Created attachment 12855 [details]
test program illustrating the \b-inside-interval regex bug

The glibc regular expression code mishandles extended regular expressions such as:

  (.*\band){2}

although it correctly processes equivalent expressions such as:

  (.*(\<|\>)and){2}

There is a similar problem with the same regular expression in BRE syntax:

  \(.*\band\)\{2\}

To reproduce the problem, compile and run the attached file b-interval-bug.c. It will exit with status 1, whereas the correct exit status is 0.

This bug was reported against GNU 'sed' here:

https://bugs.gnu.org/41558

and the original posting is from StackExchange, here:

https://unix.stackexchange.com/questions/579889/why-doesnt-this-sed-command-replace-the-3rd-to-last-and

The original posting mentions backreferences but the bug occurs even without backreferences.