Difference between revisions of "PERL/C3/Sample-PERL-program/English"

Learning objectives

• include all the major topics we covered so far
• in a sample Perl program

System Requirements

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

You can use any text editor of your choice.

Pre-requisites

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

Program outline:

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

It also contains various functions to generate the report.

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

Perl implements namespace using the package keyword.

BEGIN block is compiled and executed before the main program.

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

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

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

These will be exported into the caller namespace.

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

$weather_report is a hash reference.

“place” and “nstate” has the scalar values.

“weekly” is hash of hash references.

Each week day has four keys -

max underscore temp, min underscore temp, sunrise, sunset.

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

Let us see one by one.

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

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

Here is the code for the trim function.

Lc function returns a lowercase version of the given input.

This is used to avoid case-sensitivity.

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

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

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

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

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

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

return function of Perl returns a value.

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

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

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

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

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

use Weather semicolon.

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

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

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

The user has to enter an option to print the

1. daily weather report of a particular week day
2. daily weather report of a particular week day to an output file
3. weekly weather report

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

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

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

Next, we can see that we are calling two functions display_header() and display_daily_report().

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

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

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

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

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

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

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

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

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

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

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

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

perl weather_report. Pl

>>press Enter.

perl weather underscore report dot pl and press Enter

2.Daily Weather Report to File

3.Weekly Weather Report

4.Exit

Enter the Option: 1

>>press Enter.

Type 1 and press Enter.

>>press Enter.

I'll type 'monday' and press Enter.

perl weather_report. Pl

>>press Enter.

2.Daily Weather Report to File

3.Weekly Weather Report

4.Exit

Enter the Option: 2

>>press Enter.

>>press Enter.

I will type ‘wednesday’ and press Enter.

Let us open the file and check the content.

gedit wednesday.txt

>>press Enter.

perl weather_report. Pl

>>press Enter.

2.Daily Weather Report to File

3.Weekly Weather Report

4.Exit

Enter the Option: 3

>>press Enter.

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

Let us summarize.

Assignment

1. Write a similar Perl program employee underscore report.pl for displaying employee salary, designation, department, leave_balance details.
2. Pass Employee ID or Employee name as input.
3. Write the required functions in the module Employee.pm file.

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