+sub which($) {
+ my $prog = shift;
+ my $res = `which $prog`;
+ $res or return undef;
+ $res =~ /^no / and return undef;
+ $res =~ /not found/ and return undef;
+ return $res;
+}
+
+my $md5cmd = which("md5sum");
+$md5cmd or $md5cmd = which("md5");
+$md5cmd or die 'no md5 checksum program found, please install md5 or md5sum';
+chomp $md5cmd;
+