Difference between revisions of "Linux/C3/The-grep-command/English"

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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
 
| style="border:1pt solid #000000;padding:0.097cm;"| Welcome to the spoken tutorial on '''grep''' command
 
| style="border:1pt solid #000000;padding:0.097cm;"| Welcome to the spoken tutorial on '''grep''' command
 +
  
 
|-
 
|-
 
| style="border:1pt solid #000000;padding:0.097cm;"| Display Slide 2
 
| style="border:1pt solid #000000;padding:0.097cm;"| Display Slide 2
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| style="border:1pt solid #000000;padding:0.097cm;"| In this tutorial we will learn usage of grep command.
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| style="border:1pt solid #000000;padding:0.097cm;"| In this tutorial we will learn
 +
grep command.
 +
We will do this with the help of an examples.
  
 
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|-
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'''Ubuntu Linux''' 12.04''' Operating System''' and
 
'''Ubuntu Linux''' 12.04''' Operating System''' and
  
−
'''GNU BASH''' version 4.2.24(1)
+
'''GNU BASH''' version 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
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| style="border:1pt solid #000000;padding:0.097cm;"| To practice this tutorial,
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| style="border:1pt solid #000000;padding:0.097cm;"| As prerequisites
  
 
You should know Basics of linux terminal
 
You should know Basics of linux terminal
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To find a keyword in a paragraph or a line, we use grep command
 
To find a keyword in a paragraph or a line, we use grep command
 +
Let us move on to grep.
  
 
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|-
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“'''grepdemo.txt'''<nowiki>” [</nowiki>enter]
 
“'''grepdemo.txt'''<nowiki>” [</nowiki>enter]
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| style="border:1pt solid #000000;padding:0.097cm;"| We will demonstrate usage of '''grep''' using a demo file '''grepdemo.txt'''
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| style="border:1pt solid #000000;padding:0.097cm;"| I will demonstrate usage of '''grep''' using a demo file '''grepdemo.txt'''
  
  
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The fields are separated by a bar, which is called a '''delimiter'''.
 
The fields are separated by a bar, which is called a '''delimiter'''.
 +
  
 
|-
 
|-
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−
Say we want to see who are the students in the '''computers''' stream.
+
Say we want to use grep command to see who are the students in the '''computers''' stream.
 +
For this we have to open the terminal.
 +
So press '''CTRL + ALT and T''' keys simultaneously on your keyboard.
  
−
I would type:
+
Now type on the terminal:
  
  
−
'''grep '''space (in double quotes) '''computers''' space '''grepdemo.txt'''
+
'''grep '''space (within double quotes) '''computers''' space '''grepdemo.txt'''
  
  
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−
Compare the result with the original file.  
+
Now Compare the result with the original file.
 +
Come back to our text editor.
  
−
We see that the entry for''' Zubin''' is not enlisted.
+
We see that the entry for ''' Zubin''' is not enlisted.
  
  
−
Why is this so?
+
Why this is so?
  
 
This is because '''grep''' searched for the pattern '''“computers”''' with small '''c'''  
 
This is because '''grep''' searched for the pattern '''“computers”''' with small '''c'''  
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| style="border:1pt solid #000000;padding:0.097cm;"| The pattern matching is case sensitive.
 
| style="border:1pt solid #000000;padding:0.097cm;"| The pattern matching is case sensitive.
  
−
To make it case insensitive, we need to use the '''minus i '''option with '''grep'''.
+
To make it case insensitive, we need to use the '''minus i ''' option with '''grep'''.
  
 
Type:
 
Type:
  
−
'''grep''' space (minus''') i''' space (in double quotes) “'''computers”''' space '''grepdemo.txt'''
+
'''grep''' space (minus''') i''' space (within double quotes) “'''computers”''' after the double quotes space '''grepdemo.txt'''
  
  
−
Press''' Enter.'''
+
Press ''' Enter.'''
  
  
 
This will now enlist all the four entries.
 
This will now enlist all the four entries.
 +
  
 
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|-
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−
Type:
+
For this Type:
  
  
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'''press Enter'''
 
'''press Enter'''
 +
The output is displayed.
  
 
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|-
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At the prompt type:
 
At the prompt type:
  
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'''grep''' space '''minus i''' space in double quotes '''fail''' space '''grepdemo.txt'''
+
'''grep''' space '''minus i''' space within double quotes '''fail''' after the double quotes space '''grepdemo.txt'''
  
  
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We have the '''minus n''' option
 
We have the '''minus n''' option
−
 
−
 
  
  

Revision as of 13:24, 14 December 2013

Title of script: The grep command and Regular Expressions

Author : Sachin Patil

Keywords:Search,Pattern,regular expressions,extended regular expression


Visual Cue
Narration
Display Slide 1 Welcome to the spoken tutorial on grep command


Display Slide 2 In this tutorial we will learn

grep command. We will do this with the help of an examples.

