entityMap|0|type|LINK|mutability|MUTABLE|data|url|http://www.regular-expressions.info/modifiers.html|1|https://www.regular-expressions.info/modifiers.html|2|?-i|blocks|key|ev955|text|假设您希望整个正则表达式忽略大小写，您应该寻找i标志。几乎所有的正则表达式引擎都支持它：|unstyled|depth|inlineStyleRanges|offset|length|style|CODE|entityRanges|6l4pn|/G[a-b].*/i

string.match("G[a-b].*",+"i")|code-block|syntax|javascript|1269b|查看您的语言/平台/工具的文档，了解匹配模式是如何指定的。|fh4fj|如果你只想零件如果正则表达式不区分大小写(正如我最初的答案所假定的那样)，那么您有两个选择：|d6rgc|使用(?i)和可选(?-i)模式修饰符：|ordered-list-item|39gt9|(?i)Ga-b..。*将所有变体(即小写和大写)放入正则表达式中-如果不支持模式修饰符，则非常有用：+[gG][a-bA-B].*|a6pa1|最后一点:如果您正在处理除ASCII之外的Unicode字符，请检查您的正则表达式引擎是否正确地支持它们。^0|N|1|N|1|0|O|2|1|0|0|0|0|2|4|9|5|0|5|3|2|0^^$0|$1|$2|3|4|5|6|$7|8]]|9|$2|3|4|5|6|$7|A]]|B|$2|3|4|5|6|$7|C]]]|D|@$E|F|G|H|2|I|J|16|K|@$L|17|M|18|N|O]]|P|@$L|19|M|1A|E|1B]|$L|1C|M|1D|E|1E]]|6|$]]|$E|Q|G|R|2|S|J|1F|K|@]|P|@]|6|$T|U]]|$E|V|G|W|2|I|J|1G|K|@]|P|@]|6|$]]|$E|X|G|Y|2|I|J|1H|K|@]|P|@]|6|$]]|$E|Z|G|10|2|11|J|1I|K|@$L|1J|M|1K|N|O]|$L|1L|M|1M|N|O]]|P|@]|6|$]]|$E|12|G|13|2|11|J|1N|K|@]|P|@$L|1O|M|1P|E|1Q]]|6|$]]|$E|14|G|15|2|I|J|1R|K|@]|P|@]|6|$]]]]

Assuming you want the whole regex to ignore case, you should look for the <a href="http://www.regular-expressions.info/modifiers.html"><code>i</code> flag</a>. Nearly all regex engines support it:

<pre><code>/G[a-b].*/i

string.match("G[a-b].*", "i")
</code></pre>

Check the documentation for your language/platform/tool to find how the matching modes are specified.

If you want only part of the regex to be case insensitive (as my original answer presumed), then you have two options:

<ol>
<li>Use the <code>(?i)</code> and [optionally] <code>(?-i)</code> mode modifiers:

<pre><code>(?i)G[a-b](?-i).*
</code></pre></li>
<li>Put all the variations (i.e. lowercase and uppercase) in the regex - useful if mode modifiers are not supported:

<pre><code>[gG][a-bA-B].*
</code></pre></li>
</ol>

One last note: if you're dealing with Unicode characters besides ASCII, check whether or not your regex engine properly supports them.

entityMap|0|type|LINK|mutability|MUTABLE|data|url|https://www.regular-expressions.info/modifiers.html|blocks|key|aqqlf|text|依赖于实现，但我将使用|unstyled|depth|inlineStyleRanges|entityRanges|ctffb|(?i)G[a-b].|code-block|syntax|js|atqol|变体：|offset|length|style|BOLD|fb25p|(?i)+case-insensitive+mode+ON++++
(?-i)+case-insensitive+mode+OFF|javascript|c8eam|现代的regex风格允许您仅将修饰符应用于正则表达式的一部分。如果在正则表达式中间插入修饰符(?im)，则修饰符仅应用于修饰符右侧的正则表达式部分。使用这些风格，您可以通过在模式前面加上减号(?-i)来关闭模式。|9q70d|描述来自页面：https://www.regular-expressions.info/modifiers.html^0|0|0|0|3|0|0|0|7|1F|0^^$0|$1|$2|3|4|5|6|$7|8]]]|9|@$A|B|C|D|2|E|F|10|G|@]|H|@]|6|$]]|$A|I|C|J|2|K|F|11|G|@]|H|@]|6|$L|M]]|$A|N|C|O|2|E|F|12|G|@$P|13|Q|14|R|S]]|H|@]|6|$]]|$A|T|C|U|2|K|F|15|G|@]|H|@]|6|$L|V]]|$A|W|C|X|2|E|F|16|G|@]|H|@]|6|$]]|$A|Y|C|Z|2|E|F|17|G|@]|H|@$P|18|Q|19|A|1A]]|6|$]]]]

