Linux/C2/Basic-Commands/English-timed

Time	Narration
0:00	Dear friends, welcome to a spoken tutorial on the Linux Operating System.
0:05	In this tutorial, we will study some basic commands.
0:10	I am using Ubuntu 10.04.
0:12	We assume that you know how to get started with the Linux operating system.
0:17	If you are interested, it is available through another spoken tutorial, on the website http://spoken-tutorial.org.
0:26	In this tutorial, we will see what are commands and what is a command interpreter.
0:33	Then we will learn about how to find help in Linux using the man command.
0:39	Now the first question is, "what are commands?".
0:43	In simplest terms we can say that Linux commands are words that when keyed in cause some actions to take place.
0:52	Linux commands are seldom more than four character in length like ls, who, ps etc.
0:59	The commands are in lower case and they are case sensitive. Let us see an example .
1:05	Go to the applications menu.
1:08	Select accessories and then click on terminal from the available options
1:14	or press ctrl alt t on your keyboard to open a terminal window.
1:20	Now we can see a prompt ($) and a cursor blinking next to it. This is where we need to type in a command.
1:29	Type in the words who and press enter.
1:34	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.
1:47	But which entity is converting these commands which are nothing more than a few letters into actions?
1:54	This is the job of the Command Interpreter, also called the shell.
1:59	We can define a shell as a program that acts as the interface between us and the Linux system,
2:08	allowing us to enter commands for the operating system to execute.
2:13	On Linux it’s quite feasible to have multiple shells installed, with different users able to pick the one they prefer.
2:22	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.
2:35	The commands we would be covering in this tutorial are generic and can run on most of the Linux shells with slight variations.
2:44	Nevertheless, we would be using the bash as the shell for demonstration in this tutorial.
2:51	It is because bash is the most popular shell and portable to almost all UNIX.
2:58	Other shells include the Bourne shell which is the original Unix shell, C Shell and Korn shell
3:08	To see which shell we are using
3:11	go to the terminal and type the command echo space dollar in capital SHELL and press enter
3:27	Normally the output is /bin/bash which gives us the bash shell.
3:34	There are ways by which we can activate different shells. Those will be covered in an advanced tutorial.
3:42	Commands are actually files containing programs, often written in C.
3:47	These files are contained in directories. To find out where a command is stored, we can use the type command.
3:55	Type at the command prompt. Type--space-- ps and press enter.
4:03	This shows that ps is actually a file stored in the /bin directory.
4:09	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.
4:18	If it is found, then the program corresponding to that file is executed, else a “command not found” error is given.
4:27	The list of directories searched is specified by the PATH variable, as we will see later.
4:34	For now, if we want to see this list, just type the command echo space dollar PATH
4:44	in capital and press enter
4:52	Talking of commands, there is one important thing that we need to know.
4:57	Linux commands are of two types: External commands and internal commands.
5:02	Now external commands are those which exist as separate files/programs.
5:07	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.
5:18	These are internal commands.
5:20	The echo command, which we will see later, is in fact an internal command.
5:25	Go to the terminal and type at the command,
5:33	type space echo and press enter.
5:40	The output shows echo as a shell built-in.
5:43	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.
5:56	Another important thing which we need to understand is the structure of commands.
6:01	Commands can be of one word or multiple words, separated by white spaces.
6:08	In the second case the first word is the actual name of the command while the other words are the arguments.
6:16	Arguments can be options or expressions or file names.
6:20	A command can perform different tasks depending on the option specified.
6:26	They are generally preceded by a single or double minus sign(-), called short and long option, respectively.
6:35	Go to the terminal window and type the commands and see their outputs.
6:40	Type clear to clear the terminal window
6:44	Then type ls and press enter
6:49	Again, type clear and press enter
6:55	Type ls space minus a and enter.
7:04	Type clear to clear the terminal window
7:11	Now type ls space minus minus all and press enter.
7:19	Again, type clear to clear the terminal .
7:23	Now type ls space minus d and press enter.
7:32	At this point it is enough to understand how the command's behavior changes with change of options
7:40	In Linux we have a larger number of commands,
7:45	each of which have many different options.
7:48	Commands can also be combined together as we will see later. So how do we keep so much in mind?
7:55	In reality you don't have to. This is because of the excellent online help facility available in Linux.
8:01	The man command provides documentation on just about every available command on the system.
8:08	For instance, to know about say, the ls command, all you have to do is to go to the terminal
8:16	and type man command with ls as argument that is type man space ls and press enter
8:30	Press q to come out.
8:35	man is the system’s manual pager. Each argument given to man is normally the name of a program, utility or function.
8:43	The manual page associated with each of these arguments is then found and displayed.
8:49	A section, if provided, will direct man to look only in that section of the manual.
8:55	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.
9:07	You can use man command to know more about the command man itself.
9:14	Go to the terminal and type man space man and press enter.
9:23	Press q to come out of it.
9:26	man command has many options.
9:30	Here let me tell the most useful ones. Sometimes we know what we want to do but do not know the exact command. Then what can we do?
9:41	man provides the -k option which takes a keyword and return a list of commands and their brief purpose.
9:50	For example, create a directory, we may not know the exact command,
9:56	so we can go to the command prompt and type man space minus k space directories and press enter.
10:12	Now we can search each of these commands to see what we actually need.
10:17	The same thing can be achieved using apropos command.
10:21	Type at the command prompt apropos space directories and press enter to see the output.
10:36	Some times we do not need too much details. We only need to know what a command does.
10:40	In that case we can use the whatis command or man -f. Both give one line description about the command.
10:52	Go to the terminal type clear to clear the terminal window
10:58	now type whatis space ls and press enter
11:06	Some commands have many options. We may want to obtain a list of the different options that a command has.
11:13	Then we use the minus help option.
11:18	Go to the command prompt and type ls space minus minus help and press enter
11:29	I will scroll up so that u can see all the options on this manual page
11:45	Thats 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.
11:56	More information on the same is available at the following link .
12:00	This script has been contributed by ----------------------(name of the translator) and this is -----------------------(name of the recorder) from --------------------------(name of the place)signing off. Good bye

Contributors and Content Editors

Minal, Pratik kamble, Sandhya.np14