使用正则表达式验证img url

Question

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!

Answer 1

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).