PHP regex check if contains a specific word but doesn't contain another

Question

How can I check using PHP regular expressions, whether my string variable $str contains the word 'cat' but does not contain the word 'dog'.

I have tried this and it works but I was wondering if there was a single regular expression to do it

$str = "My pet: dog and cat";
if (preg_match('/(\bdog\b)/', $str) && !preg_match('/(\bcat\b)/', $str)) echo 'TRUE';
else echo 'FALSE';

anubhava · Accepted Answer · 2015-05-04 14:15:19Z

6

You can use a negative and a positive lookahead for this:

^(?=.*?cat)(?!.*?dog).*$

To check for complete words use \b:

^(?=.*?\bcat\b)(?!.*?\bdog\b).*$

answered May 4, 2015 at 14:15

anubhava

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2 Comments

I tried this preg_match('^(?=.*?\bcat\b)(?!.*?\bdog\b).*$', $str) but I am getting an error: No ending delimiter '^' found

You have to use: preg_match('/^(?=.*?\bcat\b)(?!.*?\bdog\b).*$/', $str);