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Using a Terminal

Aug 26, 2023, 5 min read

The Rundown

The terminal (or “CLI”) is an essential part of coding. It’s a way to interact with your computer using “shell” commands.

There are various shells, but the most popular one is called Bash. Windows has its own variation, PowerShell or Command Prompt.

Why Use a Terminal?

The terminal is powerful. It can automate tasks, run programs, and do things that would be difficult to do otherwise. It’s also fast. It’s often faster to type a command than to click through a GUI. It’s also portable. You can use the same commands on any computer.

The Basics

Opening a Terminal

On Mac, open the “Terminal” app. On Windows, open the “Command Prompt” app. On Linux, open the “Terminal” app.

A core concept of the terminal is the “current directory.” This is the directory that you’re currently in. You can see the current directory by running the pwd command (print working directory).

What’s a directory? It’s a folder. Directories can contain files and other directories. To see what’s in the current directory, run the ls command (list directory contents).

ls-example.txt
$ ls
Tensor.py    TensorMap.py __init__.py  __pycache__
 
$ ls -lah
total 16
drwxr-xr-x  6 user  staff   192B Sep 12 13:46 .
drwxr-xr-x  5 user  staff   160B Sep 12 13:46 ..
-rw-r--r--  1 user  staff   2.6K Sep 12 13:46 Tensor.py
-rw-r--r--  1 user  staff   2.0K Sep 12 13:46 TensorMap.py
-rw-r--r--  1 user  staff     0B Sep 12 13:46 __init__.py
drwxr-xr-x  5 user  staff   160B Sep 12 13:46 __pycache__

To move into a directory, run the cd command (change directory). For example, to move into the “Documents” directory, run cd Documents.

To move to an “absolute” directory, run cd /path/to/directory. To move to a “relative” directory, run cd path/to/directory. To move back out of a directory, run cd ...

Creating Files and Directories

There are various commands to do these kinds of tasks, but most of the time you’ll be using touch and mkdir to create files and directories respectively.

touch-example.txt
$ touch hello.txt
$ ls
hello.txt

Alternatively, you can create a file that contains text like this:

echo-example.txt
$ echo "Hello, World!" > hello.txt
$ cat hello.txt # cat prints the contents of a file
Hello, World!

Using a Text Editor

vim is a widely used text editor for the terminal. It’s a bit difficult to master, but learning the basics isn’t that bad. Check out the learning-vim page. nano is a simpler text editor that’s with many less features.

Running Programs

To run a program, first it needs to be “executable.” To make a program executable, you’ll use chmod +x .... Assuming the program is executable, you can run it by typing the name of the program. For example, to run a program called “hello”, run ./hello.

Advanced Concepts

Pipes

Pipes are a way to connect the output of one command to the input of another command. For example, to print the contents of a file and then count the number of lines, you can run cat hello.txt | wc -l.

Environment Variables

Environment variables are variables that are available to all programs. They’re often used to store configuration information. To set an environment variable, run export VAR_NAME=var_value. To see all environment variables, run env.

$PATH

The $PATH variable is a special environment variable that contains a list of directories. When you run a command, the terminal will look through each directory in $PATH to find the command. If you ever see an error like “command not found”, it’s likely because the command isn’t in $PATH.

One Liners

  • tail -f long-file.log
    • Follows the end (tail) of a file that is being written to (like a log)

Beginner Friendly Tools

Note

Some of these tools are built-in and some need to be installed. On Windows, you may need a Unix emulator like Cygwin. Linux or macOS is a better experience in my opinion.

  • git - A version control system.
  • tldr - A simplified version of man.
  • ping - A command-line tool for testing network connections.
  • tree - A command-line tool for displaying directories as a tree.
  • bat - A prettier version of cat.
  • ps - A command-line tool for listing processes.
  • file - A command-line tool for determining the type of a file.
  • htop - A command-line tool for monitoring system resources.
  • brew - A package manager for Mac.
  • apt - A package manager for Linux.
  • chocolatey - A package manager for Windows.
  • oh-my-zsh - A framework for managing zsh.
  • npm - A package manager for JavaScript.
  • man - A command-line tool for reading documentation on any command.
  • mkdir - A command-line tool for creating directories.
  • touch - A command-line tool for creating files.
  • echo - A command-line tool for printing text.
  • cat - A command-line tool for printing files.
  • dig - A command-line tool for querying DNS.
  • cp - A command-line tool for copying files.
  • mv - A command-line tool for moving files.
  • rm - A command-line tool for removing files
    • Be careful! There is no trash bin with rm.
  • date - A command-line tool for printing the date.

More Advanced Tools

These tools take more time to learn, but they can be very useful.

  • tmux - A terminal multiplexer.
  • ffmpeg - A command-line tool for manipulating video.
  • jq - A command-line JSON processor.
  • grep - A command-line tool for searching text.
  • sed - A command-line tool for editing text.
  • awk - A command-line tool for processing text.
  • curl - A command-line tool for transferring data.
  • docker - A tool for running containers.
  • Fx - A command-line JSON viewer.

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