Difference between revisions of "BOSS-Linux/C2/Working-with-Regular-Files/English-timed"
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|To compare 'file1' and 'file2', we would write '''cmp space file1 space file2.''' | |To compare 'file1' and 'file2', we would write '''cmp space file1 space file2.''' | ||
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|If the two files have exactly the same contents then no message would be shown. | |If the two files have exactly the same contents then no message would be shown. | ||
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|If there are differences in their contents then the location of the first mismatch will be printed on the '''terminal'''. | |If there are differences in their contents then the location of the first mismatch will be printed on the '''terminal'''. | ||
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|Type: '''cat sample1''' and press '''Enter'''. It contains the text- '''"This is a Linux file to test the cmp command"'''. | |Type: '''cat sample1''' and press '''Enter'''. It contains the text- '''"This is a Linux file to test the cmp command"'''. | ||
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|The other file '''sample2''' will contain the text and to see that we will type: '''cat sample2''' and press '''Enter'''. | |The other file '''sample2''' will contain the text and to see that we will type: '''cat sample2''' and press '''Enter'''. | ||
Latest revision as of 11:53, 24 March 2017
| Time | Narration |
| 00:00 | Welcome to this spoken tutorial on working with regular files in Linux. |
| 00:07 | Files and directories together form the Linux File System. |
| 00:13 | In a previous tutorial, we have already seen how to work with directories. You can find the tutorial at this website. |
| 00:25 | In this tutorial, we will see how to handle regular files. |
| 00:32 | We have already seen in another tutorial how we can create a file using the cat command. For details, please visit this website. |
| 00:46 | Let us see how to copy a file from one place to another. For this, we have the cp command. |
| 00:56 | Let us see how the command is used. |
| 01:00 | To copy a single file, we type: cp space one or more of the [OPTIONs]... space the name of the SOURCE file space the name of the destination file. |
| 01:15 | To copy multiple files at the same time, we write: cp space one or more of the [OPTIONs]...the name of the SOURCE files that we want to copy and the name of the destination DIRECTORY in which these files would be copied. |
| 01:34 | Let us now see an Example. First we open a terminal. |
| 01:42 | We already have a file named "test1" in our home directory. |
| 01:49 | To see what is in test1, we type $ cat space test1 and press Enter. |
| 02:00 | As we can see the content of test1 is shown. Now if we want to copy it into another file called test2, we would write:
$ cp space test1 space test2 and press Enter. |
| 02:22 | Now the file has been copied. |
| 02:25 | If 'test2' doesn't exist, it would be first created and then the content of 'test1' will be copied to it. |
| 02:35 | If it already existed then it would be silently overwritten. To see the copied file, type:
cat test2 and press Enter. |
| 02:52 | We can also copy files from and to different directories. For example-
type: cp space /home/anirban/arc/demo1 which is the name of the file that we want to copy, space /home/anirban/demo2 and press Enter. |
| 03:32 | What this will do is that it will copy the file 'demo1' from source diretory- /home/anirban/arc/ to the destination directory- /home/anirban; it will copy to a file whose name is demo2. |
| 03:51 | To see that the 'demo2' is there, type: ls space /home/anirban and press Enter. |
| 04:07 | And as you can see, here is demo2. |
| 04:12 | Before moving ahead, let us clear the screen. |
| 04:17 | If you want the file to have the same name in the destination directory, you may not even mention the file name. For example- |
| 04:27 | Type: cp space /home/anirban/arc/demo1 space /home/anirban/ and press Enter. |
| 04:55 | This will again copy the file 'demo1' presenting the /home/anirban/arc/ directory to /home/anirban directory to a file whose name will be 'demo1' as well. |
| 05:11 | As before, to see the demo1, type: ls/home/anirban and press Enter. |
| 05:25 | And, as you can see the demo1 file is there. |
| 05:30 | Again, before moving ahead, let us clear the screen. |
| 05:37 | Another instance when we do not need to give the destination file name is when we want to copy multiple files. |
| 05:44 | We assume that we have three files named test1, test2, test3 in our home directory. |
| 05:53 | Now, we type: cp space test1 space test2 space test3 space /home/anirban/testdir and press Enter. |
