是否可以在R[重复]中转义“[”

 a = list("a","b","cdef", "[")
 grep("a",a)
 #[1] 1
 grep("[",a)
 #Error during wrapup: invalid regular expression '[', reason 'Missing ']''
 grep('\[',a)
 #Error during wrapup: '\[' is an unrecognized escape in character string starting "'\["
 grep("\[",a)
 #Error during wrapup: '\[' is an unrecognized escape in character string starting ""\["
 grep("\133",a)
 #Error during wrapup: invalid regular expression '[', reason 'Missing ']''

我想根据这里找到的信息进行“\133”: http://cran.r-project.org/doc/manuals/R-lang.html#Literal-constants 不幸的是,它不起作用。