On 2014-12-29 14:01, Gil Dawson wrote:
I'm having a little problem understanding the Unix
terminology.
You may find Chapter 2 of the freely available book "The Linux
Command Line" (
http://linuxcommand.org/tlcl.php ) to be helpful.
Although this book is about Linux, not MacOS X, both are based on
Unix.
This paragraph has me stumped.
'...if the filenames ... begin with "/"'
--
I cannot imagine how a filename could begin with
"/".
Does the author possibly mean pathname?
A pathname might begin with either a "/" or a "~", would
it not?
Configuration and log files are files, whereas pathnames can point
to anything. So although it may be confusing, I think that
"filename" is the correct terminology here. The filename may be
just the name of a file without any directory component, or it may
include a relative directory component or an absolute directory
component. Examples:
Simple filename: extra-stuff.conf (look for the file
"extra-stuff.conf" inside the current directory)
With relative directory: my-stuff/extra-stuff.conf (look for the
file "extra-stuff.conf" inside the directory "my-stuff" which in
turn is in the current directory"). Note that this is the same as
./my-stuff/extra-stuff.conf
Another example with a relative directory:
../../another-place/extra-stuff.conf (go up two directory levels
from the current directory, then into the directory "another-place"
and then the file is extra-stuff.conf).
Absolute directory component: /private/etc/apache2/extra-stuff.conf
"If the filenames do *not* begin with "/", ...
"/private/var/log/apache2/foo_log"
-- This
is an example of a filename that does not begin with "/",
right?
I don't get it. I see "/" at the beginning of
everything.
What would be an example of a filename that does begin
with "/"?
/private/var/log/apache2/foo_log" *does* begin with "/". You're
trying to make too much of a distinction between pathnames and
filenames.
"/usr//private/..."
-- What is the meaning of
"//" in this context?
It has no meaning, extra slashes between directory components are
ignored. This lets scripts and other programs construct filenames
without having to detect and remove extraneous slashes; if a script
always adds a slash, it will be there when needed and won't cause
problems if it is not needed. The following are all equivalent:
/usr/private
/usr//private
/usr/private/
/////usr/////private/////
For more reading, see
http://teaching.idallen.com/cst8207/12f/notes/160_pathnames.html
--
Mark Montague
mark@xxxxxxxxxxx
