Linux/C3/The-grep-command/English

Title of script: The grep command and Regular Expressions

Author : Anirban Roy Choudhury

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 usage of grep command.
Display Slide 3	To record this tutorial, I am using Ubuntu Linux 12.04 Operating System and GNU BASH version 4.2.24(1) Please note, GNU bash version 4 or above is recommended to practice this tutorial.
Display Slide 4	To practice this tutorial, 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
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]	We 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 see who are the students in the computers stream. I would type: grep space (in double quotes) computers space grepdemo.txt This would enlist those entries where stream is computers Compare the result with the original file. We see that the entry for Zubin is not enlisted. Why is this 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 (in double quotes) “computers” 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 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
At the prompt type “grep -i “fail” grepdemo.txt” [enter]	Now At the prompt type: grep space minus i space in double quotes fail 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.

Contributors and Content Editors

Ashwini, Nancyvarkey