Difference between revisions of "Linux-AWK/C2/More-on-Single-Dimensional-Array-in-awk/English"

• Using awk array with file
• Scan the elements of an array
• Delete statement
• ARGV array and ENVIRON array

We will do this through some examples.

System requirement

• Ubuntu Linux 16.04 Operating System and
• gedit text editor 3.20.1

You can use any text editor of your choice.

prerequisite

You should have some basic knowledge of any programming language like C or C++.

If not, then please go through the corresponding tutorials on our website.

Please download and extract them.

Now let us see how we can use awk array with a file.

Let us first calculate the HRA for all students.

Here, HRA is 30% of their stipend amount.

I have already written the code and saved it as calculate_hra.awk.

Let us look in to that file now.

and highlight appropriately

Then, in the action section we are initializing the array elements.

This section will get executed once for each line of an input file.

I have declared HRA as an array variable and dollar one as index.

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.

So, array HRA at index roll number will contain the corresponding HRA amount as a value.

You should use this variation of for loop.

This loop executes statements once for each index in the array.

The variable var will be set to the index values one by one.

and highlight appropriately

This section will be executed after awk has processed all the lines of the input file.

Variable i will be initialized to every index value or roll number one by one.

In each iteration of the for loop, the HRA for a particular roll number will be printed.

Open the terminal by pressing Ctrl, Alt and T keys.

awk -f calculate_hra.awk awkdemo.txt

[Enter]

awk space hyphen small f space calculate_hra.awk space awkdemo.txt

Press Enter

So, we have to delete the array element at index S02.

Let me do this using the calculate_hra.awk code.

delete hra["S02"] before for loop

delete space hra within square brackets within double quotes S02

[Enter]

Press the Up arrow key to get the previously executed command.

Press Enter.

• So, any array element can be deleted using the delete command.
• You have to mention the array name with the index.
• What if I want to delete an entire array?
• It can be done by specifying only the array name in the delete statement

Let us switch to the code to try this.

[Enter]

Press the Up arrow key to get the previously executed command.

Now press Enter.

The entire array has been deleted.

ARGC implies the number of command line arguments.

ARGV is an array that stores the command line arguments.

How can we show their values?

Let us see.

Let us check the contents.

Point as per narration

First we are printing the number of arguments, that is the value of ARGV.

Next, using the for loop, we are looping for the value of i from 0 to ARGC-1.

And we are printing ARGV at index i

Switch to the terminal and execute the file.

awk space hyphen small f space argc underscore argv dot awk space one space two space three

Here one two three are the command line arguments.

Press Enter to execute the command.

But recall that we have supplied only 3 arguments.

Let us have a look at the individual arguments.

First argument or argv at index 0 is actually awk, the command name.

Next we have three arguments that we supplied in the command line.

That is why the value of ARGC is always the number of command line arguments supplied plus one.

Built-in variable ENVIRON is an associative array of environment variables.

The array element values are the values of the particular environment variables.

First, let us print our username.

We need to print the value of environment variable USER.

awk 'BEGIN { print ENVIRON["USER"] }'

[Enter]

Press Enter

This brings us to the end of this tutorial.

Let us summarize.

Summary

• Using awk array with file
• Scan the elements of an array
• Delete statement
• ARGV array and ENVIRON array

Assignment

Calculate certain allowances for the students who have passed.

1. Paper presentation allowance which is 80% of the stipend
2. Performance incentive which is 20% of the stipend

Assignment

Print the total amount required for each allowance and the average.

Print the value of environment variable PATH from awk program.

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