1 2
grep -Fqx /bin/csh /etc/shells || echo /bin/csh >> /etc/shells grep -Fqx /bin/tcsh /etc/shells || echo /bin/tcsh >> /etc/shells
# do not edit /etc/shells on upgrades test "$1" = 0 && sed -i -e '/^\/bin\/t?csh$/d' /etc/shells || true