douchi0471
douchi0471
2014-04-01 08:49

这个preg_match语法与“。+?”匹配的是什么

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I know perl style regular expresions fairly well, but today I found one that I do not understand:

preg_match('/^On.+?wrote:.+?$/i',$line); //reduced example

What does the .+? mean? I undarstand the .+ alone, I understand .? alone. But .+?? It seems a bug to me.

The line should match popular citation prefixes in the email body and it is much more complicated along with look behinds, but this is the only part i can't understand, and still the regexp seems to work correclty.

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3条回答

  • dongqiao1158 dongqiao1158 7年前

    + means one or more and is greedy. +? means the same, it just is not greedy like usual regex are.

    Edit: I wanted to explain it a little further, but the comment of deceze already explains enough.^^

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  • dongmu1914 dongmu1914 7年前

    Lazy not Greedy

    .+? matches any character (except newline)

    Quantifier: Between one and unlimited times, as few times as possible, expanding as needed [lazy]
    

    check at regex101.com

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  • douzhuangxuan3268 douzhuangxuan3268 7年前

    In short, when you add ? its matching least amount possible, where as without ? its matching most amount possible:

    Here is the explanation:

    NODE                     EXPLANATION
    --------------------------------------------------------------------------------
      .+?                      any character except 
     (1 or more times
                               (matching the least amount possible))
    --------------------------------------------------------------------------------
      .+                       any character except 
     (1 or more times
                               (matching the most amount possible))
    
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