 Welcome everyone, yeah. If you have a question please ask. From Rajarachmi Engineering College Chennai, please ask your question. We will give some more examples later to touch the man. Sure, we will give examples. Certainly, we will see more examples, yeah. Any other question? Okay, we have finished all the questions. If somebody else has some question, please use the hand raise button in your ABU and we can come to those questions. Some statements written on chat, let me read it out. So, somebody has asked me to change the background of the terminal. This we will certainly do very soon now. Then the question is about the touch command. About the touch command, we will see immediately after we see about which question. So, there was this question that when you type LS, that time you just see the names of the files and directories. When you do LS minus L, that time it gives some total on the top. What is that number? Yeah, and also when you, even if the directory is empty, still some 4096 bytes are used. That is what it says as the file size, directory size, even though there is nothing inside. About that, Harish? Yeah. About that, Harish will quickly explain. So, basically, when you do LS minus L, you get something called a total. A person there came and told me that the total basically represents the size in kilobytes of the directory that is being listed. So, LS minus L dir gives a total. That total represents the size in kilobytes of dir. So, one of the questions was about the file command. So, about the touch command. So, both touch and file are the commands we have seen. We have also seen CD make dir. Make dir means make directory and CD means change directory. So, why these short forms? See, CD is the command we use so often and LS is the list. We use so often, better to have just two letters for the name of the command. LS is so frequently we want to use this command. What about touch? Touch is not used anywhere comparable to CD. Touch is something we are using because we want to create new files. So, let us see the names of the files. F6.doc file 1. So, there are these different files. We also were going to copy one other file. So, let us see in little more detail about the file command and also in detail about the touch command. Touch we used only for creating a new file as of now, but clearly touch has much more significant usage. Let us copy this particular file here. So, we have copied. CP means copy. We will see in more detail about the CP, but right now to discuss about the file command, I have copied one AR3.pdf which is genuinely a PDF file. It can be opened by various PDF viewers. You might have heard of only Acrobat reader, but Evans for example, on Ubuntu. Evans, I think default comes. Evans AR3.pdf can be used for one of the questions on chat is that I should clear the terminal frequently. That is indeed a very good command. So, clear screen. Very good. So, AR, Evans is a way of viewing a PDF file. So, I use Evans command to view the PDF file. So, this is genuinely a PDF file. Let us see Evans. There is some other file. This is not. It says unable to open document. File type plain text. It is not really a PDF file. Some error has come. Why? Because see file file 5.pdf, it is a empty file. Now, let us see file AR. Yeah, it says PDF document version 1.4. Coming back to the file command. File AR3.pdf tells that it is a PDF document. So, you cannot cheat the file command by just choosing extensions. Let us copy this AR3.pdf into new.doc file. Doc file. So, the worst of the file extensions in my opinion. Let us take file new.doc. It still says it is a PDF document. Inside that file, not just in the extension. Inside that file, there is genuine information of what that file is. You wrongly giving some other extension and trying to cheat the reader, the user. Reader might get cheated, but the file command is the right one to use to find out what type of file that is. So, in latex, when we are doing latex, we will have lot of need to use the tech extension. Yeah, we can copy the AR3.pdf to file file 6.tech file. In latex, which we will see next, we can tech tex. That extension is going to be widely used. So, let us see file. No points for guessing that it will again say it is a PDF file. Yeah, the file is used to find out what type of file it is. If it is a directory then same command file can still be used for dir and it will say it is a directory. That is as far as file command is concerned. So, please note file is very useful to know what type of the file, what type of file is that particular argument. Yeah, and we already saw how to give addition options. We also saw detail just how to use a file, how to use a command. You can type enter and it will tell you this. It will not give the usage for everything because for example, ls, it did not tell what is the usage, why? Because ls is a command that can also execute without an argument. Yeah, ls can take an argument. For example, dir4, it will tell what all is there inside dir4. But just by ls will tell all the files and directories in the current directory. This is same as ls. This is the current directory. Dot stands for current directory. Yeah, ls, we can also see ls.dot. Motall are there in the previous directory. So, this is the present working directory. Present working directory means we are inside dir3. Inside dir3, what is there? These are the ones. What is there in the previous one? ls.dot. Yeah, just list. We are not changing directory. We are not going to that directory. We are just listing motall is there in the parent directory. That is being shown by and of course, where which directory we are now currently had better also be there. Yeah, will it always be there? Not necessarily. Can you think of an example where we are in the present working directory, some particular directory name that you have to think about? There is small exercise for you to do now. Think of some name of the current directory. You go and sit inside that directory and after sitting inside that directory, when you do ls.dot.dot, that name that directory inside which you are sitting is not even visible to the parent. Not even visible in the parent directory. Yeah, that will have to be that name of that directory into which inside which you have to be sitting has to be carefully thought. And we have already