View source for Linux/C3/Basics-of-awk/Khasi

{| border=1
| '''Time'''
| '''Narration'''

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|  00:01
| Pdiang sngewbha sha kane ka spoken tutorial halor ka '''awk''' command.

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|00:05 
| Ha kane ka tutorial, ngin pule iaka jingpyndonkam In this tutorial we will learn '''awk command.'''

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| 00:09
| We will do this through some examples.

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| 00:12
| To record this tutorial, I am using:
Ubuntu Linux 12.04 OS
GNU BASH v. 4.2.24

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| 00:23
| Please note, GNU Bash version 4 or above is recommended to practice this tutorial.

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| 00:29
| Let us start with an introduction to '''awk'''.

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| 00:33
| The''' awk''' command is a very powerful text manipulation tool.

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| 00:38
| It is named after its authors, Aho, Weinberger and Kernighan.

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| 00:44
| It can perform several functions. 

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| 00:46
| It operates at the field level of a record. 

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| 00:51
| So, it can easily access and edit the individual fields of the record.

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| 00:56
| Let us see some examples. 

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| 00:59
| For demonstration purpose, we use the '''awkdemo.txt''' file. 

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| 01:04
| Let us see the contents of '''awkdemo.txt''' file.

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| 01:09
| Now open the '''terminal''' window by pressing '''Ctrl + Alt''' and '''T''' keys simultaneously on your keyboard.

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| 01:17
| Let us see how to print using '''awk command.''' 

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| 01:22
| 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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| 01:38
| Press '''Enter'''.

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| 01:40
|Here, '''Pass''' is the selection criteria. 

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| 01:44
| All the lines of the '''awkdemo''' where '''Pass''' occurs are printed. 

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| 01:49
| The action here is print. 

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| 01:52
| We can also use '''regular expressions''' in '''awk'''.

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| 01:56
| Say, we want to print records of students with name "Mira."

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| 02:01
| We would type:
'''awk space '/M (opening square bracket) [ ei (closing square bracket) ]*ra */{print}' space awkdemo.txt'''

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| 02:27
| Press '''Enter.'''

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| 02:29
| ''' "*" '''  will give one or more occurrences of previous character.

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| 02:33
| Thus, entries with more than one occurrence for '''i, e''' and '''a''' will be listed.

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| 02:40
| For example, 

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| 02:42
| Mira with M I R A

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|02:45 
| Meera with M double E R A

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| 02:47
| and Meeraa with M double E R double A

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| 02:52
| '''awk''' supports the '''extended regular expressions (ERE)'''

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| 02:58
| Which means we can match multiple patterns separated by a '''PIPE'''.
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|03:03
|Let me clear the prompt.

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|03:05
|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'''

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| 03:23
| Press '''Enter.'''

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| 03:26
| Now entries for both "civil" and "electrical" are given.

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| 03:31
|  Let us go back to our slides. 

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| 03:34
| Parameters: '''awk''' has some special parameters to identify individual fields of a line. 

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| 03:41
| '''$1(Dollar 1)''' would indicate the first field. 

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| 03:45
| Similarly we can have '''$2, $3''' and so on for respective fields. 

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| 03:53
| '''$0''' represents the entire line.

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|03:56
|come back to our terminal.

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| 03:59
|Note that each word is separated by '''PIPE''' in the file '''awkdemo.txt.'''

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| 04:05
| In this case '''PIPE '''is called a '''delimiter.'''

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| 04:09
| A '''delimiter''' separates words from each other.

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| 04:13
| A '''delimiter''' can also be a single '''white space.'''

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| 04:16
| To specify a '''delimiter''', we have to give '''- capital F flag''' followed by a '''delimiter'''.

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|04:24
| 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'''

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| 04:51
| Press '''Enter'''.

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| 04:53
| This prints the entire line since we have used '''$0.'''

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| 04:58
| Notice that '''names''' and '''stream of students''' are the second and third fields.

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| 05:04
|Say we only want to print two fields.

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| 05:08
| We will replace '''$0''' with '''$2 and $3''' in the above command.

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| 05:15
| Press '''Enter '''.

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| 05:18
| Only two fields are shown.

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| 05:21
| Though it gives the right result, the display is all jagged and un-formatted. 

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| 05:26
|  We can provide formatted output by using the '''C''' style '''printf '''statement. 

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| 05:32
| We can also provide a serial number by using a built-in variable '''NR'''. 

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| 05:40
| We will see more about built-in variables later.

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| 05:44
| Now Type '''awk''' space '''minus capital F within double quotes (Pipe)''' after the double quotes space ''' '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'''  

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| 06:33
| Press '''Enter.'''  We see the difference.

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| 06:37
| Here,  '''NR''' stands for number of records. 

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| 06:41
| Records are '''integers''', hence we have written '''%d'''. 

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| 06:45
| '''Name''' and '''Stream''' are '''strings'''. So we have used '''%s'''. 

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| 06:50
| Here '''25s''' will reserve 25 '''spaces''' for '''Name''' field.

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| 06:55
| '''15s''' will reserve 15 '''spaces''' for '''Stream''' field.

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| 07:01
| The '''minus sign''' is used to left justify the output.

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| 07:05
| This brings us to the end of this tutorial.

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| 07:08
| Let us move back to our slides.

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| 07:10
| Let us summarize.  In this tutorial we learnt: * To print using awk

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| 07:16
| Regular expression in awk * To list the entries for a particular stream

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| 07:21
| To list only the second and the third fields

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| 07:24
| To display a formatted output.

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| 07:28
| As an assignment,  display '''roll no., stream''' and '''marks''' of Ankit Saraf.

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| 07:34
|  Watch the video available at the link shown below.

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| 07:37
| It summarizes the Spoken Tutorial project.

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| 07:40
| If you do not have good bandwidth, you can download and watch it.

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|07:45
|The Spoken Tutorial Project Team: Conducts workshops using spoken tutorials.

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| 07:48
| Gives certificates to those who pass an online test.

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| 07:52
| For more details, please write to contact@spoken-tutorial.org

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| 07:58
|Spoken Tutorial Project is a part of the Talk to a Teacher project.

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| 08:01
| It is supported by the National Mission on Education through ICT,MHRD,Government of India.

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| 08:07
| More information on this Mission is available at:  [http://spokentutorial.org\NMEICT-Intro]

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| 08:12
|This is Ashwini Patil from IIT Bombay, signning off. Thank you for joining.

|}