Grep isn't a difficult skill to acquire but I wouldn't hire someone that didn't know it. Some skills can be good proxies for a range of other skills an experience and a lot of developers are in that "don't know what they don't know" range.
Sure, I just have to disagree on IRC being a good indicator for that.
Also, fwiw, most of my colleagues use IDE "search project for string" in places where I use grep. Also, if I'm being honest, you should hire nearly all of them before you hire me.