奇數行中的雙字符（GREP）

Question

我需要在Unix中使用grep編寫正則表達式，該行發現雙字符出現奇數次的行。

例如：

unix AA unixAA unix helpme AA //**true**, because 'AA' occurs 3 times 

??red blue pink yellow red pink //**true**, because '??' occurs once 

unixA unixAA unix unixAA unix //**false**, because 'AA' occurs 2 times 

??red blue?? pink?? yellow?? //**false**, because '??' occurs 4 times 

感謝您的幫助:)

Answer 1

這是相當複雜的正則表達式的問題。您將需要GNU grep命令能夠使用 向前看符號來解決這個複雜的正則表達式：

^(?:(?!(.)\1).)*((.)\3)((?:(?:(?!\2).)*\2){2})*(?:(?!\2).)*$ 

在grep使用：

grep -P '^(?:(?!(.)\1).)*((.)\3)((?:(?:(?!\2).)*\2){2})*(?:(?!\2).)*$' file 

unix AA unixAA unix helpme AA 
??red blue pink yellow red pink 

RegEx Demo

正則表達式破碎：

^       # Start 
(?:(?!(.)\1).)*   # Match 0+ characters that don't repeat at start 
((.)\3)     # Match 2 repeats of same character and capture in group #2 
((?:(?:(?!\2).)*\2){2})* # match 0+ occurrence of some text followed by group #2 
(?:(?!\2).)*    # match anything in the end that doesn't have group #2 
$       # End