Linux-AWK/C2/More-on-Single-Dimensional-Array-in-awk/English-timed
From Script | Spoken-Tutorial
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| 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. |
| 08:48 | The video at the following link summarises the Spoken Tutorial project.
Please download and watch it. |
| 08:56 | The Spoken Tutorial Project team conducts workshops using spoken tutorials.
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| 09:08 | Please post your timed queries in this forum. |
| 09:12 | Spoken Tutorial Project is funded by NMEICT, MHRD, Government of India.
More information on this mission is available at this link. |
| 09:24 | The script has been contributed by Antara.
And, this is Praveen from IIT Bombay, signing off. Thank you for joining. |
