[Music] There are two editors in Linux which work on the terminal environment and give you a visual appearance. One is called the pico, and the other is called the nano. So let us look at those. So, which pico? And if there is an editor like that, which nano? And sure enough, there's an editor like that. So we want to look at how these are implemented. So the pico editor, let us look at it. `less -l /usr/bin/pico`. And it looks like it's a symbolic link to something else. So now I want to go and look at what is that file. And now that is a symbolic link to something else. Let me look at what is that. And you can see that finally there is an application called nano. So when you are invoking pico editor in Ubuntu 20.04 at least, then actually you are only calling nano editor. Okay. And if you want to refer to these links, you could also use a command called `readlink -f /usr/bin/pico`, and it will tell you ultimately after

whatever number of hops what is the final executable it is pointing to. So read link is a very good utility, so you can actually know about it by using the man page. So it says resolved symbolic links or canonical file names has to be printed onto the screen. So that's a very useful utility that you may want to look at. So basically whether you run pico or nano, it's the same editor. So we may as well call it by the actual name, namely nano. So nano editor can be started now. Which file we would like to edit. So I want to use the nano editor to show you the so-called bash rc file. So my ls minus l dot rc. So this is a file which is not very big and it is used every time that you open the bash shell and certain commands that are written in this bash rc are going to be executed. So I don't want to make any mistake of changing it and then ending up with some errors. So what I would do is I will make a copy of it and then go on to change it.

would say copy dot bash rc, and then I want to copy to my home directory something else so I would say test dot dash rc. Okay, now I have a file which I can go and play with it. So I would use the nano editor to play with the test dot rc. So you can see that the nano editor looks fairly visual because you have a cursor that is blinking at the corner here. You can see that is blinking at the very first character, and it is also sensitive to the syntax. So any line in a shell script that starts with the hash is a comment. So you can see that it is showing the comments in a different color, and then there are some loops that we would actually understand in a moment which are applicable for a batch language, and then there are lines which are actually active so which are shown in white color, and you can also separate out the words from operators so they are also colored differently. Even options are being colored in differently, and so this is a shell script which is

being executed every time you run the bash executable. So all these commands are being run and they are basically preparing the environment for your bash shell to be there. Now here are some aliases which I have added to my bash rc so that when I type ll it would execute the command ls minus alf and when I type the command l it will run ls minus cf. So it is just my own way of shortening the commands by using aliases and you can put anything else in the end and those commands will always be applicable. So you could actually go on to edit now. So let us say I want to edit this file and first initially start with a command. So you can say edited on and then we can give a date. Okay so let us say on 20th Jan 2022. Okay so you can write already without any effort. This is like almost like a notepad of Windows environment and you can start making some changes. So I would also give one more comment in the end appended a line to test dot rc.

today okay. And then I want to also have something on the screen to be displayed. So let me have, say, echo then modified the rc. Okay, so I am writing a command there. So this command will be executed if you run that particular script. Now we have done some editing. We were able to go up or down, left or right using the keys. And we are able to add text directly. And how do we save this? So, control o would write the file to whatever file name you have given. So that is the file which we open. So we will overwrite those content using this command, ctrl o. And once you have already written, then you can come out using ctrl x. Now you can go ahead and look at the file once more using, let us say, less command. And you can see that at the bottom, you can make out the changes that you have just now made. So you can see that the editing we have done just now is all available in the file. So it was successful editing of the file. So you could use nano to edit files quite.

comfortably. And some of these features, let us just review the commands that you can use to explore the nano editor. So here are some features of the nano editor that we have just now looked at. So you could save the file using control + s. You could write the contents of the buffer into the file using ctrl + o. And you could also read a different file content into the current file using ctrl + r at the current position of the cursor. And control + x, you could come out of the window if you have made changes and you want to come out. It would always prompt you whether you want to save the changes or not. So that way, it is quite user-friendly. And you have various editing features to cut and paste stuff. You also have the ability to search and replace using control + q or alt + q. And then you also have the ability to delete text either character by character or word by word or line by line. And at any point, you can also look at what is the position of the current cursor with respect to the whole file. And you could also look at this help.

