Command Line Basics

The CLI, or Command Line Interface is a text-based way to do stuff on your Linux computer. (Back in the old days, this was actually the only way to interact with the computer).

Terminology

• directory = folder

Filesystem hierarchy

• All files in Linux are arranged in a hierarchical directory structure
• a directory can hold 2 things:
  1. Files
  2. Other directories
• the topmost directory (or outermost folder) is ‘/’ and is called the root directory
• inside the root directory, there are many directories (most of them, you don't need to worry about). One of them is called ‘home’
  • inside ‘home’, each user has their own ‘home directory’ named after their username. All your personal files are in your home directory
• If there's a directory or file inside another directory, then you can append its name to the parent directory to get its full path name
  • for ex. bob's home directory would be called /home/bob
  • another example: /home/bob/Documents/school/math/homework.pdf

Note: if you append a slash (/) to a directory name, it doesn't change the meaning (it doesn't matter). This is not the case for files, however.

Terminal

• the ‘Terminal’ is a program that allows you to use the CLI
• open with Ctrl-Alt-T or search for ‘Terminal’ in the applications menu
• When using the terminal, you can think of the terminal as being ‘in’ a directory at all times
• You interact with the computer by typing ‘commands’ and then pressing Enter

Commands

1. pwd - print working directory

• outputs the ‘current’ directory, or in other words, the directory that the terminal is ‘in’ currently
• you can see the same information written in blue text on the terminal
• a tilde (~) is short for your home directory (which is /home/bob, but replacing bob with your username)

2. ls - list

• lists all files and directories in the current directory
• shows you what you would normally see in a graphical file browser
• type ls -a to show all files, including hidden files. Hidden files are those that start with a dot (.).
• In general, you can replace the ‘a’ with other letters to modify the effect of a command. These are known as ‘options’.
  • For example, you can use the ‘l’ option with the ls command (type ls -l) to see some more info about the files and directories (don't worry about what it means)
  • Other commands have options too

3. cd <name> - change directory

• change the current directory. Replace <name> with the name of the directory that you wish to enter. Equivalent to clicking on a folder in a graphical file browser
• type cd .. to go to the parent directory
• you can chain multiple directories like so:

cd Documents/notes/

You can even chain ‘..’, like this:

cd ../../../

• you can use ‘absolute’ and ‘relative’ path names of the directories
  • absolute names start with ‘/’. for ex. /home/bob/Documents/english
  • relative names don't start with ‘/’ and are assumed to begin from the current directory. for ex. Documents/english

4. man <command> - manual

• shows you information about the usage of a command
• replace <command> with a command, like ‘ls’ or ‘cd’
• press q to quit
• although the ‘man pages’ (which is the common name for these manual entries) may seem hard to understand at first, I encourage you to at least try to read the Description section. Over time, you will learn the jargon and the man pages will become more and more helpful.
• man pages also list all the commands’ options, and what each option does