Linux-AWK/C2/User-Defined-Functions-in-awk/English-timed

Time	Narration
00:01	Hello and welcome to this Spoken Tutorial on User-defined functions in awk.
00:07	In this tutorial, we will learn about- syntax of function definition, function call and 'Return' statement.
00:17	We will do this through some examples.
00:21	To record this tutorial, I am using: Ubuntu Linux 16.04 Operating System and gedit text editor 3.20.1
00:34	You can use any text editor of your choice.
00:38	To practice this tutorial, you should have gone through the earlier awk tutorials on this website.
00:45	You should have some knowledge of any programming language like C or C++.
00:52	If not, then please go through the corresponding tutorials on our website.
00:58	The files used in this tutorial are available in the Code Files link on this tutorial page. Please download and extract them.
01:08	Now, let us learn about user defined functions. The function syntax is as follows.
01:16	And, the syntax is self-explanatory.
01:20	Here, the keyword function is mandatory.
01:24	To call a function, write the name of the function followed by the arguments in parentheses.
01:31	Note: space is not allowed between the function name and the open parentheses of the argument.
01:39	We will see one example now.
01:42	In our awkdemo.txt file, the sixth field represents stipend.
01:47	Assume that stipend is either zero or consists of four digits.
01:54	Suppose, stipend is 8900. Print it as 8 thousand 9 hundred in words.
02:03	If stipend is 0, print as zero in words.
02:08	I have already written the code in a file named user_function.awk
02:15	Here, I have written a function named changeit with a single argument 'argval'.
02:23	Here, argval is basically our sixth field which is stipend.
02:29	Inside the function, the first code will check if argval is zero or not.
02:36	If yes, it will print “Zero” in words.
02:40	If not, then else part of the code will be executed.
02:46	In the else part, first we will extract each digit one by one using the substring function.
02:54	And, we'll store the values in an array a at different indices.
03:00	For example- a[1] will give the first digit from left hand side or the thousand’s place digit.
03:08	Since we have only four digits, I have used four indices.
03:13	Next, we will check whether the elements are not equal to zero. And print them in a proper order.
03:21	At the end, we print a backslash n character to provide a new line break in the output.
03:28	Then, inside the awk script, we have printed dollar 2 which is the second field that is name.
03:35	Then we call the function changeit with the parameter dollar 6 which is stipend. Let’s execute the file.
03:43	Switch to the terminal. Next, go to the folder where you have downloaded and extracted the file using cd command.
03:53	Now, type the following command and press Enter.
04:00	We get the output as expected.
04:03	A user-defined function can also include a return statement.
04:08	This statement returns control to the calling part of the awk program.
04:13	It can also be used to return a value for use in the rest of the awk program.
04:20	It looks like this:return space expression. Here, the expression part is optional.
04:29	Let’s write a function to return average of an array.
04:34	I have written the code in the file average.awk Let’s view the contents.
04:41	We have defined a function named avg for this purpose.
04:46	It has five parameters. arr is the array for which the average is to be calculated.
04:55	i is array loop variable.
04:58	sum is the summation of all array elements.
05:03	n indicates the number of elements in array.
05:07	ret represents the variable to be returned from the function avg. ret will store the calculated average.
05:17	The extra space before i indicates that the variables i, sum, n and ret are local variables.
05:27	Actually, the local variables are not intended to be arguments.
05:32	You should follow this convention when defining functions.
05:36	Inside the for loop, we have calculated the total number and summation of array elements.
05:43	We have calculated the average by dividing summation with the total number of elements and stored that value in variable ret.
05:54	This function avg() returns the value of the variable ret.
06:01	Inside the BEGIN section, we have defined array nums with 5 different numbers.
06:07	In the print statement, we call the function avg() with one argument which is the array name.
06:14	So, you do not have to pass local variables as arguments.
06:20	Switch back to the terminal. Let me clear the terminal.
06:26	Type the following command- awk space hyphen f space average dot awk. Press Enter.
06:37	We get the output as 3.6. You can validate it by using a calculator.
06:44	Let us look at one more example.
06:47	I have written a code to reverse a string and named it as reverse.awk. recursive function is used to reverse a string.
06:57	Pause the video here and look at the code to understand how the control flows. Then execute it to see the output.
07:07	As an assignment, use the function rev to reverse the Roll number field in awkdemo.txt file.
07:16	For example, if the roll number is A001, output should be 100A.
07:24	The code for the same is provided as reverse_roll.awk in the Code Files link.
07:31	This brings us to the end of this tutorial. Let us summarize.
07:36	In this tutorial we learnt about- syntax of function definition,
07:41	function call and Return statement.
07:45	As an assignment- Write a function to create a transpose of a 2D matrix.
07:52	Write a function to return the minimum value element from an array.
07:58	The video at the following link summarises the Spoken Tutorial project. Please download and watch it.
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08:36	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