Name   Age  Regn No.
 A     50    r1
 B     40    r2  
 C     30    r3

##</code><code>##

#!/usr/bin/perl 
use warnings;   
################################################
my %studentsDB; 
my $key=shift || 0; 
##############################################
## Output to a TEXT File using file handle:
##############################################
$output="Rdata.txt";
open (my $fh,">",$output) or die"Cannot open file
  '$output'.\n";
############################
# Constants:        
 $colon=":"; $dash="~~~";   
############################  
 do {
  print"\n\n Press 1 to insert new data: ";
  print"\n Press 2 to view data:   "; 
  print"\n Press 3 to call specific data:   ";
  $entry=<STDIN>; chomp $entry;     

  if ($entry==1) { 
 print"\n\n Enter Student's Name: "; 
  $nme1=<STDIN>; chomp $nme1; $nme=$nme1.$colon; push @nme, $nme; 
 print"\n Enter Age (yr): "; 
  $age1=<STDIN>; chomp $age1; $age=$age1.$colon; push @age, $age; 
 print"\n Enter Regn Number: ";
  $rgn1=<STDIN>; chomp $rgn1; $rgn=$rgn1.$dash; push @rgn, $rgn;
 print"\n"; 
 $ind=$nme.$age.$rgn;  push @ind, $ind; $ind2=join ('',@ind);} 
 
 elsif ($entry==2) {
  $ind=$nme.$age.$rgn;  push @ind, $ind; 
  $ind2=join ('',@ind); pop(@ind); 
  $data=join ('',@ind); 
#################################
## Now split DATA:            ###
#################################  
my @values = split('~~~', $data);  
my $val='';  
   print"\n\n\n Here goes the Final Database:\n";   
 foreach $val (@values) {    
   print $fh "$val";
   print $fh "\n"; 
   print"\n";                    
   print"$val"; }   
 close $output;}  

 elsif ($entry==3) { 
  while (<Rdata.txt>) { 
  my ($name, $age, $reg_no )=split":";   
  $studentsDB {$reg_no}={Name => $name,  # Line 52: uninitialized reg_no
                    Age => $age,};} 

 print"\n Enter the Regn Number for detailed information:\n";  
  $key=<STDIN>; chomp $key;   
 if ($key) {
    # Print the details of the preselected student: 
    print "Information for student with registration number $key is: \n";
    print " Name: " . $studentsDB{$key}{Name} . "\n";
    print " Age: " . $studentsDB{$key}{Age} . "\n"; }  

 else {
  # Print the name for each student we have a record for:  
    print "\n List of All Students:\n";
    foreach my $id (sort keys %studentsDB) {
        print " Registration Number: " . $id . "\n";
        print "   Name: " . $studentsDB{$id}{Name} . "\n";
        print "    Age: " . $studentsDB{$id}{Age} . "\n";  } } 
     } } until ($entry==3); 
exit;

##</code><code>##

Microsoft Windows [Version 6.1.7600]
Copyright (c) 2009 Microsoft Corporation.  All rights reserved.
C:\Users\x>cd desktop
C:\Users\x\Desktop>d2.pl

 Press 1 to insert new data:
 Press 2 to view data:
 Press 3 to call specific data:   1


 Enter Student's Name: A

 Enter Age (yr): 50

 Enter Regn Number: r1


 Press 1 to insert new data:
 Press 2 to view data:
 Press 3 to call specific data:   1


 Enter Student's Name: B

 Enter Age (yr): 40

 Enter Regn Number: r2


 Press 1 to insert new data:
 Press 2 to view data:
 Press 3 to call specific data:   1


 Enter Student's Name: C

 Enter Age (yr): 30

 Enter Regn Number: r3


 Press 1 to insert new data:
 Press 2 to view data:
 Press 3 to call specific data:   2



 Here goes the Final Database:

A:50:r1
B:40:r2
C:30:r3

 Press 1 to insert new data:
 Press 2 to view data:
 Press 3 to call specific data:   3  

Use of uninitialized value $reg_no in hash element at C:\Users\x\Desktop\d2.pl line 52, <STDIN> line 17.

 Enter the Regn Number for detailed information: