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

sub make_word_dispensor {
   my $infile = shift;
   open INFILE, "<$infile" 
      or die "Can't open $infile: $!\n";
   my @words = ();
   return sub {
      unless (@words or (@words = split /\s/, <INFILE>)) {
         close INFILE;
         return undef;
      }
      return shift @words;
   }
}

my $word_dispensor = make_word_dispensor("test.txt");
my $line_length = 50;
my $line = '';
while (my $word = &$word_dispensor()) {
   if (length("$line $word") > $line_length) {
      print "$line\n";
      $line = $word;
   }
   else {
      $line .= ($line ? ' ' : '') . $word;
   }
}
print "$line\n";