#!/usr/local/bin/perl -wl
use strict;

sub my_printf {
    my $text = shift;
    my $arg;
    while ($arg = shift) {
	$text =~ s/(?<!\%)\%([^\%])/&replace_arg($1,$arg)/e;
    }
    $text =~ s/%%/%/g;
    return $text;
}

sub replace_arg {
    # takes in a replacement 'code' and an arg
    # converts the arg, per the code
    my ($code, $arg) = @_;
    if ('a' eq $code) {         # %a means flat substitution
	return $arg;
    } elsif ('b' eq $code) {    # %b means length of the arg
	return length $arg;
    } # else..

    return "humina:$code?";

}

print my_printf("foo %a bar %b", "baz", "baz");
print my_printf("oy %%9");
print my_printf("the %a is %% %b", "probability", "foo bar");

__END__
foo baz bar 3
oy %9
the probability is % 7