如何检查段落中是否存在img标记或在段落的末尾

how I can check if there are img tags only in a paragraph or or at the end of the paragraph?

$input = '<p><img src="#" /></p>'; // ok
$input = '<p><img src="#" /><img src="#" /></p>'; // ok
$input = '<p>xxx<img src="#" /></p>'; // ok

$input = '<p><img src="#" />xxx</p>'; // NOT ok

if(preg_match("/img/$", $input) { ... };

Any other better methods than preg_match and regex?

You can use DOMDocument, and check if there are any text contents on the <p> node:

$doc = new DOMDocument;
$doc->loadHTML( $input);

$p = $doc->getElementsByTagName('p')->item(0);
$children = $p->childNodes;

$img_found = false; $error = false;

foreach( $children as $child) {
    if( $child->nodeType == XML_TEXT_NODE && !$img_found) {
        // Text before the image, OK, continue on
        continue;
    }
    if( $child->nodeType == XML_ELEMENT_NODE) {
        // DOMElement node
        if( !($child->tagName == 'img')) {
            // echo "Invalid HTML element found";
            $error = true;
        } else {
            $img_found = true;
        }
    } else {
        // echo "Invalid node type!";
        $error = true;
    }
}

// No errors and we found at least one image, we're good
if( $img_found && !$error) {
    echo 'ok' . "
";
} else {
    echo 'NOT ok' . "
";
}

You can see in this demo that is passes all of your tests. It fulfills the requirements:

1. Only images and text inside the <p> tag. Any other tags, are invalid. If this is untrue, modify it for your needs.
2. If there is text, it must come before we detect an <img> tag.

Try this regular expression:

/<p[^>]*>.*<img[^>]*></p>/

Explanation: If you want to match a tag with unknown attributes with regex you can use <TAGNAME[^>]*>. The expression [^>]* matches every character zero or n times besides > , thus accepting any numbers of attributes.

Use this one:

if (preg_match("/<img\s[^<>]*><\/p>/i", $input) { ... };