PHP用自定义字符串替换bbcode

Question

我有这种情况

<?php
$string = "Hello, how are you, have a good day. [pictureblock]78[/pictureblock] Some other text.";
?>

我需要替换这个：[pictureblock] ID [/ pictureblock]

用这个：

$show div = '<div class="pictures">
<a href="img/sml/pic_one.jpg"><img class="imagethumb" src="img/sml/sml_pic_one.jpg"></img></a><a href="img/sml/pic_two.jpg"><img class="imagethumb" src="img/sml/sml_pic_two.jpg"></img></a>
</div>';

我需要从[pictureblock] THISID [/ picureblock]获取ID文本文件并使用此功能：

$dat_get = substr(file_get_contents("THISID.txt"),0,100000000000);

但我需要第二次替换，$ dat_get输出：

[d]pic_one[/d][d][/pic_two]

需要转换为：

$show div = '<div class="pictures">
<a href="img/sml/pic_one.jpg"><img class="imagethumb" src="img/sml/sml_pic_one.jpg"></img></a><a href="img/sml/pic_two.jpg"><img class="imagethumb" src="img/sml/sml_pic_two.jpg"></img></a>
</div>';