prerm is in csh 20110502-2ubuntu1.
This file is a maintainer script. It is executed when installing (*inst) or removing (*rm) the package.
The actual contents of the file can be viewed below.
| 1 2 3 4 5 6 7 8 9 10 | #!/bin/sh
set -e
if [ "$1" = remove ]; then
	update-alternatives --remove csh /bin/bsd-csh
	if which remove-shell >/dev/null 2>&1; then
		remove-shell /bin/csh
	fi
fi
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