Depends on implementation
but I would use

<pre><code>(?i)G[a-b].
</code></pre>

VARIATIONS: 

<pre><code>(?i) case-insensitive mode ON 
(?-i) case-insensitive mode OFF
</code></pre>

Modern regex flavors allow you to apply modifiers to only part of the regular expression. If you insert the modifier (?im) in the middle of the regex then the modifier only applies to the part of the regex to the right of the modifier. With these flavors, you can turn off modes by preceding them with a minus sign (?-i). 

Description is from the page:
<a href="https://www.regular-expressions.info/modifiers.html" rel="noreferrer">https://www.regular-expressions.info/modifiers.html</a>

entityMap|blocks|key|72r30|text|用于验证'abc‘的正则表达式忽略区分大小写|type|unstyled|depth|inlineStyleRanges|entityRanges|data|eqa4c|(?i)(abc)|code-block|syntax|js^0|0^^$0|$]|1|@$2|3|4|5|6|7|8|H|9|@]|A|@]|B|$]]|$2|C|4|D|6|E|8|I|9|@]|A|@]|B|$F|G]]]]

regular expression for validate 'abc' ignoring case sensitive 

<pre><code>(?i)(abc)
</code></pre>

entityMap|blocks|key|6h4p5|text|Thei标志通常用于不区分大小写。您在这里没有给出语言，但它可能是这样的|type|unstyled|depth|inlineStyleRanges|offset|length|style|CODE|entityRanges|data|572f4|/G[ab].*/i或者/(?i)G[ab].*/..。^0|3|1|0|0|A|C|D^^$0|$]|1|@$2|3|4|5|6|7|8|I|9|@$A|J|B|K|C|D]]|E|@]|F|$]]|$2|G|4|H|6|7|8|L|9|@$A|M|B|N|C|D]|$A|O|B|P|C|D]]|E|@]|F|$]]]]

The <code>i</code> flag is normally used for case insensitivity. You don't give a language here, but it'll probably be something like <code>/G[ab].*/i</code> or <code>/(?i)G[ab].*/</code>.

entityMap|blocks|key|ethia|text|为了完整起见，我想用Unicode在C%2B%2B中添加正则表达式的解决方案：|type|unstyled|depth|inlineStyleRanges|entityRanges|data|e2pib|std::tr1::wregex+pattern(szPattern,+std::tr1::regex_constants::icase);

if+(std::tr1::regex_match(szString,+pattern))
{
...
}|code-block|syntax|javascript^0|0^^$0|$]|1|@$2|3|4|5|6|7|8|H|9|@]|A|@]|B|$]]|$2|C|4|D|6|E|8|I|9|@]|A|@]|B|$F|G]]]]

Just for the sake of completeness I wanted to add the solution for regular expressions in C++ with Unicode:

