Re: [sr-dev] [kamailio/kamailio] core: allow empty matches (#2869)

@btriller - looking again at this one, wouldn't it be the same to do:

subst_hf("X-My-Header", "/^(.+)$/prefix \1/", "a");
subst_hf("X-My-Header", "/^(.+)$/\1 suffix/", "a");

instead of:

subst_hf("X-My-Header", "/^/prefix /", "a");
subst_hf("X-My-Header", "/$/ suffix/", "a");

Knowing that ``` % echo blub|sed 's/^/prefix /' prefix blub % echo blub|sed 's/$/ suffix/' blub suffix ``` works, it felt weird to write ``` subst_hf("X-My-Header", "/^(.)/prefix \1/", "a"); subst_hf("X-My-Header", "/(.)$/\1 suffix/", "a"); ``` As most of the time, there are other ways to do it (above suggested or `remove_hf()`, looping over all headers and `append_hf()`). I understand the concerns, so I don't mind if the PR is closed.