Linux-AWK/C2/More-on-Single-Dimensional-Array-in-awk/English-timed

Time	Narration
00:01	Hello and welcome to this spoken tutorial- More on single dimensional array in awk.
00:07	In this tutorial, we will learn about- Using awk array with file,
00:13	scan the elements of an array,
00:16	Delete statement,
00:18	ARGV array and ENVIRON array.
00:22	We will do this through some examples.
00:25	To record this tutorial, I am using: Ubuntu Linux 16.04 Operating System and gedit text editor 3.20.1
00:37	You can use any text editor of your choice.
00:41	To practice this tutorial, you should have gone through previous awk tutorial on array in our website.
00:48	You should have some basic knowledge of any programming language like C or C++.
00:55	If not, then please go through the corresponding tutorials on our website.
01:00	The files used in this tutorial are available in the Code Files link on this tutorial page. Please download and extract them.
01:10	Previously we covered some aspects of awk arrays.
01:14	Now let us see how we can use awk array with a file.
01:19	We will use the same file awkdemo.txt that we have used earlier.
01:25	Here, the first field is roll number and sixth field is stipend of the student.
01:32	Let us first calculate the HRA for all students.
01:36	Here, HRA is 30% of their stipend amount.
01:41	I have already written the code and saved it as calculate_hra.awk. Let us look into that file now.
01:51	Inside the BEGIN section, the field separator is initialized with the Pipe symbol.
01:57	Then, in the action section we are initializing the array elements.
02:02	This section will get executed once for each line of an input file.
02:08	I have declared HRA as an array variable and dollar one as index.
02:14	Here dollar 1 indicates the 1st field, that is roll number. And, the value is dollar 6 multiplied by zero point 3 wherein dollar six is the stipend value.
02:27	So, array HRA at index roll number will contain the corresponding HRA amount as a value.
02:35	How can we scan all the elements of this array?
02:39	You should use this variation of for loop.
02:43	This loop executes statements once for each index in the array.
02:48	The variable var will be set to the index values one by one.
02:53	The code is written inside END section.
02:57	This section will be executed after awk has processed all the lines of the input file.
03:04	Variable i will be initialized to every index value or roll number one by one.
03:10	In each iteration of the for loop, the HRA for a particular roll number will be printed.
03:16	Switch to the terminal and execute the file. Open the terminal by pressing Ctrl, Alt and T keys.
03:24	Go to the folder in which you downloaded and extracted the Code Files using 'cd' command.
03:31	Now, type: awk space hyphen small f space calculate_hra.awk space awkdemo.txt . Press Enter.
03:45	The output shows the roll number and HRA for all the students.
03:50	Now say, I want to delete the record for the student with roll S02.
03:56	So, we have to delete the array element at index S02.
04:01	Let me do this using the calculate_hra.awk code.
04:06	Before the for loop, press Enter and type the following code: delete space hra within square brackets within double quotes S02.
04:19	Save the file and switch to the terminal.
04:23	Let me clear the terminal.
04:26	Press the up arrow key to get the previously executed command. Press Enter.
04:33	The record for the student with roll number S02 is not printed in the output.
04:39	So, any array element can be deleted using the delete command.
04:44	You have to mention the array name with the index.
04:48	What if I want to delete an entire array? It can be done by specifying only the array name in the delete statement.
04:56	Let us switch to the code to try this.
04:59	Delete the index S02 along with the quotes and square brackets from the delete statement.
05:07	Save the file and switch to the terminal.
05:10	Clear the terminal. Press the up arrow key to get the previously executed command. Now press Enter.
05:19	See, we are not getting any output. The entire array has been deleted.
05:25	Remember, in an earlier tutorial on awk built-in variables, we had said- ARGC implies the number of command line arguments.
05:36	ARGV is an array that stores the command line arguments. How can we show their values? Let us see.
05:45	I have already written the code in argc_argv.awk. Let us check the contents.
05:53	The code is written within awk BEGIN section.
05:57	First we are printing the number of arguments, that is the value of ARGC.
06:03	Next, using the for loop, we are looping for the value of i from 0 to ARGC-1.
06:11	And, we are printing ARGV at index i. Switch to the terminal and execute the file.
06:19	Now, type on the terminal- awk space hyphen small f space argc underscore argv dot awk space one space two space three.
06:35	Here, one two three are the command line arguments. Press Enter to execute the command.
06:43	We get the number of arguments as 4. But recall that we have supplied only 3 arguments.
06:50	Let us have a look at the individual arguments. First argument or argv at index 0 is actually awk, the command name.
07:02	Next, we have three arguments that we supplied in the command line.
07:07	That is why the value of ARGC is always the number of command line arguments supplied plus one.
07:16	Let us take one more example. Built-in variable ENVIRON is an associative array of environment variables.
07:24	The array element indices are the environment variable names. The array element values are the values of the particular environment variables.
07:35	Let us see how we can see the values of different environment variables.
07:40	First, let us print our username.
07:43	We need to print the value of environment variable USER.
07:48	At the command prompt, type the following.
07:53	Press Enter.
07:55	The output will show the name of the user who logged in.
08:00	This brings us to the end of this tutorial. Let us summarize.
08:05	In this tutorial, we learnt about- Using awk array with file,
08:11	Scan the elements of an array,
08:14	Delete statement, ARGV array and ENVIRON array.
08:20	As an assignment- Calculate certain allowances for the students who have passed.
08:25	Paper presentation allowance which is 80% of the stipend,
08:30	Performance incentive which is 20% of the stipend.
08:35	Store the allowances in two different arrays.
08:38	Print the total amount required for each allowance and the average.
08:43	Print the value of environment variable PATH from awk program.
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09:24	The script has been contributed by Antara. And, this is Praveen from IIT Bombay, signing off. Thank you for joining.

Contributors and Content Editors

PoojaMoolya, Sandhya.np14