+# Make sure we are in the worktree, not under .git; die otherwise
+ensure_git_repo_or_die()
+{
+ local is_inside_repo is_inside_git_dir
+ is_inside_repo=1
+ is_inside_git_dir=$(git rev-parse --is-inside-git-dir 2>/dev/null) ||
+ is_inside_repo=0
+
+ case "$is_inside_repo/$is_inside_git_dir" in
+ 0*) die "Cannot run outside of a Git repository.";;
+ 1/true) die "Cannot run from inside \`.git\` hierarchy, please switch to work-tree.";;
+ esac
+}
+
+# cat_file TOPIC:PATH [FROM]
+# cat the file PATH from branch TOPIC when FROM is empty.
+# FROM can be -i or -w, than the file will be from the index or worktree,
+# respectively. The caller should than ensure that HEAD is TOPIC, to make sense.