Difference between revisions of "BASH/C3/Using-File-Descriptors/English-timed"
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{|border = 1 | {|border = 1 | ||
− | | Time | + | |'''Time''' |
− | | | + | |'''Narration''' |
|- | |- | ||
− | | 00 | + | | 00:01 |
− | | Dear friends, | + | | Dear friends, welcome to the '''spoken tutorial''' on''' Using File Descriptors'''. |
|- | |- | ||
− | | 00 | + | | 00:08 |
− | | In this tutorial, we will learn to | + | | In this tutorial, we will learn to: |
|- | |- | ||
− | | 00 | + | | 00:11 |
− | | | + | |Assign an '''output file descriptor''' |
|- | |- | ||
− | | 00 | + | | 00:14 |
− | | | + | |Assign an '''input file descriptor''' |
|- | |- | ||
− | | 00 | + | | 00:17 |
− | | | + | |Close the '''file descriptor (fd)''' |
|- | |- | ||
− | | | + | |00:19 |
− | | | + | | with the help of some examples. |
|- | |- | ||
− | |00 | + | |00:23 |
− | | To follow this tutorial you should have knowledge of '''Shell Scripting''' in''' BASH.''' | + | | To follow this tutorial, you should have knowledge of '''Shell Scripting''' in''' BASH.''' |
|- | |- | ||
− | | | + | |00:29 |
− | | If not, for relevant tutorials please visit our website which is as shown | + | |If not, for relevant tutorials, please visit our website which is as shown. '''http://www.spoken-tutorial.org''' |
|- | |- | ||
− | | | + | |00:35 |
− | | | + | |For this tutorial, I am using: |
|- | |- | ||
− | | | + | |00:38 |
− | | | + | |'''Ubuntu Linux''' 12.04''' '''Operating System |
|- | |- | ||
− | | | + | |00:43 |
− | | | + | |'''GNU BASH''' version 4.2 |
|- | |- | ||
− | | | + | |00:46 |
| Please note,''' GNU Bash''' '''version 4''' or above is recommended for practice. | | Please note,''' GNU Bash''' '''version 4''' or above is recommended for practice. | ||
|- | |- | ||
− | | | + | |00:54 |
− | | | + | |Let us start with an introduction. |
|- | |- | ||
− | | | + | |00:56 |
− | | We have already studied about '''file descriptors''' in the previous tutorial. | + | |We have already studied about '''file descriptors''' in the previous tutorial. |
|- | |- | ||
− | | | + | |01:02 |
− | | | + | |0, 1 and 2 are the standard '''file descriptors''' for''' stdin,''' '''stdout''' and '''stderr'''. |
|- | |- | ||
− | | | + | |01:15 |
− | | | + | |'''File descriptors''' are used for '''i/o redirection'''. |
|- | |- | ||
− | | | + | |01:20 |
− | | | + | |The syntax to assign a '''file descriptor '''to an '''output file''' is: |
|- | |- | ||
− | | | + | |01:25 |
| '''exec [File descriptor] greater than symbol filename''' | | '''exec [File descriptor] greater than symbol filename''' | ||
|- | |- | ||
− | | | + | |01:31 |
| Let us see an example. | | Let us see an example. | ||
|- | |- | ||
− | | | + | |01:33 |
− | | I have a code file with the name '''fdassign dot sh''' | + | | I have a '''code file''' with the name '''fdassign dot sh'''. |
|- | |- | ||
− | | 01 | + | |01:43 |
− | | | + | |The first line is the '''shebang line.''' |
|- | |- | ||
− | | | + | |01:49 |
− | | | + | |The '''"exec"''' command replaces the current '''shell process'''. |
|- | |- | ||
− | | | + | |01:56 |
− | | It will be executed in the place of the current '''shell '''without creating a new process. | + | |It will be executed in the place of the current '''shell '''without creating a new '''process'''. |
|- | |- | ||
− | | | + | |02:04 |
− | | We know that 0, 1, and 2 are standard '''file descriptors. ''' | + | | We know that 0, 1, and 2 are standard '''file descriptors.''' |
|- | |- | ||
− | | | + | |02:09 |
| For any newly opened file, we have additional '''file descriptors''' from 3 to 9. | | For any newly opened file, we have additional '''file descriptors''' from 3 to 9. | ||
|- | |- | ||
− | | 02 | + | | 02:19 |
− | | Here, | + | | Here, 3 is the '''file descriptor'''. |
|- | |- | ||
− | | 02 | + | | 02:22 |
− | | This will write the output to the '''output dot txt''' file. | + | | This will write the '''output''' to the '''output dot txt''' file. |
