Thanks Daniel. I didn’t know “$null” existed. But I’ll use is_present_hf since I’m not interested in the contain of the header. From: sr-users-bounces(a)lists.sip-router.org [mailto:sr-users-bounces@lists.sip-router.org] On Behalf Of Daniel-Constantin Mierla Sent: Thursday, 26 June 2014 7:57 p.m. To: Kamailio (SER) - Users Mailing List Subject: Re: [SR-Users] How to find whether or not certain header exists? Hello, you can use: if(is_present_hf("aaa")) ... Also, it should work like: if($hdr("aaa") != $null) ... The is_present_hf() should be slightly faster as it just walks through the list of headers, not parsing the header body and not returning its value. Cheers, Daniel On 26/06/14 06:35, Allen Zhang wrote: Hi, If I normally receive a INVITE that has a header ‘aaa’ with value ‘bbb’, but it’s possible that some INVITEs don’t have this header. How do I determine in the config file if the header exists? To check the value of the header I do if($hdr(aaa) == "bbb"). But what if the header doesn’t exist? Cheer, Allen _______________________________________________ SIP Express Router (SER) and Kamailio (OpenSER) - sr-users mailing list sr-users@lists.sip-router.org<mailto:sr-users@lists.sip-router.org> http://lists.sip-router.org/cgi-bin/mailman/listinfo/sr-users -- Daniel-Constantin Mierla - http://www.asipto.com http://twitter.com/#!/miconda - http://www.linkedin.com/in/miconda