Perl script to read a Newick tree file from TreeFam, and print out the orthologs of a particular input gene based on the tree.

get_orths_from_newick_tree.pl

#!/usr/bin/perl

#---------------------------------------------------------------------------------------------#
#
# A Perl script to read a Newick tree file from Treefam, and
# print out the orthologues of a particular input gene.
#
# Avril Coghlan. 6-Dec-04.
# [email protected]
#
# For the Treefam project.
#
# The command-line format id:
# % perl <get_orths_from_newick_tree.pl> <tree> <mygene>
# where tree is the tree file,
#       mygene is the gene of interest.
#
#---------------------------------------------------------------------------------------------#

# CHECK IF THERE ARE THE CORRECT NUMBER OF COMMAND-LINE ARGUMENTS:

$num_args                  = $#ARGV + 1;
if ($num_args != 2)
{
   print "Usage of get_orths_from_newick_tree.pl\n\n";
   print "perl get_orths_from_newick_tree.pl <tree> <mygene>\n";
   print "where <tree> is the tree file,\n";
   print "      <mygene> is the gene of interest.\n";
   print "For example, >perl get_orths_from_newick_tree.pl /nfs/treefam/work/families/TF300307/full.nhx\n";
   print "KO1C8.10.1_CAEEL\n";
   exit;
}

# FIND THE NAME OF THE INPUT TREE FILE:

$tree_file                 = $ARGV[0];

# FIND THE NAME OF THE GENE OF INTEREST:

$mygene                    = $ARGV[1];

#------------------------------------------------------------------#

# PARAMETERS:

$PRINT_BRACKET_DETAILS          = 0; # PRINTS OUT EXTRA DETAILS OF THE RUN.
$PRINT_FORK_DETAILS             = 0; 

# READ IN THE NEWICK TREE:

$tree                           = read_newick_tree($tree_file);

# FIND THE BIFURCATIONS IN THE TREE:

&find_tree_bifurcations($tree);

# GO THROUGH EACH OF THE BIFURCATIONS AND SEE WHICH BRANCHES THEY SPLIT INTO.
# EACH BIFURCATION IS A NODE WHICH SPLITS TO TWO THINGS, EITHER TWO MORE
# NODES, OR ONE SEQUENCE AND ONE NODE, OR TWO SEQUENCES. 
# EACH NODE OR SEQUENCE HAS A PARENT NODE FROM WHICH IT SPLIT OFF,
# AND EACH PARENT NODE HAS TWO CHILD NODES.

&find_what_nodes_split_into;

# FIND THE ORTHOLOGUES FOR EACH SEQUENCE IN THE TREE:

&find_orthologues;

print STDERR "FINISHED.\n";

#---------------------------------------------------------------------------------------------#

sub find_connecting_nodes
{
   # FIND THE NODES THAT CONNECT TO A CERTAIN INPUT NODE:

   my $node             = $_[0];
   my @temp;
   my @nodes;
   my $connecting;
 
   if ($PARENT{$node})
   {
      $connecting       = $PARENT{$node};
      if ($connecting ne $node && !($SEEN{$connecting}))
      {
         @nodes         = (@nodes,$connecting);
      }
   }   

   if ($node =~ /NODE/) { @temp = split(/NODE/,$node); $node = $temp[1];}
   if ($SPLITS_INTO{$node})
   {
      $connecting       = $SPLITS_INTO{$node};
      @temp             = split(/\,/,$connecting);
      if ($temp[0] ne $node && !($SEEN{$temp[0]}))
      {
         @nodes         = (@nodes,$temp[0]);
      }
      if ($temp[1] ne $node && !($SEEN{$temp[1]}))
      {
         @nodes         =  (@nodes,$temp[1]);
      }
   }

   return @nodes;
}

#---------------------------------------------------------------------------------------------#

sub check_if_node_above_outgroup
{
   # CHECK IF A CERTAIN NODE IS ABOVE THE OUTGROUP:

   my $node             = $_[0];
   my @seqs;
   my $no_seqs;
   my $i;  
   my $node_above_outgroup = 0;  
 
