PHP显示替换字符

<?php
$input = "Hello, world!";
$search = "world";
$replacement = "PHP";
$result = str_replace($search, $replacement, $input);
echo $result; // 输出: Hello, PHP!
?>

<?php
$input = "Hello, world! This is a test.";
$pattern = "/\bworld\b/i";
$replacement = "PHP";
$result = preg_replace($pattern, $replacement, $input);
echo $result; // 输出: Hello, PHP! This is a test.
?>

<?php
$input = "Hello, world!";
$pattern = "/\bworld\b/i";
if (preg_match($pattern, $input, $matches)) {
    echo "Pattern matched!";
} else {
    echo "Pattern not matched!";
}
?>

<?php
$input = "Large amount of data..."; // 假设这是一个非常大的字符串
$pattern = "/\b(?:word1|word2|word3)\b/i";
$replacement = "REPLACED";
$result = preg_replace($pattern, $replacement, $input);
echo $result;
?>