my $tokens = $ARGV[0];
my %meta = ( 
    't' => \&time,
    'l' => \&log_level,
    'm' => \&message,
    '%' => sub { '%' }, # So you can put "50%%" into your template and have it render as "50%"
);
($output = $tokens) =~ s/%(.)/$meta{$1}->()/ge;