Which of the following environment variables can help you see the current number of shells a. PS1 b. SHELL c. SHLVL d. PS2

The correct answer is:

c. SHLVL

Explanation:

The SHLVL (shell level) environment variable keeps track of how many shells are currently nested. Every time a new shell is opened (for example, by running the `bash` command from an existing shell), the value of SHLVL is incremented by 1. You can use the `echo` command to see the current value of SHLVL:

echo $SHLVL

The PS1 and PS2 environment variables are used to customize the prompt in the shell, and the SHELL environment variable stores the path to the default shell for the current user.

相关问题

use Linux Write a shell script that displays the value of HOMEPAT H SHLVL, and LOGNAME variables in the following format: HOME= ———————— PATH= ———————— SHLVL= ———————— LOGNAME=————————

Sure, here's a shell script that will display the values of the HOMEPATH, PATH, SHLVL, and LOGNAME variables in the required format:

#!/bin/bash

echo "HOME= ${HOMEPATH}"
echo "PATH= ${PATH}"
echo "SHLVL= ${SHLVL}"
echo "LOGNAME= ${LOGNAME}"

Save this script with a file extension of `.sh`, and make it executable using the command `chmod +x script_name.sh`. Then, simply run the script using `./script_name.sh` and it will display the values of the specified variables in the required format.

You need to specify one of the following as an environment variable: - MYSQL_ROOT_PASSWORD - MYSQL_ALLOW_EMPTY_PASSWORD - MYSQL_RANDOM_ROOT_PASSWORD

When setting up a MySQL container, you need to specify one of the following environment variables to configure the root password:

1. `MYSQL_ROOT_PASSWORD`: This variable sets the password for the root user explicitly.

2. `MYSQL_ALLOW_EMPTY_PASSWORD`: Setting this variable to any value allows the root user to have an empty password. Note that this is not recommended for production environments.

3. `MYSQL_RANDOM_ROOT_PASSWORD`: If you set this variable to any value, it will generate a random password for the root user.

Choose one of these variables based on your requirements and provide the appropriate value when running the MySQL container.

Here's an example of how you can set the `MYSQL_ROOT_PASSWORD` environment variable:

docker run --name mysql-container -e MYSQL_ROOT_PASSWORD=your_password -d mysql:tag

Replace `your_password` with your desired root password and `tag` with the appropriate MySQL version or tag you want to use.

Remember to use a strong and secure password for production environments.