如何將mb_convert_case與正則表達式配合使用實現靈活的大小寫轉換？

gitbox 2025-09-19

1. mb_convert_case的基本用法

mb_convert_case函數可以將字符串中的字符按指定的大小寫轉換，支持三種模式：

MB_CASE_UPPER ：轉換為全大寫。
MB_CASE_LOWER ：轉換為全小寫。
MB_CASE_TITLE ：將每個單詞的首字母轉換為大寫，其餘字母小寫。

示例代碼：

 <span><span><span class="hljs-variable">$string</span></span><span> = </span><span><span class="hljs-string">"hello world! 你好，世界！"</span></span><span>;

</span><span><span class="hljs-keyword">echo</span></span><span> </span><span><span class="hljs-title function_ invoke__">mb_convert_case</span></span><span>(</span><span><span class="hljs-variable">$string</span></span><span>, MB_CASE_UPPER, </span><span><span class="hljs-string">"UTF-8"</span></span><span>);  </span><span><span class="hljs-comment">// 輸出：HELLO WORLD! 你好，世界！</span></span><span>
</span><span><span class="hljs-keyword">echo</span></span><span> </span><span><span class="hljs-title function_ invoke__">mb_convert_case</span></span><span>(</span><span><span class="hljs-variable">$string</span></span><span>, MB_CASE_LOWER, </span><span><span class="hljs-string">"UTF-8"</span></span><span>);  </span><span><span class="hljs-comment">// 輸出：hello world! 你好，世界！</span></span><span>
</span><span><span class="hljs-keyword">echo</span></span><span> </span><span><span class="hljs-title function_ invoke__">mb_convert_case</span></span><span>(</span><span><span class="hljs-variable">$string</span></span><span>, MB_CASE_TITLE, </span><span><span class="hljs-string">"UTF-8"</span></span><span>); </span><span><span class="hljs-comment">// 輸出：Hello World! 你好，世界！</span></span><span>
</span></span>

2. 正則表達式的作用

正則表達式（RegEx）是一種強大的字符串模式匹配工具。在處理複雜的字符串轉換時，正則表達式能夠幫助我們精準地定位需要轉換的部分，比如特定的單詞、字母或符號，進而對這些部分進行大小寫轉換。

通過正則表達式，我們可以定義一些規則，結合mb_convert_case對匹配到的部分進行轉換，達到更加靈活的效果。

3. 將mb_convert_case與正則表達式結合

3.1 例子：將字符串中的每個單詞首字母大寫，其他字母小寫

假設我們有一個字符串，需要將其中的每個單詞首字母大寫，其他字母小寫，但同時我們希望保留某些特定的單詞（如“PHP”）的大小寫不受影響。這個時候，可以通過正則表達式找到每個單詞並使用mb_convert_case來實現。

示例代碼：

 <span><span><span class="hljs-variable">$string</span></span><span> = </span><span><span class="hljs-string">"this is a php test, check PHP again."</span></span><span>;

</span><span><span class="hljs-variable">$pattern</span></span><span> = </span><span><span class="hljs-string">'/\b(\w+)\b/'</span></span><span>; </span><span><span class="hljs-comment">// 匹配單詞邊界</span></span><span>
</span><span><span class="hljs-variable">$callback</span></span><span> = </span><span><span class="hljs-function"><span class="hljs-keyword">function</span></span></span><span> (</span><span><span class="hljs-params"><span class="hljs-variable">$matches</span></span></span><span>) {
    </span><span><span class="hljs-comment">// 對匹配的單詞進行首字母大寫處理</span></span><span>
    </span><span><span class="hljs-keyword">return</span></span><span> </span><span><span class="hljs-title function_ invoke__">mb_convert_case</span></span><span>(</span><span><span class="hljs-variable">$matches</span></span><span>[</span><span><span class="hljs-number">0</span></span><span>], MB_CASE_TITLE, </span><span><span class="hljs-string">'UTF-8'</span></span><span>);
};

</span><span><span class="hljs-variable">$result</span></span><span> = </span><span><span class="hljs-title function_ invoke__">preg_replace_callback</span></span><span>(</span><span><span class="hljs-variable">$pattern</span></span><span>, </span><span><span class="hljs-variable">$callback</span></span><span>, </span><span><span class="hljs-variable">$string</span></span><span>);

</span><span><span class="hljs-keyword">echo</span></span><span> </span><span><span class="hljs-variable">$result</span></span><span>;  </span><span><span class="hljs-comment">// 輸出：This Is A Php Test, Check Php Again.</span></span><span>
</span></span>

在這個例子中，正則表達式/\b(\w+)\b/匹配了所有單詞邊界的內容（即每個單詞），然後通過preg_replace_callback回調函數，使用mb_convert_case將每個單詞的首字母轉換為大寫，其餘字母小寫。

