The -M and -S options are extensions that are patched into the Debian ports of the FreeBSD ncal command.  They have not been contributed back to the original, and some of the weekday calculations (that involve querying what the current locale&#x27;s idea of the first day of the week is using the SUS2 nl_langinfo() library function) are tied to GNU libc.<p>* <a href="http:&#x2F;&#x2F;anonscm.debian.org&#x2F;cgit&#x2F;bsdmainutils&#x2F;bsdmainutils.git&#x2F;tree&#x2F;debian&#x2F;patches&#x2F;ncal_fdow.diff" rel="nofollow">http:&#x2F;&#x2F;anonscm.debian.org&#x2F;cgit&#x2F;bsdmainutils&#x2F;bsdmainutils.git...</a><p>* <a href="http:&#x2F;&#x2F;anonscm.debian.org&#x2F;cgit&#x2F;bsdmainutils&#x2F;bsdmainutils.git&#x2F;tree&#x2F;debian&#x2F;patches" rel="nofollow">http:&#x2F;&#x2F;anonscm.debian.org&#x2F;cgit&#x2F;bsdmainutils&#x2F;bsdmainutils.git...</a>