blocks|key|1418192|text|您可以尝试String#[]+(就像在variableName[/regular+expression/]中一样)。|type|unstyled|depth|inlineStyleRanges|offset|length|style|CODE|entityRanges|data|1418193|以下是IRB的输出示例：|1418194|names+=+"erik+kalle+johan+anders+erik+kalle+johan+anders"
#+=>+"erik+kalle+johan+anders+erik+kalle+johan+anders"
names[/kalle/]
#+=>+"kalle"|code-block|syntax|javascript|1418195|entityMap|0|LINK|mutability|MUTABLE|url|https://ruby-doc.org/core-3.0.0/String.html#method-i-5B-5D^0|5|9|J|Y|5|9|0|0|0|0^^$0|@$1|2|3|4|5|6|7|U|8|@$9|V|A|W|B|C]|$9|X|A|Y|B|C]]|D|@$9|Z|A|10|1|11]]|E|$]]|$1|F|3|G|5|6|7|12|8|@]|D|@]|E|$]]|$1|H|3|I|5|J|7|13|8|@]|D|@]|E|$K|L]]|$1|M|3|-4|5|6|7|14|8|@]|D|@]|E|$]]]|N|$O|$5|P|Q|R|E|$S|T]]]]

You could try <a href="https://ruby-doc.org/core-3.0.0/String.html#method-i-5B-5D" rel="noreferrer"><code>String#[]</code></a> (as in <code>variableName[/regular expression/]</code>).
This is an example output from IRB:
<pre><code>names = &quot;erik kalle johan anders erik kalle johan anders&quot;
# =&gt; &quot;erik kalle johan anders erik kalle johan anders&quot;
names[/kalle/]
# =&gt; &quot;kalle&quot;
</code></pre>

blocks|key|1418246|text|如果只有一个匹配项的存在是重要的，你可以使用|type|unstyled|depth|inlineStyleRanges|entityRanges|data|1418247|/regexp/+=~+"string"|code-block|syntax|javascript|1418248|无论哪种方式，match应该只返回第一个匹配项，而scan会搜索整个字符串。因此，如果|offset|length|style|CODE|1418249|matchData+=+"string+string".match(/string/)
matchData[0]++++#+=>+"string"
matchData[1]++++#+=>+nil+-+it's+the+first+capture+group+not+a+second+match|1418250|entityMap^0|0|0|7|5|P|4|0|0^^$0|@$1|2|3|4|5|6|7|Q|8|@]|9|@]|A|$]]|$1|B|3|C|5|D|7|R|8|@]|9|@]|A|$E|F]]|$1|G|3|H|5|6|7|S|8|@$I|T|J|U|K|L]|$I|V|J|W|K|L]]|9|@]|A|$]]|$1|M|3|N|5|D|7|X|8|@]|9|@]|A|$E|F]]|$1|O|3|-4|5|6|7|Y|8|@]|9|@]|A|$]]]|P|$]]

If only an existence of a match is important, you can go with 

<pre><code>/regexp/ =~ "string"
</code></pre>

Either way, <code>match</code> should only return the first hit, while <code>scan</code> searches throughout entire string. Therefore if 

<pre><code>matchData = "string string".match(/string/)
matchData[0] # =&gt; "string"
matchData[1] # =&gt; nil - it's the first capture group not a second match
</code></pre>

blocks|key|1418332|text|正则表达式(regex)只不过是一个有限状态机(FSM)。|type|unstyled|depth|inlineStyleRanges|entityRanges|data|1418333|FSM尝试回答问题“这种状态可能吗？”|1418334|它不断尝试进行模式匹配，直到找到匹配(成功)，或者直到搜索完所有路径但没有找到匹配(失败)。|1418335|在成功时，问题是“这种状态可能吗？”得到的回答是“是”。因此，不需要进一步的匹配，正则表达式返回。|1418336|有关这方面的更多信息，请参阅this和this。|offset|length|1418337|进一步:演示正则表达式如何工作的here+is+an+interesting+example。这里，正则表达式用于检测给定数字是否为质数。这个示例是用perl编写的，但也可以用ruby编写。|1418338|entityMap|0|LINK|mutability|MUTABLE|url|http://www.proofwiki.org/wiki/Regular_Expressions_and_Finite_State_Machines|1|https://stackoverflow.com/a/525043/1243123|2|http://www.noulakaz.net/weblog/2007/03/18/a-regular-expression-to-check-for-prime-numbers/^0|0|0|0|0|E|4|0|J|4|1|0|G|U|2|0^^$0|@$1|2|3|4|5|6|7|Z|8|@]|9|@]|A|$]]|$1|B|3|C|5|6|7|10|8|@]|9|@]|A|$]]|$1|D|3|E|5|6|7|11|8|@]|9|@]|A|$]]|$1|F|3|G|5|6|7|12|8|@]|9|@]|A|$]]|$1|H|3|I|5|6|7|13|8|@]|9|@$J|14|K|15|1|16]|$J|17|K|18|1|19]]|A|$]]|$1|L|3|M|5|6|7|1A|8|@]|9|@$J|1B|K|1C|1|1D]]|A|$]]|$1|N|3|-4|5|6|7|1E|8|@]|9|@]|A|$]]]|O|$P|$5|Q|R|S|A|$T|U]]|V|$5|Q|R|S|A|$T|W]]|X|$5|Q|R|S|A|$T|Y]]]]

A Regular Expression (regex) is nothing but a finite state machine (FSM). 

