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

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We can also provide a serial number by using a builtin variable NR.  
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We can also provide a serial number by using a builtin variable '''NR'''.  
  
  
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Here the NR stands for number of records.  
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Here the '''NR''' stands for number of records.  
  
  
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records are integers, hence we have written %d.  
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Records are '''integers''', hence we have written''' %d'''.  
  
  
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Name and stream are strings. So we have used %s.  
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'''Name''' and '''Stream''' are '''strings'''. So we have used '''%s'''.  
  
  
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Here 25s will reserve 25 spaces for Name field.
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Here '''25s''' will reserve 25 spaces for '''Name''' field.
  
  
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15s will reserve for Stream field.
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'''15s''' will reserve for '''Stream''' field.
  
  
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The minus sign is used to left justify the output.
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The '''minus sign''' is used to left justify the output.
  
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This brings us to the end of this tutorial.
 
  
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Let us move back to our slides.
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|-
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| style="border:1pt solid #000000;padding:0.097cm;"| Display Slide 8
  
  
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|style="border:1pt solid #000000;padding:0.176cm;"| This brings us to the end of this tutorial.
  
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|-
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| style="border:1pt solid #000000;padding:0.097cm;"| Display Slide 8
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Let us move back to our slides.
  
  
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|style="border:1pt solid #000000;padding:0.176cm;"| Let us summarize.
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Let us summarize.
  
 
In this tutorial we learnt
 
In this tutorial we learnt

Latest revision as of 16:32, 22 March 2018

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


Introduction

Let us start with an introduction to awk.

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.


Now open the terminal by pressing

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 '/M opening 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 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 and$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.


Display Slide 8


This brings us to the end of this tutorial.


Let us move back to our slides.


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 10

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 11

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 12

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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