Explain what os.read() returns at end of file.

This closes SF bug #550409.

diff --git a/Doc/lib/libos.tex b/Doc/lib/libos.tex
index ca9a206d854cf33c4da497b0216f78d2a29f3dc1..d40aa076b1fce31b370c83ff335cb6831b003c3c 100644 (file)
--- a/Doc/lib/libos.tex
+++ b/Doc/lib/libos.tex
@@ -453,7 +453,9 @@ Availability: \UNIX{}, Windows.
 
 \begin{funcdesc}{read}{fd, n}
 Read at most \var{n} bytes from file descriptor \var{fd}.
-Return a string containing the bytes read.
+Return a string containing the bytes read.  If the end of the file
+referred to by \var{fd} has been reached, an empty string is
+returned.
 Availability: Macintosh, \UNIX{}, Windows.
 
 Note: this function is intended for low-level I/O and must be applied