my %HoA; 
while (<FILE>) { 
     ($key, $value) = split; 
     push @{$HoA{$key}}, $value; 
}

use strict; 
use warnings; 
 
my %connections; 
 
 
while (<DATA>){ 
    my ($value1, $value2) = split(' '); 
     
    $connections{$value1} = [] if ! defined $connections{$value1}; 
     
    push (@{$connections{$value1}},$value2); 
     
} 
 
 
for my $keys (keys %connections){ 
    print "$keys : "; 
    for my $array (@{$connections{$keys}}){ 
        print "$array"; 
    } 
    print "\n"; 
} 
 
 
__DATA__ 
a b  
c d  
a d  
c a  
f g  
f h

c : da 
a : bd 
f : gh

# Takes input in the form 'a,b|c' 
# How to run :  perl code.pl 'a,b|c' 'c,d|e' 'a,d|e' 
# Outputs a NX3 for the above input data. 
# Outputs connections in Nx2 form  
use Data::Dumper; 
 
 
$arg=join(' ',@ARGV);  
@det=split //, $arg; 
 
for ($i=0; $i <=8; $i++) 
{$trip[$i]=$det[2*$i];} 
 
my @array; 
while (@trip) { 
  push(@array, [ splice(@trip, 0, 3) ]); 
} 
print "@$_\n" for @array; 
  
for ($i=0; $i <=2; $i++) 
 { 
   for ($j=0; $j <=1; $j++) 
   { $con[$i][$j]=$array[$i][$j];} 
  }  
print "\n==========connections======\n"; 
print "from->to\n";  
print " @$_\n" for @con;

%connections=(a=>[b,d],c=>[d]);

# Takes input in the form 'a,b|c'  
# How to run :  perl code.pl 'a,b|c' 'c,d|e' 'a,d|e'  
# Outputs a NX3 for the above input data.  
# Outputs connections in Nx2 form   
use Data::Dumper;  
  
  
$arg=join(' ',@ARGV);   
@det=split //, $arg;  
  
for ($i=0; $i <=8; $i++)  
{$trip[$i]=$det[2*$i];}  
  
my @array;  
while (@trip) {  
  push(@array, [ splice(@trip, 0, 3) ]);  
}  
print "@$_\n" for @array;  
   
for ($i=0; $i <=2; $i++)  
 {  
   for ($j=0; $j <=1; $j++)  
   { $con[$i][$j]=$array[$i][$j];}  
  }   
print "\n==========connections======\n";  
print "from->to\n";   
print " @$_\n" for @con; 
 
my %HoA;  
while (@con) {  
     ($key, $value) = split;  
     push @{$HoA{$key}}, $value;  
}

foreach (@con) {  
 
  # ...

  
my %HoA;   
foreach (@con) {   
     ($key, $value) = split;   
     push @{$HoA{$key}}, $value;   
} 
# PRINTING 
foreach (keys %HoA) { 
print "$_ => $HoA{$_}\n"; 
}

my %HoA;  
while (<DATA>) { 
        ($key, $value) = split; 
        push @{$HoA{$key}}, $value if defined $value; 
}   
 
foreach my $key (keys %HoA) {  
 print "\n $key =>  ";  
 print "$_ " foreach (@{$HoA{$key}}); 
} 
print "\n";  
 
 
__DATA__  
a b   
c d   
a f   
c a   
f g 
f h

my %HoA;   
foreach (@con) {  
        ($key, $value) = split;  
        push @{$HoA{$key}}, $value if defined $value;  
}    
  
foreach my $key (keys %HoA) {   
 print "\n $key =>  ";   
 print "$_ " foreach (@{$HoA{$key}});  
}  
print "\n";

__DATA__   
a b    
c d    
a f    
c a    
f g  
f h

$con[0] may contain "a b" 
$con[1] may contain "foo bar" 
$con[2] may contain "Jan 01" 
$con[3] may contain "Feb 02" 
etc.

foreach (@con) { 
     ($one, $two) = split ; 
     # ... 
}

  
 
# Takes input in the form 'a,b|c' 
# How to run :  perl code.pl 'a,b|c' 'c,d|e' 'a,d|e' 
# Outputs a NX3 for the above input data. 
# Outputs connections in Nx2 form 
use strict; 
use warnings;  
 
@ARGV =  ('a,b|c', 'c,d|e', 'a,d|e') unless @ARGV;  
 
my %HoA; 
foreach ( @ARGV ) { 
    m/^([a-z])[,]([a-z])[|]([a-z])$/ ; 
    push @{$HoA{$1}}, $2; 
} 
print "\n===========\@HoA=====\n"; 
print "from->to\n"; 
while (my ($key, $values) = each %HoA) { 
    print $key, "=>   [", join(',', @$values), "]\n"; 
}  
 
SAMPLE_OUTPUT (default data)  
 
 
=========HOA=======  
 
from->to 
c=>   [d] 
a=>   [b,d]