<?php
$str = 'bq. sometext
[quote author="author" date="unix time in secs"]
some text
[/quote]' ;
'#bq\. (\S+)#' ,
'<blockquote author="author" timestamp="unix time in secs">$1</blockquote>' ,
$str
) ;
'#\[quote(?=[^\]]*author="([^"]*))(?=[^\]]*date="([^"]*))[^\]]*\](.*?)\[/quote\]#s' ,
'<blockquote author="$1" timestamp="$2">$3</blockquote>' ,
$str
) ;
echo $str ;
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