3.2 例子：對指定單詞進行大小寫轉換

有時我們可能只需要對某些特定的單詞進行大小寫轉換，而不影響其他內容。例如，我們可以將所有的“php”轉為“PHP”，而其他單詞保持不變。

示例代碼：

 <span><span><span class="hljs-variable">$string</span></span><span> = </span><span><span class="hljs-string">"I love php, and I am learning php in 2025."</span></span><span>;

</span><span><span class="hljs-variable">$pattern</span></span><span> = </span><span><span class="hljs-string">'/\bphp\b/i'</span></span><span>;  </span><span><span class="hljs-comment">// 匹配“php”，不區分大小寫</span></span><span>
</span><span><span class="hljs-variable">$callback</span></span><span> = </span><span><span class="hljs-function"><span class="hljs-keyword">function</span></span></span><span> (</span><span><span class="hljs-params"><span class="hljs-variable">$matches</span></span></span><span>) {
    </span><span><span class="hljs-comment">// 將匹配到的“php”轉換為大寫</span></span><span>
    </span><span><span class="hljs-keyword">return</span></span><span> </span><span><span class="hljs-title function_ invoke__">mb_convert_case</span></span><span>(</span><span><span class="hljs-variable">$matches</span></span><span>[</span><span><span class="hljs-number">0</span></span><span>], MB_CASE_UPPER, </span><span><span class="hljs-string">'UTF-8'</span></span><span>);
};

</span><span><span class="hljs-variable">$result</span></span><span> = </span><span><span class="hljs-title function_ invoke__">preg_replace_callback</span></span><span>(</span><span><span class="hljs-variable">$pattern</span></span><span>, </span><span><span class="hljs-variable">$callback</span></span><span>, </span><span><span class="hljs-variable">$string</span></span><span>);

</span><span><span class="hljs-keyword">echo</span></span><span> </span><span><span class="hljs-variable">$result</span></span><span>;  </span><span><span class="hljs-comment">// 輸出：I love PHP, and I am learning PHP in 2025.</span></span><span>
</span></span>

這裡的正則表達式/\bphp\b/i匹配了所有不區分大小寫的“php”單詞。 mb_convert_case將它們轉換為大寫。

4. 高級應用：根據字符的上下文條件進行轉換

在一些複雜的場景中，可能需要根據字符在上下文中的位置來決定是否轉換大小寫。比如，某些縮寫或代碼片段（如“API”）應保持原樣，而其他單詞則可以進行大小寫轉換。

示例代碼：

 <span><span><span class="hljs-variable">$string</span></span><span> = </span><span><span class="hljs-string">"the API is a powerful tool, API is awesome."</span></span><span>;

</span><span><span class="hljs-comment">// 使用負向前瞻來排除已出現的“API”</span></span><span>
</span><span><span class="hljs-comment">// 這樣就可以保證“API”不被轉換，而其他單詞正常轉換</span></span><span>
</span><span><span class="hljs-variable">$pattern</span></span><span> = </span><span><span class="hljs-string">'/\b(?!API\b)\w+\b/'</span></span><span>;
</span><span><span class="hljs-variable">$callback</span></span><span> = </span><span><span class="hljs-function"><span class="hljs-keyword">function</span></span></span><span> (</span><span><span class="hljs-params"><span class="hljs-variable">$matches</span></span></span><span>) {
    </span><span><span class="hljs-keyword">return</span></span><span> </span><span><span class="hljs-title function_ invoke__">mb_convert_case</span></span><span>(</span><span><span class="hljs-variable">$matches</span></span><span>[</span><span><span class="hljs-number">0</span></span><span>], MB_CASE_TITLE, </span><span><span class="hljs-string">'UTF-8'</span></span><span>);
};

</span><span><span class="hljs-variable">$result</span></span><span> = </span><span><span class="hljs-title function_ invoke__">preg_replace_callback</span></span><span>(</span><span><span class="hljs-variable">$pattern</span></span><span>, </span><span><span class="hljs-variable">$callback</span></span><span>, </span><span><span class="hljs-variable">$string</span></span><span>);

</span><span><span class="hljs-keyword">echo</span></span><span> </span><span><span class="hljs-variable">$result</span></span><span>;  </span><span><span class="hljs-comment">// 輸出：The API is A Powerful Tool, API is Awesome.</span></span><span>
</span></span>

在這個例子中，我們通過負向前瞻(?!API\b)來確保“API”不被轉換，同時其他單詞都進行了首字母大寫的轉換。

5. 小結

結合mb_convert_case和正則表達式，可以實現更為複雜和靈活的大小寫轉換。這種方法尤其適用於需要根據特定規則（如匹配特定單詞、排除某些部分或根據上下文）來控製字符大小寫的場景。無論是簡單的全局大小寫轉換，還是需要精細控制的情形， mb_convert_case和正則表達式的組合都能提供非常高效且定制化的解決方案。