COMP2560- Lab 3 Solved

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.

                         

 

 

 

1          60-256 System Programming                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                     Dr.       Chen   

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.

 

 

             

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