covered the answers, covered the topic for you to be able to answer this. What is the question? Present working directory has dir3 in the end. Whatever is highlighted, this present working directory is indeed the directory 3 is indeed one of the directories of the parent directory. Yeah, that is why when you do ls.dot, dir3 is also there. Yeah, dir3 is there and of course, we are already sitting in dir3. Yeah, are we sitting in dir2? No, we are not sitting in dir2, but dir2 is also a sub directory inside the parent directory. So, now what directory name should we create now? We go and sit inside the directory and when you do ls.dot, that name will not be visible even though that sub directory is there. Further what option to give to ls, then that name will be visible. Yeah, so please try this for a minute. Please try it while I try to change the background. Yeah, this was one of the request. So, this is exercise time for all of you to try to think of a directory name, go and sit inside the directory and do ls.dot. And the directory which is certainly there is not visible exercise for all of you also while I quickly try to change the profile preferences. So, I hope all of you have been able to create a directory name. So, let me quickly tell the solution to this to make one directory called dot dir5. Yeah, go to dot dir5. So, there is nothing inside quite expectedly. What is the present working directory? We are inside dot dir5. What is there here? Nothing. What is the backside? These are the various things here. But look dir5 is not there. Why? Why because dot it starts with dot. ls minus a dot dot will show all this. It will show not just this dot file 3 that also was not visible here. It will also show us dot dir5 inside which we are currently and we know it is there. So, because it starts with dot it is not visible with just ls. ls minus a a for all I think will show all these extra things also. That was the small exercise we had given you. So, we are going to be giving many exercises at the end of each weekend, maybe at the end of Saturday, at the end of Sunday. So, please work on all these assignments. Yeah. Why should these assignments are not required to be submitted? We will clarify all these procedures in more detail. But please try all of these because exams will have similar difficulty questions. Exams might have some of these itself. So, it will be very helpful that you do all of these. If you can do all of these then you we are sure you will do well in the exam also. Yeah. And you doing well in the exam is very important for us. We count all of you as future assets for conducting such workshops. We consider you all will help in spreading force, spreading linux, latex, python. So, hence please do these exercises nicely. So, our next topic is, so let us go back to the various slides. So, touch. Come in and ask for touch also. So, meanwhile there is a question from Kakinada. So, why do not we take this question quickly and then continue with touch. Please ask from Kakinada. Please ask. The question is, how we will come to know the access time, modified time and change your time of a puddler file? And how can I change the timestamp of a puddler file using the touch command? And how can I see, how can I get the last access time or modified or changed time of a puddler file? So, we will see in more detail about how to change the timestamp, how to see when it was last modified, how to modify the time itself. So, we will see all those things very soon. So, when you do LS minus L, you can see all the date, time, etcetera. So, how to clear the screen? C L E A R is actually the command to type, to clear the screen, but there are some shortcuts. If you press in bash, I think there is a shortcut for bash, if you press control and L, that will also clear the screen. Control with many commands have different meanings. Control L means clear. So, what is the time that all these files were created? 1038 on this day, 2011, November, yeah, 2011 November, yeah, and on 5th November, yeah, at 1038, yeah. What is the time now? That can be seen by date. Date it says now it is 12, well, 4 minutes past 12 on, according to India's time, when this laptop was configured, we are told that we are in India, that is why it is automatically Indian standard time. And while these files were created at so and so time, yeah. Now, what does this touch do? Actually, touch is not just for creating a empty file, yeah. When you do touch, file 2, when you do touch file 2, let us do LS minus L of only file 2 again, yeah. So, now you see here, it was actually created at 1038, that is when it touched. As soon as, if touch and some name, if that file is not existing, it will create it. As soon as it is created, it will have touched also, but more generally touch of a file name, which we typed just now, will touch that file now, as soon as it is touched, the last modified time, the time when it was last modified will change to the time at which it was touched, yeah. So, just now it has been touched. So, the time has become 5 minutes past 12, yeah. It was, you see, when we press the date command, it was 54 seconds past, yeah, 54 minutes and 54 seconds, yeah. When we press the touch command, then it was only 5 minutes past 12, and indeed that is the time stamp of the file, file 2. Why do not we do LS minus L, everything? We see all other files are still 1038, yeah. File 1 was not touched just now, while file 2 was touched now, and that is why it is 12-5. So, this particular column tells the time at which it was last modified, yeah. You might have modified it. Even if you do not modify, you just touch it, and the time stamp will become the time at which it was touched, yeah. So, you can press date. Now, it is almost 7 minutes past 12. Why do not we touch another file, file 1, and the LS minus L, yeah. File 1 also has got the time stamp of 6 minutes past 12, yeah. This is how one uses touch command. It is extremely important when you are writing many shell scripts, and you have done all these operations, and you want to keep track that you did all these operations. All those operations at what time they were done, that can be stored by just touching a very specific file, whose time stamp will have this information. When you, it will have the information about at what time you did all those operations. Why? Because