|- | |- | ||
− | | 02 | + | | 02:30 |
− | | The string '''"Welcome to BASH learning" | + | | The '''string''' "Welcome to BASH learning" is sent to the file '''output dot txt'''. |
|- | |- | ||
− | | 02 | + | | 02:36 |
| This is done via '''file descriptor 3'''. | | This is done via '''file descriptor 3'''. | ||
|- | |- | ||
− | | | + | |02:42 |
− | | This is similar to redirecting a string to a file. | + | |This is similar to redirecting a '''string''' to a file. |
|- | |- | ||
− | | | + | |02:49 |
− | | | + | |Each new string will be appended to the file. |
|- | |- | ||
− | | | + | |02:52 |
− | | For example: | + | |For example: |
|- | |- | ||
− | | | + | |02:54 |
| We will append the current '''system date''' to the''' output dot txt''' file. | | We will append the current '''system date''' to the''' output dot txt''' file. | ||
|- | |- | ||
− | | | + | |03:00 |
− | | The syntax is: '''date SPACE greater-than symbol ampersand sign 3''' | + | |The syntax is: '''date SPACE greater-than symbol ampersand sign 3'''. |
|- | |- | ||
− | | | + | |03:13 |
− | | | + | |Here, we close the '''file descriptor'''. |
|- | |- | ||
− | | | + | |03:16 |
− | | After this line, the '''descriptor '''cannot write anything to the '''output dot txt''' file. | + | |After this line, the '''descriptor '''cannot write anything to the '''output dot txt''' file. |
|- | |- | ||
− | | | + | |03:23 |
− | | | + | |Let us '''execute''' the '''code''' and see the '''output'''. |
|- | |- | ||
− | | | + | |03:26 |
− | | Open the '''terminal '''using '''CTRL+ALT+T''' keys. | + | |Open the '''terminal '''using '''CTRL+ALT+T''' keys. |
|- | |- | ||
− | | | + | |03:34 |
− | | | + | |Type: '''chmod space plus x space fdassign dot sh''' |
|- | |- | ||
− | | | + | |03:41 |
− | | | + | |Type: '''dot slash fdassign dot sh''' |
|- | |- | ||
− | | 03 | + | | 03:46 |
− | | Let us check the output now by typing '''cat space output dot txt''' | + | | Let us check the '''output''' now by typing '''cat space output dot txt'''. |
|- | |- | ||
− | | 03 | + | | 03:56 |
− | | We can see that the string '''Welcome to BASH learning''' and the current '''system date''' is displayed. | + | | We can see that the string '''"Welcome to BASH learning"''' and the current '''system date''' is displayed. |
|- | |- | ||
− | | 04 | + | | 04:05 |
− | | Let us go back to the editor. | + | | Let us go back to the '''editor'''. |
|- | |- | ||
− | | 04 | + | | 04:11 |
| Now I will type '''echo '''at the end, after the '''descriptor '''is closed. | | Now I will type '''echo '''at the end, after the '''descriptor '''is closed. | ||
|- | |- | ||
− | | 04 | + | | 04:17 |
− | | Type: '''echo within double quotes Hi after quotes space greater than symbol ampersand sign 3''' | + | | Type: '''echo space''' within double quotes '''Hi''' after quotes '''space''' '''greater than''' symbol '''ampersand''' sign '''3''' |
|- | |- | ||
− | | 04 | + | | 04:31 |
| Click on '''Save'''. | | Click on '''Save'''. | ||
|- | |- | ||
− | | 04 | + | | 04:35 |
− | | Let us execute the script once again and see what happens. | + | | Let us '''execute''' the '''script''' once again and see what happens. |
|- | |- | ||
− | | 04 | + | | 04:38 |
− | | On the '''terminal''', press the | + | | On the '''terminal''', press the up-arrow key twice, recall the previous command '''dot slash fdassign dot sh'''. |
|- | |- | ||
− | | 04 | + | | 04:50 |
| press '''Enter.''' | | press '''Enter.''' | ||
|- | |- | ||
− | | 04 | + | | 04:52 |
− | | We see an error | + | | We see an error: |
|- | |- | ||
− | | 04 | + | | 04:55 |
− | | '''Bad file descriptor''' | + | | '''"Bad file descriptor"'''. |
|- | |- | ||
− | | 04 | + | | 04:58 |
| Let us fix this error. | | Let us fix this error. | ||
|- | |- | ||
− | | 05 | + | | 05:00 |
− | | Come back to the editor. | + | | Come back to the '''editor'''. |
