If $alt variable empty then fall back to $title in Wordpress custom function

I have constructed a custom gallery type as a new shortcode in Wordpress.

However I want to make it a little more SEO friendly so am trying to call the alt tag, and if the alt tag is not found replace it with the title.

So far I have the following (and it works fine) but I am stuck at trying to have $alt fallback to title if $alt is empty? Any ideas/help appreciated!

$bigimageUrl = wp_get_attachment_image_src($attachment_id,$size='full-size');
$littleimageUrl = wp_get_attachment_image_src($attachment_id,$size='thumbnail');
$title_raw = $attachment->post_title;
$title = preg_replace("/[^a-zA-Z0-9\s]/", " ", $title_raw);
$alt_raw = get_post_meta($attachment_id, '_wp_attachment_image_alt', true);
$alt = preg_replace("/[^a-zA-Z0-9\s]/", " ", $alt_raw);

echo '<img class="gallerytype" title="'; echo $title; echo '" alt="'; echo $alt; echo '" data-rsTmb="'; echo $littleimageUrl[0]; echo '" src="'; echo $bigimageUrl[0]; echo '"/> ';

Solution

Instead of using one echo after the other:

echo '<img class="gallerytype" title="';
echo $title; 
echo '" alt="'; 
echo $alt; echo '" data-rsTmb="'; 
echo $littleimageUrl[0]; 
echo '" src="'; 
echo $bigimageUrl[0]; echo '"/> ';

You can use a comma (,) to separate expressions to be output:

echo '<img class="gallerytype" title="', $title, '" alt="', ..., '"/> ';

That should already help you to make the code a little mit more readable.

Then you want to set $alt to $title if it is empty. So do that before the output:

empty($alt) && $alt = $title;

Read as: $alt is empty and $alt is $title.

You could also write that with an if clause:

if (empty($alt)) $alt = $title;

That should do it for you.