What does third symbol in "rw-" file mode mean in OS X ls manual page?

Question

I have trouble understanding ls's manual regarding a file that has rw- mode. Here's the quote:

1. If r, the file is readable; if −, it is not readable.

2. If w, the file is writable; if −, it is not writable.

3. The first of the following that applies:

   S     If in the owner permissions, the file is not executable and set-user-ID mode is set.  If in the group permissions, the file is not executable and set-group-ID mode is set.

   s     If in the owner permissions, the file is executable and set-user-ID mode is set.  If in the group permissions, the file is executable and setgroup-ID mode is set.

   x     The file is executable or the directory is searchable.

   −     The file is neither readable, writable, executable, nor set-user-ID nor set-group-ID mode, nor sticky.

In particular, it seem that two sections in bold contradict each other: according to the first one, since the mode begins with r, the file is readable, but according to the last one, the file is not readable. But, obviously, that is not the case.

So, what does that third section mean about file being "neither readable, writable..."?

---

Bibliography

• apple.com seems to be the source of the text quoted above.  This is the man page (for OS X version 10.9, titled "BSD General Commands Manual"), and this is a discussion page that quotes it.
• ss64.com also has a copy of the OS X ls man page.
• tuhs.org has the 4.4 BSD man page.  Beware: it uses wwoorrdd for bold and _w_o_r_d for underline.
• freebsd.org has the FreeBSD 10.1 man page, dated March 15, 2013.
• unix.com has a copy of the bad page under the man-page/freebsd directory (for FreeBSD 11.0).  Note that they also have a copy of the correct page under man-page/posix.
• The "A+ 4 Real StudyExam4Less Computer Series" contains the text quoted in the question, plus a couple of paragraphs about T and t, but not the entire man page.  It is talking about OS X.  You can see pages from two slightly different versions (editions?) of this book on books.google.com here and here.   certiguide.com seems to be quoting them.
• stevens.edu is a PDF file containing the BSD (General Commands Manual) version of ls(1). It is dated September 24, 2011.

Better:

• quora.com has the same text, but with the formatting (indentation) corrupted so badly that the meaning is ambiguous.

Better yet:

• cyberciti.biz and hurricanelabs.com have the same text, but with the indentation corrected to the point that one could argue that it's essentially OK.  But they're both still really a mess.

Answer 1

This answer was previously posted on Stack Exchange, before I noticed the question was being moved.

Each numbered point in your quote applies in turn to each of the three characters.

If the first character is 'r', the file is readable

If the second character is 'w', the file is writable

If the third character is 'x/s/S', the file has the executable and/or set-userid/setgroupid property as appropriate

If the character is '-', then the file does not have that property.

The first three characters (after the directory identifier) apply to user permissions, the second three to group permissions, and the third to everyone else.

Answer 2

You're right — it doesn't make sense.  It looks like some sort of copy & paste error (although I see that it appears on multiple sites on the web.)

Answer 3

When changing permissions on a file it is possible to indicate two permissions with a simple rw- or wx- meaning that BOTH r AND w are to be set to NO. In the second example BOTH w AND x are set to NO.

You could also indicate r+w- to set READ to YES and WRITE to NO. Or rx+ for setting Read AND Execute to YES.