How about this:

#!/usr/local/bin/perl -w

use strict;

my $string = <<END;
Lorem Ipsum is simply dummy text of the printing and typesetting indus
+try. 
Lorem Ipsum has been the industry's standard dummy text ever since the
+ 1500s,
when an unknown printer took a galley of type and scrambled it to make
+ a type 
specimen book. It has survived not only five centuries, but also the l
+eap into
electronic typesetting, remaining essentially unchanged. It was popula
+rised in
the 1960s with the release of Letraset sheets containing Lorem Ipsum p
+assages
, and more recently with desktop publishing software like Aldus PageMa
+ker
including versions of Lorem Ipsum.
END

my $trunk = substr($string,0,50); # cut to 50 chars
$trunk =~ s/\S+$//; # remove ending non-whitespace
$trunk =~ s/\s+$//; # remove ending whitespace

print "'",$trunk,"'\n";
[download]

It guarantees a maximum of 50 chars, but it cuts off the last word if it ends on the 50th char.