<pre><code>std::tr1::wregex pattern(szPattern, std::tr1::regex_constants::icase);

if (std::tr1::regex_match(szString, pattern))
{
...
}
</code></pre>

entityMap|0|type|LINK|mutability|MUTABLE|data|url|https://stackoverflow.com/questions/5228892/ignorecase-in-awk/|blocks|key|8hfnv|text|正如我在这篇类似的帖子中所发现的那样(忽略AWK中的大小写)，在旧版本的awk上(例如在普通的Mac+OS+X上)，您可能需要使用'tolower($0)+~+/pattern/'..。IGNORECASE或者(?i)或者/pattern/i将为每一行生成错误或返回true。|unstyled|depth|inlineStyleRanges|offset|length|style|CODE|entityRanges^0|1T|P|2L|A|2X|4|33|A|J|5|0^^$0|$1|$2|3|4|5|6|$7|8]]]|9|@$A|B|C|D|2|E|F|M|G|@$H|N|I|O|J|K]|$H|P|I|Q|J|K]|$H|R|I|S|J|K]|$H|T|I|U|J|K]]|L|@$H|V|I|W|A|X]]|6|$]]]]

As I discovered from this similar post (<a href="https://stackoverflow.com/questions/5228892/ignorecase-in-awk/">ignorecase in AWK</a>), on old versions of awk (such as on vanilla Mac OS X), you may need to use <code>'tolower($0) ~ /pattern/'</code>. 

<code>IGNORECASE</code> or <code>(?i)</code> or <code>/pattern/i</code> will either generate an error or return true for every line.

entityMap|blocks|key|3a2gq|text|[gG][aAbB].*如果模式不是太复杂或太长，可能会有简单的解决方案。|type|unstyled|depth|inlineStyleRanges|entityRanges|data^0^^$0|$]|1|@$2|3|4|5|6|7|8|C|9|@]|A|@]|B|$]]]]

[gG][aAbB].* probably simples solution if the pattern is not too complicated or long.

entityMap|blocks|key|6m38g|text|C#|type|unstyled|depth|inlineStyleRanges|entityRanges|data|1d9rv|using+System.Text.RegularExpressions;
...++++
Regex.Match(
++++input:+"Check+This+String",
++++pattern:+"Regex+Pattern",
++++options:+RegexOptions.IgnoreCase)|code-block|syntax|javascript|ege6o|具体来说：选项:+RegexOptions.IgnoreCase|offset|length|style|BOLD^0|0|0|5|R^^$0|$]|1|@$2|3|4|5|6|7|8|N|9|@]|A|@]|B|$]]|$2|C|4|D|6|E|8|O|9|@]|A|@]|B|$F|G]]|$2|H|4|I|6|7|8|P|9|@$J|Q|K|R|L|M]]|A|@]|B|$]]]]

C#

<pre><code>using System.Text.RegularExpressions;
... 
Regex.Match(
 input: "Check This String",
 pattern: "Regex Pattern",
 options: RegexOptions.IgnoreCase)
</code></pre>

specifically: options: RegexOptions.IgnoreCase

entityMap|0|type|LINK|mutability|MUTABLE|data|url|https://developer.mozilla.org/en-US/docs/Web/JavaScript/Guide/Regular_Expressions#advanced_searching_with_flags|blocks|key|87um8|text|在JavaScript中，您应该将i标志添加到RegExp构造函数，如MDN|unstyled|depth|inlineStyleRanges|offset|length|style|CODE|entityRanges|1btco|const+regex+=+new+RegExp('(abc)',+'i');

regex.test('ABc');+//+true|code-block|syntax|javascript^0|H|1|N|6|Z|3|0|0^^$0|$1|$2|3|4|5|6|$7|8]]]|9|@$A|B|C|D|2|E|F|R|G|@$H|S|I|T|J|K]|$H|U|I|V|J|K]]|L|@$H|W|I|X|A|Y]]|6|$]]|$A|M|C|N|2|O|F|Z|G|@]|L|@]|6|$P|Q]]]]

In JavaScript you should pass the <code>i</code> flag to the <code>RegExp</code> constructor as stated in <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Guide/Regular_Expressions#advanced_searching_with_flags" rel="nofollow noreferrer">MDN</a>:
<pre><code>const regex = new RegExp('(abc)', 'i');

regex.test('ABc'); // true
</code></pre>

entityMap|blocks|key|frq91|text|JavaScript|type|unstyled|depth|inlineStyleRanges|offset|length|style|BOLD|entityRanges|data|a6dut|如果想让它不区分大小写，只需添加i在regex的末尾：'Test'.match(/[A-Z]/gi)//返回"T"，"e"，"s"，"t“|CODE|3fhal|没有i'Test'.match(/[A-Z]/g)//返回"T“^0|0|A|0|G|1|R|N|0|2|N^^$0|$]|1|@$2|3|4|5|6|7|8|L|9|@$A|M|B|N|C|D]]|E|@]|F|$]]|$2|G|4|H|6|7|8|O|9|@$A|P|B|Q|C|I]|$A|R|B|S|C|I]]|E|@]|F|$]]|$2|J|4|K|6|7|8|T|9|@$A|U|B|V|C|I]]|E|@]|F|$]]]]

