Difference between revisions of "PERL/C3/File-Handling/English-timed"

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|  00:06
 
|  00:06
 
|  In this tutorial, we will learn how to:
 
|  In this tutorial, we will learn how to:
−
* Open a file in '''read mode'''
+
Open a file in '''read mode'''
−
* Write to a file
+
Write to a file
−
* Open a file in '''append mode'''
+
Open a file in '''append mode'''
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* Close the '''file handle'''.
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Close the '''file handle'''.
  
 
|-
 
|-
 
| 00:17
 
| 00:17
 
|  For this tutorial, I am using:
 
|  For this tutorial, I am using:
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* '''Ubuntu Linux 12.04''' operating system
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'''Ubuntu Linux 12.04''' operating system
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* '''Perl 5.14.2''' and the
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'''Perl 5.14.2''' and the
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* ''' gedit''' Text Editor.
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''' gedit''' Text Editor.
  
 
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|-
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|  00:43
 
|  00:43
 
|  The basic operations we can do with files in '''Perl '''are:
 
|  The basic operations we can do with files in '''Perl '''are:
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* open a file
+
open a file
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* read from a file
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read from a file
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* write to a file and
+
write to a file and
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* close a file.
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close a file.
  
 
|-
 
|-
 
|00:54
 
|00:54
 
|  The default '''file handle'''s are:
 
|  The default '''file handle'''s are:
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* '''STDIN'''
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'''STDIN'''
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* '''STDOUT'''  
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'''STDOUT'''  
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* '''STDERR'''
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'''STDERR'''
  
 
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|-
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|  03:22
 
|  03:22
 
|  Lastly, close the file with the''' FILEHANDLE''' name which we had given in the '''open''' statement.
 
|  Lastly, close the file with the''' FILEHANDLE''' name which we had given in the '''open''' statement.
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|-
 
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|-
 
|-
 
|  05:41
 
|  05:41
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| In the 'writefile.pl', ''' comment'''  the previous '''print''' Statement.
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| In the 'writefile.pl', ''' comment'''  the previous '''print''' statement.
  
 
|-
 
|-
 
| 05:46
 
| 05:46
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| Add the below '''print''' command.  
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| Add the '''print''' command shown below.  
  
 
|-
 
|-
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|-
 
|-
 
|  06:04
 
|  06:04
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|  Type: ''' gedit second.txt''' and press '''Enter'''.
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|  Type: "gedit second.txt" and press '''Enter'''.
  
 
|-
 
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|-
 
|-
 
|  06:38
 
|  06:38
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|  Now I will open the '''writefile dot pl''' again in '''gedit'''.
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|  Now, I will open the '''writefile dot pl''' again in '''gedit'''.
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+
  
 
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|-
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|  07:53
 
|  07:53
 
|  In this tutorial, we learnt to:  
 
|  In this tutorial, we learnt to:  
−
* Open a file in "read" mode
+
Open a file in "read" mode
−
* Write to a file
+
Write to a file
−
* Open a file in "append" mode and
+
Open a file in "append" mode and
−
* Close the '''file handle'''.
+
Close the '''file handle'''.
  
 
|-
 
|-
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|  08:29
 
|  08:29
 
|  The''' Spoken Tutorial Project''' team:
 
|  The''' Spoken Tutorial Project''' team:
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* conducts workshops using spoken tutorials and
+
conducts workshops using spoken tutorials and
−
* gives certificates on passing online tests.
+
gives certificates on passing online tests.
  
 
|-
 
|-

Latest revision as of 18:16, 20 February 2017

Time Narration
00:01 Welcome to the Spoken Tutorial on File Handling in PERL.
00:06 In this tutorial, we will learn how to:

Open a file in read mode Write to a file Open a file in append mode Close the file handle.

00:17 For this tutorial, I am using:

Ubuntu Linux 12.04 operating system Perl 5.14.2 and the gedit Text Editor.

00:28 You can use any text editor of your choice.
00:32 To follow this tutorial, you should have working knowledge of Perl programming.
00:37 If not, then go through the relevant Perl spoken tutorials on the spoken tutorial website.
00:43 The basic operations we can do with files in Perl are:

open a file read from a file write to a file and close a file.

00:54 The default file handles are:

