how to merge similar lines in linux

Question

I have a file test.txt on my linux system which has data in following format :

first second third fourth 10  
first second third fourth 20  
fifth sixth sevent         


        

Answer 1

Perl solution:

perl -ne '/^(.*) (\S+)/ and push @{ $h{$1} },$2 }{ print "$_ @{$h{$_}}\n" for keys %h' < test.txt