RegEx and exclusion

[Mr Phuzz]

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

[Colin Fine]

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

[Colin Fine]

Colin Fine wrote:

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

But on second thought, many people would prefer two matches (even if it
is a tiny bit less efficient) rather than using such an obscure pattern.

You could then also capture the file type and use it in the second pattern:

if(preg_match("/\.(jpg|jpeg|gif|png|bmp)$/i", $filename, $match) &&
!preg_match("/_thumb\.$match[1]$/i", $filename)){
Colin