ACF check if variable has http, if else return string

Question

Trying to check if $link has http:// in front of it or not. If someone puts in www.google.com for the link field it acts as a link within the WordPress site, ie: www.website.com/www.google.com.

$link = get_field('advertisement_link');

$ad_code = '<a href="'.$link.'" target="_blank">Test</a>';

Sample code above I am working with. This is a general PHP question as well. How do I do this the right way? Tried below, replaces the_content() with the $link.

$link = get_field('advertisement_link');

if(strpos($link, 'http://') !== 0) {
    return 'http://' . $link;
} else {
    return $link;
}

$ad_code = '<a href="'.$link.'" target="_blank">Test</a>';

Edit: I need to keep $ad_code because I'm using it inside return prefix_insert_after_paragraph( $ad_code, 3, $content ); to insert this ad into a post every 3 paragraphs.

Answer 1

You must not return the value, but alter the varialbe $link

if(strpos($link, 'http://') !== 0) {
    $link = 'http://' . $link;
} //no else needed

Be aware that if your link begins with https:// it will also prepend the http:// and result in http://https://example.com.

The better way to do this would be from here, adjusted to your needs:

In functions.php:

function addhttp($url) {
    if (!preg_match("~^(?:f|ht)tps?://~i", $url)) {
        $url = "http://" . $url;
    }
    return $url;
}

Code for you:

$link = addhttp( get_field('advertisement_link') );
$ad_code = '<a href="'.$link.'" target="_blank">Test</a>';

Answer 2

I guess this is a possible duplicate of – or at least similar to "Checking if string contains HTTP://" over at stackoverflow – but still: First instead of checking for "0" you should check for "false". And then you should also check for "https://". I would probably do something like this:

if (substr($link, 0, 7) == 'http://') {
    // do nothing
} elseif (substr($link, 0, 8) == 'https://') {
    // do nothing
} else {
    $link = 'http://'.$link;
}

( I'm aware there are more elegant ways to write this )