#!usr/bin/perl -w 
use strict;

open FILE, '<', "input.txt" or die "unable to open input.txt";
# the $! variable adds the O/S specific info, but it is not
# not always that useful.

my @all_words;

while (<FILE>) 
{ 
   my @these_words = split(' ', $_);
   foreach my $this_word (@these_words)
   {
      push @all_words, $this_word;
   }
}