Unix questions asked in aptitude and inteviews for MCA,BCA,ME,BE,M.Tech AND B.Tech

Unix Aptitude Questions

1.Display the first line of a file is using the "head" command.
$> head -1 file.txt

2.Display the first 2 records of the file using the "head" command.
$> head -2 file.txt

3.Another way can be by using "sed" command.
Sed is a very powerful text editor which can be used for various text manipulation purposes like this.
$> sed '2,$ d' file.txt
The 'd' parameter basically tells "sed" to delete all the records from display from line 2 to last line
of the file (last line is represented by $ symbol). It does not actually delete those lines from the file,
it just does not display those lines in standard output screen. So you only see the remaining line which is the 1st line.

4.Display the last line of a file using "tail" command.
$> tail -1 file.txt

5.Display the last line of a file using "sed" command.
$> sed -n '$ p' test
'$' stands for the last line of the file. So '$ p' basically prints (p for print) the last line in standard output screen. '-n' switch takes sed to silent mode so that sed does not print anything else in the output.

6.Display n-th line of a file.
$> sed –n ' p' file.txt
   indicates actual line number whose content is to be displayed. So if you want to print the 8th line, the command will be
$> sed –n '8 p' test

7.Display n-th line of a file using "head"and "tail" command.
$> head -  file.txt | tail -1
You need to replace with the actual line number. So if you want to print the 8th line, the command will be
$> head -8 file.txt | tail -1

8.Remove the first line or header from a file?
$> sed '1 d' file.txt
It just prints out all the lines except the first line of the file on the standard output. It does not really change the file in-place.

9.Delete the first line from the file itself.
there are two ways to do it :-
i)Either you can redirect the output of the file to some other file and then rename it back to original file.
$> sed '1 d' file.txt > new_file.txt
$> mv  new_file.txt  file.txt
ii) Use an inbuilt  "sed switch '–i' which changes the file in-place.
$> sed –i '1 d' file.txt

10.Remove the last line or trailer from a file in Unix script?
$> sed –i '$ d' file.txt

11.How to remove certain lines from a file in Unix?
To remove content  from line    to line  from a given file :-
$> sed –i '5,7 d' file.txt
The above command will delete line 5 to line 7 from the file file.txt