Type Regex Successful if the enclosed subexpression . . .
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Positive Lookbehind (?<=......) successful if can match to the leftNegative Lookbehind (?<!......) successful if can not match to the left
Positive Lookahead (?=......) successful if can match to the right
Negative Lookahead (?!......) successful if can not match to the right
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## lookahead , 光看不吃,只匹配,不消耗任何字符,對$1,$2...等特殊變量沒有影響。
## 以上列表按照順序分別是向左匹配,向左不匹配,向右匹配,向右不匹配。
## 個人感覺在不修改原來的字符串,只是定位,然後插入字符串的時候比較有用。