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

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Revision as of 13:30, 9 May 2014

Visual Cue Narration
0:00 Welcome to this spoken tutorial on working with regular files in Linux.
0:07 Files and directories together form the Linux File System.
0:13 In a previous tutorial we have already seen how to work with directories. You can find the tutorial at this website.
0:25 In this tutorial we will see how to handle regular files.
0:31 We have already seen in another tutorial how we can create a file using the cat command. For details please visit this website.
0:46 Let us see how to copy a file from one place to another. For this we have the cp command.
0:55 Let us see how the command is used.
1:00 To copy a single file we type 
cp space one or more of the [OPTION]... space the name of the SOURCE file space the name of the destination file DEST.
1:15 To copy multiple files at the same time. 
We write cp space one or more of the [OPTION]...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.
1:34 Let us now see an Eg.First we open a terminal.
1:42 We already have a file named test1 in /home/anirban/arc/
1:49 To see what is in test1.We type 
$ cat test1 and press enter.
2:00 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.

2:22 Now the file has been copied.
2:25 If test2 doesn't exist it would be first created and then the content of test1 will be copied to it.
2:35 If it already existed then it would be silently overwritten.To see the copied file type

$ cat test2 and press enter.

2:52 You can also copy files from and to different directories.For example.


type

$ cp /home/anirban/arc/demo1 /home/anirban/demo2 and press enter.

3:31 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.
3:51 To see that the demo2 is there type

ls space /home/anirban and press enter.

4:13 We scroll up as you can see here is demo2.
4:19 Before moving a head let us clear the screen.
4:25 If you want the file to have the same name in the destination directory, you may not even mention the file name.For example
4:35 Type $ cp /home/anirban/arc/demo1 /home/anirban/ and press enter.
5:03 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.
5:20 As before to see the demo1 type

ls/home/anirban and press enter.

5:33 Here again we would scroll up and as you can see the demo1 file is there.
5:40 Again before moving a head let us clear the screen.
5:48 Another instance when we do not need to give the destination file name is when we want to copy multiple files.
5:56 We assume that we have three files named test1 test2 test3 in our home directory.
6:04 Now we type $ cp test1 test2 test3 /home/anirban/testdir and press enter.
6:27 This will copy all the three files test1,test2 and test3 to the directory /home/anirban/testdir without changing their names.
6:41 You see that this files have actually been copied.We will type ls /home/anirban/testdir and press enter.
7:03 As you can see test1,test2 and test3 are present in this directory.


7:10 There are many options that go with cp. Here we will see only the most important of them.
7:18 Let us first will go back to the slides.
7:23 Among the options -R is an important one. It causes recursive copying of an entire directory structure.
7:33 Let us see an example.
7:38 Let us try to copy all the contents of the testdir directory to a directory called test.
7:48 For that we would type cp testdir/ test and press enter.
8:02 As you can see from the output message.
8:06 Normally we cannot copy a directory having a some content directly with cp command.
8:14 But using the -R option we can do this.
8:19 Now we type cp -R testdir/ test and press enter.
8:36 The files have now been copied, to see that the test directory actually exist type ls and press enter.
8:47 As you can see the test directory exists. Let us clear the screen.
8:57 To see the contents inside test type ls test and press enter.
9:08 You can see the contents of the test directory.
9:13 Now we go back to the slides.
9:16 We have seen if a file is copied to another file that already exists the existing file is overwritten.
9:25 Now what if we inadvertently overwrite an important file?
9:30 To prevent anything like this to occur, we have the -b option.
9:36 This makes a backup of each exiting destination file.
9:41 We can also use the -i(interactive)option, this always warns us before overwriting any destination file.
9:54 Now let us see how the mv command works.
9:59 This is used for moving files. Now how is that useful?
10:04 It has two major uses.
10:07 It is used for rename 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 this 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 this files abc1 and abc2.
15:23 For this we would type rm testdir/abc1 testdir/abc2 and press enter.
15:45 This remove 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 do delete a single file we write rm and than 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 this 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 content, 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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