What is a CLI?
A command line interface (CLI) is a software mechanism you use to interact with your operating system using your keyboard. Another mechanism is a graphical UI (GUI), which is popular today with all applications and software systems. You can use a GUI to visually navigate and click on icons and images to make things work. However, a GUI is inefficient for system administration tasks, especially if the environment is virtual or remote. With a command line interface, you can enter text commands to configure, navigate, or run programs on any server or computer system. All operating systems—including Linux, macOS, and Windows—provide a CLI for faster system interaction.
What are the benefits of a CLI?
A command line interface (CLI) offers several benefits.
Efficiency
Instead of spending time to find and click on individual files, you can use the CLI to perform actions on several files in one text command. If you are familiar with the commands, you can rapidly navigate and interact with your system. You can also create scripts that perform several commands in the CLI to automate monotonous or repetitive tasks.
Remote access
CLI applications often consume fewer network resources compared to graphical applications. This makes CLI applications suitable for systems with limited hardware capabilities or remote server environments.
You can manage servers remotely by submitting commands over a secure shell, even with low bandwidth connections. It’s a preferred method for managing servers and cloud instances, especially in headless environments where no graphical interface is available.
Troubleshooting
For developers and system administrators, using command line interfaces is a valuable skill that encourages a deeper understanding of the underlying system. It can make you more proficient with various tools and utilities and improve error management.
For instance, you can use a CLI to see system logs and quickly find comprehensive error messages and debugging information. The text-based commands can also be documented easily. This helps ensure tasks can be reproduced and makes it easier to troubleshoot steps in the future.
What are the use cases of a CLI?
You can use a command line interface (CLI) in many use cases due to its versatility. For example, if you’re a system administrator, software engineer, data scientist, or technical user who wants more control, you can benefit from using the CLI. We give some examples next.
System administration
System administrators use CLIs to fix system-related issues, check the operating system configurations, and change or update configurations on remote machines. They can run commands and control systems at scale.
Software development
Software developers regularly use CLI tools to save time and streamline their workflows. For instance, they frequently access third-party libraries while working. If they add references to these libraries using a CLI, they can do so with one inserted command instead of leaving instructions to search for the library using the GUI. This approach saves time for both the developer and future users that interact with the system.
Cloud computing
In cloud environments, a CLI is essential for managing virtual machines, containers, cloud services, and server configurations. Developers and administrators use CLIs to interact with cloud providers' APIs, automate resource provisioning, and deploy applications.
Network management
Network administrators use CLIs to configure routers, switches, firewalls, and other networking devices. CLI tools help when you want to monitor network traffic, troubleshoot connectivity issues, and implement security policies. Penetration testers also use command line tools for vulnerability scanning, network reconnaissance, and incident analysis.
How does a CLI work?
A command line interface (CLI) is a text-based interface where you can input commands that interact with a computer’s operating system. The CLI operates with the help of the default shell, which is between the operating system and the user.
CLI shell
A shell refers to a program that is an intermediary between the user and the operating system. Examples include Bash, cmd.exe, PowerShell, and others for more specific functions.
The shell is responsible for handling various tasks such as command parsing, environment management, and process execution. Shells also support features like these:
- Command history, where you can access previously entered commands using arrow keys or other shortcuts
- Input and output redirection
- Piping—where you connect the output of one command as the input of another—and environment variable management
Additionally, you can customize your shell environment. To do this, you can set environment variables, define aliases (shortcuts for longer commands), and create shell scripts for automation or repeated tasks.
How commands work
When you enter a command in the CLI, the following steps occur:
- The shell command line interpreter parses the entered command to understand its structure and separate the command name, options, and arguments.
- The shell looks up the command name in its list of available commands. The command name represents the action the user wants the operating system to perform.
- It searches the system's PATH variable (a list of directories where system files are located) to find the corresponding file associated with the command.
- The CLI shell calls the appropriate file passing any specified options and arguments as input.
- The operating system performs the required actions.
- It may produce output, such as informational messages, error messages, the requested data, or result of the operation.
