C99 says that CHAR_BIT must be at least 8; POSIX says it must be exactly 8; on Windows it's 8. That's about all the platforms it's worth caring about.

Some DSPs use CHAR_BIT=16 or CHAR_BIT=32, but they're never going to run Perl anyway.

How to get it? This is cheating I'm sure...

use strict;
use warnings;

my $char_bit;
open my $fh, "<", "/usr/include/limits.h";
while (<$fh>) {
    ($char_bit = $1, last) if /^#\s*define\s*CHAR_BIT\s*([0-9]+)/;
}

print "$char_bit\n";
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It's the kind of detail you might expect to be provided by Config, but no such luck :-(

Update: meh... I wasn't looking hard enough...

use strict;
use warnings;
use Config;

print "$Config{charbits}\n";
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