GIT: I want to unstage all files matching a certain pattern

for i in `git status --porcelain | grep '^D.*\.foo$' | sed 's/^D \+//'`; do
    git reset HEAD "$i"
    git checkout "$i"
done

If you are using Powershell the following will work.

gci -re -in *foo | %{ git reset $_ } 

This should work in cygwin and unix env

git reset $(git diff --name-only --cached | grep *.foo)