   # FIND THE SEQUENCES IN THE CLADE BELOW $node:

   @seqs                = find_seqs_in_clade($node); 
   $no_seqs             = $#seqs + 1;
   for ($i = 0; $i < $no_seqs; $i++)
   {
      if ($seqs[$i] =~ /YEAST/ || $seqs[$i] =~ /SCHPO/ || $seqs[$i] =~ /ARATH/)
      {
         $node_above_outgroup = 1;
      }
   }
   
   return $node_above_outgroup;
}

#---------------------------------------------------------------------------------------------#

sub check_if_node_is_outgroup
{
   # CHECK IF A CERTAIN NODE IS ONLY ABOVE OUTGROUP SEQUENCES:
                                                                                                                                                        
   my $node             = $_[0];
   my @seqs;
   my $no_seqs;
   my $i;
   my $node_is_outgroup = 1;   
                                                                                                                                                        
   # FIND THE SEQUENCES IN THE CLADE BELOW $node:
                                                                                                                                                        
   @seqs                = find_seqs_in_clade($node);
   $no_seqs             = $#seqs + 1;

   for ($i = 0; $i < $no_seqs; $i++)
   {
      if (!($seqs[$i] =~ /YEAST/ || $seqs[$i] =~ /SCHPO/ || $seqs[$i] =~ /ARATH/))
      {
         $node_is_outgroup = 0;    
      }
   }
                                                                                                                                                        
   return $node_is_outgroup;
}
                                                                                                                                                        
#---------------------------------------------------------------------------------------------#

sub find_orthologues
{
   # GO THROUGH EACH SEQUENCE IN THE TREE AND FIND ITS ORTHOLOGUES:

   my $no_sequences     = $#sequences + 1;
   my $i;
   my $sequence;   
   my @nodes;
   my $node;
   my $found_outgroup;
   my $no_nodes;
   my $node1;
   my $node2;
   my $node1_above_outgroup;
   my $node2_above_outgroup;
   my $node1_is_outgroup;
   my $node2_is_outgroup;
   my @seqs;
   my $no_seqs;
   my $j;
   my $found_orth;

   for ($i = 0; $i < $no_sequences; $i++)
   {
      $sequence         = $sequences[$i];
      $found_orth       = 0;

      if ($sequence ne $mygene) { goto FOUND_OUTGROUP;}
       
      if ($sequence =~ /\_YEAST/ || $sequence =~ /\_SCHPO/ || $sequence =~ /\_ARATH/) { goto FOUND_OUTGROUP;}

      print "----------------------------------------------------------\n";
      print "FINDING ORTHOLOGUES OF $sequence ...\n";

      # FIND THE ORTHOLOGUES FOR $sequence IN THE TREE, BY MOVING UP THE TREE
      # NODE BY NODE, UPWARDS FROM $sequence:

      $node             = $sequence;
      $found_outgroup   = 0;

      %SEEN             = ();
      while($found_outgroup == 0)
      {
         # FIND WHICH NODES ARE CONNECTED TO NODE $node;    
 
         $SEEN{$node}   = 1;
         @nodes         = find_connecting_nodes($node);

         # FIND WHAT SEQUENCES ARE BELOW EACH NODE THAT CONNECTS TO $node:
 
         $no_nodes      = $#nodes + 1;
         if ($no_nodes == 1)
         {
            $node       = $nodes[0];
         } 
         elsif ($no_nodes == 2)
         {
            # WE WANT TO CHECK WHETHER EACH OF THE NODES BELOW $node CONTAINS
            # THE OUTGROUP OR NOT:

            $node1       = $nodes[0];
            $node2       = $nodes[1];
 
