_credentials( $url, '', true, false, null );
			_e( 'Credentials are required to save the file', 'your_text_domain' );
			exit();
		}

		// Populate class private members with what was obtained.
		$this->file_system = $wp_filesystem;
		//..other code here

                // Then, in other methods, you just use similar to this:
                $this->file_system->mkdir( "your_folder_name" );

                // Or you can write to a file.
                global $wp_filesystem;
                $this->file_system->put_contents(
						'/tmp/example.txt',
  						'Example contents of a file',
  						FS_CHMOD_FILE // predefined mode settings for WP files
		);

                // MORE INFO HERE: https://codex.wordpress.org/Filesystem_API
	}

}