Sandhya.np14 at 06:00, 10 July 2019

2019-07-10T06:00:18Z

PoojaMoolya at 05:25, 22 January 2019

2019-01-22T05:25:59Z

PoojaMoolya: Created page with " {| border=1 | '''Time''' | '''Narration''' |- | 00:01 | Hello and Welcome to this spoken tutorial on''' built-in functions''' in '''awk'''..."

2018-12-14T06:09:20Z

Created page with " {| border=1 | <center>'''Time'''</center> | <center>'''Narration'''</center> |- | 00:01 | Hello and Welcome to this spoken tutorial on''' built-in functions''' in '''awk'''..."

New page

{| border=1
| <center>'''Time'''</center>
| <center>'''Narration'''</center>

|-
| 00:01
| Hello and Welcome to this spoken tutorial on''' built-in functions''' in '''awk'''.

|-
| 00:07
| In this tutorial we will learn about different types of '''built-in functions''' like-

'''Arithmetic functions'''

|-
| 00:15
| '''String functions'''

|-
| 00:17
| '''Input/Output functions '''and '''Time-stamp functions'''

|-
| 00:23
|We will do this through some examples.

|-
| 00:26
| To record this tutorial, I am using '''Ubuntu Linux '''16.04 operating system and

'''gedit text editor '''3.20.1

|-
| 00:38
|You can use any text editor of your choice.

|-
|00:42
| To practice this tutorial, you should have gone through the earlier '''awk''' tutorials on this website.

|-
| 00:49
|You should have some knowledge of any programming language like '''C''' or '''C++'''.

|-
| 00:56
|If not, then please go through the corresponding tutorials on our website.

|-
| 01:02
| The files used in this tutorial are available in the '''Code Files''' link on this tutorial page.

Please download and extract them.

|-
| 01:12
| '''Built-in functions''' are always available for '''awk''' to call.

|-
| 01:17
|First we will learn about the '''arithmetic functions.'''

'''square root function (sqrt (x))''' returns positive '''square root''' of a number '''x'''

|-
| 01:27
| '''int''' function truncates '''x''' to an integer value

|-
| 01:32
| '''exponential function''' gives the exponential of '''x'''

|-
| 01:37
| '''log function''' returns natural '''logarithm''' value of '''x'''

|-
| 01:43
| '''sin''' and '''cos''' gives '''sine(x)''' and '''cosine(x)''' respectively

|-
| 01:49
| Please note that '''argument x '''should be mentioned in '''radians'''.

|-
| 01:55
| Let’s look at an example to understand these '''functions'''.

|-
| 02:00
| I have already written the code in a file '''arithmetic underscore function dot awk'''

The same is available in the '''Code Files''' link.

|-
| 02:10
| Here, we are printing the '''square root''' of a positive and negative number respectively.

|-
| 02:17
| Next we are printing the integer value for a positive and negative number respectively.

|-
| 02:24
| Then we are printing exponential of a small number and a very large number.

|-
| 02:31
| After that, natural '''logarithm''' of positive and negative numbers are printed.

|-
| 02:38
| We are also printing '''sine''' and '''cosine''' values of '''0.52 radian''', that is actually '''30 degree.'''

Let us execute the file in the '''terminal.'''

|-
| 02:50
| Open the terminal by pressing Ctrl, Alt and T Keys.

|-
| 02:55
| Next go to the folder where you have downloaded and extracted the file using '''cd''' command.

|-
|03:03
| Now type '''awk space -f space arithmetic_function.awk '''

And press '''Enter '''to see the output.

|-
| 03:14
| Couple of things are clear from this output.

|-
| 03:18
| '''sqrt() function''' gives square root of a positive number.

|-
| 03:23
| It returns '''nan''' or '''not a number''' if the number is negative.

|-
| 03:29
| '''int()''' gives the truncated integer of any positive or negative number.

|-
| 03:36
| '''exp()''' gives exponential of a number.

If the number is very large, the '''function''' will return '''inf'''.

|-
| 03:47
| Natural '''logarithm''' of positive number is given by '''log() function'''.

|-
| 03:53
| If the number if negative, the '''function '''returns '''nan'''.

|-
| 03:58
| '''Sine '''and '''cosine functions '''return corresponding values.

You can verify the value using your calculator.

|-
| 04:07
| Now, let us look at '''random functions.'''

|-
| 04:11
| '''rand()''' returns any random number between 0 and 1. But never returns 0 or 1.

|-
|04:21
| Generated numbers will be random within one '''awk '''execution.

|-
| 04:27
| But predictable across different executions of the '''awk''' program.

|-
|04:33
| '''srand(x)''' is used to provide '''seed value x''' for '''random function.'''

|-
| 04:39
| In absence of '''x''', date and time of day is used as the '''seed value.'''

Let us understand these with an example.

|-
| 04:49
| I have written a code for the '''random function '''and saved it as '''random.awk'''

|-
| 04:56
| Here, inside the '''for loop, rand() function '''will generate a random number between 0 and 1.

|-
| 05:04
| Then the generated number will be multiplied by 50 and get printed.

|-
| 05:10
| So, this code will generate 5 random numbers within 50.

|-
|05:16
| Switch to the '''terminal''' and execute the file.

Let me clear the '''terminal'''.

|-
| 05:23
| Type: '''awk space hyphen f space random dot awk''' and press '''Enter.'''

|-
| 05:31
| See, it is giving 5 random numbers.

|-
| 05:35
| What happens if I execute the code again?

|-
| 05:39
| Press the Up arrow key to get the previously executed command and press '''Enter'''.

|-
| 05:47
| We are getting the same output. Which means, '''awk '''is generating the same set of random numbers for every execution of the script.

|-
| 05:57
| Then how can we get a new set of random numbers in every execution?