            # CHECK IF $node1 OR $node2 CONTAINS ONLY OUTGROUP SEQUENCES:

            $node1_is_outgroup    = check_if_node_is_outgroup($node1);
            $node2_is_outgroup    = check_if_node_is_outgroup($node2);


            # CHECK IF $node1 OR $node2 IS ABOVE THE OUTGROUP:

            $node1_above_outgroup = check_if_node_above_outgroup($node1);
            $node2_above_outgroup = check_if_node_above_outgroup($node2);

            if    ($node1_above_outgroup == 1 && $node2_above_outgroup == 0)
            {
               # ALL THE SEQUENCES UNDER $node2 ARE ORTHOLOGUES OF $sequence:
               $found_orth = 1;
               @seqs     = find_seqs_in_clade($node2);         
               $no_seqs  = $#seqs + 1;
               for ($j = 0; $j < $no_seqs; $j++) { print "$sequence ---> $seqs[$j]\n";}
               $node     = $node1;
            }
            elsif ($node1_above_outgroup == 0 && $node2_above_outgroup == 1)
            {
               # ALL THE SEQUENCES UNDER $node1 ARE ORTHOLOGUES OF $sequence:
               $found_orth = 1;
               @seqs     = find_seqs_in_clade($node1);
               $no_seqs  = $#seqs + 1;
               for ($j = 0; $j < $no_seqs; $j++) { print "$sequence ---> $seqs[$j]\n";}
               $node     = $node2;
            }
            elsif ($node1_above_outgroup == 1 && $node2_above_outgroup == 1)
            { 
               # THE TREE HAS MORE THAN ONE OUTGROUP:
               $found_outgroup = 1;
               goto FOUND_OUTGROUP;
            }
            else
            {
                # xxx NO OUTGROUP IN THE TREE - WE NEED TO FIX THIS.
                print STDERR "ERROR: node1_above $node1_above_outgroup node2_above $node2_above_outgroup.\n"; 
                exit;
            }

            if ($node1_is_outgroup == 1 || $node2_is_outgroup == 1) { $found_outgroup = 1; goto FOUND_OUTGROUP;}
      
         }
         elsif ($no_nodes == 3)
         {
            print STDERR "ERROR: 3 nodes below $node.\n"; exit;
         }
         else
         {
            # IF THERE IS NO OUTGROUP IN THE TREE - WE NEED TO FIX THIS xxx
            print STDERR "ERROR: $no_nodes below $node.\n"; exit;
         }
      }
      FOUND_OUTGROUP:

      if ($found_orth == 0 && $sequence eq $mygene) { print "Did not find any orthologue for $sequence.\n";}
      if ($i == $#sequences) { goto END;}

   }
   END:

}

#---------------------------------------------------------------------------------------------#

sub find_seqs_in_clade
{
   my $node             = $_[0];
   my @temp             = split(/\s+/,$node);
   if ($#temp > 0) { $node = $temp[1];}
   my @nodes;
   my $no_nodes;
   my $i;
   my $j;
   my @seqs;
   my @new_nodes;
   my $no_new_nodes;
   my $added            = 0;
   @nodes               = (@nodes,$node);
   my %CHECKED          = ();

   # CHECK IF $node IS A SEQUENCE:

   if (!($node =~ /NODE/))
   {
      @seqs             = (@seqs,$node);
      return @seqs;
   }

   FIND_SEQS_UNDER_NODES:
   $no_nodes            = $#nodes + 1;
   $added               = 0;
   for ($i = 0; $i < $no_nodes; $i++)
   {
      # FIND ALL THE NODES THAT $nodes[$i] CONNECTS TO:
      if ($CHECKED{$nodes[$i]}) { goto NEXT_NODEI;}
      @new_nodes        = find_connecting_nodes($nodes[$i]);
      
