/usr/bin/git-touch is in git-extras 1.9.1-2.
This file is owned by root:root, with mode 0o755.
The actual contents of the file can be viewed below.
1 2 3 4 5 6 7 8 | #!/bin/sh
filename="$*"
test -z "$filename" && echo "filename required" 1>&2 && exit 1
touch "$filename" \
&& git add "$filename"
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