How to match all >< except bold tag

Question

I have a regular expression [&<>] for matching < and > in text.

Like <i>text</i> - will match <, >, <, >,

But I don't want it to match <b> and </b>

How can I do this?

Example: <i>match me</i> <b>don't match me</b> <i>match me</i>

Will match only < and > for italic tags

Answer 1

You can achieve this using negative lookarounds:

(?<!b)>|(?!<b)(?!</b)<

Demo

Explanation:

(?<!b)>|(?!<b)(?!</b)<
       |                # match either
      >                 # a >,
(?<!b)                  # not preceeded by a b
                     <  # or a <,
        (?!<b)          # not preceeded by a <b
              (?!</b)   # and neither by </b

Lookaround assertions typically have to have a fixed length, which is why we need two for the opening angle bracket: one for <b>, and one for </b>.