And for all you know "grep -E" isn't supported on some system people use. This is not really a concern if you're just writing script for yourself (which are rea

And for all you know "grep -E" isn't supported on some system people use. This is not really a concern if you're just writing script for yourself (which are really >90% of scripts; portability often isn't really a concern), but knowing it will work on all systems – new and old – is pretty hard, and sometimes it does matter. Does it work on NetBSD? HP-UX? Solaris? Last year autoconf changed the `..` command substitution syntax to the "new" $(..) syntax and someone complained it broke on their ancient Solaris system. So ... people will stick with what works, like "egrep".