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

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(Created page with ''''Title of script''': The Awk tool Part 1 '''Author: Sachin Patil''' '''Keywords: Selection criteria, action, formatted printing, fields, Regular expressions, Variables''' …')
 
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'''Title of script''': The Awk tool Part 1
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'''Title of script''': The Awk Command
  
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'''Author: Sachin Patil'''
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'''Author: Sachin Patil and Anirban'''
  
 
'''Keywords: Selection criteria, action, formatted printing, fields, Regular expressions, Variables'''
 
'''Keywords: Selection criteria, action, formatted printing, fields, Regular expressions, Variables'''
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|-
 
|-
 
| style="border:1pt solid #000000;padding:0.097cm;"| Display Slide 1
 
| style="border:1pt solid #000000;padding:0.097cm;"| Display Slide 1
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| style="border:1pt solid #000000;padding:0.097cm;"| Welcome to this spoken tutorial on the '''awk''' command.
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| style="border:1pt solid #000000;padding:0.097cm;"| Welcome to the spoken tutorial on the '''awk''' command.
  
 
|-
 
|-
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awk command.
 
awk command.
 +
 +
We will do this through some examples.
  
 
|-
 
|-
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Ubuntu Linux 12.04 OS
 
Ubuntu Linux 12.04 OS
  
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GNU BASH v. 4.2.24(1)
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GNU BASH v. 4.2.24
  
 
Please note, GNU bash version 4 or above is recommended to practice this tutorial.
 
Please note, GNU bash version 4 or above is recommended to practice this tutorial.
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|-
 
|-
 
| style="border:1pt solid #000000;padding:0.097cm;"| Display Slide 4
 
| style="border:1pt solid #000000;padding:0.097cm;"| Display Slide 4
 +
 +
Let us start with an introduction to awk.
  
 
Introduction
 
Introduction
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| style="border:1pt solid #000000;padding:0.097cm;"| The''' awk''' command is a very powerful text manipulation tool of Linux.  
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| style="border:1pt solid #000000;padding:0.097cm;"| The''' awk''' command is a very powerful text manipulation tool.
  
 
It is named after its authors, Aho, Weinberger and Kernighan.
 
It is named after its authors, Aho, Weinberger and Kernighan.
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For demonstration purpose we use the''' awkdemo.txt '''file.  
 
For demonstration purpose we use the''' awkdemo.txt '''file.  
  
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Let us see the contents of '''awkdemo.txt'''.
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Let us see the contents of '''awkdemo.txt''' file.
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+
  
 
|-
 
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|-
 
|-
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| style="border:1pt solid #000000;padding:0.176cm;"| Open the terminal
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| style="border:1pt solid #000000;padding:0.176cm;"| Now open the terminal  
  
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'''ctrl+alt+t'''
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'''CTRL + ALT and T keys''' simultaneosuly on your keyboard.
  
  
 
type:
 
type:
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| style="border:1pt solid #000000;padding:0.097cm;"| Now open the terminal by pressing '''ctrl+alt+t'''
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| style="border:1pt solid #000000;padding:0.097cm;"| Now open the terminal by pressing '''CTRL + ALT and T keys''' simultaneosuly on your keyboard.
  
 
|-
 
|-
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"awk '/Pass/ {print}' awkdemo.txt<nowiki>" [</nowiki>enter]
 
"awk '/Pass/ {print}' awkdemo.txt<nowiki>" [</nowiki>enter]
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| style="border:1pt solid #000000;padding:0.097cm;"| Now type:
+
| style="border:1pt solid #000000;padding:0.097cm;"| 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'''
  
−
'''awk''' space (opening single quote) (front slash) ‘'''/Pass '''(front slash)'''/'''(in curly brace) '''{print}''' (closing single quote) space '''awkdemo.txt'''
 
  
 +
Press '''Enter'''
  
 
Here '''Pass''' is the selection criterion.  
 