- The CLI shell displays the output, so you can see the outcome of the command.
The CLI shell operates in a loop, waiting for you to enter another command. The process of command entry, parsing, execution, and output display repeats as you interact with the CLI shell. This provides a continuous interface for command-based interactions.
How do you open the command line interface on your system?
Each major operating system has a slightly different way of access the command line interface (CLI).
Windows
Here is how you open the CLI in Windows on Windows 8 or beyond:
- Press the Windows key and “S”
- Type “cmd” into the search field
- Right-click “Command Prompt” and select “Run as Administrator”
- You can now enter a command prompt
Mac
Here is how you open the CLI on Mac:
- Locate the Finder application, which is usually on your toolbar
- Move through /Applications/Utilities
- Select “Terminal”
- You can now enter a command prompt
Linux
Linux has a simple way of accessing the CLI: use the shortcut CTRL+ALT+T.
Alternatively, you can use ALT+F2 and then enter “gnome-terminal.”
What are some common command line interface commands?
A command line interface (CLI) has many different commands for different types of tasks. The commands vary slightly between operating systems. We give several different command examples next.
File system commands
| CLI command |
Windows |
Linux |
| Change directory |
cd |
cd |
| Last files |
dir |
ls |
| Create directory |
mkdir |
mkdir |
| Remove directory |
rmdir |
rmdir |
| Copy files |
copy |
cp |
| Move files |
move |
mv |
| Remane files |
ren |
mv |
| Display files |
type |
cat |
| Delete files |
del |
rm |
| Change personmissions |
cacls/chmod |
chmod |
Network commands
| CLI command |
Windows |
Linux |
| Ping |
ping |
ping |
| Traceroute |
tracert |
traceroute |
| Network config |
ipconfig |
ifconfig |
| Route table |
route |
route |
| DNS lookup |
nslookup |
nslookup |
| Network diagnostics |
netsh |
netstat |
Information commands
| CLI command |
Windows |
Linux |
| List processes |
tasklist |
ps |
| End process |
taskkill |
kill |
| System info |
systeminfo |
uname -a |
| Disk usage |
wmic/fsutil |
df |
| System monitoring |
perfmon |
top/htop |
What are CLI best practices?
While a command line interface (CLI) is useful and can provide remote access, it requires you to be precise and know the correct commands. Understanding the commands you input will ensure you get the desired result. If you’re unfamiliar with a command, you should research what it does before you input it into the CLI. Similarly, make sure you input the command without any variations or spelling mistakes.
Another important practice is to restrict the CLI for any non-privileged users. Granting administrator rights only to trusted parties limits unnecessary interactions with the system. You can prevent unauthorized access to critical resources.
An additional security practice you should consider is keeping your system up to date. Updates release bug fixes, performance improvements, and, importantly, security patches. Keeping your CLI up to date ensures your system is as secure as possible. Finally, it’s a good idea to log all CLI activities in order to detect changes, spot suspicious behavior, and troubleshoot if anything goes wrong.
What is AWS Command Line Interface?
The AWS Command Line Interface (AWS CLI) is an open source tool from Amazon Web Services (AWS). You can use it to interact with AWS services using commands in your command line shell.
With minimal configuration, you can use the AWS CLI to commands that implement functionality equivalent to that provided by the browser-based AWS Management Console. Here’s what you can do from the command prompt in your terminal program:
- Use common Linus shell programs such as Bash, zsh, and tcsh to run commands in Linux or macOS.
- Run commands on Windows at the Windows command prompt or in PowerShell.
- Remotely run commands on Amazon Elastic Compute Cloud (Amazon EC2) instances through a remote terminal program such as PuTTY, SSH, or with AWS Systems Manager.
Using AWS CloudShell, a browser-based shell, you can quickly run scripts with the AWS CLI, experiment with service APIs, and use other tools to increase your productivity. The CloudShell icon appears in AWS Regions where CloudShell is available.
Get started with AWS CLI by creating an account today.
