Truncate a file

use NativeCall;

sub truncate(Str, int32 --> int32) is native {*}

sub MAIN (Str $file, Int $to) {
    given $file.IO { 
        .e        or die "$file doesn't exist";
        .w        or die "$file isn't writable";
        .s >= $to or die "$file is not big enough to truncate";
    }
    truncate($file, $to) == 0 or die "Truncation was unsuccessful";
}

The external truncate routine could be replaced with the following line (in which case no need for NativeCall):

spurt $file, slurp($file).substr($to);