      # GO THROUGH ALL THE NODES THAT CONNECT TO $nodes[$i]:

      $no_new_nodes     = $#new_nodes + 1;
      for ($j = 0; $j < $no_new_nodes; $j++)
      {
         if (!($new_nodes[$j] =~ /NODE/)) 
         {
            @seqs       = (@seqs,$new_nodes[$j]);
         }   
         else
         {
            @nodes      = (@nodes,$new_nodes[$j]);
            $added      = 1;
         }
      }
      $CHECKED{$nodes[$i]} = 1;
      NEXT_NODEI:
   } 
   if ($added == 1) { goto FIND_SEQS_UNDER_NODES;}
    
   return @seqs;
}

#---------------------------------------------------------------------------------------------#

# WE HAVE FOUND A COMMA IN THE NEWICK TREE. NOW LOOK TO THE RIGHT FOR THE NEAREST ) AND TO
# THE LEFT FOR THE NEAREST ( AND FIND THE REGION (CONTAINING ,) BRACKETED BY ().

sub find_bracketed_region
{
   my $i                = $_[0]; # POSITION OF THE COMMA OF INTEREST.
   my $len              = $_[1]; # LENGTH OF THE WHOLE TREE.
   my $tree             = $_[2];
   my $j;
   my $char;
   my $bracket_start;
   my $bracket_end;
   my $bracket_len;
   my $bracketed;
   my $num_brackets;
   my $x;
   my $look_as_far;
   my $bracket_num;

   # THE INDEX OF THE COMMA IN THE NEWICK TREE IS CHARACTER $i.

   #------------------------------------------------------------------------------------------#
   # LOOK FOR THE INDEX OF THE FIRST ( BEFORE THE COMMA:
    
   for ($j = $i; $j >= 0; $j--)
   {
      $char             = substr($tree,$j,1);
      if ($char eq '(' && !($USED_BRACKET{$j})) 
      { 
         $bracket_start = $j; # THE INDEX OF THE PREVIOUS ( BEFORE THE COMMA. 
         goto FOUND_STARTING_BRACKET;
      }
   }
   FOUND_STARTING_BRACKET:

   #------------------------------------------------------------------------------------------# 
   # LOOK FOR THE INDEX OF THE FIRST ) AFTER THE COMMA:   

   for ($j = $i; $j < $len; $j++)
   {
      $char             = substr($tree,$j,1);
      if ($char eq ')' && !($USED_BRACKET{$j})) 
      { 
         $bracket_end   = $j; # THE INDEX OF THE NEXT ) AFTER THE COMMA.
         goto FOUND_ENDING_BRACKET;
      }
   }
   FOUND_ENDING_BRACKET:

   #------------------------------------------------------------------------------------------#
   # FIND THE LENGTH OF THE REGION ENCLOSED BY THE PARENTHESES ():

   # (xxxx)
   # 123456
   # eg., $bracket_len = 6 - 1 + 1 = 6, ie., $bracket_len INCLUDES THE ().
   $bracket_len         = $bracket_end - $bracket_start + 1;
   if ($bracket_len < 0) 
   { 
      goto COMMA_NOT_OKAY;
   }

   #------------------------------------------------------------------------------------------#
   # FIND THE REGION ENCLOSED BY THE PARENTHESES:

   $bracketed           = substr($tree,$bracket_start,$bracket_len);
  
   # COUNT THE NUMBER OF BRACKETS IN THE BRACKETED REGION: IF THERE ARE MORE )s THAN (s SOMETHING IS WRONG:

   $num_brackets        = 0;
   for ($x = 0; $x < $bracket_len; $x++)
   {
      $char             = substr($bracketed,$x,1);
      if    ($char eq '(') { $num_brackets++;}
      elsif ($char eq ')') { $num_brackets--;} 
      if ($num_brackets < 0) # THERE ARE MORE )s THAN (s, SOMETHING IS WRONG.
      { 
         goto COMMA_NOT_OKAY; 
      }
   }
  
