Question

I have a test file:

1
2
3
4
5
6
7
8

This command prints the last 4 lines of the file:

$ awk 'BEGIN{"wc -l < file" | getline b}{if(NR>b-4) print}' file
5 
6 
7 
8 
userpc@userpc-desktop

Now I want to do the same, but the command system ():

$ awk '{if( NR > (system("wc -l < file")-4) ) print}' file
8 
1 
8 
2 
8 
3 
8 
4 
8 
5 
8 
6 
8 
7 
8 
8 
userpc@userpc-desktop:

How to improve the last command system ()? I also want to print 4 last lines of the file.
Thank you for your help.

Answer 1

awk is definitely not the right tool for this. It’s common to do: sed '1{N;N;N;}; N; D; $p', and you can do something similar with awk:

awk '{for( i=0;i<3;i++) a[i]=a[i+1];a[3]=$0} END {print a[0],a[1],a[2],a[3]}' OFS='\n'

Basically, you keep track of the last four lines seen, and print them all when you get to the end of the file. You can be a little more obscure and efficient with:

awk '{a[++i%4]=$0} END {print a[++i%4],a[++i%4],a[++i%4],a[++i%4]}' OFS='\n'

but, really, why would you?