+# Corrupt the checksum on the index.
+# Add 1 to the last byte in the SHA.
+corrupt_index_checksum () {
+ perl -w -e '
+ use Fcntl ":seek";
+ open my $fh, "+<", ".git/index" or die "open: $!";
+ binmode $fh;
+ seek $fh, -1, SEEK_END or die "seek: $!";
+ read $fh, my $in_byte, 1 or die "read: $!";
+
+ $in_value = unpack("C", $in_byte);
+ $out_value = ($in_value + 1) & 255;
+
+ $out_byte = pack("C", $out_value);
+
+ seek $fh, -1, SEEK_END or die "seek: $!";
+ print $fh $out_byte;
+ close $fh or die "close: $!";
+ '
+}
+
+# Corrupt the checksum on the index and then
+# verify that only fsck notices.