   #------------------------------------------------------------------------------------------#
   # THE BRACKETED REGION SHOULD NOT CONTAIN ANY BRACKETS THAT WE HAVE NOT ALREADY EXAMINED, AS
   # WE WANT TO LOOK AT INTERNAL BIFURCATIONS, AND WORK UPWARDS TOWARDS THE ROOT OF THE TREE: 

   $look_as_far         = $bracket_len - 1; # LOOK UP TO JUST BEFORE THE END ) BRACKET.
   for ($x = 1; $x < $look_as_far; $x++)
   {
      $char             = substr($bracketed,$x,1);
      if ($char eq '(' || $char eq ')')
      {
         # FIND THE INDEX OF THIS BRACKET IN THE WHOLE TREE:

         $bracket_num   = $x + $bracket_start;

         if (!($USED_BRACKET{$bracket_num})) # THERE IS AN INTERNAL BRACKET THAT HAS NOT YET BEEN EXAMINED.
         { 
            goto COMMA_NOT_OKAY;
         }
      }
   }
   
   #------------------------------------------------------------------------------------------#
   # IF THERE IS AN EVEN NUMBER OF BRACKETS AND WE HAVE NOT ALREADY GOT THIS BRACKETED REGION,
   # THEN ADD THIS BRACKETED REGION INTO OUR ARRAY @bracketeds OF BRACKETED REGIONS:

   if (!($HAVE_BRACKETED{$bracketed}) && $num_brackets == 0)
   {
      if ($PRINT_BRACKET_DETAILS == 1) 
      {
         print "The bracketed bit is $bracketed.\n";
      }

      $USED_BRACKET{$bracket_start} = 1;
      $USED_BRACKET{$bracket_end}   = 1; 
      $USED_COMMA{$i}               = 1;
      $HAVE_BRACKETED{$bracketed}   = 1;
      (@bracketeds)                 = (@bracketeds,$bracketed);
   } 
   COMMA_NOT_OKAY:
}

#---------------------------------------------------------------------------------------------#

# NIBBLE FORWARD AND BACK TO THE FIRST INSTANCES OF THE STRING $thechar.

sub nibble_to_characters
{
   my $name                         = $_[0];
   my $thechar                      = $_[1];

   if ($name =~ /$thechar/)
   {
      $name =~ s/$thechar//g;
   }
   return $name;
}

#---------------------------------------------------------------------------------------------#

# TAKE OFF STARTING OR ENDING SINGLE CHARACTERS OF $thechar.

sub nibble_off_characters
{
   my $name                         = $_[0];
   my $thechar                      = $_[1];
   my $len;
   my $index;
   my $x;
   my $char;
    
   $len    = length($name);

   # TAKE OFF DASHES AT THE START:

   $index  = 0;
   for ($x = 0; $x < $len; $x++)
   {
      $char= substr($name,$x,1);
      if ($char eq $thechar) { $index = $x + 1; }
      else                   { goto FOUND_START;}
   }
   FOUND_START:
   $name   = substr($name,$index,$len-$index);

   # TAKE OFF DASHES AT THE END:

   $len    = length($name);
   $index  = $len;
   for ($x = $len-1; $x >= 0; $x--)
   {
      $char= substr($name,$x,1);
      if ($char eq $thechar) { $index = $x-1; }
      else                   { goto FOUND_END;  }
   }
   FOUND_END:
   $name   = substr($name,0,$index);
   
   return $name;
}

#---------------------------------------------------------------------------------------------#

# GO THROUGH EACH OF THE BIFURCATIONS AND SEE WHICH BRANCHES THEY SPLIT INTO.
# EACH BIFURCATION IS A NODE WHICH SPLITS TO TWO THINGS, EITHER TWO MORE
# NODES, OR ONE SEQUENCE AND ONE NODE, OR TWO SEQUENCES. EACH NODE OR SEQUENCE
# HAS A PARENT NODE FROM WHICH IT SPLIT OFF, AND EACH PARENT NODE HAS TWO CHILD NODES.