right on the screen, and there are various ways by which you can move around within the nano editor. Either character by character, or word by word, or going to the start of the line, or end of the line, upwards or downwards, even block by block in terms of text blocks, or even page by page. And also the very first claim or the last line. And you also have an ability to use features which are quite interesting for programmers. For example, you could actually use alt+n to make the line numbers visible or not, like a toggle. And that's quite useful when you are writing code, so you do not have to have the line numbers always visible because it seems to clutter the window, but you could have them switched on whenever you like to refer. So that way, nano is a very powerful and quite a good editor. And look at the link that I have provided here to have a copy of the cheat sheet and print it out and practice all the commands so that you make yourself comfortable with this editor. And it is pretty good that you can actually use it for most of your

programming needs in a terminal environment. People say that the most complex editor in the Linux world is vi. That is because it has acquired so many features over the years that the list of commands itself runs into several pages. So, I will show you some commands that are very useful for you to get going in the vi editor. Because if you can make yourself comfortable with this editor, then you almost do not need to know any other editor in any other environment. Because the newly improved version of the vi editor, called the vim, is available for all operating systems. So, there are three major modes of vi editor. It is a command mode, which by default is open when you open the file. And by pressing escape symbol, you can go into the command mode. You can press multiple times because it doesn't hurt. So, escape being the last character on the left side of the keyboard, left top. So, you can keep pressing that to ensure that you are in the command mode. And if you are in the insert mode, then what you type will actually go into the text buffer or into the file.

and there are some characters which trigger the insertion. So, 'i' (small i) would insert the characters from the current position of the cursor, and 'o' will insert a new line, and 'a' will also insert text as an appending. Therefore, all these characters 'i', 'o', 'u' both the capital and the small would actually start the insert mode. And at the bottom of the window in the vi editor, you will also see a help that says that you are right now in insert mode, so whatever you type will actually go into the file. So, it is like an alert. And when you press escape and come out of the insert mode into the command mode, you could also enter what is called x mode. That is in the command mode, you can press colon and then the cursor will be going to the bottom of the screen, and there you can write some commands which are same as the x commands or the add commands we have seen just now. And so that is called the x mode. So, there are three modes and we will see them right now as a demonstration. So here are some very basic commands.

that you need to be familiar so very often when you get into an editor. First thing you have to figure out is how to get out of the editor. So w would actually write the contents of the file and x would write save the contents and then quit. W q would actually save and quit, so is the same as x. Sometimes you have not made any change so you can just quit without making any changes to the file by using q. And if you have actually made some changes but you do not want to save them, so you can quit by pressing colon, queue exclamation, so that you are coming out by force without writing any changes in the buffer to the original file. Now navigation within the file in a visual mode is done using multiple keys. So you can use the arrow keys, no problem they will work. But sometimes if the terminal has not been configured properly, particularly for non-English keyboards, then you can always rely on the h, k, l, and j characters for navigating within the text file. So I have put an underline here for j because on the keyboard you

can feel the j character, and you see that there is a small line below it, so that is a guide for your finger so you can place it on j. Then your middle finger will be on k, and the ring finger will be on l. So that is usually the way that va editors would actually start working, okay? And the k would actually take you upwards in the screen. After some practice, you start getting used to it, so you don't need the arrow keys at all, but they also work if there's no problem with the settings of the terminal. The backspace would remove the text only if you are in the insert mode, but if you are in the command mode, then the backspace is the same as moving to the left. Similarly, if you press the space bar, if you are in the insert mode, it will insert a space, but if you are in the command mode, it would actually take the cursor to the right side. So watch out that what you press will be interpreted differently depending upon which mode you are, and by default, you are in the

command mode. And you have to always watch out at the bottom of the screen whether you are in the insert mode or in the command mode. So here are some simple commands. Control f and control b will take the screen forward or backward so you can move the text within the window. And control d and control u would actually move the text by half a screen only so that what you are reading is still within the viewport but some more lines are available for you to read and edit. And sometimes let us say you have made some changes and in a very slow terminal you would like to refresh the screen. Control l would do that the same thing as what you do on the shell. Control r would also do it by deleting some characters that you have done with some commands. So if the terminal was not fast enough then you can actually ask it to refresh it for you by pressing these keys. You can actually navigate within the file quite well using va so you could go to the beginning of the line by pressing 0 and end of the line pressing dollar.

