Thanks for help ;-)

I've actually made it work by taking a slightly different approach. The rewrote the to_case() sub to return a reference to appropriate case subroutine (lc(), or uc() ...)

use strict;

sub to_case
{
    my ($char) = @_;

    if ($char eq "\U$char") {
        return sub {uc(shift)};
    } else {
        return sub {lc(shift)};
    }
}

print to_case("FOO")->("bAr") ."\n";
print to_case("foo")->("BaR") ."\n";
[download]

Here's the output produced by the script:

BAR
bar
[download]

Sometimes, asking questions helps to come come up with an answer (eventually ;-). I'd appreciate it if you could show me another approach to solving my 'problem'. I'm not sure if returning sub references is a good thing?

Of course, I realize that my 'solution' presented here is way worse than what you've suggested since I might as well just pass that string which I want to modify (it's case) to the sub and simply return it's modified version in the end. However, in my script I might need to format a number of separate strings to matching case, and most of those strings may not be 'known' at the time i first invoke the to_case() sub (say, i may call it once and store sub reference for later use...).

"There is no system but GNU, and Linux is one of its kernels." -- Confession of Faith