sub find_what_nodes_split_into
{
   %SPLITS_INTO      = (); # HASH TABLE TO RECORD WHICH NODES A NODE SPLITS INTO.
   %PARENT           = (); # HASH TABLE TO RECORD THE PARENT NODE OF EACH NODE.
   %SISTER           = (); # HASH TABLE TO RECORD THE SISTER NODE OF EACH NODE.
   my %HAVE          = ();
   my %CNT           = ();
   %BRANCHLENGTH     = (); # THE BRANCHLENGTH.

   my $i;
   my $num_bracketeds;
   my $no_loops;
   my $bracketed;
   my @temp;
   my $num_things;
   my $first;
   my $second;
   my $branchlength;
   my $last_letter;
   my $first_one;
   my $second_one;
   my $inside_node;
   my $inside;
   my $x;
   my $y;
   my $start;
   my $len;
   my $j;

   $num_bracketeds   = $#bracketeds + 1;
   $no_loops         = 0;
   for ($i = $num_bracketeds - 1; $i > -1; $i--)
   {
      if ($PRINT_FORK_DETAILS == 1) {print "=========================================== \n";}
      $bracketed     = $bracketeds[$i];

      #---------------------------------------------------------------------------------------#
      # SEE WHICH TWO THINGS THIS NODE SPLITS INTO:

      RETRY:
      $no_loops++;
      if ($no_loops > 500) { print "ERROR: $tree_file: have looped $no_loops times now.\n"; exit;}
      @temp          = split(/,/,$bracketed);
      $num_things    = $#temp + 1;
 
      if ($num_things == 2) # THIS NODE SPLITS UP INTO TWO SEQUENCES:
      {
         $first      = $temp[0];
         $second     = $temp[1];
         $first      = nibble_off_characters($first,"(");
         $first      = nibble_off_characters($first,"_");
         @temp       = split(/:/,$first);
         if    ($temp[0] =~ /[A-Z]/ || $temp[0] =~ /[a-z]/) { $first = $temp[0]; $branchlength = $temp[1];}
         elsif ($temp[1] =~ /[A-Z]/ || $temp[1] =~ /[a-z]/) { $first = $temp[1]; $branchlength = $temp[0];}
         $first       =~ tr/[a-z]/[A-Z]/;
         $last_letter = substr($first,length($first)-1,1);
         if ($last_letter =~ /[A-Z]/ && !($first =~ /_/)) { chop($first);}
         @temp        = split(/\s+/,$first);
         if ($#temp > 0) { $first = $temp[1];}
         # TAKE OFF ENDING CHARACTERS THAT ARE NOT NUMBERS:
         if ($first =~ /NODE/)
         {
            $first    = nibble_off_letters($first);
         }
         if ($HAVE{$first}) { if (!($CNT{$first})){$CNT{$first} = 2;} else { $CNT{$first}++;} $first = $first.$CNT{$first};}
         $HAVE{$first}= 1;
         $BRANCHLENGTH{$first}= $branchlength;
 
         $second      = nibble_off_characters($second,")");
         $second      = nibble_off_characters($second,"_");
         @temp        = split(/:/,$second);
         if    ($temp[0] =~ /[A-Z]/ || $temp[0] =~ /[a-z]/) { $second = $temp[0]; $branchlength = $temp[1];}
         elsif ($temp[1] =~ /[A-Z]/ || $temp[1] =~ /[a-z]/) { $second = $temp[1]; $branchlength = $temp[0];}
         $second      =~ tr/[a-z]/[A-Z]/;
         $last_letter = substr($second,length($second)-1,1);
         if ($last_letter =~ /[A-Z]/ && !($second =~ /_/)) { chop($second);}
         @temp                = split(/\s+/,$second);
         if ($#temp > 0) { $second = $temp[1];}
         # TAKE OFF ENDING CHARACTERS THAT ARE NOT NUMBERS:
         if ($second =~ /NODE/)
         {
            $second   = nibble_off_letters($second);
         }
         if ($HAVE{$second}) { if (!($CNT{$second})){$CNT{$second} = 2;} else { $CNT{$second}++;} $second = $second.$CNT{$second};}
         $HAVE{$second}       = 1;
         $BRANCHLENGTH{$second} = $branchlength;

