Posted by Colin Fine on 10/01/06 23:50

Mr Phuzz wrote:
> Hello,
>
> I'm pretty new to PHP and am wrestling with regexp's right now. I am
> trying to figure something out with no luck. Hopefully someone can
> help.
>
> I am trying to filter out file names. I want to write a regexp that
> matches all image file names, such as ".jpg", ".bmp", ".png", etc...
> but not file names that end with "_thumb.***" (where *** is the
> extension of the file name... which can be 3 or 4 chars long). So...
>
> somepic.jpg <--- should match
> somepic_thumb.jpg <--- should not match
> anotherpic.png <--- should match
> this_thumb.is_broken.jpg <--- should match
>
> Currently, I do this using two regexps. First, I compare to determine
> if the file is an image by looking at the end and seeing if it's .jpg,
> .png, etc. If that passes, I compare again to see if it contains
> "_thumb.***" at the end (allowing for 3 or 4 chars, such as jpg or
> jpeg), as such:
>
> if(preg_match("/(.jpg|.jpeg|.gif|.png|.bmp)$/i", $filename)){
> if(!preg_match("/(_thumb.).{3,4}$/i", $filename)){
> $files[]=$filename;
> print("$filename<br>");
> }
> }
>
> How can I, if possible, combine these into one regexp?
>
> Thanks for your time,
> Mr Phuzz
>

You can do it by a negative lookbehind assertion:

'/(?<!_thumb)\.(jpg|jpeg|gif|png|bmp)$/'

finds an instance of .jpg etc that is not preceded by _thumb

(You want to escape the . anyway, as otherwise it will match any character.)

Colin

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