If this is an educational program I have 2 issues with it:

• you do not use strict or warnings: adding a couple of my here and there does not make the script more verbose but let you show students a piece of code that follow the accepted best practices in the Perl community,
• the core of your script is the same line, repeated 8 times: this is most definitely a case where you should use a loop to simplify the code. A good part of learning programming involves learning how to extract similar operations and put them in a loop or in a subroutine, and I really think students should be exposed to it as early as possible.

Here is an example of how you can write this:

#!/bin/perl -w
use strict;

my $input;

do {
  print "Enter a character or word: ";
  chomp( $input = <STDIN>);

  my @chars = split ('',$input);
  foreach ( @chars )
    { my $dec = ord( $_);
      my @bin;
      for( reverse 0..7)
        { if( $dec >= 2**$_) { push @bin, 1; $dec -= 2**$_; }
          else               { push @bin, 0;                }
        }
     print "$_: " . join('',@bin) . "\n";
    }
  }while( $input);
[download]

While this is probably not the most clever, or even the clearest piece of code that could be written to solve your problem (the for (reverse 0..7) is a bit kludgy for example) I think it would be a better example to students than the original version.

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