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';