请写一个nginx平滑升级脚本

以下是一个基于 Bash 脚本的 Nginx 平滑升级的示例：

#!/bin/bash

# Nginx 进程 ID 文件路径
pid_file="/var/run/nginx.pid"

# Nginx 命令
nginx_bin="/usr/sbin/nginx"

# 停止 Nginx
function stop_nginx() {
    if [ -f $pid_file ]; then
        pid=$(cat $pid_file)
        kill -QUIT $pid
        echo "Nginx stopped."
    else
        echo "Nginx is not running."
    fi
}

# 启动 Nginx
function start_nginx() {
    $nginx_bin
    echo "Nginx started."
}

# 重启 Nginx
function reload_nginx() {
    if [ -f $pid_file ]; then
        pid=$(cat $pid_file)
        kill -HUP $pid
        echo "Nginx reloaded."
    else
        echo "Nginx is not running."
        start_nginx
    fi
}

# 平滑升级 Nginx
function upgrade_nginx() {
    stop_nginx
    start_nginx
}

# 根据命令行参数选择执行不同的操作
if [ $# -eq 0 ]; then
    echo "Usage: $0 {start|stop|reload|upgrade}"
    exit 1
fi

if [ "$1" == "start" ]; then
    start_nginx
elif [ "$1" == "stop" ]; then
    stop_nginx
elif [ "$1" == "reload" ]; then
    reload_nginx
elif [ "$1" == "upgrade" ]; then
    upgrade_nginx
else
    echo "Invalid command: $1"
    echo "Usage: $0 {start|stop|reload|upgrade}"
    exit 1
fi

使用该脚本可以通过命令行进行 Nginx 的启动、停止、重新加载和平滑升级操作。在执行平滑升级操作时，脚本会先停止当前运行的 Nginx 进程，再启动新版本的 Nginx。