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Welcome to the spoken tutorial on  Hash in Perl.

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In this tutorial, we will learn about;

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Hash  in Perl and

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Accessing element of a hash

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For this tutorial, I am using

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Ubuntu Linux12.04 operating system

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Perl 5.14.2 and

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gedit Text Editor

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You can use any text editor of your choice.

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To practise this tutorial, you should have knowledge of  Variables & Data Structures in Perl.

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Knowledge of comments, loops, conditional statements and Arrays will be an added advantage.

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Please go through the relevant spoken tutorials on the  spoken tutorial website.

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Hash is an unordered collection of data

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It's a  key/value pair data structure

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Hash keys are unique

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However,  Hash can have duplicate values

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This is the declaration of a  hash .

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Let us see how to get the value of a  key from hash.

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The syntax for accessing the value of a  key is

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dollar hashName open curly bracket single quote keyName single quote close curly bracket

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Let us understand  hash using a sample program.

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I have already typed the code in  perlHash dot pl file in gedit.

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Type the code as shown in your  perlHash dot pl file.

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Hash in  Perl is declared with percentage sign.

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These are the keys of hash.

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And these are the values of hash.

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Note: To access  key of hash, one has to use dollar sign.

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Press  Ctrl + S to save the file.

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Then switch to   terminal and execute the Perl script as

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perl perlHash dot pl

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and press  Enter.

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The output is as shown on the terminal.

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Now let us see add and delete of  keys from  hash.

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The syntax for .

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adding key is  dollar hashName open curly bracket

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single quote KeyName single quote

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close curly bracket equal to $value semicolon

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deleting key is  delete dollar hashName open curly bracket

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single quote KeyName single quote close curly bracket semicolon

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Now, let us understand this using a sample program.

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I have already typed the code in  hashKeyOperations dot pl file.

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This is the declaration of  hash.

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We'll be adding, deleting the  keys from this  hash.

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Here we are adding a key to an already created hash.

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It is like assigning a value to a variable.

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delete keyword is used to delete the  key.

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We need to pass the key to delete it.

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Press  Ctrl+S to save the file.

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Switch to the terminal and execute the  Perl script as

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perl hashKeyOperations dot pl

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and press  Enter.

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Output will be as shown on the terminal.

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Let us look at  sorting of a  hash keys and values.

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Syntax to  sort keys is

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sort open bracket keys percentage hashName close bracket semicolon

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Similarly, we can sort hash values as

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sort open bracket values percentage hashName close bracket semicolon

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Let us understand  sorting functionality using a sample program.

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Let me switch to  sortHash dot pl  on  gedit.

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Type the code as displayed on the screen in your  sortHash dot pl file.

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Here we have declared  hash of address.

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Here, to sort the  keys we have used the sort inbuilt function, along with the keys function.

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This will sort the hash keys in alphabetical order.

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Similarly, we can use the sort function on values of hash.

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Sorting can also be done on  numeric keys and/or values.

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Save the file and switch to terminal.

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Execute the script by typing  perl sortHash dot pl and Press  Enter

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The output will be as shown on the terminal.

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Now, let us see how to get all  keys  and  values of hash.

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Perl provides inbuilt  function to fetch all the  hash keys and  values.

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keys function is used to retrive all the  keys of  hash

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values function returns  values of all the  keys whereas

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each function iterates over  hash and returns  key/value pair from  hash

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Let us understand these  using a sample program.

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For this, we'll use perlHash dot pl script, which we have created earlier in this tutorial.

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Type the following piece of code as shown on the screen;

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Let us understand the code now.

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keys function on  hash, returns an array which contains all keys of hash.

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values function on  hash returns an array of values for all keys of hash.

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each  function returns the  key/value pair.

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Here, we have used the  while loop.

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It will iterate over each  key/value pair of  hash, that is returned by each function.

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Press  Ctrl+S to save the file.

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Now, let us execute the script on the terminal by typing

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perl perlHash dot pl

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And Press  Enter

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The following output will be seen on the terminal.

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Now let us see few other ways of looping over  hash.

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We can use  foreach loop to iterate over each key of hash.

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Then perform a set of actions on the value of a key.

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The syntax is as displayed on the screen.

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Here, each iteration of  foreach loop will assign key from  hash to  $variable.

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Then it will use that  $variable to fetch the  value or to perform a set of actions.

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Similarly, we can loop over hash values as shown on the screen.

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We will look at sample program.

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So, let me switch to  loopingOverHash dot pl in gedit.

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Type the following piece of code as shown in your  loopingOverHash dot pl

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This piece of code returns single  key of hash.

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Here in our case,

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1st time  dollar key ($key) contains the  Department as  key.

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In the next iteration of foreach, Name key is returned.

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Note:  Hash is an unordered collection of data.

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So,  keys returned will not be in the sequence defined at the time of creating hash.

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The loop on  values works in a similar way.

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Press  Ctrl + S to save the file.

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Then, switch to terminal and execute the  Perl script as

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perl loopingOverHash dot pl

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and press  Enter.

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The following output is displayed on the terminal.

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Let us summarize.

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In this tutorial, we learnt -

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Hash in Perl and

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Accessing elements of a hash

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using sample programs.

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Here is assignment for you -

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Declare hash having student name as key

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And his/her percentage as the value.

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Loop over hash using keys, values and each function

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Then print the  percentage of each student.

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Watch the video available at the following link

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It summaries the Spoken Tutorial project

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If you do not have good bandwidth, you can download and watch it

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The Spoken Tutorial Project Team  Conducts workshops using spoken tutorials

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Gives certificates to those who pass an online  test

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For more details, please write to contact at spoken hyphen tutorial dot org

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Spoken Tutorial Project is a part of the Talk to a  Teacher project

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It is supported by the National Mission on Education through ICT, MHRD, Government of India.

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More information on this Mission is available at spoken hyphen tutorial dot org slash NMEICT hyphen Intro

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Hope you enjoyed this Perl tutorial.

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This is Amol signing off.

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Thanks for joining.