it’s posix shell, also it produces an output similar to your post unlike watch, which everyone is rushing to point out as if it were the ultimate superninja haxxor secret tool that nobody knows about :DDD
first of all, it only searches for occurrences in already installed packages and is more or less a grep -l xxx /var/lib/dpkg/info/*.list. So you can’t use it in order to determine which package to install, for that you use packages.debian.org or apt-file instead.
Secondly, what you search for isn’t relative to anything (wtf):