JavaScript
If you want to make it case insensitive just add <code>i</code> at the end of regex:
<code>'Test'.match(/[A-Z]/gi)</code> //Returns [&quot;T&quot;, &quot;e&quot;, &quot;s&quot;, &quot;t&quot;]
Without <code>i</code>
<code>'Test'.match(/[A-Z]/g)</code> //Returns [&quot;T&quot;]

entityMap|0|type|LINK|mutability|MUTABLE|data|url|https://regex101.com/|1|IMAGE|IMMUTABLE|imageUrl|https://ask.qcloudimg.com/http-save/actteam/f5443201a26c7f3471a3b4d1928b2a40.png|imageAlt|2|http://droptips.com/using-grep-and-ignoring-case-case-insensitive-grep|blocks|key|5nqb8|text|除了已经接受的答案之外：|unstyled|depth|inlineStyleRanges|entityRanges|9hedp|Grep用法：|header-two|offset|length|style|BOLD|5s1pp|请注意，对于grep它只是简单地添加了-i修饰符。例如：grep+-rni+regular_expression要搜索此“常规”，请执行以下操作_|CODE|6gi5f|表达式‘’r‘，case’i‘不敏感，在结果中显示行’n‘个数字。|bat2l|另外，这是一个验证正则表达式的很好的工具：https://regex101.com/|e9u9k|示例:请参阅此图中的表达式和解释。|2lp1b|?|atomic|4sq5k|参考文献：|2f2r1|手册页(man+grep)|unordered-list-item|cor5p^0|0|0|7|0|6|4|J|2|S|S|0|0|L|L|0|0|0|0|1|1|0|0|5|0|4|8|0|0|1Y|2^^$0|$1|$2|3|4|5|6|$7|8]]|9|$2|A|4|B|6|$C|D|E|-4]]|F|$2|3|4|5|6|$7|G]]]|H|@$I|J|K|L|2|M|N|1F|O|@]|P|@]|6|$]]|$I|Q|K|R|2|S|N|1G|O|@$T|1H|U|1I|V|W]]|P|@]|6|$]]|$I|X|K|Y|2|M|N|1J|O|@$T|1K|U|1L|V|Z]|$T|1M|U|1N|V|Z]|$T|1O|U|1P|V|Z]]|P|@]|6|$]]|$I|10|K|11|2|M|N|1Q|O|@]|P|@]|6|$]]|$I|12|K|13|2|M|N|1R|O|@]|P|@$T|1S|U|1T|I|1U]]|6|$]]|$I|14|K|15|2|M|N|1V|O|@]|P|@]|6|$]]|$I|16|K|17|2|18|N|1W|O|@]|P|@$T|1X|U|1Y|I|1Z]]|6|$]]|$I|19|K|1A|2|M|N|20|O|@$T|21|U|22|V|W]]|P|@]|6|$]]|$I|1B|K|1C|2|1D|N|23|O|@$T|24|U|25|V|Z]]|P|@]|6|$]]|$I|1E|K|G|2|1D|N|26|O|@]|P|@$T|27|U|28|I|29]]|6|$]]]]

Addition to the already-accepted answers:

<h2>Grep usage:</h2>

Note that for <code>grep</code>ing it is simply the addition of the <code>-i</code> modifier. Ex: <code>grep -rni regular_expression</code> to search for this 'regular_expression' 'r'ecursively, case 'i'nsensitive, showing line 'n'umbers in the result.

Also, here's a great tool for verifying regular expressions: <a href="https://regex101.com/" rel="nofollow noreferrer">https://regex101.com/</a>

Ex: See the expression and Explanation in this image.

