use strict;
use warnings;

my %hash = ( 
             "a" => "abc",
             "d" => "def",
             "g" => "ghi"
           );

my $text = "%a% %d% %g%";

print "Before: $text\n";
print "After : ", fillTemplate($text, \%hash), "\n";

sub fillTemplate {
  my ($text, $hash) = @_;
  $text =~ s/%(\w)%/$hash->{$1}/g;
  return $text;
}