Try this (assuming you want to see the entire original string, broken into lines of less than 45 characters each):

while (length($longstring)>45) {
  my $break = rindex( $longstring, " ", 45 );
  print substr( $longstring, 0, $break ), $/;
  $longstring = substr( $longstring, $break  );
}
print $longstring;
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