along with all those operations, you also include this command called touch, a particular file. That particular file's time stamp will have this information, yeah. Of course, touch has actually not modified it. It is only storing that information. It is extremely useful. For example, I will tell you when we used to use it. At a time, I mean 10, 12 years ago, 15 years ago, data storage was very tough, yeah. We all had very small quota. We all could have only around 2 or 3 MB in our home directory. We did not have personal computers. There used to be one computer in which we had an access, and we could have at most 2 MB. So what happens when you exceed 2 MB? You get one week to delete all unnecessary files, yeah. And this one week starts, when does it start? From the time you exceeded 2 MB. You just do a time stamp. You just say make them all small, jizzip them, and make them large again. Again you get one week, yeah. So why? Because we knew that the program that this systems administrator is using, they are seeing when did you exceed 3 MB? They will see all that by the time stamps that tomorrow you modify a file, but you have still exceeded 3 MB. So your 3, your one week will not begin from the next time you modify. It will begin from the last time that you exceeded 2 MB, some quota checks. In all those places, the time stamp is of very critical value. Also, for example, you might have seen in many servers when you log in again and again, it will tell what was the last time, when was the previous time you logged in, yeah. It wants to know when was the last time some important file was modified. The time stamp is extremely important for various reasons. I tried giving only some reasons. So touch is a command for touching a file and thus modifying its time stamp. This time stamp will become the time now at which you touch it. Whatever actually modifying it, yeah. How do you modify it? You have to actually change the content, yeah. Content is still, we will see how to compare two files, how to check whether some changes in the taken place. But actually to modify the file, you need something like an editor, yeah. All these different file extensions we have given, they have not modified any file. Touch, new file, we will just create a new file, yeah. What was the time stamp? The time stamp at which it was touched because the file was not existing, it has also created that file. What file is it? It is a empty file, yeah. So how to edit the contents inside the file will indeed be a topic we will cover. Let us see what is the next topic to cover. We will see this immediately after we answer a doubt from Periyar Maniyam Mai College in Tanjabur. Please ask your question now from Tanjabur. What is the difference between creating a file using startwith.comand or without startwith.comand, dot character in the file name, using in the touch command? Dot, if the file name starts with dot, so your question is what exactly is the difference between starting the file name with a dot and without starting with a dot, what is the difference as far as the touch command is concerned, yeah. If that is the question, the answer is whether the file name starts with dot or not matters only when you do ls, when you do ls without the option minus a, all the files starting with dot, all the file names, directory names starting with dot will not be visible. If you put minus a option to ls command, then the files and directories with startwith dot will also be available, will also be visible, will also be listed and in particular dot, the current directory and the parent directory, dot dot will also hence be visible. But as far as the touch command is concerned, you can touch command does not care whether the file name starts with dot or not, yeah, whether it will be visible when whether it will get whether it will get listed when you use the ls command that depends on whether the file name starts with dot or not. So, the two are different issues, yeah, any other questions please ask. Using a touch command, we are creating a multiple files at the time. So, what I am asking is, suppose we want to update the data in multiple files at the time, what is the command? So, the question is, can you touch multiple files and change the time stamp? Yeah, touch command is for changing time stamps. Contents are not getting changed by touching the file. Yeah, we can think of, I mean, when you touch some object, only fingerprint remains, actually nothing of the object changes. Yeah, touch is just to change the time stamp, nothing more. If the file is not there, it will get created. This is some extra advantage instead of giving an error that the file does not exist, it will create the file and put the time stamp. But touch command is only for time stamp. It is also, it will also create the file if it is not there. But if the file is there, multiple files, no editing, no modification takes place. Only time stamp gets modified. Yeah. Thank you, sir. The next question is from Manit Bhopal. What is the difference between file created using a file and file created using a touch? Any other questions, please ask, because answering this question will not take any time. Please ask any other questions if you have from Bhopal. First of all, I am creating a directory x, then two sub-directory y and z, then go to the y-directory and what is the difference between ls and ls double dot, because both times y and z, both are visible. But you are seeing the y is visible and z is not visible. Okay. Any other? If we are creating a file by using the touch command, then how we can insert or data from that file. Can we copy another data in that file? Sure. I have question that we have already discussed. The particular value that is showing when we press the ls minus l, actually I have run the create a one directory and create a file, it will give a 4kb values and 6kb for the inode. So that will indicate the size of the memory, memory taken by this directory that contain the inode structure and as well as the file structure. Yeah. Yeah. Yeah. We heard the question. We heard the question. I will start answering all of them one by one. What is the value of that value which is shown after the ls minus l command? Sure. Excuse me sir, I have solved it. I have just seen that it is a inode information and file information. Okay. Thank