Here '''Pass''' is the selection criterion.  
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'''awk''' space ''''/M<nowiki>[</nowiki>ei]*ra<nowiki>*/{</nowiki>print}'''' space '''awkdemo.txt'''
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'''awk''' space ''''/M<nowiki>opening square bracket [</nowiki>ei closing square bracket ]*ra<nowiki>*/{</nowiki>print}'''' space '''awkdemo.txt'''
  
  
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Meeraa
 
Meeraa
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−
 
  
  
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"awk '/civil|electrical/ {print}' awkdemo<nowiki>" [</nowiki>enter]
 
"awk '/civil|electrical/ {print}' awkdemo<nowiki>" [</nowiki>enter]
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| style="border:1pt solid #000000;padding:0.097cm;"| Type at the terminal:
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| style="border:1pt solid #000000;padding:0.097cm;"| Now type:
  
  
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| style="border:1pt solid #000000;padding:0.097cm;"| Lets go back to the slides.  
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| style="border:1pt solid #000000;padding:0.097cm;"| Let us go back to our slides.  
  
  
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To specify a delimiter we have to give '''-F '''flag followed by a delimiter.
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To specify a delimiter we have to give '''- capital F '''flag followed by a delimiter.
  
  
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Within curly braces''' print''' space '''dollar0 '''now outside the quotes space''' awkdemo.txt'''
 
Within curly braces''' print''' space '''dollar0 '''now outside the quotes space''' awkdemo.txt'''
  
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Press '''Enter'''
  
 
This print the entire line since we have used '''$0.'''
 
This print the entire line since we have used '''$0.'''
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Let’s try.
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press '''Enter '''
  
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Only two fields are shown.
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press '''Enter '''
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|-
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We would write:
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Now type:
  
 
'''awk''' space '''-F”|”''' space ''''/Pass/{printf “%4d %-25s %-15s \n”,''' '''NR,$2,$3 }'''' space '''awkdemo.txt'''  
 
'''awk''' space '''-F”|”''' space ''''/Pass/{printf “%4d %-25s %-15s \n”,''' '''NR,$2,$3 }'''' space '''awkdemo.txt'''  
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'''Press Enter.'''
 
'''Press Enter.'''
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We see the difference.
  
  
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The minus sign is used to left justify the output.
 
The minus sign is used to left justify the output.
  
 +
This brings us to the end of this tutorial.
 +
 +
Let us move back to our slides.
 +
 +
 +
 +
|-
 +
| style="border:1pt solid #000000;padding:0.097cm;"| Display Slide 8
 +
 +
| Let us summarize.
 +
 +
In this tutorial we learnt
 +
 +
To print using awk
 +
 +
Regular expression in awk
 +
 +
To list the enteries for a paritcular stream
 +
 +
To list only the second and the third fileds
 +
 +
To display a formatted output
 +
 +
 +
|-
 +
| style="border:1pt solid #000000;padding:0.097cm;"| Display Slide 9
 +
 +
| As an assignment
  
 +
Display roll no., stream and marks of Ankti Saraf
  
  

Revision as of 15:50, 14 December 2013

Title of script: The Awk Command

Author: Sachin Patil and Anirban

Keywords: Selection criteria, action, formatted printing, fields, Regular expressions, Variables


Visual Cue
Narration
Display Slide 1 Welcome to the spoken tutorial on the awk command.
Display Slide 2

Learning Objective

In this tutorial we will learn,

awk command.

We will do this through some examples.

Display Slide 3

System requirement

To record this tutorial, I am using

Ubuntu Linux 12.04 OS

GNU BASH v. 4.2.24

Please note, GNU bash version 4 or above is recommended to practice this tutorial.

Display Slide 4

Let us start with an introduction to awk.

Introduction

The awk command is a very powerful text manipulation tool.

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

Continue Slide


It can perform several functions.

It operates at the field level of a record.

So, it can easily access and edit the individual fields of the record.

