Detailed explanation of four methods to stop PHP scripts

In PHP programming, sometimes it is necessary to stop or close the currently running script. Common situations include:

1. The program execution time is too long, exceeding the max_execution_time value in the PHP configuration file. Causes the script to be forcibly stopped;
2. The user cancels the current operation and needs to terminate the script that has been started;
3. The script needs to be forcibly stopped according to some specific conditions.

This article will introduce several methods in PHP to stop PHP scripts under various circumstances.

1. exit() function

The exit() function in PHP is the only way to officially stop the running of a script. This function can accept an optional parameter to specify the exit status code.

For example:

// 停止脚本执行，并返回状态码为1
exit(1);

Note: When exit() is called, PHP immediately stops executing the current script, and the max_execution_time value in php.ini has no effect. At the same time, the exit() function can also return status code to the external program or script caller, which is of great use in some situations.

2. die() function

The die() function has almost the same effect as the exit() function, but the function name is different. The die() function also accepts an optional status code parameter.

For example:

// 停止脚本执行，并返回状态码为2
die(2);

The difference is that the die() function can directly output a specified string. This string will be used as the content returned to the browser.

For example:

// 停止脚本执行，并输出一段提示字符串
die('操作失败，请重试！');

3. Terminate the script based on conditions

During the execution of the script, if you encounter some unpredictable situations, you need to stop the script. . At this time, the script can be stopped by judging certain conditions.

For example:

// 判断两个整数相加是否超过了指定阈值
$a = 100;
$b = 200;
$limit = 150;
if (($a+$b) > $limit) {
    die('计算结果超过了限制！');
}

The above code determines whether the result of adding two integers exceeds a given threshold. If it does, it stops the script and outputs an error message.

4. Set signal processing function

In some special cases, it is necessary to receive system signals (such as SIGTERM, SIGHUP, SIGINT, etc.) to stop the script from running. At this time, you can write a signal processing function yourself:

For example:

// 自定义信号处理函数
function sig_handler($signo) {
    switch ($signo) {
        case SIGTERM:
            echo "收到停止信号，正在执行清理操作!\n";
            exit;
            break;
        case SIGHUP:
            echo "收到重启信号!\n";
            break;
        case SIGUSR1:
            echo "收到自定义信号!\n";
            break;
        default:
            // 处理其他信号
    }
}

// 捕捉指定的信号
pcntl_signal(SIGTERM, "sig_handler");
pcntl_signal(SIGHUP, "sig_handler");
pcntl_signal(SIGUSR1, "sig_handler");

// 下面是脚本执行的主体部分
echo "脚本正在运行...\n";
while (true) {
    // 循环执行某个任务
}

In the above example, we first define a signal processing function sig_handler(), and then capture it through the pcntl_signal() function these signals. When receiving the SIGTERM signal, the program will output a prompt text and exit execution.

It should be noted that the pcntl_signal() function is only available in Unix/Linux environments and must be enabled when PHP is compiled (by adding the --enable-pcntl option).

Summary

The above are several ways to stop PHP scripts, among which exit() and die() are the most commonly used methods. They are simple to use and have obvious effects. The method of terminating scripts based on conditions is more flexible and can be adjusted according to the actual situation. If necessary, you can set up a signal processing function to receive system signals and implement the script stop function.

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