An FSM attempts to answer the question "Is this state possible or not?"

It keeps attempting to make a pattern match until a match is found (success), or until all paths are explored and no match was found (failure).

On success, the question "Is this state possible or not?" has been answered with a "yes". Hence no further matching is necessary and the regex returns. 

See <a href="http://www.proofwiki.org/wiki/Regular_Expressions_and_Finite_State_Machines" rel="nofollow noreferrer">this</a> and <a href="https://stackoverflow.com/a/525043/1243123">this</a> for more on this.

Further: <a href="http://www.noulakaz.net/weblog/2007/03/18/a-regular-expression-to-check-for-prime-numbers/" rel="nofollow noreferrer">here is an interesting example</a> to demonstrate how regex works. Here, a regex is used to detect if a give number is prime. This example is in perl, but it can as well be written in ruby.

blocks|key|1418372|text|您可以使用[]：(类似于match)|type|unstyled|depth|inlineStyleRanges|offset|length|style|CODE|entityRanges|data|1418373|"foo%2Baccount2@gmail.com"[/\%2B([%5E@]%2B)/,+1]+#+matches+capture+group+1,+i.e.+what+is+inside+()
#+=>+"account2"
"foo%2Baccount2@gmail.com"[/\%2B([%5E@]%2B)/]++++#+matches+capture+group+0,+i.e.+the+whole+match
#+=>+"%2Baccount2"|code-block|syntax|javascript|1418374|entityMap^0|5|2|C|5|0|0^^$0|@$1|2|3|4|5|6|7|M|8|@$9|N|A|O|B|C]|$9|P|A|Q|B|C]]|D|@]|E|$]]|$1|F|3|G|5|H|7|R|8|@]|D|@]|E|$I|J]]|$1|K|3|-4|5|6|7|S|8|@]|D|@]|E|$]]]|L|$]]

You can use <code>[]</code>: (which is like <code>match</code>)
<pre><code>&quot;foo+account2@gmail.com&quot;[/\+([^@]+)/, 1] # matches capture group 1, i.e. what is inside ()
# =&gt; &quot;account2&quot;
&quot;foo+account2@gmail.com&quot;[/\+([^@]+)/] # matches capture group 0, i.e. the whole match
# =&gt; &quot;+account2&quot;
</code></pre>

blocks|key|1418427|text|我还不确定这个特性是很棒还是非常疯狂，但是你的正则表达式可以定义局部变量。|type|unstyled|depth|inlineStyleRanges|entityRanges|data|1418428|/\$(?<dollars>\d%2B)\.(?<cents>\d%2B)/+=~+"$3.67"+#=>+0
dollars+#=>+"3"|code-block|syntax|javascript|1418429|(摘自http://ruby-doc.org/core-2.1.1/Regexp.html)。|offset|length|1418430|entityMap|0|LINK|mutability|MUTABLE|url|http://ruby-doc.org/core-2.1.1/Regexp.html^0|0|0|3|16|0|0^^$0|@$1|2|3|4|5|6|7|S|8|@]|9|@]|A|$]]|$1|B|3|C|5|D|7|T|8|@]|9|@]|A|$E|F]]|$1|G|3|H|5|6|7|U|8|@]|9|@$I|V|J|W|1|X]]|A|$]]|$1|K|3|-4|5|6|7|Y|8|@]|9|@]|A|$]]]|L|$M|$5|N|O|P|A|$Q|R]]]]

I am not yet sure whether this feature is awesome or just totally crazy, but your regex can define local variables.

<pre><code>/\$(?&lt;dollars&gt;\d+)\.(?&lt;cents&gt;\d+)/ =~ "$3.67" #=&gt; 0
dollars #=&gt; "3"
</code></pre>

(Taken from <a href="http://ruby-doc.org/core-2.1.1/Regexp.html" rel="noreferrer">http://ruby-doc.org/core-2.1.1/Regexp.html</a>).

I'm looking for a way to perform a regex match on a string in Ruby and have it short-circuit on the first match.

The string I'm processing is long and from what it looks like the standard way (<code>match</code> method) would process the whole thing, collect each match, and return a MatchData object containing all matches.

<pre><code>match = string.match(/regex/)[0].to_s
</code></pre>

Return first match of Ruby regex

我正在寻找一种方法，在Ruby中对字符串执行正则表达式匹配，并在第一次匹配时使其短路。我正在处理的字符串很长，从外观上看，标准方法(match方法)将处理整个字符串，收集每个匹配项，并返回一个包含所有匹配项的MatchData对象。match = string.match(/regex/)[0].to_s

问返回Ruby regex的第一个匹配项
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