ed after the substitution OLD=NEW is performed.
    
    A useful alias to use with this is r='fc -s', so that typing `r cc'
    runs the last command beginning with `cc' and typing `r' re-executes
    the last command.
    
    The history builtin also operates on the history list.
    
    Exit Status:
    Returns success or status of executed command; non-zero if an error occurs.