资料来源 : Free On-Line Dictionary of Computing

egrep
     
        An extended version of the {Unix} command {grep}.  Egrep
        accepts extended {regular expression}s (RE) including "*"
        following multi-character REs; "+" (one or more matches); "?"
        (zero or one matches); "|" separating two REs matches either.
        REs may be bracketed with ().  Despite its additional
        complexity, egrep is usually faster that {fgrep} or {grep}.