Switch to the code once again.

|-
| 06:06
| Before the '''for loop''', type '''srand() function'''

|-
| 06:11
| Press Crtl and S keys to the save the file.

|-
| 06:16
| Now switch to the '''terminal.'''

|-
| 06:19
| Press the Up arrow key to get the previously executed command and press '''Enter'''.

|-
| 06:27
| It is giving a different set of random numbers.

|-
| 06:31
| So, we can generate a new set of random numbers using '''srand function''', when it’s used without an '''argument'''.

|-
| 06:40
| Next will see some '''string functions'''.

'''length function''' gives the length of a particular string '''s'''

|-
| 06:49
| '''index function''' determines the position of''' string s2 '''within the larger '''string s1.'''

|-
| 06:57
| For example, '''index within parentheses within double quotes linux comma within double quotes n''', returns 3.

Let us see an example.

|-
| 07:10
| Open the file '''awkdemo.txt'''

|-
| 07:14
| We know that each student in the '''awkdemo.txt '''file has a 4 digit roll number.

|-
| 07:21
| Due to typing error, the roll numbers may have wrong number of digits.

We can easily detect these using '''awk commands.'''

|-
| 07:30
| Switch to the '''terminal '''.

Let me clear the '''terminal'''.

|-
| 07:36
| Now type the '''command '''as shown here.

Here we are checking the length of the 1st field is equal to 4 or not.

|-
| 07:46
| If not, then that particular record will get printed.

Press '''Enter'''.

|-
| 07:53
| See, there is one roll-number '''S02''' that has been typed incorrectly.

|-
| 08:00
| It has three digits, whereas all others have four digits.

|-
| 08:07
| The '''substr(s,a,b) function '''extracts a '''substring '''from a larger '''string s.'''

|-
| 08:14
| Let me explain the parameters.

|-
| 08:17
| Here '''s''' is the '''string'''

|-
| 08:20
| '''a''' denotes the position in '''s '''from which the extraction would start

|-
| 08:26
| '''b''' denotes the number of characters that would be extracted.

Let us see one example.

|-
| 08:33
| Switch to the''' awkdemo.txt''' file.

|-
| 08:37
| The first letter of the roll numbers represents the '''Hostel code''' where the particular student resides.

|-
| 08:46
| Say we want to find the list of students, who are staying in Hostel '''A'''.

|-
| 08:52
| To get that, let’s switch to the '''terminal'''.

|-
| 08:56
| Type the command as shown here.

|-
| 09:00
| Here we take the '''string''' denoted by '''$1'''.

|-
| 09:05
| As we know '''$1''' represents the first '''field''', that is roll number in our case.

|-
|09:12
| Next, we extract a '''substring''' that starts at position '''one''' with the character length '''one'''.

|-
|09:19
| Then, if it is equal to capital '''A''', then that line from the file will get printed.

Press '''Enter''' to see the output.

|-
| 09:29
| We got the list of students who are in Hostel '''A'''.

|-
| 09:34
| We have seen the '''function split''' earlier.

So, I am not explaining the details here.

|-
| 09:40
| Please refer to the earlier '''awk''' tutorials if you have any doubt.

|-
| 09:45
| There are some other '''functions''' which are related to '''Input/Output'''.

'''system() function''' - helps us to run any '''unix command '''within '''awk'''.

|-
| 09:56
| Now, we will run the '''unix command date''' through '''awk command.'''

|-
|10:01
| In the '''terminal''' type the command as shown here.

And press '''Enter.'''

|-
|10:09
| Today’s date and time is displayed on the '''terminal''' as an output.

|-
| 10:15
| Now, why do we need this? We have kept only the '''BEGIN''' section of the '''awk command. '''

|-
| 10:21
| In real world scenarios, we may want to print the '''system date, '''before displaying the required output.

|-
| 10:28
| In that case, we would need to execute '''system commands''' from '''awk command.'''

|-
| 10:34
| There are some '''functions''' dealing with '''time stamps''' like

'''systime()''', '''strftime() ''', etc.

|-
| 10:43
| Browse through the Internet to know about these '''functions'''.

|-
| 10:48
| This brings us to the end of this tutorial.

Let us summarize.

|-
| 10:53
| In this tutorial we learnt about different types of '''built-in functions''' like

'''Arithmetic functions''', '''String functions''', '''Input/Output functions''' and '''Time stamps functions'''

|-
| 11:06
| As an assignment-Write an '''awk''' program to print the last '''field''' of every record

|-
| 11:13
| where name of the student has small '''u''' as the third letter using the '''awkdemo.txt '''file.

|-
| 11:22
| The video at the following link summarises the Spoken Tutorial project.

Please download and watch it.

|-
| 11:30
| The '''Spoken Tutorial Project''' team conducts workshops using spoken tutorials.

And gives certificates on passing online tests.

For more details, please write to us.

|-
|11:43
| Please post your timed queries in this forum.

|-
| 11:47
| Spoken Tutorial Project is funded by NMEICT, MHRD, Government of India.

More information on this mission is available at this link.

|-
| 11:59
| The script has been contributed by Antara. And this is Praveen from IIT Bombay signing off.

Thank you for joining

|}

Linux-AWK/C2/Built-in-Variables-in-awk/English-timed - Revision history

Sandhya.np14 at 06:00, 10 July 2019

PoojaMoolya at 05:25, 22 January 2019

PoojaMoolya: Created page with " {| border=1 | '''Time''' | '''Narration''' |- | 00:01 | Hello and Welcome to this spoken tutorial on''' built-in functions''' in '''awk'''..."