最初想筛选以sh结尾但前面没有.的文件, 对应的Regex为(?<!\.)sh$, 但是! 刚开始不知道(?!),(?=),(?<!)这种写法规则, 就在想用逻辑与写出以sh结尾的字符但不以.sh结尾, 但这本身就矛盾啊, 以.sh结尾本身就是以sh结尾啊,,, 研究了俩小时, 太菜了,,,, 又快凌晨一点了,

在StackOverflow看到一个好的回答,

Given the string foobarbarfoo:

bar(?=bar)     finds the 1st bar ("bar" which has "bar" after it)
bar(?!bar)     finds the 2nd bar ("bar" which does not have "bar" after it)
(?<=foo)bar    finds the 1st bar ("bar" which has "foo" before it)
(?<!foo)bar    finds the 2nd bar ("bar" which does not have "foo" before it)

You can also combine them:

(?<=foo)bar(?=bar)    finds the 1st bar ("bar" with "foo" before it and "bar" after it)

使用这种 lookaround 句型的时候要注意上面的写法, 即 (?!bar) 就是用来指定某个单词后不含有什么的, 还有一个重要的点如下:

In the meantime, if there is one thing you should remember, it is this: a lookahead or a lookbehind does not “consume” any characters on the string. This means that after the lookahead or lookbehind’s closing parenthesis, the regex engine is left standing on the very same spot in the string from which it started looking: it hasn’t moved. From that position, then engine can start matching characters again.

即这些Lookaround只是用来检查check的, 是个附加条件:

$ printf "handle_test.go" | grep -P 'test(?=.)go'

凭直觉 'test(?=.)go' 匹配的是含有 test 且其后紧跟着 .go, 可是 "handle_test.go" 并不满足 'test(?=.)go', 因为(?=.) 匹配到了 . 并没有消耗掉它, 要这么写才行: 'test(?=.).go' ,但这样看着很奇怪 并不是这么用的, 其实直接写 'test(?=.go)' 就好了,

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