I think you're forgetting that my produces a lexical variable that isn't attached to a package namespace.

That being the case, (and I'm agreeing with you) why does this work?

use Inline::Files;
use Data::Dumper;

open CACHE or die $!;   # read access (uses $CACHE to locate file)
eval join "", <CACHE>;
close CACHE or die $!;

print "\$var was ’$var’\n";
while (<>) {
chomp;
$var = $_;
print "\$var now ’$var’\n";
}

open CACHE, ">$CACHE" or die $!;    # write access
print CACHE Data::Dumper->Dump([$var],['var']);
close CACHE or die $!;

__CACHE__
$var = 'old value';
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