you. Thank you. So we will answer the various questions that came from NIT Vopal. First one was what is the difference between using file and touch commands for creating a file? So file command is not for creating a file. File cannot create a new file. File is a command only to check what type is a file. If the file does not exist, it might most likely say file does not exist. Why do not we see this here? So here we see ls. So clearly f8 is not there. Is there f8? Is there a file called f8? No, ls cannot access f8. No such file or directory. If you use touch f8, then f8 will indeed get created. Why do not we use file f8? It is an error. Cannot open f8. Why? Because file as a command cannot create new files if they do not exist. File is only for telling you what type of file it is. Provided it exists. So file, file6.tech. It says it is a PDF document. Remember that even we had created this tech file. Just to tell you that extension does not have any information, we copied some PDF file as this tech file. But anyway, at least the file exists. If the file does not exist, file is not the command to create that file. Touch f8 will create that file if it does not exist. Now we do ls-lf8 and it will tell you look, it was created just now. It was touched also. When you are creating it, it will touch it. So touch is the only command between create, between file and touch. File cannot create a new command. File cannot create a new file. But touch can create a new file even though the intended purpose is to touch it, to change the time stamp. It will, if the file already exists, the time stamp will become the time of now. So please note, file and touch are not commands for the same purpose. It will not help to compare them. File is the command we used along with touch. Only to see that the files that were created using the command touch were all empty files. So we can use file f8 and see that it is empty. To see the conclusion that it is empty is what is coming out by using the command file. Another question was that when you do ls and if you create two directories, ls dot dot and ls, both are showing the same output. So why do not we make a directory called? They are 9. They are 99 because of my keyboard. Why do not we go to this 99 directory? ls is showing nothing. Of course, we created the directory just now. How will there be anything? ls minus a, it is showing two things. One is a dot, which is the current directory. One is double dot, which is the parent directory. These are the two things that start with dot. That is why just ls did not show it. But ls minus a is showing it. Minus a as an option means what if you are interested in these additional things then on it will show you. If you create touch dot another dot file, if you create this, another non dot file. We are using multiple touch can change the time stamps of multiple files. It can also create multiple files in one go. Why? Because it is not modifying it anyway. It is just creating it or changing the time stamp. We are creating two files in one go. One is a dot file, one is not a dot file. Why do not we do ls? Only the non dot file is visible. That is because it does not start with dot. What about ls minus a? It will show you the dot, which is the current directory, double dot, which is the parent directory. It will show this other file name which starts with dot with a different color and this one, which was anyway visible even without the minus a option. Now, if you create a directory, you cannot create directories using touch. For creating directories, you have to use mkdir dot der 100. Now, if you do ls, that new directory is not visible, but dot ls minus a option will show you dot der 100 also. If you go to dot der 100 now, of course, let us see the present working directory. What is there in the previous directory? It is showing only this. It is not showing dot der 100. This was the exercise that we had given. Why it is not showing? Because we did not give minus a option. But if you give minus a option now and now ask that all the files in the previous directory, all the files and directories in the parent directory be shown. How are you specifying all by minus a option? Now, when you do, now will dot der 100 be visible or not? Let us try this. But before you try, you should try to answer the question. So, now will it be visible or not? Now, dot der 100 is visible. All these other files are also visible. This one was starting with dot. What is this double dot? This double dot is the parent directory of our parent directory. It is not just the parent directory where we are checking. It is its parent directory. It is like a grandfather for us. If we are allowed to use that word parent of parent, this current is the current directory of this parent directory. We are already listing everything in the parent directory. It is like we are asking what all uncles do we have? What all siblings our parent has? I hope this answers the question. Why something was visible with dot dot? Why something was not because it was starting with dot? Then another question was, can we change the data inside file using file or touch? No, touch will only change the timestamp. File command will not change anything. It will not even change timestamp. It is only for seeing the type of a file, nothing more. And if the file does not exist, file will not even create it for you. It will only tell there is an error. Look, that file does not even exist. It does not open. We already tried this. So, somebody else had asked, how do you see all the history, meaning when the file was created? As soon as you create a file using touch, ls minus l, another, sorry, another is not here. Let us go back. ls, another. It just says ls, another is there. If it were a directory, it would have shown the contents also. Let us see long. So, these are all the information in which this is the timestamp when it was last modified. Incidentally, it was, this time is also the time it was created. After creation, if it has not undergone any modification, then the time of creation is itself the last modified time also. Now, if you touch the same thing again, if you touch it again, now it has become the recent time. Notice that the time has changed. Now, after you have created one time, modified at a later time, you might want to know all the history