-f $filename or die "$filename is not a file";
(-s _ < 100_000) or die "$filename is too large"; # avoid a second stat() syscall by using the special handle "_"
my $blob=do {
    open my $f,'<:raw',$filename or die "Can't open $filename: $!";
    local $/; # slurp mode
    <$f>; # slurp
    # leaving the do block auto-closes $f
};
# Accept only CR, LF, TAB, and printable characters from 0x20 to 0x7E.
$blob=~/^[\r\n\t\x20-\x7E]*$/s or die "$filename is not ASCII";