Noobs guide to CLI

Command Line Interface https://en.wikipedia.org/wiki/Command-line_interface

How it all works

                 +--------+       +---------------------+
                 |        |       |                     |
                 |        |       |                     |
                 |        |       |                     |
                 |        |       |    Graphical        |
 +----------+    |        |       |      User           |
 |          |    |        |       |       Interface     |
 | keyboard |--->| shell  |======>|                     |
 |  mouse   |    |        |       |       OR            |
 |          |    |        |       |                     |
 +----------+    |        |       |    Monitor          |
                 |        |       |                     |
                 |        |       |                     |
                 |        |       |                     |
                 +--------+       +---------------------+

Shell is the program which interact with you and provides you with the output displayed on a output device like monitor.

e.g.

• you press s on keyboard, then this signal is send to the shell send a signal to display the letter s on the monitor.
• you press Tab on the keyboard, this signal is also send to the shell, usually Tab triggers autocompletion, so the shell will try to do autocompletion from the previous letter you have typed.
• Ctrl+L on most linux shell clears the screen, this also happen in the same way.

In early days of computing, only one program used to run that displayed the output of the shell, but now days different you can run multiple gui terminals/console-applications.

Note: Comparing Unix/Linux terms with Microsoft Windows won't make much sense if you go in details, they are completely different.

Additional notes:

• Most console application on windows open in conhost.exe, which looks too old, it's new replacement is windows terminal.
• Besides windows terminal, other applications like it are also available, like Conemu, hyper, alacritty.
• There is also a application called MinTTY which is used by application like git-bash by default.
  • It was made by mingw team, a big project to support gcc compilers on windows
  • it add more functionality to conhost.exe, you can say it is superior to conhost.exe
• There are many terminal emulators available on linux, such as alacritty, gnome-terminal, konsole, and many more.

Useful Tips

• If you are on windows, try using Windows Terminal, it comes with some shell by default but you can and more shells to it.

Scripting

When you have a bunch of commands you want to run, you can just paste them to a file and make a script. Every shell support some type of scripting.

Moreover, you can add conditional and iterative constructs in the scripts.

Environment of a shell

The value of the variables in a shell determines its environment. One most commonly known environment variable is, PATH, which specifies a list of directory/folders where the shell will search for any command/application you run.

Internal and External Commands

• Internal Commands - Commands which are built into the shell.
• External Commands - The shell searches them in the directories in the PATH variable

Since no searching is done when internal command is used, they are usually more fast.

Command structure

A command consists of command name and some (or none) arguments.

e.g.

• ls
  • ls - command name
• echo "Hello world"
  • echo - command name
  • "hello world" - argument one
• echo -e "hello world"
  • echo - command name
  • -e - argument one
  • "hello world" - argument two
• ls --color
  • ls - command name
  • --color - argument one
• del /s *.txt
  • del - command name
  • /s - argument one
  • *.txt - argument two

Additional Notes

• --color the arguments starting with -- are more descriptive and with one - are less
• /s this type of argument is found usually in cmd.exe of microsoft
• some commands arguments also have values like
  • -color=red
  • -color red
  • -color "red"
• In linux, unix, mac file/directory path are separated using / while in windows using \

CMD.exe

• This is the default shell in the windows.
• It doesn't have a configuration file.
• Have only limited functionality and features for command history and completion.

How to get help for a command

• in cmd to get help for all commands use command help
  • this will show you list of all supported commands and there simple description
• to get help on a particular command use -h or \? as a argument
  • cd \? will give help about cd command
• another way is to use help [command-name]

Some basic commands

Powershell

• Cross platform shell by microsoft.
• It has two versions, one is Powershell core and another is just Powershell.
• Powershell core has some added functionality (modules) for windows.
• It does have configuration file.
• Not a conventional shell, it introduces many new features like objects, instead of text

How to get help for a command

• Get-Help -Name command-name
• command-name --help

Some Basic Commands

Bash

• For unix like systems
• Mingw project version of add is also available for windows
• Have nice tab-completion features, and many more

How to get help for a command

• man command-name
• command-name --help
• command-name -h

Basic Commands