         $first_one    = $first;
         $second_one   = $second;

         $SPLITS_INTO{$i}     = $first_one.",".$second_one; # NODE $i SPLITS INTO $first_one AND $second_one.
         $PARENT{$first_one}  = "NODE".$i;
         $PARENT{$second_one} = "NODE".$i;
         $SISTER{$first_one}  = $second_one;
         $SISTER{$second_one} = $first_one;
         $BRANCHLENGTH{$first_one} = $BRANCHLENGTH{$first};
         $BRANCHLENGTH{$second_one}= $BRANCHLENGTH{$second};

         if ($PRINT_FORK_DETAILS == 1) 
         {
            print "Node i $i ($PARENT{$first_one}) splits into $first_one ($BRANCHLENGTH{$first_one}) and $second_one ($BRANCHLENGTH{$second_one})\n";
         }

         #---------------------------------------------------------------------------------------------#
         # CHECK WHETHER THE NODE SPLITS INTO SEQUENCES OR INTO MORE NODES:         

         if (!($first =~ /node/) && !($first =~ /NODE/))  
         {
            @sequences    = (@sequences,$first);
         }
         if (!($second =~ /node/) && !($second =~ /NODE/))
         {
            @sequences    = (@sequences,$second);
         }
      }    # END OF IF THIS NODE SPLITS UP INTO TWO SEQUENCES.  
      else # THERE ARE OTHER NODES INSIDE THIS NODE.
      {
         # CHECK IF ANY OTHER NODES ARE INSIDE THIS NODE, AND IF THERE ARE,
         # DELETE THEM FROM THE OUTER BRACKETED REGION.

         for ($j = $num_bracketeds-1; $j >=0; $j--)
         {
            if ($j != $i)
            {
               $inside_node= $bracketeds[$j];

               # CHECK WHETHER $inside_node IS WITHIN $bracketed:

               $inside     = index($bracketed,$inside_node);

               if ($inside != -1) # $inside_node IS WITHIN $bracketed:
               {
                  # FIND THE LENGTH OF $inside_node (WE CANNOT USE THE length() FUNCTION AS BRACKETS CONFUSE IT):

                  $x       = 0;
                  while(substr($inside_node,$x,1) ne '')
                  {
                     $x++;
                  }

                  # FIND THE LENGTH OF $bracketed:

                  $y       = 0;
                  while(substr($bracketed,$y,1) ne '')
                  {
                     $y++;
                  }

                  # FIND THE START OF $inside_node IN $bracketed:

                  $start   = $x + $inside;

                  # FIND THE LENGTH OF $inside_node IN $bracketed:

                  $len     = $y - $x - ($inside - 1);

                  # MAKE $bracketed BE A SUBSTRING OF ITSELF WITH $inside_node DELETED:

                  $bracketed = substr($bracketed,0,$inside)."NODE$j".substr($bracketed,$start,$len);
               }
            }
         }

         goto RETRY;

      } # END OF IF THERE ARE OTHER NODES INSIDE THIS NODE.

      if ($i == 0) { goto JUMP_OUT_OF_LOOP;}

   } # END OF LOOKING THROUGH EACH OF THE BIFURCATIONS TO SEE WHAT THEY SPLIT INTO.

