use strict; 
use warnings; 
my $str = "In this example, A plus B equals C, D plus E plus F equals G and H plus I plus J plus K equals L"; 
my $word = "plus"; 
my @results = ();
1 while $str =~ s/(.{2}\b$word\b.{2})/push(@results,"$1\n")/e;
print @results;