|- | |- | ||
− | | 05 | + | | 05:03 |
− | | I will cut the last line of code and paste it below the '''date command''' | + | | I will cut the last line of code and paste it below the '''date command'''. |
|- | |- | ||
− | | 05 | + | | 05:11 |
| Click on '''Save'''. | | Click on '''Save'''. | ||
|- | |- | ||
− | | 05 | + | | 05:13 |
− | | Let us execute the code once again | + | | Let us '''execute''' the '''code''' once again, on the '''terminal'''. |
|- | |- | ||
− | | 05 | + | | 05:19 |
− | | Recall the previous command '''dot slash fdassign.sh''' | + | | Recall the previous command '''dot slash fdassign.sh'''. |
|- | |- | ||
− | | 05 | + | | 05:24 |
| press '''Enter.''' | | press '''Enter.''' | ||
|- | |- | ||
− | | 05 | + | | 05:26 |
| Now let us open the '''output dot txt''' file. | | Now let us open the '''output dot txt''' file. | ||
|- | |- | ||
− | | 05 | + | | 05:29 |
| Type: '''cat space output dot txt''' | | Type: '''cat space output dot txt''' | ||
|- | |- | ||
− | | 05 | + | | 05:41 |
| We can see the output. | | We can see the output. | ||
|- | |- | ||
− | | 05 | + | | 05:43 |
− | | The string | + | | The string "Hi" is displayed at the end. |
|- | |- | ||
− | | 05 | + | | 05:49 |
− | | Now we will assign the '''file descriptor''' to the input file. | + | | Now we will assign the '''file descriptor''' to the '''input file'''. |
|- | |- | ||
− | | 05 | + | | 05:54 |
| Let us see an example. | | Let us see an example. | ||
|- | |- | ||
− | | 05 | + | | 05:56 |
− | | I have a file named '''fdread dot sh''' | + | | I have a file named '''fdread dot sh'''. |
|- | |- | ||
− | | 06 | + | | 06:03 |
| Let us go through it. | | Let us go through it. | ||
|- | |- | ||
− | | 06 | + | | 06:07 |
− | | This is the '''exec | + | | This is the''' 'exec' '''command. |
|- | |- | ||
− | | 06 | + | | 06:13 |
− | | Here we will read the file '''output dot txt''' | + | | Here we will read the file '''output dot txt'''. |
|- | |- | ||
− | | 06 | + | | 06:19 |
− | | The line '''exec 3 | + | | The line '''exec 3 lesser than symbol output dot txt''' will open the file for reading. |
|- | |- | ||
− | | 06 | + | | 06:30 |
− | | '''cat | + | | ''' 'cat' '''command will display the content of the file. |
|- | |- | ||
− | | 06 | + | | 06:35 |
− | | And finally we close the '''file descriptor.''' | + | | And finally, we close the '''file descriptor.''' |
|- | |- | ||
− | | 06 | + | | 06:39 |
− | | Now let us execute this '''shell script'''. | + | | Now, let us '''execute''' this '''shell script'''. |
|- | |- | ||
− | | 06 | + | | 06:42 |
| On the '''terminal''', let me clear the '''prompt'''. | | On the '''terminal''', let me clear the '''prompt'''. | ||
|- | |- | ||
− | | 06 | + | | 06:47 |
| Type: '''chmod space plus x space fdread dot sh''' | | Type: '''chmod space plus x space fdread dot sh''' | ||
|- | |- | ||
− | | 06 | + | | 06:55 |
| Type '''dot slash fdread dot sh''' | | Type '''dot slash fdread dot sh''' | ||
|- | |- | ||
− | | 07 | + | | 07:01 |
| We can see the output on the '''terminal'''. | | We can see the output on the '''terminal'''. | ||
|- | |- | ||
− | | 07 | + | | 07:05 |
| The content of '''output dot txt''' file is displayed. | | The content of '''output dot txt''' file is displayed. | ||
|- | |- | ||
− | | 07 | + | | 07:10 |
| This brings us to the end of this tutorial. | | This brings us to the end of this tutorial. | ||
|- | |- | ||
− | | 07 | + | | 07:13 |
− | | Come back to the slides. | + | | Come back to the '''slides'''. |
|- | |- | ||
− | | 07 | + | | 07:16 |
− | | Let us summarize. | + | | Let us summarize. In this tutorial, we learned to: |
|- | |- | ||
− | | 07 | + | | 07:19 |
− | | | + | |Assign the '''output file descriptor''' |
|- | |- | ||
− | | | + | |07:22 |
− | | | + | |Assign the '''input file descriptor''' |
|- | |- | ||
− | | | + | |07:26 |
− | | | + | |Close the '''file descriptor'''. |
|- | |- | ||
− | | | + | |07:28 |
