The answer is essentially the same for Windows users as for *nix users such as Jazzbo, except you have to put single quotes around the curly brackets, e.g.:

'{' flac - -8 -o %f '}'

Make sure there is a space between each ' and the code before or after it inside the curly brackets.

When I want to perform a fix and compress to a non-default level of flac compression, I make a custom batch file and I create the custom file type as a variable. This makes the code a little easier to read, and I can easily cut and paste from one batch file into another for other fixes. I create a variable called 'typ' (for file type) at the beginning of the batch file like this:

set typ=cust ext=flac '{' flac -o %%f -V -8 - '}'

I then use 'typ' as my shntool file format with the -o argument, like this:

shntool fix -s r -o %typ% [input files]

You can use the 'typ' variable with any shntool command. For a straight conversion, for instance, set the typ variable as above, then use a command such as the following:

shntool conv -o %typ% *.shn