[SR-Users] Understanding regex format for subst_hf

Hey guys, I'm trying to do a replacement regex using subst_hf but I can't seem to get the format right and the docs are confusing. *subst_hf: *docs say it uses perl-like regex (as I understand it, that would mean PCRE). Docs also say in the 'subexp' param that it uses the same format as *subst.* *subst: *at the beginning it says it uses perl or sed format, but in the '/re/repl/flags' param it says that sed format. https://www.kamailio.org/docs/modules/devel/modules/textops.html#textops.f.… 4.20. subst_hf(hf, subexp, flags) Perl-like substitutions in the body of a header field. Meaning of the parameters is as follows: - *hf* - header field name. - *subexp* - substitution expression in the same format as of the 'subst' function parameter. - *flags* - control flags - it has to be one of: a - all headers matching the name; f - only first header matching the name; l - only the last header matching the name. 4.16. subst('/re/repl/flags') Replaces re with repl (sed or perl like). Meaning of the parameters is as follows: - *'/re/repl/flags'* - sed like regular expression. flags can be a combination of i (case insensitive), g (global) or s (match newline don't treat it as end of line). 're' - is regular expression 'repl' - is replacement string - may contain pseudo-variables 'flags' - substitution flags (i - ignore case, g - global) I'm trying to use this: subst_hf("X-myheader", "/^(?!string1 |example2-|text3 )(.*)/myprefix \1/", "a") In an online tester using PCRE, the format is correct, but Kamailio doesn't like it: Oct 4 09:29:16 cops-n1 cops[15957]: ERROR: <core> [core/re.c:285]: subst_parser(): bad regular expression ^(?!string1 |example2-|text3 )(.*) in /^(?!string1 |example2-|text3 )(.*)/myprefix \1/ If I remove the negative lookahead chars (?!) then kamailio doesn't complain but the regex doesn't do what I want. Does this mean that Kamailio won't support negative lookahead for subst regex replacements? What I'm trying to achieve is something along: "If the value of the header Myheader doesn't start with ABC, DEF or HIJ, then prefix it with XYZ" Any suggestions/ideas on how to achieve this? Thanks, Joel.