This is not clever but it might be of some help if you are completely stuck. Caution : It doesn't work if the space available for the text is too small.

use strict;
use warnings;

my $in_string = q(It should be clear to any frequent
air passenger that in order to reach one city from another the cost of
+ the shorter flight may be more than the cost of longer flights.
In other words, it may pay you well to cool your heels in an airport w
+aiting for a connecting flight rather than take a 
more direct flight or one in which the connecting time is shorter. For
+ example, consider the following flight schedule.); 


#
# Work out how many spaces are needed in the text in total and divide 
+by
# the number of lines to get an approximate number of spaces per line.
+ 
# Break the text into lines on total word lengths assuming this number
+ 
# of spaces is added to each line.
# Recalculate the break points after each line.
#

my $NO_OF_LINES   = 12;
my $CHAR_PER_LINE = 45;

# check it is not impossible
if ( length($in_string) > ($NO_OF_LINES * $CHAR_PER_LINE) ){ die "Can'
+t be done\n" };

# split into words and calculate total characters
my @words = split /\s/,$in_string;
my $total_chars = 0;
for (@words){
  $total_chars += length($_);  ;
}

# how many spaces must there be in the text
my $spaces_to_add = ( $NO_OF_LINES * $CHAR_PER_LINE ) - $total_chars;

# initialize
my $line="";
my $lines_left  = $NO_OF_LINES;
my $space_avail = $CHAR_PER_LINE - int ( $spaces_to_add / $lines_left 
+) ;

# process
for my $w (@words){
   my $w_length = length($w); 

   if ( $w_length == $space_avail ){
     $line .= $w;
     $w = "";
   } else {
     if ( $w_length < $space_avail ){
       $line .= "$w ";
       $space_avail -= $w_length;
       --$spaces_to_add;
       next;
     }
   }
       
   # reduce by those that will be added when justified
   $spaces_to_add -= ( $CHAR_PER_LINE - length($line) );

   # print the result
   print &justify_line($line)."|\n";

   # recalculate space_available for characters for the next lines
   --$lines_left;
   if ($lines_left > 1){
     $space_avail = $CHAR_PER_LINE - int ( $spaces_to_add  / $lines_le
+ft ) ;
   } else {
     $space_avail = $CHAR_PER_LINE - $spaces_to_add ;
   }

   # prepare next line
   $line = $w;
   if ($w ne ""){
     $line .= " ";
     --$spaces_to_add;
     $space_avail -= length($w);
   } 

}

#
# add spaces between words to justify a line
#
sub justify_line {

  my @words = split ' ',shift;
  my $spaces_left = $CHAR_PER_LINE;  
  for (@words){$spaces_left -= length($_)};
  my $new_line = $words[0];

  # add equal space to each word 
  for my $i (1..$#words){
    # calc number a spaces per word
    my $no_of_spaces = int ($spaces_left / ($#words + 1 - $i));
    $spaces_left -= $no_of_spaces;
    $new_line .= " " x $no_of_spaces . $words[$i];
  }
  return $new_line; 
};
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poj