Why is the DOS path character "\"?

http://blogs.msdn.com/b/larryosterman/archive/2005/06/24/432386.aspx

269 66 14 years ago

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program• 14 years ago

This article remind me of my first days of C coding and the problems generated with escaped "c:\haracters in strings".

After years I still think that the use of forward slash is the worst decision ever. At least Apple chose ":" on Mac OS classic.

harshreality• 14 years ago

If you're referring to \ it's a backslash not a forward slash.

vacri• 14 years ago

In my time supporting naive endusers, it's always amused me that people at a level where they have trouble with left and right mouse buttons can remember slash and backslash like pros.

RegEx2• 14 years ago

A simple way to remember forward/backslash (which I probably read on HN) is the phrase "Backslash is by the backspace"

Edit: This is for the standard US keyboard. A more general way of thinking about it, though a bit more to remember: associate "positive" with "forward", and see that '/' has a positive slope. Or just go listen to a BBC podcast, and let the sound of the broadcaster saying "bbc dot co dot uk forward-slash newspod" resonate in your head.

mmisu• 14 years ago

Fortunately today you can use string literals with most programming languages.

yuhong2• 14 years ago

The comments has the story on that, which involved IBM.

PaulHoule• 14 years ago

The early DOS developers wanted to use "/", so it turns out the underlying OS will accept either / or \. The main trouble you have is that cmd.exe and powershell think \ is the switch character -- so as long as you're not writing programs that write shell scripts or shell out you do OK.

Back when I was a Windows dev I drove the guys I worked with nuts because I used "/" instead of "\", figuring it would be more portable and I wouldn't have to write "\\" all the time. Of course, C# has @"" just to deal with that latter problem.

torme• 14 years ago

So I'm sort of nitpicking your comment here, but the purpose of @"" for verbatim strings wasn't created just to deal with directory slashes, it's just a handy way of writing string without the need for escaping in general.

Also, if you really want to make portable C# code, you should use Path.DirectorySeparatorChar, as it's not platform specific at all.

http://msdn.microsoft.com/en-us/library/system.io.path.direc...

rwmj• 14 years ago

In Microsoft tradition, this article completely ignores the fact that DOS was a CP/M clone bought wholesale from another company (originally called QDOS). The question is, did QDOS have / for command line switches? Or were all of these tools added (as the article implies) by Microsoft engineers later?

[I didn't use QDOS, but I did use CP/M and it had the most unholy command line syntax. I don't fondly remember PIP...]

jgrahamc2• 14 years ago

No, QDOS (86-DOS) did not have switches. IIRC none of the commands had any options at all. It did, however, have nice CP/M compatibility because there was a command (RDCPM?) that allowed you to read from CP/M formatted media.

pjmlp4• 14 years ago

CP/M did not have directories as well.

jgrahamc2• 14 years ago

Goes deeper than just IBM. Prior to DOS there was CP/M and CP/M had many programs with an older heritage. For example, it was possible to copy from a source (such as a file) to a destination (such as another file, or an I/O port) using a program called PIP (http://en.wikipedia.org/wiki/Peripheral_Interchange_Program). On CP/M, for example, you could print a file with the command (PRN: is the name of the printer device; at the time that was likely a parallel connected printer):

    PIP PRN:=FOO.TXT

PIP itself predates CP/M having been present on machines such as the PDP-11. Wikipedia tells me that it was first implemented on the PDP-6. For example, on the PDP-10 you could do:

    PIP DTA1:/X=DSK:*.*

which copied all the files from the disk onto tape. The /X there modifies the destination and indicates that file attributes (modification time etc.) should be preserved.

