Deleting the lines in the file from the end of a file perl

Thursday, January 03, 2013 awk , head , perl , tail 0 Comments

In general if you want to delete lines from a file based on range of lines from the begining.we can do as below:
for eg:

>cat file
1
2
3
4
5
6
7
8
9
>

now if i want to print lines from 4th to 6th i do below:
tail +4 file|head -3

logic behind this is:
tail +(4th line) file|head -(6-4+1)

suppose if you want to delte the lines from 4th to 6th then:

awk 'NR<4 || NR>6' file

Suppose if we want to delete last 5 lines in a file use below:

tail -r temp | nawk 'NR>5'|tail -r

Now the tricky thing is what if i want to delete the lines from the last i.e., the last 4th line till the last 6th line.

Below is the logic:

perl -lne 'push(@a,$_);if(eof){splice @a,$.-6,6-4+1;print join "\n",@a}' file

Logic behind this is :
perl -lne 'push(@a,$_);if(eof){splice @a,$.-(last sixth line),(last sixth line number which is 6)-(last 4th line number which is 4)+1;print join "\n",@a}' file