#!perl -w
use strict;
use Getopt::Std;

use vars qw($opt_F);

sub q2qq{
    my $i = shift;
    print $i;
    my %t = map { $_, eval "qq(\\$_)" } split // , 'befnrt';
    $i=~s/\\([befnrt])/$t{$1}/go;    
    return $i;
}

getopts('F:');
print "Before: \n";
printf($opt_F, 'foo', 'bar');

$opt_F = q2qq($opt_F);

print "\nAfter: \n\n";
printf ($opt_F, 'foo','bar');