beginning of the word following the cursor with the w. Beginning of the preceding word by b and by using colon you can also go to a specific line by giving the number there. So you can give either 0 or 1 to go to the first line and then any number to go to that particular number of line. And you could also use the capital g to go to a specific line by using 1g 2g etc. And g alone would take you to the end of the file. And that's the same as dollar with a colon in front. So you can go to the x mode and press dollar. It will go to the last line which is same as what we have seen in the add editor. And it will also work in vi. And there are some commands like how to replace a single character under the cursor using r. And then capital r would replace indefinitely till you press escape. And how to change a word. So you can cw change the word. And you can keep typing the new word.

until you press escape, okay. And if you want, you can change multiple words by using c n w n. N is the number, so c 2 w would mean the next two words would actually be changed by what you type. And capital c would actually change the text from the cursor all the way to the end of the line. And what you enter up to pressing the escape key would be inserted into the particular line. And the entire line can also be changed by using the cc command. So let us try this out in a demo to understand how they work. You could also do some minute editing by using x to delete a character exactly at the cursor position. And you can also delete a particular number of characters by using nx. Let us say 5 characters I want to delete, so 5 x will delete exactly 5. And dw would delete the word. D2w would delete two words. Capital d would delete from the cursor to the rest of the line. And dd would delete the whole line. And let us say 10 dd would delete 10 lines.

from the current cursor position, and you could do copy-paste. So y is for yanking. The yanking is like, you know, grabbing or taking away. So y is used to copy stuff. So y y would copy the current line, and 5 y y would copy 5 lines. 10 yy would copy 10 lines. So you can copy how many other lines from the cursor position, and then you can paste them anywhere in the buffer by using the cursor to move around. And then at that particular position, if you press a p, then below that line, whatever you have copied will be pasted. And when you think you have done a mistake, you can always press u and then undo the change that you have done. And you can search for whichever line contains a particular pattern using slash and then a string, which is a regular expression. And you can do the forward searching or backward searching by using either forward slash or question mark followed by the regular expression for searching. And once you have started searching, you can either move forward in identifying those

locations or backward by using either small n or capital n. So let us look at a demo of the va editor. Now I have enabled the display of keys that I have pressed at the bottom of the screen so that what I press will be visible to you. So you will see at the bottom of the screen. So I am now going to put ls, okay, and then enter. I am seeing the text here. Now I want to edit the test dot text. So v i d e s t dot text. So you can see that I have pressed two times a backspace. That is also visible, okay, and now you can see that I can start navigating. The blinking cursor would tell you where I am. So I am using the arrow keys. So I press k and I am going up. I press j I am going down. I press j once more I am going down. K I go up. I press j I am going down. I press l I am going to the right side down the line. So you can see I press multiple times.

and you can see how many times i am pressing and how the cursor is moving. Okay, and now I press h. I am going in the opposite direction. Okay, I am going down, I am going up, k k up, j down, l to the right side, h to the left side. Okay, and now the cursor is at capital a so I press 0 and the cursor is taken to the beginning of the line. Now I press dollar, I go to the end of the line. Okay, now I press colon and then 1 enter and it will take me to the first line. I press shift g and it will take me to the last line. I press a three capital g, it will go to the third line. If I want to add some text, I can press i and then I will be in insert mode. So you can watch what is happening. I press i and now you see at the bottom there is an insert mode that is displayed and now whatever I type would actually enter into the buffer. So I can right now so I can type something and it all goes

into the text now. I am still in the insert mode, so if I want to come out so that I can move around, I press escape. And then now I am in the command mode again. So now if I press anything, so you see that I am just navigating now. Okay, so watch out, for example, here again. Okay, I press a, I am in the insert mode again. So I can say, Welcome to line editor. You see commands. Let us say escape. Now I come out, then I'm able to again navigate. Now let us say I do not like this line, so I want to delete it. So I press double d, and the line is gone, but it's in the buffer as a memory. So I can print it after the current position. So I can go up, and after this current position, I want to press p, and then whatever line I have deleted has come there. Now this editing, whatever I have done, I can actually save and then come out. So I can confirm that I am in the command mode. So I press escape once or twice to ensure that I am in the command.