   JUMP_OUT_OF_LOOP:
}

#---------------------------------------------------------------------------------------------#

sub nibble_off_letters
{
   # REMOVE ANY LETTERS AT THE END OF A STRING:

   my $string        = $_[0];
   my $new           = "";
   my @temp;
   my $i;
   my $char;

   @temp             = split(/NODE/,$string);
   $string           = $temp[1];
   $length           = length($string);  
   for ($i = 1; $i <= $length; $i++)
   {
      $char          = substr($string,$i-1,1);
      if ($char =~ /[0-9]/)
      {
         $new        = $new.$char;
      }
      else
      {
         $new        = "NODE".$new;
         return $new;
      }
   }

   $new              = "NODE".$new;
   return $new;
}

#---------------------------------------------------------------------------------------------#

# READ IN THE NEWICK TREE:

sub read_newick_tree
{
   my $tree_file     = $_[0];
   my $line;
   my $tree;
   
   open(TREE,"$tree_file") || die "Cannot open $tree_file";
   $tree             = '';
   while(<TREE>)
   {
      $line          = $_;
      chomp($line);
      $tree          = $tree.$line;
   }
   close(TREE);

   return $tree;
}

#---------------------------------------------------------------------------------------------#

# FIND THE BIFURCATIONS IN THE TREE:

sub find_tree_bifurcations
{
   # THE TREE IS STORED IN A VARIABLE $tree:

   my $tree          = $_[0];
   my $len;
   my $char;
   my $round;
   %USED_BRACKET     = ();   # HASH TABLE TO SAY WHETHER WE HAVE EXAMINED A PARTICULAR BRACKET YET.
   %USED_COMMA       = ();   # HASH TABLE TO SAY WHETHER WE HAVE EXAMINED A PARTICULAR COMMA YET.
   %HAVE_BRACKETED   = ();
   my $i;

   $len              = length($tree);
   $char             = '';
   $round            = 0;

   #------------------------------------------------------------------------------------------#
   RESTART:

   $round++;

   if ($PRINT_BRACKET_DETAILS == 1) 
   {
      print "\n======================================================\n";
      print "ROUND $round of finding tree bifurcations:\n\n";
   }

   if ($round > 100) { print STDERR "ERROR: $tree_file: have reached round $round.\n\n"; exit;}

   # GO THROUGH THE TREE TO FIND COMMAS, AS COMMAS ARE BIFURCATIONS IN THE TREE. WE JUST 
   # GO THROUGH THE TREE FROM LEFT TO RIGHT:

   for ($i = 0; $i < $len; $i++)
   {
      $char          = substr($tree,$i,1);
      if ($char eq ',') # THERE IS A BIFURCATION HERE.
      {
         # LOOK TO THE RIGHT OF THE , FOR THE NEAREST ) AND TO THE LEFT OF THE
         # , FOR THE NEAREST ( AND FIND THE REGION BRACKETED BY THESE BRACKETS, ie., (reg,ion), WHERE
         # THE REGION CONTAINS THE COMMA:

         if (!($USED_COMMA{$i})) # IF WE HAVE NOT FOUND THE REGION AROUND THIS COMMA SO FAR:
         {
            &find_bracketed_region($i,$len,$tree);
         }
      }
   }
   
   #..........................................................................................#
   # NOW WE HAVE LOOKED THROUGH THE TREE FROM LEFT TO RIGHT LOOKING FOR COMMAS. WE MAY NOT
   # HAVE FULLY EXAMINED ALL COMMAS YET HOWEVER, AS SOME MAY HAVE BEEN REJECTED IN THE
   # SUBROUTINE find_bracketed_region. SO NOW WE SEARCH FOR ANY COMMAS (BIFURCATIONS) LEFT
   # UNTIL ALL COMMAS HAVE BEEN ANALYSED:

   for ($i = 0; $i < $len; $i++)
   {
      $char  = substr($tree,$i,1);
      if ($char eq ')' || $char eq '(')
      {
         if (!($USED_BRACKET{$i})) # THERE IS A BRACKET (AND SO A COMMA) WHICH HAS NOT BE ANALYSED YET.
         {
            goto RESTART;
         }
      }
   }
   #------------------------------------------------------------------------------------------#
}

#---------------------------------------------------------------------------------------------#