| 06:16 | This will copy all the three files named test1,test2 and test3 to the directory /home/anirban/testdir without changing their names. |
| 06:30 | To see that these files have actually been copied, we will type: ls space /home/anirban/testdir and press Enter. |
| 06:52 | As you can see test1,test2 and test3 are present in this directory. |
| 06:58 | There are many options that go with cp. Here, we will see only the most important of them. |
| 07:07 | Let us first go back to the slides. |
| 07:12 | Among the options, -R (The capital R) is an important one. It causes recursive copying of an entire directory structure. |
| 07:23 | Let us see an example. |
| 07:27 | Let us try to copy all the contents of the 'testdir' directory to a directory called 'test'. |
| 07:36 | For that, we would type: cp space testdir slash test and press Enter. |
| 07:51 | As you can see from the output message, |
| 07:54 | normally we cannot copy a directory having some contents directly with the 'cp command. |
| 08:02 | But using the -R (mius R ) option we can do this. |
| 08:07 | Now we type: cp space -R(minus capital R) space testdir/ test and press Enter. |
| 08:25 | The files have now been copied. To see that the test directory actually exists, type: ls and press Enter. |
| 08:37 | As you can see, the 'test' directory exists. Let us clear the screen. |
| 08:45 | To see the contents inside 'test', type: ls test and press Enter. |
| 08:57 | You can see the contents of the 'test' directory. |
| 09:01 | Now, we go back to the slides. |
| 09:05 | We have seen if a file is copied to another file that already exists, the existing file is overwritten. |
| 09:14 | Now, what if we inadvertently overwrite an important file? |
| 09:19 | To prevent anything like this to occur, we have the '-b' option. |
| 09:25 | This makes a backup of each existing destination file. |
| 09:32 | We can also use the -i(interactive)option. This always warns us before overwriting any destination file. |
| 09:43 | Now, let us see how the mv command works. |
| 09:47 | This is used for moving files. Now how is that useful? |
| 09:53 | It has two major uses. |
| 09:57 | It is used for renaming a file or directory. |
| 10:00 | It also moves a group of files to a different directory. |
| 10:05 | mv is very similar to cp which we have already seen. So, let us quickly see how mv can be used. |
| 10:17 | We open the terminal and type: mv space test1 space test2 and press Enter. |
| 10:32 | This will rename the file named test1 which was already present in the home directory to a file named test2. |
| 10:40 | If test2 already existed then it would be overwritten silently. |
| 10:49 | If we want our warning before the file is overwritten, |
| 10:54 | we can use the -i option with the mv command. |
| 10:59 | Say we have another file named 'anirban'. This file we also want to renew as 'test2'. |
| 11:08 | We will type: mv space -i space anirban space test2 and press Enter. |
| 11:21 | As you can see, a warning is provided asking whether test2 should be overwritten or not. |
| 11:30 | If we press 'y' and then press Enter, the file would be actually overwritten. |
| 11:37 | Like cp, we can use mv with multiple files but in that case the destination should be a directory. |
| 11:47 | Before moving ahead, let us clear the screen. |
| 11:52 | Suppose we have 3 files named abc.txt, pop.txt and push.txt in our home directory. |
| 12:03 | To see their presence, type ls and press Enter. |
| 12:09 | Here are the files pop.txt, push.txt and abc.txt. Let us clear the screen. |
| 12:24 | Now we want to move these three files to a directory called testdir. |
| 12:32 | What we need to do is, type: mv space abc.txt pop.txt push.txt and then the name of the destination folder which is testdir and press Enter. |
| 12:58 | To see them, type: ls testdir and press Enter. |
| 13:06 | You can see the files abc, pop and push.txt. |
| 13:14 | Now, let us see some options that go with mv'. Let us first go back to the slides. |
| 13:22 | The '-b' or '–backup' option is present with the mv command. It will backup every file in the destination before it is overwritten. |
| 13:34 | The '-i' (minus i) option that we have already seen, warns us before overwriting any destination file. |
| 13:44 | The next command we will see is the rm command. This command is used for deleting files. |
| 13:52 | Go back to the terminal and type: ls testdir. |
| 14:00 | We can see a file name 'faq.txt' present. Say we want to delete it. |
| 14:09 | For this, we type: rm space testdir/faq.txt and press Enter. |
| 14:23 | This command will remove the file 'faq.txt' from the /testdir directory. |
| 14:32 | To see that the file has been actually removed or not, let us again press ls space testdir and press Enter. |
| 14:47 | We can no longer see the file 'faq.txt'. |