STDIN STDOUT STDERR

01:02 This is the syntax for open function.
01:05 In the syntax, FILEHANDLE is the file handle returned by the open function.
01:11 MODE represents the mode of opening the file. For eg: read, write, etc.
01:18 EXPR is the physical filename used to read or write. In this case, “First.txt” is the filename.
01:27 There is another way to write the open function, as shown here.
01:32 Let us understand how to open an existing file and read the data from it.
01:38 First we will create a text file and store some data in it. Go to the terminal and type: gedit first.txt and press Enter.
01:51 In the first dot txt file, type the following text:
01:55 Save the file and close gedit.
01:59 Now we will look at a Perl program that opens the file 'first.txt' and reads the content.
02:07 Let me open the sample program 'openfile.pl' which I have already saved.
02:13 Type: gedit openfile dot pl ampersand and press Enter.
02:19 In the openfile dot pl file, type the following code as displayed on the screen.
02:25 Let us understand the code now.
02:28 The open function opens a file for reading.
02:33 The first parameter DATA is the filehandle which allows Perl to refer to the file in future.
02:40 The second parameter “<” less than symbol denotes the READ mode.
02:44 If you fail to specify the Mode, by default the file will be opened in “READ” mode.
02:50 The third parameter 'first.txt' is the filename from where the data has to be read.
02:57 What will happen if the file 'first.txt' does not exist?
03:02 The script will die with the appropriate error message, stored in the dollar exclamation ($!)variable.
03:08 The while loop will read line by line and loop through the <DATA> file until all the lines have been read.
03:17 Print dollar underscore ('$_') variable will print the contents of the current line.
03:22 Lastly, close the file with the FILEHANDLE name which we had given in the open statement.
03:29 Closing a file prevents any accidental file changes or overwriting of the content.
03:36 Now, press Ctrl+S to save the file.
03:40 Let us execute the program.
03:42 Switch back to the terminal and type perl openfile dot pl and press Enter.
03:51 The output is displayed as shown.
03:54 This is the same content that we saw earlier in first dot txt file.
03:59 Next we will see how to write data into a file.
04:03 The open statement with greater than (>) symbol defines the WRITE mode.
04:08 Filename represents the name of the file where the data has to be written.
04:13 Let me open the sample program 'writefile.pl' which I have already saved.
04:19 Switch to the terminal.
04:21 Now, type: gedit writefile dot pl ampersand and press Enter.
04:29 In the writefile dot pl file, type the following code as displayed on the screen.
04:34 Let me explain the code now.
04:37 The open function opens a file 'second.txt' in "write" mode.
04:44 “>” - Greater than symbol before the filename denotes the "write" mode.
04:49 The first parameter "FILE1" is the FILEHANDLE.
04:53 The print function prints the given text to FILEHANDLE. i.e 'FILE1'.
04:59 Now, press Ctrl+S to save the file.
05:03 Let us execute the program.
05:05 Switch back to the terminal and type: perl writefile dot pl and press Enter.
05:12 Now, let us check whether the text has been written in 'second.txt' file.
05:18 Type: gedit second.txt and press Enter.
05:23 We can see the text: "Working with files makes data storage and retrieval a simple task!" in our 'second.txt' file.
05:32 Let us close the 'second.txt' file.
05:35 What will happen if we open the same file again in "write" mode? Let us see that.
05:41 In the 'writefile.pl', comment the previous print statement.
05:46 Add the print command shown below.
05:48 Now, press Ctrl+S to save the file. Let us execute the program.
05:54 Switch back to the terminal and type perl writefile dot pl and press Enter.
06:00 Now, let us check the 'second.txt' file once again.
06:04 Type: "gedit second.txt" and press Enter.
06:09 We can see the output: “Greater than symbol (>) overwrites the content of the file!"
06:14 The previous contents of the 'second.txt' file has been overwritten.
06:19 This is because, we had opened the file in the "write" mode again.
06:24 Let us close the 'second.txt' file.
06:27 Next, we will see how to append data to an existing file.
06:32 The open statement with two greater than (>>) symbols denotes the "APPEND" mode.
06:38 Now, I will open the writefile dot pl again in gedit.
06:44 In the open statement, type two greater (>>) than symbols. This will denote that the file is in append mode.
06:52 Comment the previous print statement, as it is already executed.
06:57 Add the line: print FILE1 within double quotes "Two greater than symbols (>>) open the file in append mode", to append to the existing data.
07:07 Now, press Ctrl+S to save the file.
07:11 Let us execute the program.
07:14 Switch back to the terminal and type: perl writefile dot pl and press Enter.
07:20 Now, let us check whether the text has been appended to the 'second.txt' file.
07:26 Type: gedit second.txt and press Enter.
07:31 We can see the text has been appended in our 'second.txt' file.
07:36 Let us close the 'second.txt' file.
07:39 Similarly, there are other modes also.
07:42 Try out these options on your own and understand what happens.
07:49 This brings us to the end of this tutorial. Let us summarize.
07:53 In this tutorial, we learnt to:

Open a file in "read" mode Write to a file Open a file in "append" mode and Close the file handle.

08:03 Here is an assignment for you. Change the file attribute to "+>" in the 'writefile.pl' program.
08:11 Save and execute the program.
08:14 Open the 'second.txt' file to see the output.
08:17 Analyze the usage of file attribute "+>".
08:22 The video at the following link summarizes the Spoken Tutorial project. Please download and watch it.
08:29 The Spoken Tutorial Project team:

conducts workshops using spoken tutorials and gives certificates on passing online tests.

08:37 For more details, please write to us.
08:41 Spoken Tutorial project is funded by NMEICT, MHRD, Government of India.
08:48 More information on this mission is available at this link.
08:53 This is Nirmala Venkat from IIT Bombay, signing off. Thanks for watching.

Contributors and Content Editors

PoojaMoolya, Sandhya.np14

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