image not uploading/moving into folder - php

Question

i am uploading an image , image title is getting added to database but the file(image is not uploading/moving to the folder), i am getting 404 error for that image , i have set that folder permissions to 0777 and also max upload is 1024MB
$article_image = $_FILES['image']['name'];
$image_tmp = $_FILES['image']['tmp_name'];
define ('SITE_ROOT', realpath(dirname('_FILE_')));
move_uploaded_file($image_tmp,SITE_ROOT.'/images/$article_image');
$add="insert into articles(article_title,article_date,article_author,category,article_image,article_keywords,article_content) values ('$article_title','$article_date','$article_author','$article_category','$article_image','$article_keywords','$article_content')" ;
if(mysqli_query($conn,$add)== 1 ){
echo "<script> alert('article added')</script>";
}
else{
echo "failed".mysqli_error($conn) ;
}
}
what mistake am i doing ?
EDIT here is my html code
<form method="post" action="addarticle.php" enctype="multipart/form-data">
<table align="center">
<tr>
<td align="center"><h1> ADD ARTICLE</h1></td>
</tr>
<tr>
<td>Article Title</td>
<td><input type="text" name="title"></td>
<tr>
<td>Article Keyword</td>
<td><input type="text" name="keywords"></td>
<tr>
<td>Article Image</td>
<td><input type="file" name="image"></td>
</tr>
<td>Article Content</td>
<td><textarea name="content" cols="90" rows="30"></textarea></td>
</tr>
<tr>
<td><input type="submit" name="submit" value="submit"></td>
</tr>
</table>
</form>

Answer 1

Check your line with:
realpath(dirname('__FILE__'));
__FILE__
is a magic constant, and should not be wrapped in single or double quotes.
If you were to echo out the result of that function call you would probably see a different path than what you're expecting.
You're also trying to use string interpolation with single quotes around the variable instead of double:
SITE_ROOT.'/images/$article_image';
Should be:
SITE_ROOT."/images/$article_image";
Example:
if (!empty($_FILES['image'])) {
$tmp_file_to_upload = $_FILES['image'];
if ($_FILES['image']['error'] == UPLOAD_ERR_OK) {
$uploaded_name = $tmp_file_to_upload['name'];
$tmp_name = $tmp_file_to_upload['tmp_name'];
$destination = realpath(dirname(__FILE__))."images/$uploaded_name";
if (!move_uploaded_file($tmp_name, $destination)) {
die('Error uploading file.');
}
} else {
die('Error uploading file.');
}
}

Answer 2

Try this, Variable concatenation issue '/images/'.$article_image
move_uploaded_file($image_tmp,SITE_ROOT.'/images/'.$article_image);
instead of
move_uploaded_file($image_tmp,SITE_ROOT.'/images/$article_image');