Re: [SR-Users] Understanding regex format for subst_hf

Update: I managed to achieve it using the "regex" module with "pcre_match()", that will take negative lookahead nicely. On Mon, Oct 4, 2021 at 10:18 AM Joel Serrano &lt;joel(a)textplus.com&gt; wrote: > 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. > > > >