Let us see some examples.

For demonstration purpose we use the awkdemo.txt file.

Let us see the contents of awkdemo.txt file.

awkdemo.txt This is the content of awkdemo.txt file.
Now open the terminal

CTRL + ALT and T keys simultaneosuly on your keyboard.


type:

Now open the terminal by pressing CTRL + ALT and T keys simultaneosuly on your keyboard.
type:


"awk '/Pass/ {print}' awkdemo.txt" [enter]

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 criterion.


All the lines of the awkdemo where Pass occurs are printed.


The action here is print.

Type

"awk '/M[ei]*ra*/ {print}' awkdemo.txt" [enter]

We can also use regular expressions in awk


Say we want to print records of students with name Mira.


We would type:


awk space '/Mopening square bracket [ei closing square bracket ]*ra*/{print}' space awkdemo.txt


Press Enter.


* 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 ex. Meera

Mira

Meeraa


awk supports the extended regular expressions (ERE).

Which means we can match multiple patterns separated by a PIPE.

Type

"awk '/civil|electrical/ {print}' awkdemo" [enter]

Now type:


awk space (in single quotes)(front slash) ‘/civil (vertical bar)|electrical (front slash)/{print}' awkdemo.txt


Press Enter.


Now entries for both civil and electrical are shown.

Display slide 7


Let us go back to our slides.


Awk has some special parameters to identify individual fields of a line.


$1(Dollar 1) would indicate the first field.


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


$0 represents the entire line.

Switch to the terminal


Type: cat awkdemo.txt

Note that each word is separated by PIPE in the file awkdemo.txt.


In this case PIPE is called a delimiter.


A delimiter separates words from each other.


A delimiter can also be a single whitespace.


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



Type

“awk -F "|" '/civil|electrical/ {print $0}' awkdemo ” [enter]


Lets go back to the terminal.


So we can write the last command as:


awk space minus capital F space


Within double quotes PIPE space


Within single quote front slash civil PIPE electrical front slash


Within curly braces print space dollar0 now outside the quotes space awkdemo.txt

Press Enter

This print the entire line since we have used $0.

Type

“awk -F"|" '/Pass/ {print $2, $3}' awkdemo” [enter]

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,$3 in the above command.


press Enter

Only two fields are shown.

Though it gives the right result the display is all jagged and unformatted.



“awk -F"|" '/Pass/ {printf "%4d %-25s %-15s \n",

NR,$2,$3 }' awkdemo” [enter]


We can provide formatted output by using the C style printf statement.


We can also provide a serial number by using a builtin variable NR.


We will see more about builtin variables later.


Now type:

awk space -F”|” space '/Pass/{printf “%4d %-25s %-15s \n”, NR,$2,$3 }' space awkdemo.txt


Press Enter.

We see the difference.


Here the NR stands for number of records.


records are integers, hence we have written %d.


Name and stream are strings. So we have used %s.


Here 25s will reserve 25 spaces for Name field.


15s will reserve for Stream field.


The minus sign is used to left justify the output.

This brings us to the end of this tutorial.

Let us move back to our slides.


Display Slide 8 Let us summarize.

In this tutorial we learnt

To print using awk

Regular expression in awk

To list the enteries for a paritcular stream

To list only the second and the third fileds

To display a formatted output


Display Slide 9 As an assignment

Display roll no., stream and marks of Ankti Saraf


Display Slide 11

Acknowledgement Slide


Watch the video available at the link shown below

It summarises the Spoken Tutorial project

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

Display Slide 12

Spoken Tutorial Workshops


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

Display Slide 13

Acknowledgement


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://spoken-tutorial.org\NMEICT-Intro

No Last Slide for tutorials created at IITB

Display the previous slide only and narrate this line.

The script has been contributed by Sachin Patil.

This is Ashwini Patil from IIT Bombay signning off. Thank you for joining.

Contributors and Content Editors

Ashwini, Nancyvarkey

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