Abstract of regular expressions

wonder3

I just copied it from the "man grep".


regular expressions:
    single character
    \meta-character
    bracket expression:[set of char],is for a single char in the set.
     range expression:seems a kind of bracket expression,is for any char betweet the two char besides the hyphen.
     predefined:[:alnum:],[:alpha:],[:cntrl:],[:digit:],[:graph:],[:lower:],[:print:],[:punct:],[:space:],[:upper:],[:xdigit:] for example(i dont kown what's this),[[:alnum:]] for [0-9A-Za-z]
.           :any single char
\w          :[[:alnum:]]
\W          :[^[:alnum:]]
^,$         :match at the beginning and the end of a line
\        :.................................of a word
\b          :at the edge of a word
\B          :not at the edge of a word


repetition char:
?     :at most once
*     :zero or more
+     :one or more
{n}   :exactly n times
{n,}  :n to infinite
{m,n} :m to n




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