determined by the @var{mode} string. The way in which this is
interpreted is similar to C stdio. The first character must be
one of the following:
+
@table @samp
@item r
Open an existing file for input.
The "append mode" can be turned off while the port is in use
@pxref{Ports and File Descriptors, fcntl}
@end table
+
The following additional characters can be appended:
+
@table @samp
@item +
Open the port for both input and output. E.g., @code{r+}: open
@item l
Add line-buffering to the port. The port output buffer will be
automatically flushed whenever a newline character is written.
+@item b
+Use binary mode. On DOS systems the default text mode converts CR+LF
+in the file to newline for the program, whereas binary mode reads and
+writes all bytes unchanged. On Unix-like systems there is no such
+distinction, text files already contain just newlines and no
+conversion is ever made. The @code{b} flag is accepted on all
+systems, but has no effect on Unix-like systems.
+
+(For reference, Guile leaves text versus binary up to the C library,
+@code{b} here just adds @code{O_BINARY} to the underlying @code{open}
+call, when that flag is available.)
@end table
+
In theory we could create read/write ports which were buffered
in one direction only. However this isn't included in the
current interfaces. If a file cannot be opened with the access