PHP代码IP查询逻辑失效，疑似跳过else分支问题求助

我熟悉bash脚本编写，但刚接触PHP。我编写了一段从HTML表单加载变量的代码，输入域名进行查询时功能正常，但仅输入IP地址查询时完全失效，似乎跳过了整个else分支。以下是我的代码：

<?php
header('Content-type: text/plain');
if(isset($_GET['subject1'], $_GET['subject2'])) {

    $text1 = $_GET['subject1'];
    $text2 = $_GET['subject2'];

    $text1 = escapeshellarg($text1);
    $text2 = escapeshellarg($text2);
    echo "THE VARIABLES THAT YOU HAVE SUBMITTED ARE "  . "\n";
    echo "You entered $text1 for the Domain Name "  . "\n";
    echo "You entered $text2 for the IP Address "  . "\n";
    echo "\n";
}

if (!empty($text1)) {
    $command1 = '/usr/bin/dig ' . '@localhost ' . "$text1 " . "+short " . "| /usr/bin/tail -n1" . "\n";
    echo "\n";
    echo "THE COMMAND THAT YOU HAVE SUBMITTED WILL THEREFORE BE "  . "\n";
    print_r($command1) . "\n";
    echo "\n";
    $output1 = shell_exec($command1);
    echo "\n";
    echo "RESULTS OF A EXTERNAL DNS (NAME TO IP) LOOKUP FOR THE DOMAIN ENTERED" . "\n";
    echo "$output1";
    echo "\n";

    $command2 = '/usr/bin/whois ' . "$text1" . "\n";
    echo "\n";
    $output2 = shell_exec($command2);
    echo "\n";
    echo "RESULTS OF A WHOIS LOOKUP AGAINST " . "$text1 " . "\n";
    echo "$output2";
    echo "\n";

    $command3 = '/usr/bin/whois ' . "$output1" . "\n";
    echo "\n";
    $output3 = shell_exec($command3);
    echo "\n";
    echo "RESULTS OF A WHOIS LOOKUP AGAINST " . "$output1 " . "\n";
    echo "$output3";
    echo "\n";
    goto END;

} else {

    $command4 = '/usr/bin/whois ' . "$text2" . "\n";
    echo "\n";
    $output4 = shell_exec($command4);
    echo "\n";
    echo "RESULTS OF A WHOIS LOOKUP AGAINST " . "$text2 " . "\n";
    echo "$output4";
    echo "\n";
    goto END;
}
END:
echo "END OF THE TEST RESULTS " . "\n";
?>

域名查询功能正常，但IP地址查询部分完全被跳过，请问我哪里出错了？

问题原因与修复方案 #

核心错误点 #

1. 判断逻辑被转义后的字符串干扰：当仅输入IP时，subject1是空字符串提交，isset($_GET['subject1'], $_GET['subject2'])条件会成立（isset只检查变量是否存在，不管值为空）。此时$text1被赋值为空字符串，经过escapeshellarg()处理后会变成''（带单引号的非空字符串），导致!empty($text1)返回true，代码会进入域名查询的if分支，而非预期的IP查询else分支。
2. 变量未初始化风险：若用户未提交某个参数，$text1或$text2会未定义，触发PHP警告。
3. 命令中的多余换行符：给命令字符串末尾加的\n会被shell当成命令的一部分，可能导致执行异常。

修复后的代码 #

<?php
header('Content-type: text/plain');

// 初始化变量并处理原始输入，trim去除首尾空白
$rawDomain = isset($_GET['subject1']) ? trim($_GET['subject1']) : '';
$rawIP = isset($_GET['subject2']) ? trim($_GET['subject2']) : '';

// 仅当原始输入非空时，转义用于shell命令的参数
$domain = !empty($rawDomain) ? escapeshellarg($rawDomain) : '';
$ip = !empty($rawIP) ? escapeshellarg($rawIP) : '';

// 输出提交的变量
echo "THE VARIABLES THAT YOU HAVE SUBMITTED ARE \n";
echo "You entered $domain for the Domain Name \n";
echo "You entered $ip for the IP Address \n\n";

// 根据原始输入的空值状态选择执行逻辑
if (!empty($rawDomain)) {
    // 域名查询逻辑
    $command1 = '/usr/bin/dig @localhost ' . $domain . ' +short | /usr/bin/tail -n1';
    echo "\nTHE COMMAND THAT YOU HAVE SUBMITTED WILL THEREFORE BE \n";
    echo $command1 . "\n\n";
    
    $output1 = shell_exec($command1);
    echo "\nRESULTS OF A EXTERNAL DNS (NAME TO IP) LOOKUP FOR THE DOMAIN ENTERED\n";
    echo $output1 . "\n";

    $command2 = '/usr/bin/whois ' . $domain;
    $output2 = shell_exec($command2);
    echo "\nRESULTS OF A WHOIS LOOKUP AGAINST " . $domain . "\n";
    echo $output2 . "\n";

    // 仅当DNS查询返回有效IP时，执行IP的whois查询
    $cleanIP = trim($output1);
    if (!empty($cleanIP)) {
        $command3 = '/usr/bin/whois ' . escapeshellarg($cleanIP);
        $output3 = shell_exec($command3);
        echo "\nRESULTS OF A WHOIS LOOKUP AGAINST " . $cleanIP . "\n";
        echo $output3 . "\n";
    }
} elseif (!empty($rawIP)) {
    // IP查询逻辑
    $command4 = '/usr/bin/whois ' . $ip;
    $output4 = shell_exec($command4);
    echo "\nRESULTS OF A WHOIS LOOKUP AGAINST " . $ip . "\n";
    echo $output4 . "\n";
} else {
    echo "\nPlease enter either a Domain Name or an IP Address.\n";
}

echo "\nEND OF THE TEST RESULTS \n";
?>

修复关键点 #

• 基于原始输入判断分支：用$rawDomain和$rawIP的空值状态触发分支，避免escapeshellarg()处理后的字符串干扰判断逻辑。
• 提前初始化变量：避免未定义变量的警告，提升代码健壮性。
• 移除命令中的换行符：确保shell命令能正确执行。
• 增加空输入提示：当两个输入都为空时给出明确提示。
• 优化IP whois查询触发条件：仅当DNS查询返回有效IP时才执行对应逻辑，避免无效命令。

内容的提问来源于stack exchange，提问作者Blacktip69