when it was created. Actually, it is very important when you have now multiple versions and if you have not yet started using version control, which is part of this course, we will certainly teach it. But if you have not yet started using it, you might want to know when it was created. All that information, how to get that out is some command called stat, which I did not know until I asked my colleagues here. So, they told me that stat is a command when you use that with another, it will tell you look, it will give you a whole lot of statistics. It will tell you when it was accessed, when it was modified, many other such information is there. Modified change, there is no change anyway. So, these are all some additional information that can come out by using stat command. Now, another person had a question about total memory iNode. Luckily, that same question got sorted out there, but we will not spend any more time on that meaning of iNode LS for two reasons. This course is for engineers other than computer science engineers who do not know about iNode. And for that same reason, I also do not know. So, I mean electrical engineering, I do not know what is iNode. This is something about how data files are stored inside the hard disk and that is some information LS is giving, but we do not require it beyond what Harish Padrinath already answered. So, any other questions, we will take them now before we continue with the slides. So, we have a question from MES IMCC Pune. So, please ask your question now. Opal's question that is whether we have any other command rather than touch to create a new file and the part B of the question will be we are having certain extensions in the file that is dot text, dot txt, dot pdf. What significance it has actually? Yeah. Okay. Sure. The questions are clear. Any other question from Pune before we start answering them? Will I correct? Create pdf file from text file and back to text file again from pdf file. This will be a third part of the question. Okay. Yeah. Thank you. Thank you for your questions. Yeah, we will certainly answer them now. So, one question was any other way to create a file? Yeah. Of course, there are plenty of ways to create a file. Yeah. We will see many other ways touch was used only to create a empty file. Yeah. We will certainly see many other ways to create the file. And another question was what is the significance of the extension? If you can name any file with any extension pdf file you take, call it doc file. What is the significance then? Does it have any significance at all anymore? Yeah. So, the significance is there but it is, the significances can all be cheated unfortunately. Only file. So, let us go back. So, here we have various files. So, file.file5.pdf. These are some files we created. Incidentally, file5.pdf. So, we already saw file, file6.tech. Yeah. Some pdf file. So, and sorry for confusing all of you with giving all these strange extensions. Yeah. Extensions are, I mean, the file command will not get cheated by extension. That is the only conclusion to draw out. But there are other commands. For example, events. Yeah. Events is some command to view a pdf file. Yeah. So, for example, file, file5.pdf was an empty file. Yeah. What all pdf files are there? This has only two things. So, why do not we do events file? See, events command saw that starting from F, only one pdf file was there and events is anyway a pdf viewer. Yeah. So, because it is a pdf viewer, it is expecting pdf files and that pdf file it is expecting, it is going only by extension. Yeah. Quite unfortunately. Yeah. And this extension, we should be using judiciously even though file is a command that will not get cheated. There are all these other commands like events that will indeed get cheated. How did it get cheated? We pressed F. There are many files starting with F, but there is only one with extension pdf. That is why events tried to complete it to this file. But look, it is not a pdf file. Yeah. When you, when it opened it, it realized this. Yeah. More than this, we do not need to spend time on these extensions. Please note, file is a command to check what type of file it is and that file command does not go by just the extension. That is the only conclusion we needed to draw out from this. Please do not worry about if you did not understand this part. Yeah. So, we should go back to creating new files, touching the touch command, ls command directory, subdirectories, ls dot dot ls dot, those all are genuinely very important things. Extension, if you have not understood, please take your time to write on Moodle. We will certainly answer them. They are not critical for continuing for today and tomorrow. So, let us go back to the slides. Let us see how to know more about all these commands. So, there is a good amount of help already organized inside the Linux. Yeah. So, let us see how to get all this help. One very important command is called whatis. Whatis is a command that takes as its argument touch. It takes the name of the command as argument of what is command. So, on every prompt, so on this slides, dollar is the beginning of the prompt. In that prompt, you type the command first and then the argument to this command. Yeah. And now we are interested in knowing more about the command because we want to know more about the commands. This command whatis is an example. It will tell us more about various commands. What is is a command? Argument to that what is is touch. It is the command about which you want to know. Yeah. If you want to know what is touch, type what is space touch. As I said, because after the command there has to be a space. It will change the file. Let us all try this. Yeah, please try this on your own computer. Some small variations in the answer might be there. What is touch? Yeah, it says change file timestamp. It does not tell this is used for creating new file. Why? Because that is not the primary purpose of the command touch. So, touch what is touch? It changes file stamps. Yeah, of course, this is not elaborate help. You might be interested in much more help. Just touch. It says how missing file operand. Yeah, touch. If you want to know how to use this type touch help. So, this has given us some detailed information. Yeah, whether this particular command has been contributed by somebody or is