− | | | + | |As an assignment: |
|- | |- | ||
− | | 07 | + | |07:30 |
− | | | + | | Try to append a few lines to a file '''test dot txt''' using '''file descriptors'''; |
|- | |- | ||
− | | | + | |07:36 |
− | | | + | | Display the contents of the file using '''file descriptors'''. |
|- | |- | ||
− | | | + | |07:41 |
− | | | + | |Watch the video available at the link shown below. |
|- | |- | ||
− | | | + | |07:45 |
− | | | + | | It summarizes the Spoken-Tutorial project. |
|- | |- | ||
− | | | + | |07:48 |
− | + | ||
− | + | ||
− | + | ||
− | + | ||
| If you do not have good bandwidth, you can download and watch it. | | If you do not have good bandwidth, you can download and watch it. | ||
|- | |- | ||
− | | | + | |07:53 |
− | | | + | |The Spoken Tutorial Project team: Conducts workshops using spoken tutorials. |
|- | |- | ||
− | | | + | |07:58 |
− | | Gives certificates to those who pass an online test | + | | Gives certificates to those who pass an online test. |
|- | |- | ||
− | | | + | |08:02 |
| For more details, please write to '''contact@spoken-tutorial.org''' | | For more details, please write to '''contact@spoken-tutorial.org''' | ||
|- | |- | ||
− | | | + | |08:10 |
− | | | + | |'''Spoken Tutorial''' Project is a part of the '''Talk to a Teacher''' project. |
|- | |- | ||
− | | | + | |08:14 |
| It is supported by the National Mission on Education through ICT, MHRD, Government of India. | | It is supported by the National Mission on Education through ICT, MHRD, Government of India. | ||
|- | |- | ||
− | | | + | |08:22 |
− | | More information on this | + | | More information on this mission is available at the link shown below http://spoken-tutorial.org/NMEICT-Intro |
|- | |- | ||
− | | | + | |08:28 |
− | | | + | |The script has been contributed by FOSSEE and Spoken-Tutorial teams. |
|- | |- | ||
− | | | + | |08:33 |
− | | This is Ashwini Patil from IIT Bombay. | + | |This is Ashwini Patil from IIT Bombay, signing off. |
|- | |- | ||
− | | | + | |08:37 |
− | | Thank you for joining. | + | |Thank you for joining. |
|} | |} |
Latest revision as of 17:03, 23 March 2017
Time | Narration |
00:01 | Dear friends, welcome to the spoken tutorial on Using File Descriptors. |
00:08 | In this tutorial, we will learn to: |
00:11 | Assign an output file descriptor |
00:14 | Assign an input file descriptor |
00:17 | Close the file descriptor (fd) |
00:19 | with the help of some examples. |
00:23 | To follow this tutorial, you should have knowledge of Shell Scripting in BASH. |
00:29 | If not, for relevant tutorials, please visit our website which is as shown. http://www.spoken-tutorial.org |
00:35 | For this tutorial, I am using: |
00:38 | Ubuntu Linux 12.04 Operating System |
00:43 | GNU BASH version 4.2 |
00:46 | Please note, GNU Bash version 4 or above is recommended for practice. |
00:54 | Let us start with an introduction. |
00:56 | We have already studied about file descriptors in the previous tutorial. |
01:02 | 0, 1 and 2 are the standard file descriptors for stdin, stdout and stderr. |
01:15 | File descriptors are used for i/o redirection. |
01:20 | The syntax to assign a file descriptor to an output file is: |
01:25 | exec [File descriptor] greater than symbol filename |
01:31 | Let us see an example. |
01:33 | I have a code file with the name fdassign dot sh. |
01:43 | The first line is the shebang line. |
01:49 | The "exec" command replaces the current shell process. |
01:56 | It will be executed in the place of the current shell without creating a new process. |
02:04 | We know that 0, 1, and 2 are standard file descriptors. |
02:09 | For any newly opened file, we have additional file descriptors from 3 to 9. |
02:19 | Here, 3 is the file descriptor. |
02:22 | This will write the output to the output dot txt file. |
02:30 | The string "Welcome to BASH learning" is sent to the file output dot txt. |
02:36 | This is done via file descriptor 3. |
