问题
Normally the . doesn't match newline unless I specify the engine to do so with the (?s) flag. I tried this regexp on my editor's (UltraEdit v14.10) regexp engine using Perl style regexp mode:
(?s).*i
The search text contains multiple lines and each line contains many 'i' characters.
I expect the above regexp means: search as many characters (because with the '?s' the . now matches anything including newline) as possible (because of the greediness for *) until reaching the character 'i'.
This should mean "from the first character to the last 'i' in the last sentence" (greediness should reach the last sentence, right?).
But with UltraEdit's test, it turns out to be "from the first character to the last 'i' in the first sentence that contains an i". Is this result correct? Did I make any wrong interpretation of my reg expression?
e.g. given this text
aaa
bbb
aiaiaiaiaa
bbbicicid
it is
aaa
bbb
aiaiaiai
matched. But I expect:
aaa
bbb
aiaiaiaiaa
bbbicici
回答1:
Your regex is correct, and so are your expectations of its performance.
This is a long-known bug in UltraEdit's regex implementation which I have written repeatedly to support about. As far as I know, it still hasn't been fixed. The problem appears to lie in the fact that UE's regex implementation is essentially line-based, and additional lines are taken into the match only if necessary. So .* will match greedily on the current line, but it will not cross a newline boundary if it doesn't have to in order to achieve a match.
There are some other subtle bugs with line endings. For example, lookbehind doesn't work across newlines, either.
Write to IDM support, or change to an editor with decent regex support. I did both.
回答2:
Yes you are right this looks like a bug.
Your interpretation is correct. If you are in Perl mode and not Posix. However it should apply to posix as well.
Altough defining the modifiers like you do is very rare.
Mostly you provide a string with delimiters and the modifier afterwards like /.*i/s
But this doesn't matter because your way is correct too. And if it wouldnt be supported, it wouldn't match the first newline either.
So yes, this is definately a bug in your program.
回答3:
You're right that that regex should match the entire string (all 4 lines). My guess is that UltraEdit is attempting to do some sort of optimization by working line by line, and only accumulating new lines "when necessary".
来源：https://stackoverflow.com/questions/4348332/regular-expression-using-the-dot-matches-all-mode