it a core utility of the GNU of the GNU movement. These are all some information that is given there. Where to report bugs of this particular command. All that information is here. There is more. It is a man. Man as I said is for manual. Man touch. This will tell us detailed information of this particular command called touch. So, when you open man, you have to know how to come out of the man page. Yeah, there is a really so elaborate that it will not fit in one screen full. It will show screen, screen full, screen full many many pages. So, how do you come out of it? Press Q to come out of that. Yeah, after doing various things, we have come back to the prompt. This is a prompt where the cursor is where you can type your command. Yeah, it says to command not prompt. But I mean man when you do, it shows a very elaborate manual page for which command for touch. So, touch has to be given as a argument to the man command. Of course, man itself is a command. You can see man man. That will tell you press Q for quitting. Yeah, you can give various options. So, as I said for every command, these whatever is in square bracket is optional. That is the option. This particular option minus D. What does that minus D do? That you go down and it will tell one by one all these options. Minus A for intro, minus D for alias. It will tell you all of these. So, minus D will also be there somewhere. Yes, it is really elaborate. Please take your time and read in detail. Here D for debug, some debugging information. So, let us go back to man touch. It tells us touch option filing. That is how every command works. Command some options and the actual file. What options? Minus A. Minus A for change only the access time. All this access time we saw came out when you use a stat command. So, minus C. Do not create the file if it does not exist. You may not be interested in creating the file if it does not exist, but touch is sort of insisting on creating the file if it does not exist. Even though its purpose was to only change the timestamp, then you can give some extra option called minus C for not create. Do not create any files. They do not exist. Default is it will create. So, it will also say some things are default. For many things you want to know how is the default behavior. So, well for touch command it is not there. For some of them there is indeed a default option. So, man is one way where you can get detailed help. What is is also a very brief help. Just tell you what is it about. Let us go back to the slides. So, all the it will tell you various ways. And please remember to press the Q command to quit the man page. How do you browse through the man page? Just press space for going next page, next page, next page. Back B. B for back, back page, back page, previous page. Minus H or minus help also gives the summary of the command usage for many for many commands. For example, if you want to list out all files within a directory that directory might have further subdirectories then further subdirectories. So, you might want to recursively list out all the subdirectories minus R. R is usually for recursive. That option first letter typically stands for what word? First letter of that word recursively, R for recursively. Of course, sometimes R for read only for certain other commands read only might be a requirement. So, there R might stand for read only. Here capital R for recursively. For example, makedir, makedir, we said makedir we just gave one name and that if that already exists we already told. We already saw that if that directory already exists it will give an error. It will say cannot create it look that already exists. Now, if you are first interested in this directory, creating this directory then you are interested in creating Linux tools. After that you are interested in scripts. If you are finally interested in creating the script directory, you are forced to create its parents. What are the parents? Linux tools. What is the grandparent of scripts? SDS. You are forced to create all these parents also. Why? Because finally you are deciding to make the scripts. I mean when you are very organized and you come to a new computer, you have to again you will like to keep the same directory structure. And now to first make this then make this and make this three times you would have to use the makedir command. Why? Finally the purpose was scripts. For the scripts eventual sub directory what is its parent Linux tool? What is the parent of Linux tools? SDS. So, minus p option will say if the parent do not exist already just create it. That is what this says. Create a new directory along with parents if required. Finally, we are creating the grandchild creating the mid parents if required. So, this is how we have to understand this particular slide. Another way to understand various commands. So, the purpose of these two slides are to make you all more and more towards self help. Apropos is for searching commands based on the description. For example, what is we will tell you only that particular command. How that particular command what is it made for? But apropos gives you all the commands that have anything to do with remove about it. So, remove is some particular word you have in your head. You feel let me see what are all the commands that will help in removing. Removing something or the other. So, remove. What does remove? How do you want to how do you find out all the commands that have something to do with remove? Apropos remove what will it do? It will return a list of all the commands that contain this remove word that contain the search term. In this case, we are interested perhaps in the command called RM that is for removing a file. Maybe for removing a directory RMDL. We will see these commands very soon they are very important for us. But if you do not know RM, do you have to come to this course to understand what is RM? No, just do apropos RM. Apropos remove and it will tell you all the commands have something to do with remove about that command about those commands. So, why do not we do apropos remove on our command prompt? So, many commands RM that we see here is the one we actually wanted. RM, what does it say? RM is for removing files or directory. This is the one we wanted. Suppose we do not want to remember so many command names. But look, remove also