Simple way to write data to a file and save it to a Client's computer when they click a link, using only PHP and HTML.

download_file_to_client_computer.php

<?php
  
  // this is a single page that can access and write any data to a file
  //  on a clients computer when they click a link using only HTML and PHP
  //
  
  // this will keep the data between page loads
  session_start();
  
  // download file if $_GET['download_file'] is set to true
  if(
    isset($_GET['download_file'])
    AND $_GET['download_file']
  ) {
    
    // set headers to tell the browser that you're about to give it a csv file
    //
    //  - you can tell it other types of files too, but most browsers
    //    will automatically download csvs, rather than try to open them
    //  - the file will automatically download when the user clicks the link,
    //    and the filename will be `downloaded_file.csv` ( see header below )
    //
    //  - these must be set before any data is outputted
    //  - anything that is outputted within this if() statement will be written to the file
    //
    header('Content-Type: application/csv');
    header('Content-Disposition: attachement; filename="downloaded_file.csv"');

    // output data to write to file
    //
    //  - anything that is outputted will be written to the file
    //  - in this case, we're just creating a .csv with each entry in the
    //    array written on a new line
    //
    //  - this data can be manipulated and formatted however you'd like
    //
    echo implode( "\n", $_SESSION['data_for_file'] );
    
    // tada ... the file will download on the client's computer
    
  // retrieve data and store it to session for later download
  } else {
    
    // retrieve POST values
    //
    //  - you coiuld retrieve post values from a previous form submission
    //    and write those to the session to put into the file
    //
    
    // connect to database
    //
    //  - you could connect to a database and get data here that could go into the file
    //
    
    // data to save to file
    //
    //  - this can be any format and will get stored into a session variable which can contain arrays
    //
    $data_for_file = array( 'store', 'some', 'data', 'here' );
    
    // store your data, in whatever format, to your session
    //
    //  - you can store it accross lots of vars because you can maniupulate
    //    it before writing to the file.
    //
    $_SESSION['data_for_file'] = $data_for_file;
    
    // create a link to download the file
    //
    //  - notice the get parameter that will tell this page to download, rather than display this link
    //  - you could also send the user to a new page that has the above logic in it
    //    from within the `if( $_GET['download_file'] ) {` statement.
    //
    echo '<a href="?download_file=TRUE">Download File</a>';
    
  }

thanks! 👍