Use Laravel to Download table as CSV

Almost everything is fine except this line:

return Response::download($handle, 'tweets.csv', $headers);

You should change this line into:

return Response::download($filename, 'tweets.csv', $headers);

EDIT: see this answer for a better solution; I'll keep my answer below but note that it has issues like not escaping values and using unreasonable amounts of memory if generating large files.

You're unnecessarily creating a file on the disk; that induces disk IO and will cause issues if two people request that URL at the exact same time (two instances of the framework will write to that same file and bad stuff will happen such as serving a corrupted file or crashing with an exception).

Use this instead :

Route::get('/all-tweets-csv', function() {
    $tweets = Tweets::all();

    // the csv file with the first row
    $output = implode(",", array('tweet text', 'screen name', 'name', 'created at'));

    foreach ($tweets as $row) {
        // iterate over each tweet and add it to the csv
        $output .=  implode(",", array($row['tweet_text'], $row['screen_name'], $row['name'], $row['created_at'])); // append each row
    }

    // headers used to make the file "downloadable", we set them manually
    // since we can't use Laravel's Response::download() function
    $headers = array(
        'Content-Type' => 'text/csv',
        'Content-Disposition' => 'attachment; filename="tweets.csv"',
        );

    // our response, this will be equivalent to your download() but
    // without using a local file
    return Response::make(rtrim($output, "\n"), 200, $headers);
});

I stumbled in here trying to see if Laravel had something built in by default - the answers for this question worry me a bit. I agree with @andré-daniel that the proper method is to not write a file first, but his implementation is manually putting together the values, which would fail if any value contained quotes, spaces, etc.

This is a more robust solution, using Laravel's Response::stream and php's fputcsv to format each line properly (will escape quotes, and quote necessary strings. see http://php.net/manual/en/function.fputcsv.php for details)

<?php

public function download()
{
    $headers = [
            'Cache-Control'       => 'must-revalidate, post-check=0, pre-check=0'
        ,   'Content-type'        => 'text/csv'
        ,   'Content-Disposition' => 'attachment; filename=galleries.csv'
        ,   'Expires'             => '0'
        ,   'Pragma'              => 'public'
    ];

    $list = User::all()->toArray();

    # add headers for each column in the CSV download
    array_unshift($list, array_keys($list[0]));

   $callback = function() use ($list) 
    {
        $FH = fopen('php://output', 'w');
        foreach ($list as $row) { 
            fputcsv($FH, $row);
        }
        fclose($FH);
    };

    return response()->stream($callback, 200, $headers)
}