use warnings;
use strict;

my $output = 'rData.txt';

while (1) {
    my $entry = do {
        print "\n\n Press 1 to insert new data: 
    \n Press 2 to view data:   
    \n Press 3 to call specific data:  
    \n Press 4 to Exit the Program: ";
        <STDIN>;
    };

    chomp($entry);
    my %menu = (
        1 => \&menu_entry_1,
        2 => \&menu_entry_2,
        3 => \&menu_entry_3,
        4 => sub { exit }
    );

    if ($entry) { 
        $menu{$entry}->(); # call the code_ref for each menu if true
    }

}

sub read_file_DB {

    my ( $file, $code_ref ) = @_;
    open my $fh, '<', $file or die $!;
    while (<$fh>) {
        next if /^$/;
        $code_ref->($_); # code ref 
    }
}

sub menu_entry_1 {

    my $colon = ':';
    my $dash  = '~~~';
    my $data;
    print "\n\n Enter Student's Name: ";
    chomp( my $std_name = <STDIN> );
    $data .= $std_name . $colon;

    print "\n Enter Age (yr): ";
    chomp( my $std_age = <STDIN> );
    $data .= $std_age . $colon;

    print "\n Enter Regn Number: ";
    chomp( my $std_rgn = <STDIN> );
    $data .= $std_rgn . $dash . $/;

    open my $fh, '>>', $output or die "cannot open file: $!";
    print $fh $data, $/;

}

sub menu_entry_2 {

    my $code = sub { print join "" => split /~~~/, shift };
    read_file_DB( $output, $code );
}

sub menu_entry_3 {

    my $sch_ref = {};

    my $code = sub {
        my $re = qr/:|~~~/;
        my ( $name, $age, $reg_num ) = split /$re/, shift;
        $sch_ref->{$reg_num}{$name} = $age;
    };
    read_file_DB( $output, $code );

    print "Enter the Reg Number for Detailed information:";
    chomp( my $std_reg_number = <STDIN> );

    if ( $sch_ref->{$std_reg_number} ) {
        print sprintf( "The Student name is %s and Age is %d\n",
            %{ $sch_ref->{$std_reg_number} } );
    }
    else {
        use Data::Dumper;

        print Dumper $sch_ref;
    }
}