使用正则表达式验证img url

I have been trying to validate a image url using regular expression like so:

#\[img\](((http:\/\/|https:\/\/)?(www.)?(([a-zA-Z0-9-]){2,}\.){1,4}([a-zA-Z]){2,6}(\/([a-zA-Z-_\/\.0-9#:?=&;,]*)?)?))\[\/img\]#iUs

i want be to able to replace:

[img]http://www.website/folders/url_here.png[/img]
[img]https://www.website/folders/url_here.jpg[/img]
[img]https://www.website/folders/url_here.gif[/img]

with:

<img src="http(s):www.website/folders/url_here.png(jpg, gif)" />

Using:

$new_string = preg_replace($search, $replace, $string);

Thank you!

Something like this:

<?php

$rgx = '/\[img\](https?:\/\/.+?\.(?:png|gif|jpg))\[\/img\]/';
$arr = array(
'sdvsvsdvsdv[img]http://www.website/folders/url_here.png[/img]sdvsdvsvdsvdsdv',
'sdvsvdsvd[img]https://www.website/folders/url_here.jpg[/img]svsnvlkn',
'sdvsdvsdv[img]https://www.website/folders/url_here.gif[/img]svdsvd'
);

$all = 'sdvsvsdvsdv[img]http://www.website/folders/url_here.png[/img]sdvsdvsvdsvdsdv
sdvsvdsvd[img]https://www.website/folders/url_here.jpg[/img]svsnvlknsdvsdvsdv[img]https://www.website/folders/url_here.gif[/img]svdsvd';

echo "Individual strings:
";
foreach ($arr as $str) {
    echo preg_replace($rgx, '<img src="$1" alt="">', $str) . "
";
}

echo "
All together: 
";
echo preg_replace($rgx, '<img src="$1" alt="">', $all) . "
";

Codepad: http://codepad.org/n00B6akn

Some little tweaks:

Alternatively this tweak speeds up the regex I made by keeping it greedy instead of making the middle non-greedy:

$rgx = '/\[img\](https?:\/\/[^\[]*\.(?:png|gif|jpg))\[\/img\]/'

And here without as many slashes:

$rgx = '~\[img\](https?://[^\[]*\.(?:png|gif|jpg))\[/img\]~'

It makes sure the img tags are matched, and that whatever is inbetween them starts with http(s):// and ends with .png / .gif / .jpg. If you need better validation then something like what hwnd made initially (v1 of his answer) is more fitting (given you tweak his solution to your needs).

You will want to use something like:

$output = preg_replace('/\[img\]((?:https|http|ftp):\/\/.+?\.(?:png|gif|jpg))\[\/img\]/igm', '<img src="$1" alt="Image">', $input);

Where $input is your page of text and $output is your result. The regular expression evaluates the url and bbcode then adds it to a tag. I have added the alt="" attribute just to make it more html valid. I have also allowed the ftp protocol as some ftp servers allow public access to image files.

The /igm makes it case insensitive, allows subsequent searches to start from the end of the previous match and will match the start and end of a line, instead of the start and end of the whole string.

You can use the following for this.

$text = <<<DATA
[img]http://www.website/folders/url_here.png[/img]
[img]https://www.website/folders/url_here.jpg[/img]
[img]https://www.website/folders/url_here.gif[/img]
DATA;

$text = preg_replace('~\[(img)\](https?://\S+\.(?:png|gif|jpg))\[/\1\]~', 
                     '<img src="$2" />', $text);

Output

<img src="http://www.website/folders/url_here.png" />
<img src="https://www.website/folders/url_here.jpg" />
<img src="https://www.website/folders/url_here.gif" />

See Live demo