How can I bulk change file names from underscores to hyphens?

[jeroenvandepol]

When I started the webshop I made the mistake of using underscores in my file names. I want to fix that by changing the underscores to a hyphen. I was hoping that I could export the filenames to a CSV, make the changes in a spreadsheet and import again. I am happy with my filenames, so I don't want to use an app that composes filenames. Basically I want to do a good old "search and replace".