PS Now my memory is fully restored from 1980s backing store I believe that CP/M actually replaced the / in PIP with single character switches inside [] and that the route to / being switches in MS-DOS most likely comes through DEC heritage from the PDP series. For example, the W switches would ignore r/o set on a file and overwrite it. This would copy all .COM files (i.e. executables) from B: to A: and overwrite without warning:

    PIP A:=B:*.COM[W]

yread• 14 years ago

You could still do that with copy in MS-DOS, I have a feeling my mom still does it since she has a printer on parallel port. So if she wants to print a textfile it's just

     copy file.txt LPT1

she can also print multiple files or results of print to file using the /b switch (binary) ignoring EOF

That also explains why you shouldn't use LPT1 as file name - it was a special name that meant first parallel port. I remember seeing a ridiculing thread about it on HN some time ago

csamuel• 14 years ago

"And that is why, in 2009, when developing in Microsoft .NET 3.5 for ASP.NET MVC 1.0 on a Windows 7 system, you cannot include /com\d(\..)?, /lpt\d(\..)?, /con(\..)?, /aux(\..)?, /prn(\..)?, or /nul(\..)? in any of your routes."

Source: http://news.ycombinator.com/item?id=655397

rhizome• 14 years ago

I'm pretty sure you could still do this up until at least Win2k+ if your mapped printer had a port associated.

po3• 14 years ago

Interestingly, if you ever come to Japan you will find many people expect path separators to be yen symbols (¥). Their windows paths look like:

¥docs¥finance¥

To understand the reason, just check out the table on the Shift-JIS encoding:

http://en.wikipedia.org/wiki/Shift_JIS

Specifically, look at the character at 0x5C where the backslash sits in ASCII. Learning this was one of those mind-blowing moments when you try to imagine what a world where that was normal would be like.

rangibaby2• 14 years ago

Interesting! I wonder why they changed that particular character and not one that is literally everywhere in DOS.

Using ¥ as backslash still works in Windows and legacy apps (in OSX option+¥ gives a "real" \.)

This leads to some interesting situations: Word documents filled with ¥ where there should be \ and vice versa. By interesting I mean extremely annoying.

Another caveat is that anything hardcoded to use the tilde ~ will probably break because it is mapped to a completely key on Japanese keyboards. This causes endless fun in DOSBOX or even newer games: to get the console in Doom 3 I had to edit the source and recompile it with the console key mapped to another character.

tangus• 14 years ago

Several positions in the table ({ | } [ \ ] @) were meant for "national variants". I guess those characters were deemed unimportant at the time.

Here is some more info: http://www.cs.tut.fi/~jkorpela/chars.html#national-ascii

po3• 14 years ago

I wonder why they changed that particular character and not one that is literally everywhere in DOS.

I've wondered about that as well. My guess is that they looked at it and thought 'who needs two kinds of slash anyway?' I would love to know the actual thought behind that choice.

yuhong2• 14 years ago

Same for Korean with the ₩. And you can change the default system locale to Japanese or Korean and see it on any language version of Windows.

psykotic• 14 years ago

The Korean won symbol ₩ also occupies 0x5C. I never got totally used to seeing directory paths separated by ₩.

mckilljoy• 14 years ago

I have the korean QSENN DT-35 keyboard. The first time I opened up the cmd, I couldn't find the '\' and had to click random keys until I found the ₩ key :-D

darklajid4• 14 years ago

Obligatory link for this fact to the One True Source for oddities like these:

https://blogs.msdn.com/b/michkap/archive/2005/09/17/469941.a...

Iv• 14 years ago

That was one of my awkward debugging moments. We had a path issue for a Japanese clients and I was completely unaware of this specificity. The path issue was somewhere else but understanding that having ¥ instead of \ was a feature and not a bug took me a while.

makecheck• 14 years ago

What bugs me is that they chose a character right next to "Return" on the keyboard. For some reason no PC keyboard has moved it.

I've had embarrassing MS-DOS moments in the past where I was typing out something like a recursive-delete on a path. If you accidentally hit RETURN instead of a backslash then you can do things like blow away entire parent directories unintentionally. This didn't exactly improve my already-critical view of PCs. :)

drucken• 14 years ago

That is interesting, I have had the exact opposite experience!

