POSTIN

/bin/sh

if [ ! -f /etc/shells ]; then
	echo "/bin/tcsh" >> /etc/shells
	echo "/bin/csh" >> /etc/shells
else
	grep -q /bin/tcsh /etc/shells || echo "/bin/tcsh" >> /etc/shells
	grep -q /bin/csh /etc/shells || echo "/bin/csh" >> /etc/shells
fi

POSTUN

/bin/sh

if [ ! -x /bin/tcsh ]; then
    perl -ni -e 'm|/bin/t?csh| or print' /etc/shells
fi