Linux-AWK/C2/Basics-of-awk/English
Title of script: The Awk Command
Author: Sachin Patil and Anirban
Keywords: Selection criteria, action, formatted printing, fields, Regular expressions, Variables
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Display Slide 1 | Welcome to the spoken tutorial on the awk command. |
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Learning Objective |
In this tutorial we will learn,
awk command. We will do this through some examples. |
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System requirement |
To record this tutorial, I am using
Please note, GNU Bash version 4 or above is recommended to practice this tutorial. |
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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. |
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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.
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Now open the terminal by pressing
CTRL + ALT and T keys simultaneosuly on your keyboard.
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Now open the terminal by pressing CTRL + ALT and T keys simultaneosuly on your keyboard. |
type:
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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
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Here Pass is the selection criterion.
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Type
"awk '/M[ei]*ra*/ {print}' awkdemo.txt" [enter] |
We can also use regular expressions in awk
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We would type:
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"*" will give one or more occurrences of previous character.
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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:
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Display slide 7
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Let us go back to our slides.
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Switch to the terminal
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Note that each word is separated by PIPE in the file awkdemo.txt.
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Type
“awk -F "|" '/civil|electrical/ {print $0}' awkdemo ” [enter]
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Lets go back to the terminal.
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.
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Say we only want to print two fields.
Only two fields are shown. | |
Though it gives the right result, the display is all jagged and unformatted.
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“awk -F"|" '/Pass/ {printf "%4d %-25s %-15s \n",
NR,$2,$3 }' awkdemo” [enter]
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We can provide formatted output by using the C style printf statement.
awk space -F”|” space '/Pass/{printf “%4d %-25s %-15s \n”, NR,$2,$3 }' space awkdemo.txt
We see the difference.
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This brings us to the end of this tutorial.
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
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Display Slide 9 | As an assignment
Display roll no., stream and marks of Ankti Saraf
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Acknowledgement Slide
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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 |
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Spoken Tutorial Workshops
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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 |
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Acknowledgement
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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. |