02:42 | This is similar to redirecting a string to a file. |
02:49 | Each new string will be appended to the file. |
02:52 | For example: |
02:54 | We will append the current system date to the output dot txt file. |
03:00 | The syntax is: date SPACE greater-than symbol ampersand sign 3. |
03:13 | Here, we close the file descriptor. |
03:16 | After this line, the descriptor cannot write anything to the output dot txt file. |
03:23 | Let us execute the code and see the output. |
03:26 | Open the terminal using CTRL+ALT+T keys. |
03:34 | Type: chmod space plus x space fdassign dot sh |
03:41 | Type: dot slash fdassign dot sh |
03:46 | Let us check the output now by typing cat space output dot txt. |
03:56 | We can see that the string "Welcome to BASH learning" and the current system date is displayed. |
04:05 | Let us go back to the editor. |
04:11 | Now I will type echo at the end, after the descriptor is closed. |
04:17 | Type: echo space within double quotes Hi after quotes space greater than symbol ampersand sign 3 |
04:31 | Click on Save. |
04:35 | Let us execute the script once again and see what happens. |
04:38 | On the terminal, press the up-arrow key twice, recall the previous command dot slash fdassign dot sh. |
04:50 | press Enter. |
04:52 | We see an error: |
04:55 | "Bad file descriptor". |
04:58 | Let us fix this error. |
05:00 | Come back to the editor. |
05:03 | I will cut the last line of code and paste it below the date command. |
05:11 | Click on Save. |
05:13 | Let us execute the code once again, on the terminal. |
05:19 | Recall the previous command dot slash fdassign.sh. |
05:24 | press Enter. |
05:26 | Now let us open the output dot txt file. |
05:29 | Type: cat space output dot txt |
05:41 | We can see the output. |
05:43 | The string "Hi" is displayed at the end. |
05:49 | Now we will assign the file descriptor to the input file. |
05:54 | Let us see an example. |
05:56 | I have a file named fdread dot sh. |
06:03 | Let us go through it. |
06:07 | This is the 'exec' command. |
06:13 | Here we will read the file output dot txt. |
06:19 | The line exec 3 lesser than symbol output dot txt will open the file for reading. |
06:30 | 'cat' command will display the content of the file. |
06:35 | And finally, we close the file descriptor. |
06:39 | Now, let us execute this shell script. |
06:42 | On the terminal, let me clear the prompt. |
06:47 | Type: chmod space plus x space fdread dot sh |
06:55 | Type dot slash fdread dot sh |
07:01 | We can see the output on the terminal. |
07:05 | The content of output dot txt file is displayed. |
07:10 | This brings us to the end of this tutorial. |
07:13 | Come back to the slides. |
07:16 | Let us summarize. In this tutorial, we learned to: |
07:19 | Assign the output file descriptor |
07:22 | Assign the input file descriptor |
07:26 | Close the file descriptor. |
07:28 | As an assignment: |
07:30 | Try to append a few lines to a file test dot txt using file descriptors; |
07:36 | Display the contents of the file using file descriptors. |
07:41 | Watch the video available at the link shown below. |
07:45 | It summarizes the Spoken-Tutorial project. |
07:48 | If you do not have good bandwidth, you can download and watch it. |
07:53 | The Spoken Tutorial Project team: Conducts workshops using spoken tutorials. |
07:58 | Gives certificates to those who pass an online test. |
08:02 | For more details, please write to contact@spoken-tutorial.org |
08:10 | Spoken Tutorial Project is a part of the Talk to a Teacher project. |
08:14 | It is supported by the National Mission on Education through ICT, MHRD, Government of India. |
08:22 | More information on this mission is available at the link shown below http://spoken-tutorial.org/NMEICT-Intro |
08:28 | The script has been contributed by FOSSEE and Spoken-Tutorial teams. |
08:33 | This is Ashwini Patil from IIT Bombay, signing off. |
08:37 | Thank you for joining. |