PoojaMoolya: Created page with "'''Title of script''': More on grep command '''Author : Sachin Patil and Anirban''' '''Keywords:Search,Pattern,regular expressions,extended regular expression''' {| style..."

2015-01-29T07:09:26Z

Created page with "'''Title of script''': More on grep command '''Author : Sachin Patil and Anirban''' '''Keywords:Search,Pattern,regular expressions,extended regular expression''' {| style..."

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'''Title of script''': More on grep command

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

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

{| style="border-spacing:0;"
| style="border:1pt solid #000000;padding:0.106cm;"| '''Visual Cue'''
| style="border:1pt solid #000000;padding:0.106cm;"| '''Narration'''

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| style="border:1pt solid #000000;padding:0.106cm;"| Display Slide 1
| style="border:1pt solid #000000;padding:0.106cm;"| Welcome to the spoken tutorial on more on '''grep'''

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| style="border:1pt solid #000000;padding:0.106cm;"| Display Slide 2
| style="border:1pt solid #000000;padding:0.106cm;"| In this tutorial we will learn some more grep commands.

Through some examples

|-
| style="border:1pt solid #000000;padding:0.106cm;"| Display Slide 3
| style="border:1pt solid #000000;padding:0.106cm;"| To record this tutorial, I am using

'''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.

|-
| style="border:1pt solid #000000;padding:0.106cm;"| Display Slide 4
| style="border:1pt solid #000000;padding:0.106cm;"| As prerequisites

You should know Basics of linux terminal.

You should be aware of grep.

For relevant tutorials please visit our website:

http://spoken-tutorial.org

|-
| style="border:1pt solid #000000;padding:0.106cm;"| At the prompt type

“'''grep -e “electronics” -e “civil” grepdemo.txt”'''<nowiki> [</nowiki>enter]
| style="border:1pt solid #000000;padding:0.106cm;"| We can match more than one patterns as well.

Then we have to use the '''-e''' option.

I will use the same example grepdemo.txt

Say we want to find information for those who are either in '''civil''' or '''electronics'''.

We need to type on terminal:

'''grep''' space '''hyphen e''' space in double quotes '''electronics''' space '''hyphen e''' space in double quotes '''civil''' space '''grepdemo.txt'''

'''Press Enter.'''

The output is displayed.

|-
| style="border:1pt solid #000000;padding:0.106cm;"| At the prompt type

“'''grep -ie “choudhury” -ie “chowdhari” grepdemo.txt”'''<nowiki> [</nowiki>enter]
| style="border:1pt solid #000000;padding:0.106cm;"| Say you need to look into people whose title is '''choudhury'''.

The problem is different people spell their titles in different way.

So what is the solution?.

In such cases we can use '''hyphen e''' option with '''hyphen i.'''

Type:

'''grep''' space '''hyphen''' '''ie''' space in double quotes '''choudhury''' space '''hyphen ie''' space in double quotes '''chowdhari''' space '''grepdemo.txt'''

'''Press Enter.'''

The output is displayed.

But there can be many other ways in which we can write the name.

How many '''-e''' options can we give.

Obviously there needs to be a better way and that way is through Regular expressions.

|-
| style="border:1pt solid #000000;padding:0.106cm;"| Display Slide 5
| style="border:1pt solid #000000;padding:0.106cm;"| A regular expression provides a concise and flexible means for matching strings of text.

Such as particular characters, words or patterns of characters.

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| style="border:1pt solid #000000;padding:0.106cm;"|
| style="border:1pt solid #000000;padding:0.106cm;"| There are a number of regular expression characters.

Let us see them one by one.

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| style="border:1pt solid #000000;padding:0.106cm;"| Display Slide 6
| style="border:1pt solid #000000;padding:0.106cm;"| The character class.

It allows us to specify a group of characters within a pair of square brackets .

Only one out of this group of characters is matched.

Eg<nowiki>. [</nowiki>abc] would mean that this regular expression matches either a or b or c.

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| style="border:1pt solid #000000;padding:0.106cm;"| At the prompt

'''grep -i “ch<nowiki>[</nowiki>ao<nowiki>][</nowiki>uw]dh<nowiki>[</nowiki>ua]r<nowiki>[</nowiki>yi]”'''

'''grepdemo.txt'''<nowiki> [</nowiki>enter]
| style="border:1pt solid #000000;padding:0.106cm;"| To match '''choudhury''' we may type at the prompt

'''grep''' space '''hyphen i''' space in double quotes '''ch<nowiki>[</nowiki>ao<nowiki>][</nowiki>uw]dh<nowiki>[</nowiki>ua]r<nowiki>[</nowiki>yi]''' space '''grepdemo.txt'''

'''Press Enter.'''

The output is displayed.

