Difference between revisions of "Linux/C2/Working-with-Regular-Files/English-timed"

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Revision as of 11:05, 9 March 2015

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.
00:31 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.
00:55 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 (DEST).
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 eg.First we open a terminal.
01:42 We already have a file named 'test1' in /home/anirban/arc/
01:49 To see what is in test1, we type: 
$ cat 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 test1 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 You can also copy files from and to different directories. For example,

type: $ cp /home/anirban/arc/demo1 /home/anirban/demo2 and press Enter.

03:31 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 name 'demo2'.
03:51 To see that the 'demo2' is there, type:

ls space /home/anirban and press Enter.

04:13 We scroll up as you can see here is 'demo2'.
04:19 Before moving ahead let us clear the screen.
04:25 If you want the file to have the same name in the destination directory, you may not even mention the file name. For example
04:35 Type $ cp /home/anirban/arc/demo1 /home/anirban/ and press Enter.
05:03 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.
05:20 As before, to see the 'demo1' type:

ls/home/anirban and press Enter.

05:33 Here again we would scroll up and as you can see the 'demo1' file is there.
05:40 Again, before moving ahead let us clear the screen.
05:48 Another instance when we do not need to give the destination file name is when we want to copy multiple files.
05:56 We assume that we have three files named test1, test2, test3 in our home directory.
06:04 Now we type: $ cp test1 test2 test3 /home/anirban/testdir and press Enter.
06:27 This will copy all the three files test1,test2 and test3 to the directory /home/anirban/testdir without changing their names.
06:41 You see that these files have actually been copied. We will type: ls /home/anirban/testdir and press Enter.
07:03 As you can see test1, test2 and test3 are present in this directory.
07:10 There are many options that go with cp. Here we will see only the most important of them.
07:18 Let us first go back to the slides.
07:23 Among the options, -R is an important one. It causes recursive copying of an entire directory structure.
07:33 Let us see an example.
07:38 Let us try to copy all the contents of the 'testdir' directory to a directory called 'test'.
07:48 For that, we would type: cp testdir/ test and press Enter.
08:02 As you can see from the output message,
08:06 normally we cannot copy a directory having some content directly with cp command.
08:14 But using the -R option we can do this.
08:19 Now we type: cp -R testdir/ test and press Enter.
08:36 The files have now been copied. To see that the 'test' directory actually exists, type ls and press Enter.
08:47 As you can see, the 'test' directory exists. Let us clear the screen.
08:57 To see the contents inside 'test', type: ls test and press Enter.
09:08 You can see the contents of the 'test' directory.
09:13 Now we go back to the slides.
09:16 We have seen if a file is copied to another file that already exists, the existing file is overwritten.
09:25 Now what if we inadvertently overwrite an important file?
09:30 To prevent anything like this to occur, we have the -b option.
09:36 This makes a backup of each exiting destination file.
09:41 We can also use the -i (interactive)option, this always warns us before overwriting any destination file.
09:54 Now let us see how the mv command works.
09:59 This is used for moving files. Now how is that useful?
10:04 It has two major uses.
10:07 It is used for renaming a file or directory.
10:11 It also moves a group of files to a different directory.
10:17 mv is very similar to cp which we have already seen. So let us quickly see how mv can be used.
10:29 We open the terminal and type: $ mv test1 test2 and press Enter.
10:43 This will rename the file named 'test1' which was already present in the home directory to a file named 'test2'.
10:52 If 'test2' already existed then it would be overwritten silently.
11:00 If we want our warning before the file is overwritten,
11:05 we can use the -i option with the mv command.
11:10 Say we have another file named 'anirban'. This file we also want to renew as 'test2'.
11:20 We will type: mv -i anirban test2 and press Enter.
11:32 As you can see, a warning is provided asking whether 'test2' should be overwritten or not.
11:41 If we press y and then press Enter, the file would be actually overwritten.
11:49 Like cp we can use mv with multiple files but in that case the destination should be a directory.
11:58 Before moving ahead let us clear the screen.
12:03 Suppose we have 3 files named abc.txt, pop.txt and push.txt in our home directory.
12:14 To see there presence, type ls and press Enter.
12:21 Here are the files pop.txt, push.txt and abc.txt Let us clear the screen.
12:36 Now we want to move these three files to a directory called 'testdir'.
12:46 What we need to do is type: mv abc.txt pop.txt push.txt and then the name of the destination folder which is 'testdir' and press Enter.
13:14 To see them, type ls testdir and press Enter.
13:20 You can see the files abc, pop and push.txt.
13:27 Now let us see some options that go with mv. Let us first go back to the slides.
13:37 Then -b or –backup option is present with the mv command. It will backup every file in the destination before it is overwritten.
13:48 The -i option that we have already seen warns us before overwriting any destination file.
13:58 The next command we will see is the rm command. This command is used for deleting files.
14:06 Go back to the terminal and type: ls testdir
14:15 We can see a file name 'faq.txt' present. Say, we want to delete it.
14:23 For this, we type:

$ rm testdir/faq.txt and press Enter.

