my $a1 = "A" ;
my $a2 = "B" ;
my $a3 = "C" ;

foreach my $k ( 1,2,3 ) 
{
    my $msg = ${a{$k}} # this should be at runtime i am creating variable a1 and assigning it value to msg .
    print "$msg\n" ;
}

# No "my" here
$a1 = "A" ;
$a2 = "B" ;
$a3 = "C" ;

foreach my $k ( 1,2,3 )
{
    my $msg = ${"a${k}"};
    print "$msg\n" ;
}

$ARG5 = "ADD ENTRY TO DATABASE" ;
$ARG6 = "ADD ENTRY TO REG FILE" ;
$ARG7 = "SHOW DEBUG MSG" ;

foreach $k in ( 5,6,7) 
{ 
     if ...
     {
      } else 
      { 
             print ${"ARG$k"} entry invalid\n" ;      
       }
}
 
so i created array 

@ARG = ( undef ,undef, ..., "ADD ENTRY TO REG FILE",...) ;

my %ARG = (
   5 => "ADD ENTRY TO DATABASE",
   6 => "ADD ENTRY TO REG FILE",
   7 => "SHOW DEBUG MSG",
);

foreach $k in (5,6,7) {
{ 
     if ...
     {
      } else 
      { 
             print "$ARG{$k} entry invalid\n" ;      
       }
}