occurs in this particular search phrase. Some complicated commands same underscore unlink. Some symbolic link to remove that symbolic link. Something really complicated. There also if you want to remove something, remove word has occurred there also. You may say, RM I knew I was looking for some other type of remove. Remove a file or a directory. Actually remove. This is in fact remove. Let us see what else. There is something called lock file. A lock file is very important because see for example, when you are reading an email that time you are accessing that file. At the same time a new email is allowed to come. So, some lockings are very complicated. The lockings have to be shared between the user trying to read his own email. At the same time a new email has to come and get written on that email file. So, there is a lock. Lock file might have that lock of the file might have to be removed. So, some there also some remove word has come it appears. What is this? Inside remove an item. So, there are a whole lot of commands where remove has something to do with it. So, that is how apropos works. Now we know that touch. Why do not we do apropos time stamp? Time. These are all these different commands where that has something to with time. Let us see if our touch is there. Look our touch is there. You already saw touch change file time stamps. Touch is just one of those that deal with time. Let us see apropos time stamps. What are all the files that deal with time stamps? Touch is just one amongst them. There are some LU times and different complicated usages. So, this is how one finds out. If you feel that you want to move a file from here to there or copy. I told you that CP is something for copying. Had I not told you, you wanted to do something and you want to know how to copy? Why do not we just see what is the command? Copy file 1 to file 2. This look copy is not a command. It is a copy command not found. So, now what is the command for copy now? The most expected name copy is not a command. So, why do not we do apropos copy? It says these are all the various files. These various commands which have something to do with copy. For example, I use scp much because I want to copy from my server to another server. But let us see if our CP itself is there in this big list. CP is there. The most from CP copy files and write. This is the one you were looking for. From all the explanations that is coming on the screen, you will see, this is the one I am looking for. This is how apropos is supposed to be used. Had I not told you that CP is a command to use, how would you have found out the copy command? Apropos copy. Apropos expects some file. Let us come back to this. Apropos expects some word here which need not be a command. But it will tell you all the commands which have something to do with this word. This word itself is an argument to this command. So, RM, DIR. Let us start seeing the use of the command RM very soon because after this we are going to see basic file handling. Let us see this. These are all the various files. Now, I am not interested in all these wrong extension file names we have created. File name is RM file 6.tech. You just remove it. So, in my computer, luckily it is asking me whether I really want to remove or not. At least I am used to being asked. Why? Because LSTAR.PDF has so many files. I would recommend that you go and work these commands only in some place where you do not mind losing the files. Especially when we are trying out RM command, it is important that you do not remove important files. So, there are so many PDF files. So, now touch. So, why do not we create some more? Touch junk1.PDF, junk2.PDF, one genuine, genuine or PDF, junk3.PDF. Sorry. The junk3 should have, for what I am saying to work, junk3 should have not double F but single F. So, many files. Let us dissolve the PDF files. Star means anything can be there. LS space star.PDF. Star is very special. File actually does not have star itself. Star stands for all possible letters there. At least one letter has to be there. So, these are all the PDF files. All the .PDF files in this directory. How did I so easily list out only the PDF files? LS star.PDF. So, suppose it turns out genuine.PDF is the only file I actually want. All these other junk files I want to remove. Am I going to say one by one RM space junk1.PDF, RM space junk2.PDF? We do not want that. What do we do? RM star.PDF. If we do this, it will just remove all the PDF files without asking you whether to remove or not, whether you really want to remove or not. So, at least I prefer that I am asked. AR3, yeah, I want to remove. File 4, file 5, yeah. Genuine? No. N for no. Yes. Yes. Yes. Yeah. Now, at least I prefer that I am asked. Your computer does not know that you prefer. It will not ask you. If you want to try this, it will just remove the PDF files. Yeah. Very, very cruelly. Very cruelly. It will not even ask you for confirmation. It will just remove it. Are you sure you do not want to be asked? So, why I got asked in your terminal, you did not get asked. That is because see, I have already been, I have already set all my parameters here the way I want. You are supposed to do. Let us see some more. Let us just create these files again. So, there are these files. LS star.PDF, yeah. If you try this, you will end up removing all the PDF files in one go without being asked. If you want to be asked, RM minus I, yeah. This is interactive. I for interactive. It will ask you one by one. Do you want this to be removed? No. Do you want this to be removed? Yes. Yeah. Now, it is really an interactive mode. Now, when I typed this command before without minus I option, also it was in interactive mode. But in your computer, it will not be in interactive mode. Is it in interactive mode? Somebody has already checked. So, you just went ahead and removed. Is it in interactive mode? Why? You set it like that? Yeah. If you put minus I option, of course, it will ask. Otherwise, it did not ask. So, you see, who is going to each time type minus I? I always want to be asked. Elias, let us see what RM has been Elias to. See, in my computer, I have very wisely Elias RM to RM minus I. Do not worry about Elias. It is not there in the syllabus. We will certainly try to have a discussion on that. If you are wondering why in your computer, it