Question

I would like to understand awk a little better: I often search for regular expressions and many times I am interested only in the Nth occurrence. I always did this task using pipes say:

awk '/regex/' file | awk 'NR%N==0' 

How can I do the same task with awk (or perl) without piping?

Are there some instances in which using pipes is the most computationally efficient solution?

Answer 1

Every third:

awk '/line/ && !(++c%3)' infile

For example:

zsh-4.3.12[t]% cat infile
1line
2line
3line
4line
5line
6line
7line
8line
9line
10line
zsh-4.3.12[t]% awk '/line/ && !(++c%3)' infile
3line
6line
9line
zsh-4.3.12[t]% awk '/line/ && !(++c%2)' infile
2line
4line
6line
8line
10line