<a href="https://i.stack.imgur.com/KEGIz.png" rel="nofollow noreferrer"><img src="https://i.stack.imgur.com/KEGIz.png" alt="enter image description here"></a>

<h2>References:</h2>

<ul>
<li>man pages (<code>man grep</code>) </li>
<li><a href="http://droptips.com/using-grep-and-ignoring-case-case-insensitive-grep" rel="nofollow noreferrer">http://droptips.com/using-grep-and-ignoring-case-case-insensitive-grep</a></li>
</ul>

entityMap|blocks|key|3pvf0|text|在Java中，Regex构造函数具有|type|unstyled|depth|inlineStyleRanges|offset|length|style|CODE|entityRanges|data|eltgq|Regex(String+pattern,+RegexOption+option)|code-block|syntax|js|a14tm|因此，若要忽略大小写，请使用|9bh4n|option+=+RegexOption.IGNORE_CASE^0|7|5|0|0|0^^$0|$]|1|@$2|3|4|5|6|7|8|P|9|@$A|Q|B|R|C|D]]|E|@]|F|$]]|$2|G|4|H|6|I|8|S|9|@]|E|@]|F|$J|K]]|$2|L|4|M|6|7|8|T|9|@]|E|@]|F|$]]|$2|N|4|O|6|I|8|U|9|@]|E|@]|F|$J|K]]]]

In Java, <code>Regex</code> constructor has 

<pre><code>Regex(String pattern, RegexOption option)
</code></pre>

So to ignore cases, use

<pre><code>option = RegexOption.IGNORE_CASE
</code></pre>

entityMap|blocks|key|b7bn6|text|您还可以将要检查模式匹配的初始字符串前导为小写。并在您的模式中分别使用小写符号。|type|unstyled|depth|inlineStyleRanges|entityRanges|data^0^^$0|$]|1|@$2|3|4|5|6|7|8|C|9|@]|A|@]|B|$]]]]

You also can lead your initial string, which you are going to check for pattern matching, to lower case. And using in your pattern lower case symbols respectively .

entityMap|0|type|IMAGE|mutability|IMMUTABLE|data|imageUrl|https://ask.qcloudimg.com/http-save/actteam/d8f25333ab51f5fa4cecda69c7d24648.jpg|imageAlt|blocks|key|1jg3c|text|您可以使用find/replace在Visual+Studio和Visual+Studio代码中练习正则表达式。|unstyled|depth|inlineStyleRanges|entityRanges|9ruej|对于带有case的regex表达式，需要同时选择匹配大小写和正则表达式。否则A-Z将不会在此处work.enter图像描述|e6hmu|?|atomic|offset|length|3rqa1|​^0|0|0|0|1|0|0^^$0|$1|$2|3|4|5|6|$7|8|9|-4]]]|A|@$B|C|D|E|2|F|G|S|H|@]|I|@]|6|$]]|$B|J|D|K|2|F|G|T|H|@]|I|@]|6|$]]|$B|L|D|M|2|N|G|U|H|@]|I|@$O|V|P|W|B|X]]|6|$]]|$B|Q|D|R|2|F|G|Y|H|@]|I|@]|6|$]]]]

You can practice Regex In Visual Studio and Visual Studio Code using find/replace.

You need to select both Match Case and Regular Expressions for regex expressions with case. Else [A-Z] won't work.enter image description here

<img src="https://i.stack.imgur.com/HqbjG.jpg" alt="Visual Studio 2019 Community">

How can I make the following regex ignore case sensitivity? It should match all the correct characters but ignore whether they are lower or uppercase.

<pre><code>G[a-b].*
</code></pre>

Regex: ignore case sensitivity

翻译质量差，导致语言生硬或混乱。

没有提供实际的解决方法或示例。

解答不清晰，无法理解或解决问题。

页面排版不美观，阅读体验差。

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 如何让下面的正则表达式忽略大小写？它应该匹配所有正确的字符，但忽略它们是小写还是大写。 G[a-b].*

问Regex:忽略区分大小写
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