帮我写一个mysql5.7版本的centos7上的安装sehll脚本，要求大小写不敏感，在sehll脚本的开头可以自己通过手动输入的方式指定安装的目录和具体版本，代码中的注释要用英文

Sure, I can help you with that. Here's a shell script for installing MySQL 5.7 on CentOS 7:

#!/bin/bash

# Prompt the user for installation directory and MySQL version
echo "Please enter the installation directory: "
read install_directory
echo "Please enter the version of MySQL you wish to install: "
read mysql_version

# Convert version input to lowercase
mysql_version=$(echo "$mysql_version" | tr '[:upper:]' '[:lower:]')

# Install MySQL 5.7 using the appropriate package based on the version selected
if [ "$mysql_version" == "5.7" ]; then
  echo "Installing MySQL 5.7..."
  sudo yum install -y https://dev.mysql.com/get/mysql57-community-release-el7-11.noarch.rpm
  sudo yum install -y mysql-community-server
elif [ "$mysql_version" == "8.0" ]; then
  echo "Installing MySQL 8.0..."
  sudo yum install -y https://dev.mysql.com/get/mysql80-community-release-el7-3.noarch.rpm
  sudo yum install -y mysql-community-server
else
  echo "Invalid MySQL version entered. Please try again."
  exit 1
fi

# Start the MySQL service
sudo systemctl start mysqld

# Print the initial MySQL root password to the console
echo "The initial root password for MySQL is:"
sudo grep 'temporary password' /var/log/mysqld.log | awk '{print $NF}'

# Set MySQL to start automatically on boot
sudo systemctl enable mysqld

# Add the installation directory to the system path
echo "export PATH=\$PATH:$install_directory/mysql/bin" >> ~/.bashrc
source ~/.bashrc

# Print a success message
echo "MySQL $mysql_version has been installed at $install_directory/mysql."

Note that this script will prompt the user to enter the installation directory and MySQL version, and will install MySQL 5.7 or 8.0 depending on the selected version. It will also start the MySQL service, print the initial root password to the console, set MySQL to start automatically on boot, and add the installation directory to the system path.

All comments in the script are in English. Please let me know if you have any questions or concerns.