It still does not match '''choudhuree''' with double e.

|-
| style="border:1pt solid #000000;padding:0.106cm;"| Display Slide 7
| style="border:1pt solid #000000;padding:0.106cm;"| If we want to specify a large range then write:

first letter dash last letter of the range

Suppose we like to match any digit we simply write<nowiki> [0-9].

One out of this group of characters is matched. </nowiki>

|-
| style="border:1pt solid #000000;padding:0.106cm;"| Display Slide 8

| style="border:1pt solid #000000;padding:0.106cm;"| The '''<nowiki>*</nowiki>''' refers to 0 or more occurrences of the immediately preceding character.

For example '''ab<nowiki>*</nowiki>''' can match '''a,ab,abb,abbb''' etc.

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

'''grep -i “m<nowiki>[</nowiki>ei]*raa<nowiki>*” </nowiki>grepdemo.txt'''

<nowiki>[</nowiki>enter]

| style="border:1pt solid #000000;padding:0.176cm;"| So to match the students name whose name is '''Mira'''

We write at the prompt:

'''grep''' space '''hyphen i''' space in double quotes '''m<nowiki>[</nowiki>ei] asterisk r a a''' '''asterisk''' space '''grepdemo.txt'''

'''Press Enter.'''

The output is displayed.

|-
| style="border:1pt solid #000000;padding:0.106cm;"|
| style="border:1pt solid #000000;padding:0.106cm;"| The '''dot “.”'''
regular expression matches any one character.

|-
| style="border:1pt solid #000000;padding:0.106cm;"| At the prompt

'''grep “M...” grepdemo.txt'''

<nowiki>[</nowiki>enter]
| style="border:1pt solid #000000;padding:0.106cm;"| Say we want to search any words that are 4 letters long and start with '''M.'''

We would simply write

'''grep''' space within double quotes '''M...''' space after the double quote space '''grepdemo.txt'''

'''Press Enter.'''

The output is displayed.

Here the space within the quote is important.

As it would match 5 or more letter words.

|-
| style="border:1pt solid #000000;padding:0.106cm;"| Display Slide 10
| style="border:1pt solid #000000;padding:0.106cm;"| We may be specific about where in the line we want to search for our pattern.

It may be at the beginning of the line.

For that we have the '''caret sign.'''

|-
| style="border:1pt solid #000000;padding:0.106cm;"| At the prompt

'''grep “^A” grepdemo.txt'''

<nowiki>[</nowiki>enter]
| style="border:1pt solid #000000;padding:0.106cm;"| Now if we want those entries whose roll numbers start with '''A.'''

We know that roll is the first field in the file.

We write at the prompt:

'''grep '''in double quotes '''caret A''' then space '''grepdemo.txt'''

'''Press Enter.'''

|-
| style="border:1pt solid #000000;padding:0.106cm;"| Display Slide 11

At the prompt, type:

'''grep<nowiki> “[78]...$ ” </nowiki>grepdemo.txt'''

<nowiki>[</nowiki>enter]
| style="border:1pt solid #000000;padding:0.106cm;"| Similarly to match a pattern at the end of the file, we have the '''dollar sign.'''

To find stipends between '''7000 '''to '''8999''' we have to write:

'''grep''' space in double quotes'''<nowiki> [78]</nowiki>'''...'''dolar sign''' space '''grepdemo.txt'''

'''Press Enter '''

The output is displayed.

This brings me to the end of this tutorial.

Let us summarize.

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

Summary
| style="border:1pt solid #000000;padding:0.176cm;"| In this tutorial we learnt,

To match more than one pattern

To check a word that has different spelling

Character class

The use of asterisk

To match any one character using dot

To match a pattern at the beginning of the file

To match a pattern at the end of the file

|-
| style="border:1pt solid #000000;padding:0.106cm;"| Display Slide 13
| style="border:1pt solid #000000;padding:0.106cm;"| As an assignment,

List those entries that are 5 letters long and starts with Y.

|-
| style="border:1pt solid #000000;padding:0.106cm;"| Display Slide 14

Acknowledgement Slide
| style="border:1pt solid #000000;padding:0.106cm;"| 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:0.106cm;"| Display Slide 15

Spoken Tutorial Workshops
| style="border:1pt solid #000000;padding:0.106cm;"| 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:0.106cm;"| Display Slide 16

Acknowledgement
| style="border:1pt solid #000000;padding:0.106cm;"| 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

|-
| style="border:1pt solid #000000;padding:0.106cm;"| No Last Slide for tutorials created at IITB

Display the previous slide only and narrate this line.
| style="border:1pt solid #000000;padding:0.106cm;"| The script has been contributed by Sachin Patil.

This is Ashwini Patil from IIT Bombay signning off. Thank you for joining.

|}

BOSS-Linux/C3/More-on-grep-command/English - Revision history

PoojaMoolya: Created page with "'''Title of script''': More on grep command '''Author : Sachin Patil and Anirban''' '''Keywords:Search,Pattern,regular expressions,extended regular expression''' {| style..."