14:37 This command will remove the file 'faq.txt' from the '/testdir' directory.
14:46 To see that the file has been actually removed or not, let us again press:ls testdir and press Enter.
15:00 We can no longer see the file 'faq.txt'.
15:05 We can use the rm command with multiple files as well.
15:10 The 'testdir' directory contains two files 'abc2' and 'abc1'.
15:17 Suppose we want to remove these files abc1 and abc2.
15:23 For this, we would type: rm testdir/abc1 testdir/abc2 and press Enter.
15:45 This removes the files 'abc1' and 'abc2' from 'testdir' directory.
15:53 To see that they have been removed, type ls testdir again. You can no longer see 'abc1' and 'abc2'.
16:07 Let us clear the screen before moving ahead.
16:14 Now let us go back to the slides.
16:18 Let us summarize what we just said?
16:20 That is, to delete a single file we write rm and then the name of the file.
16:27 To delete multiple files we write rm and the name of the multiple files that we want to delete.
16:34 Now let us look into some of the options of the rm command.
16:40 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.
16:57 The other common option is the -r option. Let us see where this options are useful?
17:07 Let us switch back to the terminal.
17:12 rm command is not normally used for deleting directories, for that we have the rmdir command.
17:21 But rmdir command normally deletes a directory, only then it is empty.
17:27 What if we want to delete a directory that has a number of files and subdirectories inside.
17:35 Let us try the rm command to do this.
17:38 Let us type rm and the directory that we want to delete which is 'testdir' and press Enter.
17:47 From the output message we can see that we can not use the 'rm directory' to delete 'testdir'.
17:55 But if we combine the -r and -f option then we can do this.
18:03 Press: rm -rf testdir and then press Enter.
18:16 Now the 'testdir' directory has been successfully deleted.
18:22 Let us now go back to the slides to study the next command.
18:27 The cmp command.
18:29 Sometimes we need to check whether two files are same. If they are same then we may delete one of them.
18:37 Also we may want to see whether a file has changed since the last version.
18:44 For these and many other purposes we can use the cmp command.
18:49 It compares two files byte by byte.
18:54 To compare file1 and file2, we would write cmp file1 file2.
19:03 If the two files have exactly same content then no message would be shown.
19:11 Only the prompt will be printed.
19:14 If there are differences in their contents then the location of the first mismatch will be printed on the terminal.
19:25 Let us see how 'cmp' works. We have two files named 'sample1' and 'sample2' in our home directory.
19:35 Let us see what they contain?
19:38 Type cat sample1 and press Enter. It contains the text “This is a Linux file to test the cmp command”
19:50 The other file 'sample2' will contain the text and to see that we will type cat sample2 and press Enter.
20:00 It will contain the text “This is a Unix file to test the cmp command.”
20:06 Now we would apply the cmp command on these two files.
20:11 We will write: cmp sample1 sample2 and press Enter.
20:23 As we can see, the first difference between the two files 'sample1' and 'sample2' is pointed out.
20:32 Let us clear the screen before moving ahead to the next command.
20:38 The next command we will see is the wc command.
20:43 This command is used to count the number of characters, words and lines in a file.
20:50 We have a file named 'sample3' in our home directory.
20:56 Let us see its contents. For that, we will type: cat sample3 and press Enter.
21:05 This is the content of sample3.
21:10 Now let us use the wc command on this file.
21:14 For that, we would write: wc sample3 and press Enter.
21:25 The command points out that the file has 6 lines, 67 words and 385 characters.
21:38 These were some of the commands that help us to work with files.
21:43 There are many more commands. Moreover each of the command that we saw has many other options.
21:51 I encourage you to see more about them using the man command.
22:00 This brings me to the end of this tutorial at last.
22:04 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.
22:17 More information on the same is available at the following link http://spoken-tutorial.org/NMEICT-Intro.
22:34 This is Anirban signing off . Thanks for joining.

Contributors and Content Editors

Gaurav, Minal, Pratik kamble, Sandhya.np14, Vasudeva ahitanal

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