/usr/share/doc/live-config/examples/hooks/sh is in live-config-doc 5.20170112+deb9u1.
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 9 | #!/bin/sh
echo
echo "live-config hook: sh"
echo
echo "Starting shell [logout for quit]: "
sh
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