my %allowed;
$allowed{'ls'} = '/bin/ls';
$allowed{'grep'} = '/bin/grep';
$allowed{'gzip'} = '/bin/gzip';
. . .

##</code><code>##

my $good_prog = $allowed{$program1};
system($good_prog) if($good_prog != undef);

##</code><code>##

use File::Find;
my %allowed;
find(\&add, '/bin', '/usr/bin');

sub add 
{
     $allowed{$_} = $File::Find::name;
}