用PHP的ltrim/rtrim替换字符串开头/结尾的字符

<?php
$str = "   Hello, World!   ";

// 使用默认参数去除空白字符
$trimmedStr = ltrim($str);
echo "|$trimmedStr|\n"; // 输出: |Hello, World!   |

$trimmedStr = rtrim($str);
echo "|$trimmedStr|\n"; // 输出: |   Hello, World!|

// 使用自定义字符集去除特定字符
$customStr = "***Hello, World!$$$";
$trimmedCustomStr = ltrim($customStr, "*$");
echo "|$trimmedCustomStr|\n"; // 输出: |Hello, World!$$$|

$trimmedCustomStr = rtrim($customStr, "$!");
echo "|$trimmedCustomStr|\n"; // 输出: |***Hello, World!|
?>

<?php
$str = "***Hello, World!$$$";
// 错误的字符集（包含转义字符）
$trimmedStr = ltrim($str, "\*");
echo "|$trimmedStr|\n"; // 输出可能不符合预期

// 正确的字符集
$trimmedStr = ltrim($str, "*$");
echo "|$trimmedStr|\n"; // 输出: |Hello, World!$$$|
?>

<?php
$str = "***Hello, World!$$$";
$trimmedStr = trim($str, "*$");
echo "|$trimmedStr|\n"; // 输出: |Hello, World!|
?>