'command' => [
   ['summary1', 'description1',
   'regex for args of summary1', 'cmdnametocall1']
   ['summary2' , 'description2',
   'regex for args of summary2', 'cmdnametocall2']
   ...
 ]

##</code><code>##

%COMMANDS=(
    'help' => [['help or ?', 'Print this command summary.', '']],
    'delete' => [
                 ['delete NAME from LIST',
                  'Delete the name from the mailing list.',
                  '(\S+)\s+from\s+(\S+)'],
                 ['delete LIST,...', 
                  'Delete mailing lists.',
                  '(.+)', 'deletelists'],
	        ]
	  );

# Execute a command by calling the appropriate subroutine.
# The first argument contains the command to execute.
sub execute_command {
  my $line=shift || return;
  $line=~s/^\s*//; $line=~s/\s*$//;
  my ($cmd, $args)=($line=~/^(\S+)(?:\s+(.*))?$/);
  return unless $cmd;
  $args||="";
  $cmd=lc($cmd);
  if (exists($COMMANDS{$cmd})) {
    # The command is in our list of valid commands.
    my @forms=@{$COMMANDS{$cmd}};
    my $form;
    my $summaries;
    foreach $form (@forms) {
      my $regex=$form->[2];
      my $sum=$form->[0];
      # This collects summaries for an error message if arg syntax is wrong
      $summaries.="\t$sum\n";
      my @args;
      if (@args=($args=~/^$regex$/)) {
        # Got a match

        # Assign @args only if there were parenthesis in the pattern.
        @args=undef unless defined($+);

        # Now we are ready to execute the command.

        # Determine the name of the subroutine to call
        my $cmdcall=$form->[3] || $cmd;

        # Call the subroutine
        eval "command_$cmdcall".'(@args)';
        if ($@) {
          die "Internal error calling command_$cmdcall: $@\n";
        }

        # Returning undef means everything went ok.
        return;
      }
    }
    # If we get here, we didn't match any of the valid forms of the command.
    return("Invalid syntax, I expect one of:\n$summaries");
  }
  else {
    return("Unknown command:\n\t$line\n");
  }
}

# Sample command definitions

sub command_help {
  print("The current commands are: ([]'s denote optional, caps need values)\n"
);
  my $cmd;
  my $form;
  foreach $cmd (sort keys %COMMANDS) {
    foreach $form (@{$COMMANDS{$cmd}}) {
      my ($sum, $desc)=@$form;
      print "$sum: $desc\n"
    }
  }
}

sub command_delete {
  my ($name, $list)=@_
  # Delete $name from $list
}

sub command_deletelists {
  my $lists=shift;
  my @lists=split(/[,\s]+/, $lists);
  # Delete @lists
}