Display Slide 3 To record this tutorial, I am using

Ubuntu Linux 12.04 Operating System and

GNU BASH version 4.2.24

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

Display Slide 4 As prerequisites

You should know Basics of linux terminal

For relevant tutorials please visit our website:

http://spoken-tutorial.org

First let us know about regular expressions.

Regular expressions are pattern matching techniques.

When we have to find out whether a pattern exist in a line, paragraph or a file.

For ex. If you want to search a phone number in the telephone directory

Or

To find a keyword in a paragraph or a line, we use grep command Let us move on to grep.

Display Slide 5 grep searches for one or more patterns in one or more line, paragraph or a file.


If filename is not mentioned grep search for the patterns in the standard input.


If filename is missing, grep searches for the patterns in the standard input.

Open

“grepdemo.txt” [enter]

I will demonstrate usage of grep using a demo file grepdemo.txt


Let us see the content of the file


This is a file that has 13 entries.


Each entry has 6 fields roll, name, stream, marks, and stipend amount.


The fields are separated by a bar, which is called a delimiter.


At the prompt type

grep “computers” grepdemo.txt [enter]


At the prompt, type:


cat grepdemo.txt


Let us see how grep works.


Say we want to use grep command to see who are the students in the computers stream. For this we have to open the terminal. So press CTRL + ALT and T keys simultaneously on your keyboard.

Now type on the terminal:


grep space (within double quotes) computers space grepdemo.txt


This would enlist those entries where stream is computers


Now Compare the result with the original file. Come back to our text editor.

We see that the entry for Zubin is not enlisted.


Why this is so?

This is because grep searched for the pattern “computers” with small c


While for Zubin the stream is “Computers” with a capital C.

At the prompt type

“grep -i “computers” grepdemo.txt” [enter]


The pattern matching is case sensitive.

To make it case insensitive, we need to use the minus i option with grep.

Type:

grep space (minus) i space (within double quotes) “computers” after the double quotes space grepdemo.txt


Press Enter.


This will now enlist all the four entries.


At the prompt type

“grep -iv “pass” grepdemo.txt” [enter]


So we saw, grep enlists only those lines of files that match a given pattern.


We may do the reverse.


It is possible to make grep enlist only those lines that do not match the pattern.


For that we have the minus v option.


Say we want to enlist those entries of students who have not passed.

At the prompt type

“grep -iv “pass” grepdemo.txt > notpass.txt” [enter]


We can also store this result in another file


For this Type:


grep space minus iv space in double quotes pass space grepdemo.txt space greater than sign space notpass.txt


Press Enter.

At the prompt type

“cat notpass.txt”


To see the content of file type:


cat space notpass.txt


press Enter The output is displayed.

At the prompt type

“grep -i “fail” grepdemo.txt” [enter]

Now


At the prompt type:

grep space minus i space within double quotes fail after the double quotes space grepdemo.txt


Press Enter.


This is different.


This will include those students who are failed but their result is incomplete.

At the prompt type

“grep -in “fail” grepdemo.txt” [enter]

If we want to see the line number in the file at which the enlisted entries are,


We have the minus n option


At the prompt type

“grep -i “ankit saraf” grepdemo.txt” [enter]

The patterns so far have been of single word.


We may have multiword patterns as well.


But the entire pattern must be within quotes.


Type:


grep space minus i space in double quotes ankit space saraf space grepdemo.txt


Press Enter

At the prompt type

“grep -i “fail” grepdemo.txt notpass.txt” [enter]

We can also find patterns in multiple files


Type:


grep space minus i space in double quotes fail space grepdemo.txt space notpass.txt


Press Enter


With multiple files grep will write the name of the file in which the entry was found.

At the prompt type

“grep -c “Fail” grepdemo.txt” [enter]

Suppose we may only want to know the number of matches or count .


For that we have the minus c option


Type:


grep space minus c space in double quotes Fail space grepdemo.txt


Press Enter


This will give us the count of number of lines matched.

Display Slide 6

Summary

In this tutorial we learnt,

To see the content of a file

eg. cat filename


To list the entries of a particular stream

eg. grep “computers” grepdemo.txt


To ignore cases

eg. grep -i “computers” grepdemo.txt


Lines that do not match the pattern

eg. grep -iv “pass” grepdemo.txt


To list the line numbers with the entries

eg. grep -in “fail” grepdemo.txt


To store the result in another file

eg. grep -iv “pass” grepdemo.txt > notpass.txt


To know the count

eg. grep -c “Fail” grepdemo.txt

Display Slide 7 As an assignment,

Explore some other commands like -E, + and ?

Display Slide 8

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 9

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 10

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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