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Command Line Basics

This tutorial introduces the minimal set of command line concepts needed to use or develop Click-based command line interfaces (CLIs). It is written for beginners who may have little or no command line experience. All examples provide commands for both macOS/Linux (Bash) and Windows (PowerShell).

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Understanding Your System

Before using the command line, it's important to know which operating system and shell you are running. Different systems have slightly different commands, so this knowledge will help you follow tutorials and avoid errors.

macOS / Linux

uname -a # Display OS version and system information

Windows (PowerShell)

Get-ComputerInfo | Select-Object WindowsVersion, OsName, OsBuildNumber

Tip

Knowing your OS helps you troubleshoot problems more effectively.

Common mistake:

Trying to run a Linux command on Windows without an appropriate shell like WSL.

Files, Directories, and Paths

Command-line tools interact with files and directories:

  • File: A piece of stored data (text, code, image, etc.).
  • Directory (folder): A container for files or other directories.
  • Path: A reference to a file or directory location, either relative or absolute.

macOS / Linux

pwd # Print working directory
ls # List files and directories

Windows (PowerShell)

Get-Location
Get-ChildItem

Tip

Relative paths start from your current directory; absolute paths start from the root.

Common mistake:

Confusing relative and absolute paths, which can cause “file not found” errors.

Navigating the Filesystem

You can move around directories using the cd command:

macOS / Linux

cd /tmp  # Go to /tmp
cd ~     # Go to your home directory
cd ..    # Go up one directory level

Windows (PowerShell)

cd C:\Temp
cd $HOME
cd ..

Tip

Use pwd (Linux/macOS) or Get-Location (Windows) to check your current directory.

Common mistake:

Forgetting that commands like cd are case-sensitive on Linux/macOS.

Creating Directories

To organize your files, create a directory using:

macOS / Linux

mkdir myproject  # Make a new directory called myproject

Windows (PowerShell)

New-Item -ItemType Directory -Name myproject

Tip

You can create nested directories with mkdir -p myproject/subdir on Linux/macOS.

Common mistake:

Trying to create a directory that already exists will fail unless using the -p flag.

Creating Files

Create an empty file inside a directory:

macOS / Linux

touch myproject/hello.txt

Windows (PowerShell)

New-Item -ItemType File myproject/hello.txt

Tip

Files can be created in any directory you have write permissions for.

Common mistake:

Forgetting to specify the directory and ending up creating the file in the wrong place.

Editing Files

You can open and edit files with a text editor of your choice:

macOS / Linux

nano myproject/hello.txt

Windows (PowerShell)

notepad myproject/hello.txt

Add the following line to the file:

Hello from the command line!

Tip

Try a simple editor like nano or notepad first; later you can use VS Code for larger projects.

Common mistake:

Forgetting to save the file before exiting the editor.

Viewing File Contents

Check the contents of a file using these commands:

macOS / Linux

cat myproject/hello.txt

Windows (PowerShell)

Get-Content myproject/hello.txt

Tip

Use these commands to quickly verify your edits.

Common mistake:

Using cat on very large files can flood the terminal; use less instead.

Searching Within Files

Search for specific text inside a file:

macOS / Linux

grep "Hello" myproject/hello.txt

Windows (PowerShell)

Select-String -Pattern "Hello" -Path myproject/hello.txt

Tip

Use search to verify that text exists or to debug issues in configuration files.

Common mistake:

Forgetting to quote search patterns with spaces, which can break the command.

Getting Help for a CLI

Click-based CLIs support the --help option, which lists commands and options:

mycli --help

If the CLI is implemented as a Python module:

python -m mycli --help

Further Reading