[SOLVED] Why "ls /usr//bin/" works?

kaz2100 · 09-11-2014, 04:55 AM

Hya

I am absolutely confused.

Code:

>ls /usr/bin
(many files.)
...
>ls /usr/bin/ > 1
>ls /usr//bin/ > 2
>ls /usr///bin/ > 3
>diff 2 3
>diff 1 2
>

"ls /usr/bin" works as I expect, so does "ls /usr/bin/"

I thought I would get an error with "ls /usr//bin/" or ...

(Debian jessie, on X86_64)

jdkaye · 09-11-2014, 05:45 AM

I'm not sure what your question is. As long as "bin" is a folder those commands will return the contents of the "/usr/bin". If you try the same thing with a file, then you will get an error. For example:

Code:

~$ ls /usr/bin/identify/
ls: cannot access /usr/bin/identify/: Not a directory

But I'm not sure if this is what you are asking.
jdk

a4z · 09-11-2014, 05:53 AM

// in a path do not matter
all commands ignore them
this is useful, for example when you join strings to a path, you do not need to care about //s

rtmistler · 09-11-2014, 03:30 PM

I'll file this under the Learn something new everyday category.

Yes, it works. Didn't know that it would simply ignore repeated slashes.

My continual lack of expertise with regular expressions is likely my blind spot here, but maybe it's more me missing an integral understanding of how the shell interprets things. I'm sure many are more well versed with the use of back-slash.

astrogeek · 09-11-2014, 03:45 PM

It is actually from the underlying filesystem/API specifications (nothing to do with regular expressions).

I have read it somewhere in my Stevens, and as I recall it is included in POSIX. A quick search found this one from IEEE Std 1003.1, 2004 Edition (POSIX):

Quote:

3.266 Pathname

A character string that is used to identify a file. In the context of IEEE Std 1003.1-2001, a pathname consists of, at most, {PATH_MAX} bytes, including the terminating null byte. It has an optional beginning slash, followed by zero or more filenames separated by slashes. A pathname may optionally contain one or more trailing slashes. Multiple successive slashes are considered to be the same as one slash.

But the origin of the idea is hidden in the mists of Unix time and space, or before (myth has it that time itself did in fact exists prior to universal recognition of the Unix Epoch).

kaz2100 · 09-11-2014, 10:00 PM

Hya,

Thanks for replies.

1. It looks like that
http://www.linuxquestions.org//quest...hp?p=5236421//

and

http://www.linuxquestions.org/questi....php?p=5236421

also are parsed in a same way.

2. My confusion grows, as I read the POSIX site. I do not think I understand pathname and filename correct.

cheers

P.S. What does "somewhere in my Stevens" mean? I am not a native speaker.

astrogeek · 09-11-2014, 10:12 PM

Quote:

Originally Posted by kaz2100

P.S. What does "somewhere in my Stevens" mean? I am not a native speaker.

Sorry, that was a reference to (in my opinion) the most valuable Unix reference book after anything written by Ritchie, Thompson, Kernighan and company.

Advanced Programming In The Unix Environment by W. Richard Stevens

From that link:

Quote:

OSNews describes it as "one of the best tech books ever published" in a review of the second edition.

I have a first edition and a second edition with Rago, but the first is still my favorite (no Linux coverage, but more accessible) - get one if you can!