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<!DOCTYPE html> <html> <body> <h1>正则表达式修饰符：[123]</h1> <p>在文本 "W3School has been live since 2006" 中，有多少个字符是数字 "1"、"2" 或 "3"？</p> <?php $txt = "W3School has been live since 2006"; $pattern = "/[123]/"; echo preg_match_all($pattern, $txt); ?> <p>匹配到的位置如下：</p> <?php echo preg_replace($pattern, "#", $txt); ?> <p>（每个匹配项被替换为 # 字符）</p> </body> </html>