Command Line Interface (CLI)

What is a Command Line Interface (CLI)?

A command line interface is a control window that relies on text, meaning you type in commands that alter how your operating system (OS) or applications work.

Key Takeaways

The command line interface is an invaluable tool for advanced computer users who need a deeper level of control over background software functions.
While a graphic user interface (GUI) is good enough for most end users, for developers and IT managers, the CLI provides time-saving automation and configuration options.
CLIs are faster and require fewer computing resources than GUIs.
However, they also come with a steep learning curve.
Enterprise IT teams now use them to interact with cloud computing platforms and services.

How a Command Line Interface Works

A CLI typically appears on the computer screen as a small blank window with a black or white background and a blinking cursor at the upper right. The cursor indicates the ‘command prompt’ where any commands you type will appear.

Common commands include system commands that have been pre-written into the operating system (OS), launching executable programs that run text-based or graphical applications, and batch programs that wrap together a series of commands that are executed in a sequence. Batch programs can include a mix of system commands and executable programs.

Features of a Command Line Interface

Most command line interfaces offer added features designed to make life easier for users and programmers.

These can include:

The ability to adjust system variables (settings the operating system provides that enable the execution of various tasks) or display the values of any variables already input.
A CLI will usually offer scripting capability that enables users to write programs and run them from the command line.
Some CLIs come with command ‘pipes’ that allow users to direct data flows from one program to another, for example, having one program provide an output that becomes the input for another program.

CLI vs. GUI

Command Line Interface (CLI)	Graphic User Interface (GUI)
Requires knowledge of command prompts and is more difficult to use.	Intuitive and easier to use.
Used for higher precision computer functions.	Suitable for low-precision computer functions.
Executes tasks at faster speeds.	Executes tasks at slower speeds.
Low memory usage.	High memory usage.
Appearance and screen layout cannot be modified.	Appearance and layout can be modified to user preference.
No menus provided.	Multiple menus and other visual navigation guides for end users.
No graphical display. Text only.	Rich graphic and image displays.
Cannot be used with pointing devices (i.e. mouse, touch screen).	Requires pointing devices.

The Command Line Interface in Different Operating Systems

The three most popular command line interfaces are the Windows command prompt, the MacOS Terminal, and the Linux Bash. Each one has its own individual take on the CLI. While all have comparable functions and capabilities, the syntax used to enter commands differs from one to the next.

In Windows, for example, copying a file requires that you enter a ‘copy’ command into the Windows command prompt. In a MacOS machine, you would enter a ‘cp’ command in the MacOS Terminal. The Linux Bash CLI also uses ‘cp’ as the command for copying a file.

Useful CLI Commands

In addition to cp/copy, other useful CLI commands include:

nano command

Launches a command line text editor similar to NotePad or TextEdit.

alias command

Allows users to create shortcuts for frequently used commands.

rm command

Deletes a named file.

ren command

Renames a file.

cd command

Moves a task output or file into a new directory.

env command

Returns a list of the variables in the current operating system environment for a given user.

grep command

Searches files for lines that match an input and returns the results.

CLI Use Cases

CLIs are typically used by IT professionals to conduct system administration tasks like:

Automating repetitive processes.
Installing and configuring software.
Setting up web servers.
Tracking how efficiently different devices use computing resources.
Renaming multiple files in one go.
Managing system logs.
Configuring databases.

CLI Best Practices

While improvements in GUIs have made CLIs largely redundant for most end users, the shift to the cloud has given them new importance.

CLIs provide an effective way for enterprise IT teams to interact with cloud computing platforms and services, and a list of best practices has emerged to help them get the most out of CLIs as a software management tool.

Here are a few examples:

Use the command line history

Because CLIs store commands in a history file, users can list and reuse any command that’s been previously entered. That makes it easier to execute complex or repetitive tasks without retyping them each time.

Check command syntax

Always check how a command has been written and structured. If the syntax isn’t consistent with the operating system’s CLI, commands won’t run properly – or at all.

Don't expect uniformity

Test different setups across Windows, Linux, and macOS so you can solicit feedback and find any underlying flaws.?

CLI Pros and Cons

Pros

CLIs allow you to execute complex tasks faster than a GUI
The interface itself is simple and straightforward
CLIs help programmers save time by executing batch programs that allow a sequence of actions to run automatically
CLIs don’t use as many computing resources as a GUI

Cons

CLIs are text-based and require a steep learning curve
Each operating system has its own specific commands
Typos can be catastrophic, destroying progress, sending data to the wrong location, or deleting the wrong file
Commands can’t be undone. Once you press enter, the command will execute until completed

The Bottom Line

A command line interface provides advanced computer users with a fast and easily accessible way to extend control over how a computer or application works.

They are mainly used by developers and IT professionals to automate frequent tasks, configure servers, or make changes to files. A concise command line interface definition is this: an essential tool that improves computing efficiency, simplifies automation, and delivers precise control over complex tasks.