Sure ... just add the data into a hash of arrays where the key is the stuff before the = and the value is an array of the stuff afterwards:

#!/usr/bin/perl

use strict;
use warnings;

my %hash;
while( <DATA> ) {
  chomp;
  next unless $_;
  my( $key, $val ) = split( /\s+=\s+/, $_ );
  push( @{$hash{$key}}, $val );
}

foreach my $key ( sort keys %hash ) {
  print $key, " = " . join( ',', @{$hash{$key}} ), "\n";
}


__DATA__
A = 1
A = 2
A = 3

B = 5
B = 1
B = 7

C = 4
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