| 14:51 | We can use the rm command with multiple files as well. |
| 14:57 | The testdir directory contains two files 'abc2' and 'abc1.' |
| 15:03 | Suppose, we want to remove these files- 'abc1' and 'abc2.' |
| 15:09 | For this, we would type: rm space testdir/abc1 space testdir/abc2 and press Enter. |
| 15:31 | This removes the files 'abc1' and 'abc2' from testdir directory. |
| 15:39 | To see that they have been removed, type: ls space testdir again. You can no longer see abc1' and abc2. |
| 15:53 | Let us clear the screen before moving ahead. |
| 15:58 | Now, let us go back to the slides. |
| 16:02 | Let us summarize what we just said. |
| 16:04 | That is, to delete a single file we write rm and then the name of the file. |
| 16:11 | To delete multiple files, we write rm and the name of the multiple files that we want to delete. |
| 16:19 | Now, let us look into some of the options of the rm command. |
| 16:24 | Sometimes a file is write protected. Using rm will not delete the file then. In this case, we have the -f option which can be used to force delete a file. |
| 16:41 | The other common option is the -r option. Let us see where these option are useful? |
| 16:52 | Let us switch back to the terminal. |
| 16:57 | rm command is not normally used for deleting directories. For that, we have the rmdir command. |
| 17:05 | But rmdir command normally deletes a directory only when it is empty. |
| 17:12 | What if we want to delete a directory that has a number of files and sub-directories inside? |
| 17:19 | Let us try the rm command to do this. |
| 17:23 | Let us type rm and the directory that we want to delete which is testdir and press Enter. |
| 17:31 | From the output message, we can see that we can not use the rm directory to delete 'testdir'. |
| 17:39 | But if we combine the '-r' and '-f' options then we can do this. |
| 17:47 | Press rm -rf testdir and then press Enter. |
| 18:00 | Now, the testdir directory has been successfully deleted. |
| 18:06 | Let us now go back to the slides to study the next command- |
| 18:11 | the cmp command. |
| 18:13 | Sometimes we need to check whether two files are same. If they are same then we may delete one of them. |
| 18:22 | Also we may want to see whether a file has changed since the last version. |
| 18:28 | For these and many other purposes, we can use the cmp command. |
| 18:33 | It compares two files byte by byte. |
| 18:38 | To compare 'file1' and 'file2', we would write cmp space file1 space file2. |
| 18:47 | If the two files have exactly the same contents then no message would be shown. |
| 18:55 | Only the prompt will be printed. |
| 18:58 | If there are differences in their contents then the location of the first mismatch will be printed on the terminal. |
| 19:10 | Let us see how cmp works. We have two files named sample1 and sample2 in our home directory. |
| 19:19 | Let us see what they contain? |
| 19:22 | Type: cat sample1 and press Enter. It contains the text- "This is a Linux file to test the cmp command". |
| 19:34 | The other file sample2 will contain the text and to see that we will type: cat sample2 and press Enter. |
| 19:44 | It will contain the text- "This is a Unix file to test the cmp command". |
| 19:50 | Now we would apply the cmp command on these two files. |
| 19:55 | We will write: cmp space sample1 space sample2 and press Enter. |
| 20:08 | As we can see, the first difference between the two files sample1 and sample2 is pointed out. |
| 20:16 | Let us clear the screen before moving ahead to the next command. |
| 20:22 | The next command we will see is the wc command. |
| 20:26 | This command is used to count the number of characters, words and lines in a file. |
| 20:34 | We have a file named "sample3" in our home directory. |
| 20:39 | Let us see its contents. For that, we will type: cat space sample3 and press Enter. |
| 20:50 | This is the content of sample3. |
| 20:54 | Now, let us use the wc command on this file. |
| 20:59 | For that, we would write wc space sample3 and press Enter. |
| 21:10 | This command points out that the file has 6 lines, 67 words and 385 characters. |
| 21:22 | These were some of the commands that help us to work with files. |
| 21:27 | There are many more commands. Moreover each of the command that we saw has many other options. |
| 21:36 | I encourage you to see more about them using the man command. |
| 21:44 | This brings me to the end of this tutorial at last. |
| 21:48 | Spoken Tutorial Project is a part of the "Talk to a Teacher" project, supported by the National Mission on Education through ICT, MHRD, Government of India. |
| 22:02 | More information on the same is available at the following link- http://spoken-tutorial.org/NMEICT-Intro. |
| 22:18 | This is Anirban, signing off . Thanks for joining. |
