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As a "look under the covers" tutorial for myself I am building a PHP script to gather emails from a POP3 mailbox. While attempting to make use of binary attachments I am stuck trying to figure out what to do with the attachment information.

Given a string that would be gathered from an email:

------=_Part_16735_17392833.1229653992102 Content-Type: image/jpeg; name=trans2.jpg Content-Transfer-Encoding: base64 X-Attachment-Id: f_fow87t5j0 Content-Disposition: attachment; filename=trans2.jpg

/9j/4AAQSkZJRgABAgEASABIAAD/4QxrRXhpZgAATU0AKgAAAAgABwESAAMAAAABAAEAAAEaAAUA AAABAAAAYgEbAAUAAAABAAAAagEoAAMAAAABAAIAAAExAAIAAAAUAAAAcgEyAAIAAAAUAAAAhodp

(...)

EAgEAgEAgEAgEAg8IBQRL/Lbe/tJrScHqZ2lkmE4XUP2XcSDZZ2VvZ28dtbsDIYmhkbRxAIJCAQC AQCAQf/ScyAQCAQCAQCAQCAQCAQCAQCAQCAQCAQf/9k= ------=_Part_16735_17392833.1229653992102--

Is there a way to save off the data to disk so that it would be in a usable format?

If you have a lot of data to write out that needs to be decoded before writing I would suggest using stream filters so decode the data as you write it...

$fh = fopen('where_you_are_writing', 'wb');
stream_filter_append($fh, 'convert.base64-decode');
// Do a lot of writing here. It will be automatically decoded from base64.
fclose($h);
I tried the below but did not work for me, was generating an empty image file.
file_put_contents('img.png', base64_decode($base64string));
this is how it worked for me:
$data = 'data:image/png;base64,AAAFBfj42Pj4';
list($type, $data) = explode(';', $data);
list(, $data)      = explode(',', $data);
$data = base64_decode($data);
file_put_contents('/tmp/image.png', $data);
I took the code from : 
How to save a PNG image server-side, from a base64 data string
                just the list($type, $data) = explode(';', $data); list(, $data)      = explode(',', $data); fixed my code. Many thanks!
– Lucas Serafim
                Jun 22, 2017 at 21:18
function base64_decode_file($data)
    if(preg_match('/^data\:([a-zA-Z]+\/[a-zA-Z]+);base64\,([a-zA-Z0-9\+\/]+\=*)$/', $data, $matches)) {
        return [
                'mime' => $matches[1],
                'data' => base64_decode($matches[2]),
    return false;
                I guess this was down voted because it doesn't specifically answer the question but its a very useful little helper so I'm tossing you an upvote.
– Rick Kukiela
                Dec 6, 2019 at 16:40
                BTW, you had a few redundant escape characters in your regex: if(preg_match('/^data:([a-zA-Z]+\/[a-zA-Z]+);base64,([a-zA-Z0-9+\/]+=*)$/', $data, $matches)) {
– Rick Kukiela
                Dec 6, 2019 at 16:48
I had a similar situation, and this is what I did. As noted earlier, make sure to remove the extraneous lines before and after the base64 string.
$INPUT = "inputfile_base64_encoded.txt";
$OUTPUT = "output_decoded.zip";
$contents = file_get_contents($INPUT);
$bin = base64_decode($contents);
file_put_contents($OUTPUT, $bin);
For big base64 strings from a DB you need use load()
$imgdata = $FromDB['BASE64']->load();
$imgdata =  base64_decode($imgdata);
file_put_contents($fileName, $imgdata);
                @Mohammed Farag A varchar field from the database is an object, using the load method you can load a big amount of characters.
– esdebon
                Sep 17, 2018 at 4:48
        
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