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 Ubuntu 10.04.
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 http://spoken-tutorial.org.
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.
00:52	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	or press Ctrl Alt t on your keyboard to open a terminal window.
01:20	Now we can see a prompt ($) and a cursor blinking next to it. This is where we need to type in a command.
01:29	Type in the words who and press Enter.
01:34	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.
01:47	But which entity is converting these commands which are nothing more than a few letters into actions?
01:54	This is the job of the Command Interpreter, also called the shell.
01:59	We can define a shell as a program that acts as the interface between us and the Linux system,
02:08	allowing us to enter commands for the operating system to execute.
02:13	On Linux it’s quite feasible to have multiple shells installed, with different users able to pick the one they prefer.
02:22	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.
02:35	The commands we would be covering in this tutorial are generic and can run on most of the Linux shells with slight variations.
02:44	Nevertheless, we would be using the bash as the shell for demonstration in this tutorial.
02:51	It is because bash is the most popular shell and portable to almost all UNIX.
02:58	Other shells include the Bourne shell which is the original Unix shell, C Shell and Korn shell
03:08	To see which shell we are using,
03:11	go to the terminal and type the command: echo space dollar in capital SHELL and press Enter.
03:27	Normally the output is /bin/bash which gives us the bash shell.
03:34	There are ways by which we can activate different shells. Those will be covered in an advanced tutorial.
03:42	Commands are actually files containing programs, often written in C.
03:47	These files are contained in directories. To find out where a command is stored, we can use the type command.
03:55	Type at the command prompt: typespace ps and press Enter.
04:03	This shows that ps is actually a file stored in the /bin directory.
04:09	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.
04:18	If it is found, then the program corresponding to that file is executed, else a “command not found” error is given.
04:27	The list of directories searched is specified by the PATH variable, as we will see later.
04:34	For now, if we want to see this list, just type the command echo space dollar PATH
04:44	in capital and press Enter.
04:52	Talking of commands, there is one important thing that we need to know.
04:57	Linux commands are of two types: External commands and internal commands.
05:02	Now external commands are those which exist as separate files/programs.
05:07	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.
05:18	These are internal commands.
05:20	The echo command which we will see later, is in fact an internal command.
05:25	Go to the terminal and type at the command:
05:33	type space echo and press Enter.
05:40	The output shows echo is 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.
05:56	Another important thing which we need to understand is the structure of commands.
06:01	Commands can be of one word or multiple words, separated by white spaces.
06:08	In the second case the first word is the actual name of the command while the other words are the arguments.
06:16	Arguments can be options or expressions or file names.
06:20	A command can perform different tasks depending on the option specified.
06:26	They are generally preceded by a single or double minus sign(-), called short and long option, respectively.
06:35	Go to the terminal window and type the commands and see their outputs.
06:40	Type clear to clear the terminal window.
06:44	Then type ls and press Enter.
06:49	Again, type clear and press Enter.
06:55	Type ls space minus a (-a) and Enter.
07:04	Type clear to clear the terminal window.
07:11	Now type ls space minus minus all and press Enter.
07:19	Again, type clear to clear the terminal .
07:23	Now type ls space minus d (-d) and press Enter.
07:32	At this point, it is enough to understand how the command's behavior changes with change of options
07:40	In Linux we have a larger number of commands,
07:45	each of which have many different options.
07:48	Commands can also be combined together as we will see later. So how do we keep so much in mind?
07:55	In reality you don't have to. This is because of the excellent online help facility available in Linux.
08:01	The man command provides documentation on just about every available command on the system.
08:08	For instance, to know about say, the ls command, all you have to do is to go to the terminal
08:16	and type 'man' command with 'ls' as argument that is type: man space ls and press Enter.
08:30	Press q to come out.
08:35	man is the system’s manual pager. Each argument given to man is normally the name of a program, utility or function.
08:43	The manual page associated with each of these arguments is then found and displayed.
08:49	A section, if provided, will direct man to look only in that section of the manual.
08:55	The default is to search in all of the available sections, following a predefined order and to show only the first page found, even if page exists in several sections.
09:07	You can use man command to know more about the command man itself.
09:14	Go to the terminal and type: man space man and press Enter.
09:23	Press q to come out of it.
09:26	man command has many options.
09:30	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?
09:41	man provides the -k option which takes a keyword and returns a list of commands and their brief purpose.
09:50	For example, create a directory, we may not know the exact command,
09:56	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	Sometimes 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 you can see all the options on this manual page.
11:45	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.
11:56	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