mode press colon and then i am now in the x mode. In the x mode, if i press a w and q, that it will write the file and then save and come out. I am coming out of the va editor into the shell. Now i have done some editing, so let me just check are they visible, and you can see that i have done some change and that is also now visible. Ok, so line 2 has come here, which we done just now in the text editor. So let me now go back again. Okay, now i will start doing some changes, so i will go to the first line colon 0 go to the first line, and i press d and w to delete the current word. So d w i deleted the current current word. Press escape. I am done with that work. Now i go down, and again i press d and w. I can delete that word. D and w press escape. I am back to command mode. What i now do is that i delete two words. 2d w, and you can see that two words have been

Deleted escape and back to command mode. Now I want to delete only one character. I can do that with x. Okay, one character. I can delete one more character. I can delete. Okay, you can delete character by character using x. Press escape and then navigate. You could have to delete by word by word. So dw, we delete the word, and escape will come out. And I can also delete character by character x x x. So character by character also you can delete. And you can insert at any position. So you can navigate and start writing. So I can navigate to a particular position and then press i. And I can insert text at that particular position. I am now typing line 3. Okay, and if I am done with editing for now, I press escape. And I can start again going to navigate. Okay, so go to the beginning of the line using pressing 0. And then press i to start typing line - 4 space. And then escape. I am now in command mode. When I am in command mode, if I press space, I am actually going to go right side.

zero and dollar. Okay, now I can actually also see which file I am in right now. So, `pwd` was the command that we used to know what the file name is. So, it also shows that even in vi editor. And there are some nice features where you can actually see the visual nature of this editor. So, I go to the ex mode by escape followed by shift colon so that I am in the ex mode. And I type a command like `set numbers`. So, `:set number` and it will actually show me the line number, which is very convenient for source codes. And if I don't want to see it, I can say `:set nonumber` and then that is not visible anymore. Okay, now I want to repeat whatever text I have in my buffer by copying and pasting. So, I can go to the first line I want to copy, three lines. So, I can press `3yy`. I press `yy`, so three lines have been copied or yanked. Now I can paste them at a particular position. So, I go to the last line and say

p and then they will be pasted. Okay, now again I go to the first line one and I can now copy just two lines. So if you press y and enter, it's same as pressing 2 yy. So I press y and enter so two lines will be copied and I come to the bottom and press p to copy and paste. So I'm copying and pasting two lines. So y enter is same as pressing two y. Okay, now I have done all these so you can see that there is something in the front line one line two, etcetera, but this line doesn't have it. So I want to change it. So cw will change the word. So cw changing the word and until time that I type something. So I would type it as a line-hyphen-phi and then I press escape. So now the escape means changing is over. I come here and I want to remove the space by pressing x and that space is removed. Again press escape, come into the command line mode so you can see that I

am now cleaning it up and using the navigation, as well as the commands of va editor. Now the ed editor has such and search and replace features, which we can also use. So let us see the numbers. So from the first to the fifth line, I want to apply that search and replace features. So let us try that out. From the first to fifth line, I want to substitute. What do I want to substitute? I want to substitute a line with a capital word. Okay, and g is for a global substitution. Without that, only one substitution. So I just leave it as one substitution, first occurrence. Okay, and you see that the first five lines, I have changed the word from small line to capital line. And you see that there's one more line here, which would be changed here also, which would be changed if I had a g operator. So let us try that out. I undo the change right now I have made with u and now again, I will type the x command mode. So 1 comma phi substitute line with capital line and g. So which means multiple times it

occurs in the line. Then, it would be doing multiple substitutions. So, watch out what is happening to this word, this word, and this word here because they are going to be targeted by the g. And you see that those have been also modified along with the first occurrence of line in the beginning of each of these lines. Now, I could actually do for the entire buffer also if I wish. So, wherever hello is coming, I want to change it to some other word, let us say hola. So, I can actually do like this. Percentage percentage means the entire buffer, okay, that's what we discussed in the editor. So, percentage substitute hello with, let us say, hola. And everywhere it should be affected. So, you see that wherever hello is there, it will be replaced with hola. Now, this is something that is very useful for code because I want to change the name of a particular variable. So, wherever that variable name is occurring, it has to be replaced. And so, this is kind of a useful feature for that. And line numbers are being displayed.

can just set no numbers, and the clutter is now removed, so you can see that this is how we go around making simple additions or deletions, copy-paste, or search and replace in a ba editor. So I want to come out without saving it, so there is always an alert for that. So I can say that, OK, save and come out, and then we are out of that. Now cat test dot text, whatever text has been typed, is there.

Command line editors - Part 02

Scripts