PoojaMoolya: Created page with "'''Title of script''': The Awk Command '''Author: Sachin Patil and Anirban''' '''Keywords: Selection criteria, action, formatted printing, fields, Regular expressions, Varia..."

2015-01-29T07:34:00Z

Created page with "'''Title of script''': The Awk Command '''Author: Sachin Patil and Anirban''' '''Keywords: Selection criteria, action, formatted printing, fields, Regular expressions, Varia..."

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'''Title of script''': The Awk Command

'''Author: Sachin Patil and Anirban'''

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

{| style="border-spacing:0;"
| style="border:1pt solid #000000;padding:0.097cm;"| <center>'''Visual Cue'''</center>
| style="border:1pt solid #000000;padding:0.097cm;"| <center>'''Narration'''</center>

|-
| style="border:1pt solid #000000;padding:0.097cm;"| Display Slide 1
| style="border:1pt solid #000000;padding:0.097cm;"| Welcome to the spoken tutorial on the '''awk''' command.

|-
| style="border:1pt solid #000000;padding:0.176cm;"| Display Slide 2

Learning Objective
| style="border:1pt solid #000000;padding:0.176cm;"| In this tutorial we will learn,

'''awk command.'''

We will do this through some examples.

|-
| style="border:1pt solid #000000;padding:0.176cm;"| Display Slide 3

System requirement
| style="border:1pt solid #000000;padding:0.176cm;"| To record this tutorial, I am using

*Linux Operating system
*GNU BASH v. 4.2.24

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

|-
| style="border:1pt solid #000000;padding:0.097cm;"| Display Slide 4

Introduction
| style="border:1pt solid #000000;padding:0.097cm;"| 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'''.

|-
| style="border:1pt solid #000000;padding:0.097cm;"| Continue Slide

| style="border:1pt solid #000000;padding:0.097cm;"| 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.

|-
| style="border:1pt solid #000000;padding:0.097cm;"|
| style="border:1pt solid #000000;padding:0.097cm;"| Let us see some examples.

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

Let us see the contents of '''awkdemo.txt''' file.

|-
| style="border:1pt solid #000000;padding:0.176cm;"| Now open the '''terminal''' window

type:
| style="border:1pt solid #000000;padding:0.097cm;"| Now open the terminal window
|-
| style="border:1pt solid #000000;padding:0.097cm;"| type:

"awk '/Pass/ {print}' awkdemo.txt<nowiki>" [</nowiki>enter]
| 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'''

Press '''Enter'''

|-
| style="border:1pt solid #000000;padding:0.097cm;"|
| style="border:1pt solid #000000;padding:0.097cm;"|Here '''Pass''' is the selection criterion.

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

The action here is print.

|-
| style="border:1pt solid #000000;padding:0.097cm;"| Type

"awk '/M<nowiki>[</nowiki>ei]*ra<nowiki>*/ {</nowiki>print}' awkdemo.txt<nowiki>" [</nowiki>enter]
| style="border:1pt solid #000000;padding:0.097cm;"| We can also use '''regular expressions''' in '''awk'''

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

|-
| style="border:1pt solid #000000;padding:0.097cm;"|
| style="border:1pt solid #000000;padding:0.097cm;"|We would type:

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

Press '''Enter.'''

|-
| style="border:1pt solid #000000;padding:0.097cm;"|
| style="border:1pt solid #000000;padding:0.097cm;"| '''"*"''' 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.
*Mira (with M I R A)
*Meera (with M E E R A)
*Meeraa (with M E E R A A )

|-
| style="border:1pt solid #000000;padding:0.097cm;"|
| style="border:1pt solid #000000;padding:0.097cm;"| '''awk''' supports the '''extended regular expressions (ERE)'''.

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

|-
| style="border:1pt solid #000000;padding:0.097cm;"| Type

"awk '/civil|electrical/ {print}' awkdemo<nowiki>" [</nowiki>enter]
| style="border:1pt solid #000000;padding:0.097cm;"| Now type:

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

Press '''Enter.'''

Now entries for both '''civil''' and '''electrical''' are shown.

|-
| style="border:1pt solid #000000;padding:0.097cm;"| Display slide 7

| style="border:1pt solid #000000;padding:0.097cm;"| 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.

|-
| style="border:1pt solid #000000;padding:0.176cm;"| Switch to the terminal

Type: cat awkdemo.txt
| style="border:1pt solid #000000;padding:0.176cm;"| Come back to our terminal. 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'''.

|-
| style="border:1pt solid #000000;padding:0.176cm;"| Type

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

| style="border:1pt solid #000000;padding:0.176cm;"|

Let us see,

'''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.'''

|-
| style="border:1pt solid #000000;padding:0.097cm;"| Type

“awk -F"|" '/Pass/ {print $2, $3}' awkdemo<nowiki>” [</nowiki>enter]
| style="border:1pt solid #000000;padding:0.097cm;"| Notice that, '''names''' and '''stream of students''' are the second and third fields.

|-
| style="border:1pt solid #000000;padding:0.097cm;"|
| style="border:1pt solid #000000;padding:0.097cm;"|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.

|-
| style="border:1pt solid #000000;padding:0.097cm;"|
| style="border:1pt solid #000000;padding:0.097cm;"| Though it gives the right result, the display is all jagged and unformatted.

|-
| style="border:1pt solid #000000;padding:0.176cm;"| “awk -F"|" '/Pass/ {printf "%4d %-25s %-15s \n",

NR,$2,$3 }' awkdemo” <nowiki>[</nowiki>enter]

| style="border:1pt solid #000000;padding:0.176cm;"| 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.

|-
| style="border:1pt solid #000000;padding:0.097cm;"| Display Slide 8

|style="border:1pt solid #000000;padding:0.176cm;"| 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

|-
| style="border:1pt solid #000000;padding:0.097cm;"| Display Slide 9

| style="border:1pt solid #000000;padding:0.176cm;" | As an assignment

Display roll no., stream and marks of Ankti Saraf

|-
| style="border:1pt solid #000000;padding:0.097cm;"| Display Slide 10

Acknowledgement Slide

| style="border:1pt solid #000000;padding:0.097cm;"| 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

|-
| style="border:1pt solid #000000;padding:0.176cm;"| Display Slide 11

Spoken Tutorial Workshops

| style="border:1pt solid #000000;padding:0.176cm;"| 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

|-
| style="border:1pt solid #000000;padding:0.176cm;"| Display Slide 12

Acknowledgement

| style="border:1pt solid #000000;padding:0.176cm;"| 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/ http][http://spoken-tutorial.org/ ://][http://spoken-tutorial.org/ spoken][http://spoken-tutorial.org/ -][http://spoken-tutorial.org/ tutorial][http://spoken-tutorial.org/ .][http://spoken-tutorial.org/ org]\NMEICT-Intro

|-
| style="border-top:none;border-bottom:1pt solid #000000;border-left:1pt solid #000000;border-right:1pt solid #000000;padding:0.176cm;"| No Last Slide for tutorials created at IITB

Display the previous slide only and narrate this line.
| style="border-top:none;border-bottom:1pt solid #000000;border-left:1pt solid #000000;border-right:1pt solid #000000;padding:0.176cm;"| This is Ashwini Patil from IIT Bombay signning off. Thank you for joining.

|}

BOSS-Linux/C3/Basics-of-awk/English - Revision history

PoojaMoolya: Created page with "'''Title of script''': The Awk Command '''Author: Sachin Patil and Anirban''' '''Keywords: Selection criteria, action, formatted printing, fields, Regular expressions, Varia..."