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Welcome to the Spoken Tutorial on Sample PERL program.

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In this tutorial we will learn to

 include all the major topics we covered so far

 in a sample Perl program

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To record this tutorial, I am using

 Ubuntu Linux 12.04 operating system

 Perl 5.14.2

 and the gedit Text Editor

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You can use any text editor of your choice.

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As a prerequisite, you should have working knowledge of Perl Programming.

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If not, then go through the relevant Perl spoken tutorials on this website.

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The sample Perl program will give the output of various weather forecast reports of a region.

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Weather.pm is a module file that has a complex data structure to hold the data required for this program.

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It also contains various functions to generate the report.

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Weather underscore report.pl is the Perl program which makes use of this module file to give the required output.

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The same code files are available under this video on our website.

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Download and unzip the files provided in the code file link.

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Now let us see our sample Perl program Weather dot pm.

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The block of code in this program is under the namespace Weather.

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Perl implements namespace using the package keyword.

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BEGIN block is compiled and executed before the main program.

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Export allows to export the functions and variables of modules to user's namespace.

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At the rate EXPORT and at the rate EXPORT underscore OK are the two main variables used during export operation.

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At the rate EXPORT contains list of subroutines and variables of the module.

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These will be exported into the caller namespace.

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At the rate EXPORT underscore OK does export of symbols on demand basis.

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Here I have used references to create complex data structures to hold the data required for a weather report.

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$weather_report is a hash reference. “place” and “nstate” has the scalar values.

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“weekly” is hash of hash references.

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*Each week day has four keys -
 max underscore temp, 
 min underscore temp, 
 sunrise,
 sunset.

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“record underscore time” is an array reference with two index values.

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I have a few subroutines to display the weather report of various options.
Let us see one by one.

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This function prints the header information such as header of the report, place, state and current date.

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Now let us see the next function display underscore daily underscore report.

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This function prints the daily report on the screen depending upon the weekday input.

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We retrieve the parameter passed into a subroutine using the shift function.

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I have used the trim function to remove the leading and trailing spaces of the parameter value.

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Here is the code for the trim function.

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Lc function returns a lowercase version of the given input.

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This is used to avoid case-sensitivity.

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The week day - passed as parameter from the main program, is assigned to a local variable dollar week underscore day.

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The following print statements will print the data corresponding to a specified week day.

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We are using the arrow operator to dereference a value in $weather underscore report.

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When working with references, we have to understand the data type we are dereferencing.

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If it is a hash, we need to pass the key in curly braces.

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If it is an array, we need to use the square brackets with the index values.

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return function of Perl returns a value.

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This can be used to check the status of the function in the main program.

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The next function is write underscore daily underscore report.

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This function will print the report output to a file.

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The open function with the greater than (>) symbol defines the WRITE mode.

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Filename is created with the weekday name and dot txt extension.

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The print statements will print the corresponding data of a specified week day to a file.

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This prints the weekly report.

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I have declared a foreach loop to loop through each weekday of the hash reference.

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I have used curly brackets to represent the hash reference  and the arrow operator to dereference.

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I am using the “keys” in-built function to loop through the keys of the hash.

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display underscore daily underscore report function will print each element of the hash.

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Now let us see - a Perl program weather underscore report dot pl  where we will make use of this module file Weather dot pm.

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Here, use strict and use warnings are compiler flags that helps to avoid common programming mistakes.

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use Weather semicolon. Here Weather is a module name which I have used in this program.

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We have already seen that the functions required for this program have been stored in this module.

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It is not required to give the .pm file extension here.

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In this program, I'll print different reports depending upon the given options.

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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

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If option 1 is typed, it will ask the user to enter the day of a week.

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The diamond operator will read from STDIN, that is from the keyboard.

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For example, if the user enters 'monday', then it is assigned to a variable dollar dayoption, which is a local variable.

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Next, we can see that we are calling two functions-

 display_header() and

 display_daily_report().

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We have exported all functions in Weather.pm with “use Weather” statement in this file.

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So, no need to refer the functions within a package using the colon colon (::)package qualifier

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Now let's see the next option.

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If option 2 is typed, it will prompt the user to enter the day of a week.

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$dayoption is passed as the input parameter to the function write underscore daily underscore report.

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return value from the function is stored in the variable dollar result.

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Print statement asks the user to check the text file for the output.

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The filename is created with the day of the week dot txt as output file.

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If option 3 is typed, it prints the weather report for the whole week.

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display underscore weekly underscore report is the function name of the weekly report.

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This print statement draws a horizontal line for the specified number of times.

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This is just to give a good look to the report.

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Lastly, if the option is 4, it will quit the program.

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If any option, other than the ones specified, is given, the print statement says “Incorrect option”.

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Here the exit value of 0 indicates the program ran successfully.

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The exit value other than 0 means an error of some kind has occurred.

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Now let us execute the program.

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Switch to the terminal and type perl weather underscore report dot pl and press Enter

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We can see four options on the screen.

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Type 1 and press Enter.

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We are prompted to enter a day of the week. I'll type 'monday' and press Enter.

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This is the header output generated from the function display underscore header().

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Now, we can see the weather report of Monday.

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Now I'll again execute the program once again to demonstrate the other options.

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Type 2 and press Enter.

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At the prompt, we have to type any week day. I will type ‘wednesday’ and press Enter.

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We can see a message Please check the file wednesday dot txt for report output .

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The output has been written to this text file.  Let us open the file and check the content.

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Type gedit wednesday dot txt and press Enter.

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The output file has been created with the entered week day name with txt extension.

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Now let us check the next option.

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Switch to the terminal and type perl weather underscore report dot pl and press Enter

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Type 3 and press Enter.

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This time, we can see the weekly weather report.

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The hash keys and hash values are stored in a random order.

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So the displayed output is not related to the order in which they were added.

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With this, we come to the end of this tutorial. Let us summarize.

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In this tutorial we have seen a sample Perl program by covering main topics of our previous tutorials.

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As an assignment,  Write a similar Perl program employee underscore report.pl for displaying employee salary, designation, department, leave_balance details.

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Pass Employee ID or Employee name as input.

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Write the required functions in the module Employee.pm file.

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The video at the following link summarize the spoken tutorial. Please download and watch it

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We conduct workshops and give certificates for those who pass our online tests.
For more details, please write to us.

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Spoken Tutorial project is funded by NMEICT, MHRD, Government of India.
More information on this mission is available at this link.

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This is Nirmala Venkat from IIT Bombay, signing off. Thanks for watching.