BOSS-Linux/C2/Basic-Commands/English-timed

Time	Narration
00:00	Dear friends, welcome to a spoken tutorial on the Linux Operating System.
00:05	In this tutorial, we will study some basic commands.
00:10	I am using Linux Operating System.
00:12	We assume that you know how to get started with the Linux operating system.
00:17	If you are interested, it is available through another spoken tutorial, on the website [1].
00:26	In this tutorial, we will see what are commands and what is a command interpreter.
00:33	Then we will learn about how to find help in Linux using the man command.
00:39	Now the first question is, "what are commands?".
00:43	In simplest terms we can say that Linux commands are words that when keyed in cause some actions to take place.
00:51	Linux commands are seldom more than four character in length, like ls, who, ps etc.
00:59	The commands are in lower case and they are case sensitive. Let us see an example .
01:05	Go to the Applications menu.
01:08	Select Accessories and then click on Terminal from the available options.
01:14	Now we can see a prompt ($) and a cursor blinking next to it. This is where we need to type in a command.
01:22	Type the word who and press Enter.
01:28	We can see the name of the users logged in. Actually we have just executed a command called who which shows who are logged into the system.
01:41	But which entity is converting these commands which are nothing more than a few letters into actions?
01:47	This is the job of the Command Interpreter, also called the shell.
01:53	We can define a shell as a program that acts as the interface between us and the Linux system,
02:02	allowing us to enter commands for the operating system to execute.
02:07	On Linux it’s quite feasible to have multiple shells installed, with different users able to pick the one they prefer.
02:16	On Linux, the standard shell that is always installed as bin/sh is called bash, the GNU Bourne-Again Shell, from the GNU suite of tools.
02:29	The commands we would be covering in this tutorial are generic and can run on most of the Linux shells with slight variations.
02:38	Nevertheless, we would be using the bash as the shell for demonstration in this tutorial.
02:44	It is because bash is the most popular shell and portable to almost all UNIX.
02:52	Other shells include the Bourne shell which is the original Unix shell, C Shell and the Korn shell.
03:02	To see which shell we are using, go to the terminal
03:08	and type the command: echo space dollar in capital SHELL and press Enter.
03:21	Normally, the output is /bin/bash which gives us the bash shell.
03:28	There are ways by which we can activate different shells. Those will be covered in an advanced tutorial.
03:36	Commands are actually files containing programs, often written in C.
03:41	These files are contained in directories. To find out where a command is stored, we can use the type command.
03:48	Type at the command prompt: type space ps and press Enter.
03:58	This shows that ps is actually a file, stored in the /bin directory.
04:03	When we key in a command at the command prompt, the shell searches for a file matching the command name in a list of directories.
04:12	If it is found, then the program corresponding to that file is executed, else a “command not found” error is given.
04:21	The list of directories searched is specified by the PATH variable, as we will see later.
04:28	For now, if we want to see this list, just type the command echo space dollar PATH in capital.
04:40	and press Enter.
04:45	Talking of commands, there is one important thing that we need to know.
04:51	Linux commands are of two types: External commands and internal commands.
04:56	Now external commands are those which exist as separate files/programs.
05:00	Most commands in Linux are of this nature. But, there are some commands whose implementation is written within the shell and they do not exist as separate files.
05:12	These are internal commands.
05:14	The echo command which we will see later, is in fact an internal command.
05:18	Go to the terminal and type the command:
05:26	type space echo and press Enter.
05:34	The output shows: "echo as a shell built-in".
05:43	So, instead of giving a file name it shows that the echo command's implementation is internal to the shell. So, it is called internal command.
05:50	Another important thing which we need to understand is the structure of commands.
05:55	Commands can be of one word or multiple words, separated by white spaces.
06:02	In the second case, the first word is the actual name of the command while the other words are the arguments.
06:09	Arguments can be options or expressions or file names.
06:14	A command can perform different tasks depending on the option specified.
06:20	They are generally preceded by a single or double minus sign called short and long option respectively.
06:28	Go to the terminal window and type the commands and see their outputs.
06:34	Type clear to clear the terminal window.
06:37	Then type ls and press Enter.
06:43	Again, type clear and press Enter.
06:49	Type ls space minus a and Enter.
06:58	Type clear to clear the terminal window.
07:04	Now type ls space minus minus all and press Enter.
07:13	Again, type clear to clear the terminal .
07:18	Now type ls space minus d and press Enter.
07:26	At this point, it is enough to understand how the command's behavior changes with change of options.
07:33	In Linux, we have a large number of commands
07:39	each of which have many different options.
07:42	Commands can also be combined together as we will see later. So, how do we keep so much in mind?
07:48	In reality you don't have to. This is because of the excellent online help facility available in Linux.
07:55	The man command provides documentation on just about every available command on the system.
08:01	For instance, to know about say- the ls command, all you have to do is to go to the terminal
08:09	and type man command with ls as argument, that is type man space ls and press Enter.
08:23	Press q to come out.
08:29	man is the system’s manual pager. Each argument given to man is normally the name of a program, utility or function.
08:37	The manual page associated with each of these arguments is then found and displayed.
08:43	A section, if provided, will direct man to look only in that section of the manual.
08:49	The default is to search in all of the available sections, following a pre-defined order and to show only the first page found, even if page exists in several sections.
09:00	You can use man command to know more about the command man itself.
09:07	Go to the terminal and type man space man and press Enter.
09:16	Press q to come out of it.
09:20	man command has many options.
09:23	Here, let me tell the most useful ones. Sometimes, we know what we want to do but we do not know the exact command. Then what can we do?
09:35	man provides the -k option which takes a keyword and returns a list of commands and their brief purpose.
09:44	For example, create a directory; we may not know the exact command.
09:50	So, we can go to the command prompt and type man space minus k space directories and press Enter.
10:06	Now we can search each of these commands to see what we actually need.
10:11	The same thing can be achieved using apropos command.
10:15	Type at the command prompt: apropos space directories and press Enter to see the output.
10:29	Sometimes, we do not need too much details. We only need to know what a command does.
10:35	In that case, we can use the whatis command or man -f. Both give one line description about the command.
10:45	Go to the terminal, type clear to clear the terminal window.
10:51	Now, type: whatis space ls and press Enter.
10:59	Some commands have many options. We may want to obtain a list of the different options that a command has.
11:07	Then we use the - - (minus minus) help option.
11:12	Go to the command prompt and type ls space - -(minus minus) help and press Enter.
11:23	I will scroll up so that you can see all the options on this manual page.
11:38	That's it for this part of the Linux Spoken tutorial. Spoken Tutorials are a part of the "Talk to a Teacher" project, supported by the National Mission on Education through ICT.
11:49	More information on the same is available at the following link .
11:54	Thanks for joining us. This is Anuradha Amrutkar, signing off. Good Bye.

Contributors and Content Editors

PoojaMoolya, Sandhya.np14