What is a Command Line Tool?

Quick Definition: A command line tool is a text-based program that you run from your computer's command prompt or terminal. These tools enable you to perform system tasks, manage files, and automate processes without navigating through graphical interfaces. Users use the keyboard to manually type out commands instead.

Command line tools might seem old-fashioned now that we have shiny apps and colorful user interfaces. But don’t be fooled. Command line tools are actually some of the most powerful weapons in any IT pro's arsenal. Don’t get stuck clicking through endless menus and dialogs when you can get things done with a few keystrokes.

Network pros, system admins, and developers use command line tools because they're fast and scriptable while being very reliable. Sometimes it comes down to scale. If you're troubleshooting a network issue or managing dozens of servers, graphical tools start to lag behind because most of them need individual clicks and keypresses per device. 

Command line tools let you automate repetitive tasks across multiple machines and work on remote systems where graphics aren't always available.

What is a Command Line Interface (CLI)?

The command line interface is a more direct line to your computer's operating system. In simple terms, it’s just a way to communicate with a system using text commands instead of mouse clicks. You type a command, hit enter, and the system responds.

Different operating systems provide you with different command environments to work with. Windows provides the Command Prompt (cmd.exe) for legacy batch operations, reminiscent of MS-DOS. PowerShell adds more advanced Windows-based commands and applets for modern system administration, making it extremely useful in Microsoft environments. Mac and Linux systems use terminal apps that run shells like bash or zsh, which are reminiscent of the old Unix shell. Each environment has its own quirks and rules that you need to learn about to get the most out of your command line experience.

Key Terminologies and Concepts

Before you start typing commands, you need to understand what you’re doing when you interface with a computer using text. The shell is the program that interprets your commands, and it's different from the CLI window itself. 

Arguments are the extra information you give to commands, and they let you be more specific with the results that you are after. A common example is when you type ping google.com, the command is ping, and google.com is the argument.

Flags change how commands behave when they are executed. They look different depending on your system. Unix-style systems use dashes, such as -l or --help, and the Windows Command Prompt often uses forward slashes like /A or /O. 

A flag in our ping example would be the -t flag in CMD. This allows your ping to continue indefinitely, rather than ending after just four requests. (In most Linux operating systems, ping will continue to run on its own until you end it.)

The working directory is your current location in the file system, and is the place that your system will run commands from if you execute them from there. It may sound a little strange at first, but understanding this now will help prevent confusion when you're just starting out. 

To see your current working directory in Linux, you would type pwd to ‘print working directory’ , which will display where you are currently in the file structure of the shell.

Getting Started with Command Line Navigation

Navigation commands work differently on each platform, so you need specific knowledge of the available commands to get off to a good start. Here are a few basic commands you can perform. 

Displaying Current Directory

• Windows Command Prompt: Type cd with no arguments

• Windows PowerShell: Use Get-Location or its alias pwd

• Mac/Linux: Use pwd

Changing Directories

• All Systems: cd followed by the path, but with important differences

• Windows Command Prompt: Use cd /d D:\folder to change drives and directories together

• Windows (all): Change drives by typing the drive letter: D:

• Mac/Linux: Drives are mounted in one tree, so cd works for everything

Listing Files

• Windows Command Prompt: dir with switches like /A for attributes

• Windows PowerShell: Get-ChildItem (aliases: ls, dir)

• Mac/Linux: ls with flags like -l for detailed listing

The primary difference is that Windows treats drives as separate namespaces (e.g., C:, D:), whereas Unix-based systems mount everything into a single tree structure and treat all files uniformly.

What are Some Advanced Uses of Command Line Tools?

Once you understand the basics, it's time to get a bit more granular. Here are a few advanced uses of command line tools. 

Shell Scripting

Shell scripting enables single commands to be converted into automated jobs that can perform multiple operations upon execution. Running scripts is a different experience on each platform because of the architectural differences between each operating system.

Windows Scripting:

• Batch files (.bat, .cmd): Legacy scripting for Command Prompt and DOS

• PowerShell scripts (.ps1): Modern, object-oriented automation with .NET framework access

• File associations: Windows uses file extensions to determine which interpreter runs your script

Unix-like Scripting:

• Shell scripts (.sh): Sometimes you don’t even need file extensions to execute scripts

• Shebang directive: Scripts start with #!/bin/bash or similar to specify which interpreter needs to be called

• Execute permissions: Use chmod +x scriptname to make scripts executable

A good way to get into scripting is to start with simple automation tasks, like copying files to a backup folder, either on a schedule or manually by running the script. It’s not a bad idea for Windows users to focus on PowerShell for serious scripting work, as it offers some very useful capabilities. Unix users typically begin with basic bash scripts and progress to more complex shell programming when deep system automations require development.

Command Line Environment Customization

Your shell environment can be customized with configuration files and aliases, allowing you to create a more personalized experience with custom settings.

Windows Configuration:

• PowerShell: You can edit your PowerShell profile with “notepad $PROFILE”

• Command Prompt: There is limited customization here, but you can change some settings by making registry changes in Windows

• Environment Variables: If you want certain values to be available to your scripts then you can set them via System Properties or the setx command

Unix Style Configuration:

• Configuration files: The main config files that you’ll come across are .bashrc, .zshrc in your home directory

• Aliases: An alias is basically a shortcut and can be set by creating something like alias ll='ls -la'. Typing ll and hitting enter at the command prompt would execute ls -la , which lists the contents of your current directory in ‘long’ format.