did not ask. In your computer, it did not ask, but just removed. But in my computer, it has asked, please note only in this particular computer, I have already Elias RM to RM minus I because I am concerned of removing important files. And whenever I work on another person's computer, I have to be extra careful because I have got used to being asked each time, yes or no, yes or no. So, please note only my computer, I have already Elias in your computer because it has not been Elias, it will just remove. Look at all these files, RM star. Star means not just those files without an extension. Star means star dot star in Linux, most importantly. Sorry, when I do RM star, it is asking one by one, but for you all, it will not ask. So, please do not do RM star unless you are in a directory where you do not mind removing everything. If you want to force everything, it has removed everything. See, it has removed everything except directories. Directries, it will not remove for your own safety. See, directories can have sub directories, sub sub directories. We do not want a situation where all of it is removed in one go unless you are really conscious about removing it. So, how do you remove directory then? RM DIR. This was already there in the slide. Now, DIR 4 has been removed. RM minus R also will work, R for recursive. Therefore, it was not there, it has removed without asking too much. But 99 was there and RM itself can remove if you give the R option. Now, you see LS, nothing is there. Really, is nothing there? Why do not we see LS minus A? Look dot, dots escaped. Luckily, when you do RM star, dot files have escaped. If you want to remove dot, then dot star. So, notice that this dot is important. When you do RM star, the dot files did not get removed, but file dot, any file dot, dot can all got removed certainly. When you do this, so now, now my RM, now my RM is not, has not been LS to anything, it is just like yours. There are these three, RM dot star. This is a directory, directory. So, dot file 3 has got removed certainly. Why do not we do RM dot star? Nothing is there anymore, minus RM, D I R, dot, this will remove this directory. So, these are the different ways of removing a directory. These are different ways of ensuring that there is some interaction, especially when you are removing multiple files using the star. Please always go through the interactive mode unless you really become a super user. Super user means like a route for various computers. If you are familiar for many years, I would recommend 1, 2 months are not enough. At least 1, 2 years of familiarity with Linux operating system from the command line, then I think you should go ahead and not use the interactive mode. So, let us go to this next topic, basic file handling. So, this is what we already started seeing, minus R, minus R is an option for recursive, minus I, we have already seen for interactive. Cp is a command for copying one to another. So, some things are escaping to the right, where the font size have been increased and what was earlier fitting in one line is no longer fitting. Please bear with us. All the files that are on Moodle are certainly the smaller font size. They will have the correct content. So, we will see very soon Cp command. Let us see what else files, what else commands to see before we shift to the command prompt. Here also minus I option is there because we could potentially be overwriting a file. When we copy one file from a source to a destination, that same file might already be there in the destination. Do you want to overwrite it? Do you want to be asked before overwriting? Minus I means interactive mode. Whenever there is a possibility of overwriting, it will just ask you, are you sure you want to overwrite? Minus R required for copying a directory along with all its sub-directories. This also we will see. Let us just see the slides, what all has to be done on the command prompt. Similarly, move. Let us just see all these files on the command prompt. This is a good time to ask if there are any questions. So, please if you have any questions, please ask your questions now either on chat or using the hand raise option. Are there any questions from Amar Jyoti college Kerala? Please ask questions. Otherwise we will ask. Amar Jyoti college Kerala, what is important is they had a tough time today because of the transport strike and in spite of that we see a big audience. So, we really thank you all for coming for this workshop in spite of the difficulties faced there. So, as other states should know, Kerala is on the front in all open source systems because of space organization with whom we have been dealing. Say in Joseph Parley also we would like to know. So, are there any questions in Amar Jyoti college Kerala before we connect to the St. Joseph college? Sir, actually we faced some problems due to hassle, but now almost all participants have reached yesterday itself. So, now more than 49 participants are here. So, I think here is no problem at all. Okay, good. We would like to take a question from you. No sir, no questions related to this. Okay. Thank you. Thank you very much. We will now connect to St. Joseph Kerala, where there is a question. Sir, you have explained about the command. So, you have explained about the command alias and it is, it will be applicable only when the session is available. Once the person, when the user logs out of the particular cell, will it be available? The alias command that we have set right now, will it be available once the person logs out of the cell which he is using or else when he takes a different cell? Yeah, this is an extremely important question. So, it is good to see all the others in that room. So, we heard your question, let me repeat the question. The question was LS command, like all other commands, are they available after you exit from the shell? So, as I said the word shell, command prompt, terminal are all the same. They are all the, where you type your commands and you can exit out of that command, out of the command prompt, then there is no place where you will type the command. So, this is all so called bash commands. What is a bash command? What other shells are there? All that we will see little more detail today and tomorrow. So, but I think this is a good time to stop for lunch. Okay, thank you.