Command Line Interfaces

CLI

• A CLI is a way to interact with a computer by providing lines of text instructions
• Began to replace punched cards in the 60s as a way to interact with computers

Terminal

• Hardware devices used to send and receive text from a computer
• Includes text output and text input
• Modern systems may include virtual terminals

Python REPL

• Accepts and runs Python commands

Example

>>> a = 5
>>> b = 7
>>> a + b
12

Shell

• Provides an interface to the underlying operating system
• Shells may be graphical or text-based

Example

• Windows without Explorer

Text shells

• Many operating systems provide a text-based shell
• Examples include cmd (Windows), Powershell (Windows), and BASH (Unix, Linux, and MacOS)

Command Format

Prompt command param1 param2 … paramN

• Commands are generally entered following a prompt
• Commands may be internal or call an external program
• Parameters are provides by the user for the command

Working Directory

• Running programs (processes) have a current working directory used to resolve relative paths
• The shell may allow the working directory to be changed

Changing Directories

cd /home/user/documents

Listing current directory

• It is frequently helpful to be able to list the current directory
• The ls command can be used for this in most shells
• Some shells may use dir

Running a program

• One of the key features of a shell is launching programs
• This is accomplished using commands in text-based shells

Example

Run calculator using Windows:

C:\> calc

Run thonny using Bash:

> thonny