• PATH modification: You can add directories to your command search path so that you don’t need to change to a specific bin directory or type its full path every time you want to execute commands.

Good aliases can save you a massive amount of typing if you work in the CLI frequently. Creating shortcuts for complicated commands that you use regularly is handy, but don't go too crazy and start aliasing everything. 

Start with a few of the longer commands and build up your aliases over time. These settings can be saved and transferred to other systems if you want to keep your time-saving aliases with you on different computers.

Remote Access and Automation

SSH Key Setup varies by platform. Let's cover how to do it on both Windows and Mac/Linux machines. 

Windows:

• Generate keys: ssh-keygen.exe

• Copy to remote server manually or use: type %USERPROFILE%\.ssh\id_rsa.pub | ssh user@server "cat >> ~/.ssh/authorized_keys"

Mac/Linux:

• Generate keys: ssh-keygen

• Copy with convenience utility: ssh-copy-id user@server

Task Scheduling

Windows: Use Task Scheduler (GUI: taskschd.msc 

CLI: schtasks.exe

PowerShell: *-ScheduledTask cmdlets 

Mac/Linux: Use cron with crontab -e to edit schedules

The Windows Task Scheduler has a lot more features than cron, supporting event-driven triggers and complex conditions beyond simple time schedules.

Version Control with Command Line

Git works consistently across platforms, making it one of the few truly universal command line tools. Start with basic commands like git init, git add, and git commit.

There are also advanced Git operations, such as rebasing and complex merges, that are easier to control from the command line than GUI tools. You can script Git operations and create aliases for workflows you use all the time, saving you a lot of manual typing.

Installing Xcode Command Line Tools on Mac

Mac developers can’t do much without the Xcode command line tools installed. These tools give you access to dev tools like git, make, and other compilers that don't come with macOS by default.

The good news is that you don't need to install the massive Xcode IDE just to get these command line tools. Apple also has a standalone installer that gets you up and running fast.

The easiest way to install Xcode command line tools is through Terminal:

xcode-select --install

This command triggers a pop-up dialog asking if you want to install the tools. Click "Install" and wait for the download to complete. It takes about 10-15 minutes, depending on your internet connection speed.

You can verify the installation worked by checking the version:

xcode-select --version

What You Get with Xcode Command Line Tools

Installing these tools gives you access to:

• Git: Version control for your projects

• clang: C/C++ compiler for building apps

• make: Automated build tool

• nm: A symbol table utility

• otool: Object file displaying tool

These tools also integrate with package managers like Homebrew and are enough for most dev workflows on Mac. Without them, you'll get "command not found" errors when trying to compile code or use Git.

If you run into permission issues during installation, you might need to accept the Xcode license agreement first:

sudo xcodebuild -license accept

Security Measures for Command Line Tools

Command line tools give you super powers, which means they can cause a lot of damage if you aren’t careful. Double-check destructive commands like del in cmd and rm in Unix/Linux before you hit enter.

Command Verification varies by platform:

• Windows Command Prompt: Use where.exe commandname

• Windows PowerShell: Use Get-Command commandname (alias: gcm)

• Mac/Linux: Use which commandname or type commandname

Test your commands in safe environments first like a virtual machine or an old computer that you can afford to lose data on. Most CLI disasters happen because someone assumed a command would do one thing but it did something else, so practice is very important.

Permissions and Security

File permissions work completely differently between Windows and Unix-like systems.

Windows NTFS Security:

• Uses Access Control Lists (ACLs) with granular permissions

• Supports inheritance from parent folders

• Managed with icacls.exe or PowerShell's Get-Acl/Set-Acl cmdlets

• Can explicitly deny permissions that override allow permissions

Unix Style POSIX Permissions:

• Uses a simple user/group/other model with read/write/execute permissions

• Managed with chmod, chown, and chgrp commands

• Permissions shown with ls -l

These are very different security models, so you need to consider what you want to accomplish before you begin.

Backup and Recovery Strategies

Windows Backup Tools:

• robocopy: Is a native, multi-threaded file synchronization with NTFS ACL preservation

• chkdsk: File system integrity checking and repair for disk drives

Mac/Linux Backup Tools:

• rsync: Very good incremental backup with delta transfers

• fsck: File system checking and repair utilities for drive volumes

A fun project is to create backup scripts that match your platform. Backup files that have modified time stamps within a certain time range, or get logs from systems compressed to save space at set intervals. 

If you are a Windows user, you should try robocopy's switches like /MIR for mirroring and /Z for restartable file transfers. Unix users have rsync, which has many different options for remote sync for files.

Conclusion

Command line tools let you take the reins of your systems. Text-based programs aren’t flashy, but they give you direct access to your system's capabilities. They aren’t all the same though, so platform-specific knowledge is needed if you want to use them to their full potential.

Start with basic navigation and file management for your specific operating system. Build up to scripting, start automating tasks, and experiment with security permissions. Each new skill that you learn multiplies your value on the job and opens up new possibilities in your IT career.

The most important lesson is that Windows and Unix-like systems handle many concepts differently. Although there is some overlap with certain CLI tools, never assume commands work the same way across platforms. Learn about which tools are the right ones for the job in each environment you work with.

Want to learn more about Command Line Tools? This CBT Nuggets CompTIA Network+ online course is a great place to start.