PERL/C3/Sample-PERL-program/English-timed

Time	Narration
00:01	Welcome to the Spoken Tutorial on Sample PERL program.
00:06	In this tutorial, we will learn to include all the major topics we covered so far in a sample Perl program.
00:14	To record this tutorial, I am using: Ubuntu Linux 12.04 operating system Perl 5.14.2 and the gedit Text Editor.
00:25	You can use any text editor of your choice.
00:29	As a prerequisite, you should have working knowledge of Perl programming.
00:34	If not, then go through the relevant Perl spoken tutorials on this website.
00:39	The sample Perl program will give the output of various weather forecast reports of a region.
00:46	Weather dot pm is a module file that has a complex data-structure to hold the data required for this program.
00:54	It also contains various functions to generate the report.
00:59	Weather underscore report dot pl is the Perl program which makes use of this module file to give the required output.
01:08	The same code files are available under this video on our website.
01:13	Download and unzip the files provided in the code file link.
01:18	Now, let us see our sample Perl program Weather dot pm.
01:24	The block of code in this program is under the namespace Weather.
01:29	Perl implements namespace using the package keyword.
01:34	BEGIN block is compiled and executed before the main program.
01:40	Export allows to export the functions and variables of modules to user's namespace.
01:48	At the rate EXPORT and at the rate EXPORT underscore OK are the two main variables used during export operation.
01:57	At the rate EXPORT contains list of subroutines and variables of the module.
02:03	These will be exported into the caller namespace.
02:07	At the rate EXPORT underscore OK does export of symbols on demand basis.
02:14	Here, I have used references to create complex data-structures to hold the data required for a weather report.
02:24	$weather_report is a hash reference. “place” and “nstate” have the scalar values.
02:32	“weekly” is hash of hash references.
02:37	*Each week day has four keys - max underscore temp, min underscore temp, sunrise, sunset.
02:48	“record underscore time” is an array reference with two index values.
02:54	I have a few subroutines to display the weather report of various options. Let us see one by one.
03:01	This function prints the header information such as header of the report, place, state and current date.
03:10	Now, let us see the next function display underscore daily underscore report.
03:16	This function prints the daily report on the screen, depending upon the weekday input.
03:22	We retrieve the parameter passed into a subroutine using the shift function.
03:27	I have used the trim() function to remove the leading and trailing spaces of the parameter value.
03:34	Here is the code for the trim() function.
03:37	Lc() function returns a lowercase version of the given input.
03:42	This is used to avoid case-sensitivity.
03:45	The 'week day'- passed as parameter from the main program, is assigned to a local variable dollar week underscore day.
03:55	The following print statements will print the data corresponding to a specified week day.
04:01	We are using the arrow operator to dereference a value in $weather underscore report.
04:09	When working with references, we have to understand the data type we are dereferencing.
04:15	If it is a hash, we need to pass the key in curly braces.
04:20	If it is an array, we need to use the square brackets with the index values.
04:26	return function of Perl returns a value.
04:29	This can be used to check the status of the function in the main program.
04:36	The next function is write underscore daily underscore report.
04:40	This function will print the report output to a file.
04:45	The open function with the greater than (>) symbol defines the WRITE mode.
04:50	Filename is created with the weekday name and dot txt extension.
04:56	The print statements will print the corresponding data of a specified week day to a file.
05:02	This prints the weekly report.
05:05	I have declared a foreach loop to loop through each weekday of the hash reference.
05:11	I have used curly brackets to represent the hash reference and the arrow operator to dereference.
05:18	I am using the “keys” in-built function to loop through the keys of the hash.
05:23	display underscore daily underscore report function will print each element of the hash.
05:30	Now, let us see - a Perl program weather underscore report dot pl where we will make use of this module file Weather dot pm.
05:40	Here, use strict and use warnings are compiler flags that help to avoid common programming mistakes.
05:48	use Weather semicolon. Here, Weather is a module name which I have used in this program.
05:56	We have already seen that the functions required for this program have been stored in this module.
06:03	It is not required to give the dot pm file extension here.
06:08	In this program, I'll print different reports depending upon the given options.
06:14	The user has to enter an option to print the daily weather report of a particular week day, daily weather report of a particular week day to an output file, weekly weather report.
06:27	If option '1' is typed, it will ask the user to enter the day of a week.
06:32	The diamond operator will read from STDIN, that is, from the keyboard.
06:38	For example, if the user enters 'monday', then it is assigned to a variable dollar dayoption, which is a local variable.
06:47	Next, we can see that we are calling two functions- display_header() and display_daily_report().
06:56	We have exported all functions in Weather dot pm with “use Weather” statement in this file.
07:03	So, no need to refer the functions within a package using the colon colon (::)package qualifier
07:10	Now let's see the next option.
07:13	If option '2' is typed, it will prompt the user to enter the day of a week.
07:19	$dayoption is passed as the input parameter to the function write underscore daily underscore report.
07:27	return value from the function is stored in the variable dollar result.
07:33	Print statement asks the user to check the text file for the output.
07:38	The filename is created with the day of the week dot txt as output file.
07:46	If option '3' is typed, it prints the weather report for the whole week.
07:51	display underscore weekly underscore report is the function name of the weekly report.
07:57	This print statement draws a horizontal line for the specified number of times.
08:02	This is just to give a good look to the report.
08:06	Lastly, if the option is 4, it will quit the program.
08:11	If any option other than the ones specified is given, the print statement says “Incorrect option”.
08:19	Here, the exit value of '0' indicates the program ran successfully.
08:25	The exit value other than '0' means an error of some kind has occurred.
08:31	Now, let us execute the program.
08:34	Switch to the terminal and type perl weather underscore report dot pl and press Enter.
08:41	We can see four options on the screen.
08:45	Type '1 'and press Enter.
08:48	We are prompted to enter a day of the week. I'll type "monday" and press Enter.
08:56	This is the header output generated from the function display underscore header().
09:02	Now, we can see the weather report of Monday.
09:06	Now I'll again execute the program once again to demonstrate the other options.
09:13	Type 2 and press Enter.
09:17	At the prompt, we have to type any week day. I will type "wednesday" and press Enter.
09:25	We can see a message: Please check the file wednesday dot txt for report output .
09:32	The output has been written to this text file. Let us open the file and check the contents.
09:38	Type: gedit wednesday dot txt and press Enter.
09:44	The output file has been created with the entered week day name with 'txt' extension.
09:51	Now, let us check the next option.
09:54	Switch to the terminal and type: perl weather underscore report dot pl and press Enter.
10:00	Type '3 'and press Enter.
10:04	This time, we can see the weekly weather report.
10:08	The hash keys and hash values are stored in a random order.
10:13	So, the displayed output is not related to the order in which they were added.
10:19	With this, we come to the end of this tutorial. Let us summarize.
10:24	In this tutorial, we have seen a sample Perl program by covering main topics of our previous tutorials.
10:32	As an assignment, write a similar Perl program employee underscore report.pl for displaying employee salary, designation, department, leave_balance details.
10:45	Pass Employee ID or Employee name as input.
10:50	Write the required functions in the module Employee dot pm file.
10:56	The video at the following link summarize the spoken tutorial. Please download and watch it.
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11:12	Spoken Tutorial project is funded by NMEICT, MHRD, Government of India. More information on this mission is available at this link.
11:25	This is Nirmala Venkat from IIT Bombay, signing off. Thanks for watching.

Contributors and Content Editors

PoojaMoolya, Sandhya.np14