Good Morning from my Robotics Lab! This is Shadow_8472 with my third installment of How I would Relearn Linux, a series where I pick an entry-level skill I would want to re-learn first if I were to begin my Linus journey over again. The terminal is the heart of the Linux admin experience. Let’s get started!
Command Line Interface (CLI)
The most familiar paradigm of using a computer is the GUI, or Graphical User Interface. Before the GUI, computers more closely resembled increasingly fancy typewriters writing from left to right, top to bottom. Just as GUI’s are still here after VR has been on the market for years, so too has the Command Line Interface (CLI) endured. Modern terminal emulator programs are wildly customizable, but that is beyond the scope of this post as well as my capabilities.
Basic Navigation
I’ll assume you have experience with a GUI file manager. The Linux terminal can do everything those do, but instead of hitting buttons or double clicking folders, you use commands to jump around to directories. My experience is with a popular default shell known as bash.
The Command Prompt
Most beginner-level Linux distributions’ terminals display a prompt like this:
<username>@<hostname>:<directory>$ █
There may be variations like different colors or square brackets present. These are heavily customizable and often are by distribution authors. The point of the prompt is to display who is logged in to what machine and where it is working. For example:
[shadow8472@ButtonMash ~]$ ▯
In this case, username shadow8472 is logged in to ButtonMash. The ~ is a shortcut for the current user’s home directory. The hollowed out cursor means I clicked out of my terminal emulator to another window.
File Paths
Similar to other operating systems, Linux has a file system resembling the trunk, limbs, branches, etc. of a tree. Starting at the root directory, /, (often simply called “root”) absolute file paths list directories separated by additional /’s.
/home/shadow8472/Downloads/Games/TicTakToeStrat.sh
Relative paths the present working directory and work from there. So, if I were in my Downloads directory, the following path would point to the same:
Games/TicTakToeStrat.sh
A leading . (period) in a file name means a file is hidden. A lone . points to the present working directory, and a pair of periods .. points to a parent directory. These are mostly used when working with a file in the present working directory or moving the present working directory up one level, respectively, though if so inclined, a user can use them as part of a larger path:
/home/././shadow8472/Downloads/./Games/../Games/../../Downloads/Games/./TicTakToeStrat.sh
Spaces cannot be used in file names because the space character dictates the flow of control when working with commands. To get around this, the \ (backslash) may be used as in “\ ”, or the entire file path may be placed in quotation marks. I find it much simpler to use capital letters for new words.
Commands
Linux commands are special system programs accessible from anywhere. As a general rule, they follow the syntax (pattern):
$ <name> -<flags> <additional parameters>
If everything before the $ is who and where you are, everything after is what you do. I like to imagine myself as walking around on the file system as though it were a maze of rooms. More practically, pressing tab will complete a command or file name (or list the possibilities based on syntax if user presses tab multiple times).
Flag and parameter syntax will be specific to an individual command/program. In general, flags control the mode a program operates in; -h or –help is a common flag to quickly access a brief program description, acceptable syntax, other flags, and whatever the programmer thinks it is most important for users to know at a glance. Parameters are more about data – especially file paths. And if you weren’t confused enough, flags can have parameters of their own.
Point of clarification: With the exception of Java, multi-letter flags use two hyphens. WordPress's automatic conversion is wrong. --help
ls (LiSt the contents of a directory) cd <file path> (Change Directory)
When using the terminal, I will imagine myself walking around the file system as though it were a maze of rooms. I use ls to “Look Surroundings.” The command cd takes steps from one room to another – either by providing a name or using .. to take one step backwards, toward the root. While not a command per se, I envision using tab to complete directory names as of feeling around with my hands; three characters before using tab is usually enough to identify a name or otherwise save a lot of time and mental energy typing and spell checking an exact name.
cd -
I properly learned this trick specifically for this week’s post. It returns you to the previous present working directory. I’ve known about something like this for a while and I intend to use it more when “teleporting.”
pwd (Displays absolute path of Present Working Directory)
whoami (Who Am I? outputs who you are working as)
These commands may seem redundant with the prompt, but some Bash shells reduce clutter and omit the path leading up to the present working directory, which can get confusing when working around multiple instances of a program. whoami exists because some prompts only start at the dollar sign, $.
man <program name> (MANual)
The man command brings up the “man page[s]” for a program detailing exactly how to use it when -h or –help aren’t enough. If a program still eludes you, Internet search and hope your results aren’t just the man page all over again.
Takeaway
The Linux command line cannot be done justice in a single blog post. Manipulating it effectively can be considered a form of art at higher skill levels or on a VM/spare machine you can afford to break. Shell scripts effectively put the computer at its own terminal, and there exist command programs written specifically for this situation. I’m planning on a followup where I go over file manipulation. In the meantime, feel free to look up a cheat sheet and keep it somewhere safe.
Final Question
Are you familiar with the terminal? What assumptions would you say are safe make about people who have only ever used a GUI file manager?
I look forward hearing about them in the comments below or on my Socials.