其实我想要实现的是: sh脚本监听网卡变动，如果eth0和wlan0都是通的，并且它们都是同一个网段，那么路由优先走eth0, 如果eth0被拔掉了，路由就自动切换到wanl0,之后如果再插回网线到eth0,则需要马上切换路由首选eth0,请问用脚本sh如何实现？

要实现这个功能，你需要使用脚本来监听网络接口的状态，并根据接口的状态更改路由表。你可以使用以下bash脚本来实现：

#!/bin/bash

# Set the name of the primary network interface
primary_interface="eth0"

# Set the name of the secondary network interface
secondary_interface="wlan0"

# Set the IP address range of the local network
local_network="192.168.1.0/24"

# Keep running the script indefinitely
while true; do

  # Check if the primary interface is up and connected to the local network
  if ip addr show $primary_interface up | grep -q $local_network; then
    # Add a new routing table for the primary interface
    echo "200 $primary_interface_table" >> /etc/iproute2/rt_tables
    # Add default route for primary interface to the new routing table
    primary_gateway=$(ip route show | grep "default" | grep "$primary_interface" | awk '{print $3}')
    ip route add default via $primary_gateway dev $primary_interface table $primary_interface_table
    # Add a rule to route all traffic from primary interface through the new routing table
    primary_ip=$(ip addr show $primary_interface | grep "inet\b" | awk '{print $2}' | cut -d/ -f1)
    ip rule add from $primary_ip table $primary_interface_table
    # Remove any existing default route for the secondary interface
    ip route del default dev $secondary_interface
  else
    # Remove any existing routing table for the primary interface
    existing_table=$(grep -n " $primary_interface_table" /etc/iproute2/rt_tables | cut -f1 -d:)
    if [ ! -z "$existing_table" ]; then
      sed -i "${existing_table}d" /etc/iproute2/rt_tables
      ip route flush table $primary_interface_table
      ip rule del table $primary_interface_table
    fi
    # Add default route for the secondary interface
    secondary_gateway=$(ip route show | grep "default" | grep "$secondary_interface" | awk '{print $3}')
    ip route add default via $secondary_gateway dev $secondary_interface
  fi

  # Wait for 1 second before checking the network interfaces again
  sleep 1

done

此脚本将在一个无限循环中运行，并检查主要和次要网络接口的状态。如果主接口（eth0）处于活动状态并连接到本地网络，则将其设置为首选路由器，并将次要接口（wlan0）的默认路由从路由表中删除。如果主接口未连接到本地网络，则将其从路由表中删除，并将次要接口设置为默认路由器。

请注意，该脚本需要管理员权限才能运行。你可以使用“sudo”命令来运行它，如下所示：

sudo sh script.sh