Joining lines in different way

Hi all,

I'm excited to the part of unix.com forum, and noob to it.

I have an query, where I have an file and it contains data like this

use 
thread
when
posting
do
no

I was expecting the result as

use thread
thread when
when posting
posting do
do no
use thread when
thread when posting
when posting do
posting do no

I have tried

cat demo.txt | xargs -n 2

but it gave result as

use thread
when posting
do no

but I was expecting the above result only. Any advice on how to achieve the result

You are expecting that word are multiplying?

Post your real data and what is your goal, and how to come there.

For combining 2 lines

$ perl -ne 'chomp; push @a, $_; if ($#a >= 1) {@a = @a[@a-2..$#a]; print "$a[0] $a[1]\n"}' join.txt 
use thread
thread when
when posting
posting do
do no

For combining 3 lines

$ perl -ne 'chomp; push @a, $_; if ($#a >= 2) {@a = @a[@a-3..$#a]; print "$a[0] $a[1] $a[2]\n"}' join.txt 
use thread when
thread when posting
when posting do
posting do no

awk '{if(NR>1) print t,$0;t=$0}' join.txt
use thread
thread when
when posting
posting do
do no

Thank you rajamahavan, perl has done magic.

@jotne. How to do the same for combining 3 lines... ?

3

awk '{if(NR>2) print s,t,$0;s=t;t=$0}' join.txt
use thread when
thread when posting
when posting do
posting do no

4

awk '{if(NR>3) print r,s,t,$0;r=s;s=t;t=$0}' join.txt
use thread when posting
thread when posting do
when posting do no

Thank you. My first query has been solved.

I'm interested in knowing the explanation of awk and perl code. So that I can learn.........................