Difference between revisions of "Linux-AWK/C2/Basics-of-awk/English-timed"

| Welcome to the '''spoken tutorial''' on ''''awk' command'''.

|  In this tutorial, we will learn '''awk command.'''

| To record this tutorial, I am using:

'''Ubuntu Linux''' version '''12.04 OS''',

 

'''GNU BASH''' version '''4.2.24'''

| Please note, '''GNU Bash''' version 4 or above is recommended to practice this tutorial.

| It is named after its authors- Aho, Weinberger and Kernighan.

| It operates at the '''field''' level of a '''record.'''

| So, it can easily access and '''edit''' the individual '''field'''s of the '''record'''.

| For demonstration purpose, we use the '''awkdemo.txt''' file.  

| Now, open the '''terminal''' window by pressing '''Ctrl + Alt''' and '''T''' keys simultaneously on your keyboard.

| Let us see how to '''print''' using '''awk command.'''  

| Type: '''awk space''' (within single quote) (front slash) ''' '/Pass '''(front slash)'''/'''(opening curly bracket) '''{print (closing curly bracket)}''' (after the  quotes) '''space awkdemo.txt'''  

| Press '''Enter'''.

|Here, '''Pass''' is the selection criteria.  

| The action here is '''print'''.  

| We can also use '''regular expressions''' in '''awk'''.

| Say, we want to '''print record'''s of students with name "Mira."

'''awk space '/M (opening square bracket) [ ei (closing square bracket) ]*ra */{print}' space awkdemo.txt'''

| ''' "*" '''  will give one or more occurrences of previous character.

| Thus, entries with more than one occurrence for '''i, e''' and '''a''' will be listed.

| For example-

| Mira with M I R A,

| Meera with M double E R A

| and Meeraa with M double E R double A.

| '''awk''' supports the '''extended regular expressions (ERE)'''

| which means we can match multiple patterns separated by a '''PIPE'''.

|Let me clear the '''prompt'''.

|Now, type: '''awk space (within single quotes)(front slash) ‘/civil(PIPE) |electrical'''(front slash)'''space (opening curly brackets)/{print}(closing curly brackets)''' after the quotes space'''awkdemo.txt'''

| Now entries for both "civil" and "electrical" are given.

|  Let us go back to our '''slide'''s.  

| '''Parameter'''s: '''awk''' has some special parameters to identify individual '''field'''s of a line.  

| Similarly, we can have '''$2, $3''' and so on for respective fields.  

|Come back to our '''terminal'''.

| In this case, '''PIPE '''is called a '''delimiter.'''

| A '''delimiter''' can also be a single white '''space.'''

| To specify a '''delimiter''', we have to give '''- capital F flag''' followed by a '''delimiter'''.

| Let us see.  Type: '''awk space minus capital F space''' within double quotes ''' PIPE space''' within single quote '''front-slash civil PIPE electrical front-slash''' opening curly bracket '''print space dollar0 closing curly bracket after the quotes space awkdemo.txt'''

| Press '''Enter'''.

| This prints the entire line since we have used '''$0.'''

| Notice that '''names''' and '''stream of students''' are the second and third fields.

|Say, we only want to print two fields.

| We will replace '''$0''' with '''$2 and $3''' in the above command.

| Press '''Enter '''.

| Though it gives the right result, the display is all jagged and un-formatted.  

| We can also provide a serial number by using a '''built-in variable 'NR''''.  

| We will see more about '''built-in variable'''s later.

| Now, type '''awk''' space '''minus capital F within double quotes (Pipe)''' after the double quotes space now within single quotes ''' front-slash  Pass front slash opening curly bracket printf (within double quotes)  "percentage sign 4d space percentage sign -25s space percentage sign  minus 15s space backslash n”,''' after the double quotes  '''NR, $2, $3 closing curly bracket' ''' after the single quote space '''awkdemo.txt'''

| Press '''Enter.''' We see the difference.

| Here,  '''NR''' stands for number of '''record'''s.  

| Records are '''integers''', hence we have written '''%d'''.  

| '''Name''' and '''Stream''' are '''strings'''. So, we have used '''%s'''.  

| Here, '''25s''' will reserve 25 '''space'''s for '''Name''' field.

| '''15s''' will reserve 15 '''space'''s for '''Stream''' field.

| The '''minus sign''' is used to '''left justify''' the output.

| Let us move back to our '''slide'''s.

| Let us summarize. In this tutorial, we learnt:  to '''print''' using '''awk''',

| '''regular expression''' in '''awk''', 

to list the entries for a particular '''stream''',

| to list only the second and the third '''field'''s,

| to display a formatted '''output'''.

| As an assignment,  display '''roll no., stream''' and '''marks''' of Ankit Saraf.

|  Watch the video available at the '''link''' shown below.

| It summarizes the '''Spoken Tutorial''' project.

| If you do not have good bandwidth, you can download and watch it.

|The Spoken Tutorial Project Team: conducts workshops using spoken tutorials,

| gives certificates to those who pass an online test.

| For more details, please write to '''contact@spoken-tutorial.org'''

|'''Spoken Tutorial Project''' is a part of the '''Talk to a Teacher project'''.

| It is supported by the National Mission on Education through '''ICT, MHRD,''' Government of India.

| More information on this mission is available at:  [http://spokentutorial.org\NMEICT-Intro]

|This is Ashwini Patil from '''IIT Bombay''', signing off. Thank you for joining.