Shell Commands using grep, cut, head and tail

Lab #3 – Shell Commands
Type the following into a file called headandtail:
Read the help pages for commands grep, cut, head, and tail.
When using grep with -n, each line of output is prefixed with a line number within its
input file.
Check the output of the grep with line number.
When using cut, you can change the delimiter using -d.
Command head outputs the first part of files.
Check for the options for output the first n lines.
Command tail outputs the last part of files.
Part I – head and tail
Practice the following and understand the results.
head –n 5 # type in at least 5 lines
head headandtail
head –n 2 headandtail
head –c 10 # type “Joy to the world”
head –c 10 headandtail
tail –n 1 headandtail
head –n 5 headandtail | tail –n 2
Now use pipe to connect head and tail to print out the second and third lines of file
headandtail.
Part II – grep
Type this command:
grep –n line < headandtail
Check the print out and observe the line numbers separated by colons. Pipe this result
with command cut to print out only the column of line numbers.
Then pipe the above column of line numbers with command head to print out the first
line number of the line containing word line.
60-256 System Programming Dr. Chen
2
Part III
Use commands grep, cut, head and tail to write a bash script called selector. It accepts
two words as arguments, and prints out the portion of the given file between the line of
the first appearance of the first word (this line included) and the line of the first
appearance of the second word (this line included).
You can assume that the first occurrence of the first word always appears earlier than the
fist occurrence of the second word.
Sample run:
>>>>> selector line delimiter
When using grep with -n, each line of output is prefixed with the 1-based line number
within its input file.
Check the output of the grep with line number.
When using cut, you can change the delimiter using -d.
Part IV (optional)
Use bash if-statement and test expression to check if the first word appears after the
second word. If so, inform the user about this.

Answer:

PART 1

Read the help pages for commands grep, cut, head, and tail.
When using grep with -n, each line of output is prefixed with a line number within its
input file.
Check the output of the grep with line number.
When using cut, you can change the delimiter using -d.
Command head outputs the first part of files.
Check for the options for output the first n lines.
Command tail outputs the last part of files.

PART 2

Read the help pages for commands grep, cut, head, and tail.
When using grep with -n, each line of output is prefixed with a line number within its
input file.
Check the output of the grep with line number.
When using cut, you can change the delimiter using -d.
Command head outputs the first part of files.
Check for the options for output the first n lines.
Command tail outputs the last part of files.

PART 3

#! /bin/bash 

lineNumber1=$((grep -n $1 | cut -d ':' -f1 | head -n 1 ) < headandtail)
echo $lineNumber1
lineNumber2=$((grep -n $2 | cut -d ':' -f1 | head -n 1 ) < headandtail)

let i=$lineNumber2-$lineNumber1+1
head -n $lineNumber2 headandtail | tail -n  $i  

PART 4

#! /bin/bash

lineNumber1=$((grep -n $1 | cut -d ':' -f1 | head -n 1 ) < headandtail)
lineNumber2=$((grep -n $2 | cut -d ':' -f1 | head -n 1 ) < headandtail)


if [ $lineNumber2 -le $lineNumber1 ]; then
	printf "\nThe first word \"$1\" appears after the second word \"$2\", Please try again \n\n"
	
else
	let i=$lineNumber2-$lineNumber1+1
	result=$(head -n $lineNumber2 headandtail | tail -n  $i)
	echo $result
		
fi