Commands, arguments, and flags: The building blocks of CLI

If you’ve ever looked for a faster, more reliable way to handle repetitive work, you’ve probably come across the command line interface (CLI). It’s often mentioned as a useful way to automate tasks, but getting started isn’t always straightforward.

Open a terminal, and you’re met with a blinking cursor and very little guidance. It can feel like you’re expected to know a language you’ve never learned. Although it’s sometimes seen as highly technical, in reality, most commands follow simple, predictable formulas.

Once you understand how commands, arguments, and flags fit together, most CLI commands will stop looking like cryptic strings of text and will start reading like simple instructions. Automating repetitive tasks with CLI commands can help you work more efficiently, even if you don’t consider yourself a developer.

A command line interface (CLI) is a way to interact with your computer using text, instead of a graphical user interface (GUI). Instead of clicking through menus or using a mouse to navigate, you type instructions directly, and your system executes them. There are fewer layers between intention and execution, which makes it especially useful for repeatable or structured tasks. That efficiency is often what makes the CLI valuable for automation, developer tools, and AI workflows.

Most CLI commands follow a consistent structure. For instance, take this simple example from Git:

git commit -m "initial commit"

At first glance, it might look complicated, if you’re learning CLI. But it’s actually just a structured sentence made up of three parts:

1. A command
2. An argument
3. A flag

Once you understand how these pieces work together, you can begin to read and interpret almost any CLI input you come across. In this case, when you use the command “git commit,” you’re simply asking the system to save a set of changes.

What is a CLI command?

A command is the core action that you want to perform. It’s the starting point for any CLI instruction, and it functions much like a verb in a sentence. Commands define your intent for the operation, whether that’s listing files, installing a package, or committing changes.

Common examples of CLI commands include:

• cd (change directory or move between folders on your computer)
• ls (list files, or show what’s inside a folder)
• git (run Git-related actions using a tool for tracking changes to files)
• npm (run package management tasks, used to install and manage project tools or libraries)

When you run a command, you’re telling your system what kind of action to take. Everything that follows will build on that initial instruction.

What are CLI arguments?

Commands define what you want to do, and arguments define what exactly you want to do it to. Arguments are the inputs or targets of a command. They provide the context needed for it to execute correctly. 

Take this example: cd projects/

Here’s how it breaks down:

• cd is the command.
• projects/ is the argument.

The command (cd) tells your system to change directories, and the argument (projects/) tells it where to go (your projects folder)

Arguments can take many forms. They might be file names, folder paths, or values passed into a command. Understanding CLI arguments is important because they connect an action to a specific outcome. Without them, many commands wouldn’t have enough information to act.

What are CLI flags?

Flags are optional modifiers that change how a command behaves. They don’t define the action itself, but they refine or adjust it.

Most flags start with a single dash (-) or double dash (--), and they are often used to toggle specific features on or off.

For example:

• -a means “show all”
• --help displays usage information
• -m “message” attaches a message to a command

Let’s return to the earlier example: git commit -m "initial commit"

In this example:

• git commit is the command.
• -m is the flag.
• "initial commit" is the argument associated with that flag.

Flags are what give commands flexibility. Instead of having dozens of different commands for slight variations, you can adapt a single command using flags.

Using CLI flags lets you modify behavior without changing the core action, which is a key part of working efficiently in the CLI.

Once you see how commands, arguments, and flags interact, most CLI instructions will feel much easier to interpret.

Example 1

Here’s a CLI command that you could use to view all files (including hidden ones) in your projects folder, in a more detailed format.

ls -la /projects

• Command: ls (list files)
• Flags: -l (long format), -a (include hidden files)

Argument: /projects (target directory)

Example 2

Here’s a CLI command that you could use to install a tool that your project needs (like a testing library or formatting tool) and mark it as something only used during development. 

npm install package-name --save-dev

• Command: npm install
• Argument: package-name
• Flag: --save-dev

Example 3

Here’s a CLI command that you could use to pull all transactions for April and save them as a file that you can review or analyze. 

fetch-transactions --month april transactions.csv

• Command: fetch-transactions (retrieve transaction data)
• Flag: --month april (specifies the time period)
• Argument: transactions.csv (the file the data is saved to)

Even without deep technical knowledge, you can begin to read these commands as structured instructions. With CLI commands, you’re not decoding anything complex, just interpreting a consistent format.

For founders working with tools that expose data or workflows via the CLI, certain actions often appear. Whether you’re exporting data, running scripts, or interacting with APIs, the same patterns tend to repeat.

Tools related to automation, development, and AI rely on a CLI for advanced functionality.  And there are now more options for programming your operational workflows. Financial data, reporting systems, and integrations are increasingly accessible through structured inputs and defined workflows, rather than purely visual interfaces. So, once you understand how CLI commands are structured and you’re confident using them, you’ll also be better able to use these programmable tools that rely on CLI. 

Modern tools, like Mercury, bring multiple financial workflows into a single place, making it easier to apply automation and structured processes across your systems. CLI is one of the ways you can interact with this type of centralized structure more directly, especially when you’re working with exports, scripts, or integrations.

When learning CLI, the good news is that you don’t need to memorize every command. Most CLI tools follow consistent patterns, and recognizing those patterns is often enough to make progress.

One of the most useful patterns is the --help flag. Almost every CLI tool includes it, and it provides immediate guidance on how a command works. When in doubt, it’s often the fastest way to learn.

You’ll also notice that many flags follow predictable conventions. For instance, short flags use a single dash, and more descriptive options use a double dash. Arguments typically follow the command and flags, and they usually represent files, folders, or values.

Once you start recognizing these patterns, new commands will become easier to interpret and you’ll start to see how the pieces fit together.

When learning CLI, a few common mistakes tend to pop up: 

• Mixing up flags and arguments: Because flags and arguments often appear together, beginners might find it unclear which part modifies behavior and which part defines the target. Pay attention to the command structure to decode the distinction.
• Overlooking spacing and order: CLI commands rely on precise formatting, and even small deviations can cause errors. Remember, the system is very literal.
• Overcomplicating things early on: Many tasks can be accomplished with very simple commands, but beginners sometimes assume that they need more advanced solutions than necessary. A more effective approach is to keep things simple and build from there.

The best way to get comfortable with the CLI is to interact with it directly, but in a low-pressure way. Start by trying a few basic commands. Copy examples, modify them slightly, and observe what changes. This process of making small adjustments will help you build fluency and confidence. 

With practice and repetition, the structure will become more familiar, and the interface will start to feel less like a barrier and more like a helpful tool. Remember, there’s no need to master everything all at once. You’ll make progress as you keep at it and continue to try different commands and get a feel for how it works.

CLI doesn’t require you to think like a developer. You just need to learn to recognize a simple structure: Commands define what to do, arguments define what to act on, and flags shape how it happens. Once that structure clicks for you, most CLI commands will be easier to read, and you’ll find it easier to work with tools that power automation, integrations, and AI workflows. So, as you get more comfortable with using these commands, you can begin using CLI tools to automate your startup’s financial workflows. 

As your operations grow, platforms like Mercury can help bring your financial workflows into one place, making it easier to apply more structured processes across all the ways that money moves through your business.