I have never seen a PC keyboard with the backslash anywhere other than in the bottom LEFT corner next to your left smallest/pinky finger with one exception: in Germany and France, they keyboards sometimes have backslash on the top line numerical keys.

darklajid4• 14 years ago

Germany has a really awkward position for this key. You can only reach it by hitting 'Alt Gr' (the right Alt key) and a _right_ key in the row of digits. One-handed and similar (albeit mirrored) to the US layout's access to ~.

I .. switch all my keyboard to the US layout because I feel that I kill my fingers otherwise to reach {[]}| and \

chimeracoder• 14 years ago

It's funny to think of how standardized keyboards are within the US today, and yet it wasn't so long ago that you couldn't even count on the arrow keys being in the same place (or in fact, being there at all - which is why you have hjkl on Vim to this day.

On the other hand, the computers at Bell Labs had an arrow key, which is why R (which is based on S) uses '<-' for assignment, as the two-character combination was enabled for compatibility reasons.

And on a related note, I can't imagine how people use Vim without rebinding ESC to Caps_Lock. Given that ESC used to be where TAB currently is (and the latter is too useful to be removed), I don't really see a point in keeping the obsolescent Caps_Lock, especially when it's so irritating to keep moving the hand to the furthest corner of the keyboard.

cahrens2• 14 years ago

I usually swap the left ctrl and the Caps lock keys, mostly out of habit from the first computer I used (An actual computer, with the Magnetic Tape spools and punch-card boot loader).

I have also dealt with crappy tiny keyboards that don't even have any keys beyond the standard chunk (So no function keys, 10-key, or arrows / browsing control)

tesseract• 14 years ago

As a frequent vim user I probably should have done the caps-as-esc remap but by now caps-as-control is so engrained in my muscle memory that I now have a significant friction to changing it.

My favorite keyboard happens to be the Apple Extended Keyboard II, but I can't use one these days because its caps key would physically toggle between on and off states (like a typewriter caps key) which means it does not make a very good candidate for remapping.

prewett• 14 years ago

Ctrl-[, which turns out to be ESC, is one solution. Given that many people like to remap CapsLock to Ctrl, it might give you the best of both worlds.

cahrens2• 14 years ago

I have always hated how the colon is used in windows for drive letters, there have been way too many times where I would type a long path only to realize that there is a semi-colon at the beginning.

duncanj• 14 years ago

are you saying they looked into the future and chose a character next to return on a keyboard that hadn't been designed yet?

http://www.pcguide.com/ref/kb/layout/stdXT83-c.html

greggman• 14 years ago

I've always felt the better question is "Why is the UNIX path character "/"?

People use "/" as a date separator as in 12/25/1979 so effectively banning that character as a character in filenames seems a really poor choices. By that metric chosing "\" is a much better choice because "\" is used no where I know outside of computers. I've never encountered it anywhere outside of computers so arguable it's the perfect choice for a path character.

meepmorp2• 14 years ago

> I've always felt the better question is "Why is the UNIX path character "/"?

Just a guess, but it's probably because \ is used for character escapes in C (and the Bourne shell). Given that the history of Unix is inextricably tied to C, it kind of makes sense to use / over \ so you don't have to do lots of \\ to escape path names.

jeltz• 14 years ago

This is a good thing though since this encourages more people to use the ISO date formats. They are unambiguous, easy to parse and sort correctly

to3m• 14 years ago

There are other uses of the slash character. It's a poor choice.

_ or | get my vote, but it's a bit late now to fix the mistakes of the past. There are enough special chars needed anyway that collisions are inevitable.

At least they didn't pick 'E'.

darklajid4• 14 years ago

Other people use '.' in dates. Or '-'. Especially the latter would end up with the same problem: Why is - and -- used as a switch character if it is used in dates (and even quite common in normal text, names)?

And given that the history of '\' as a path separator is that long, maybe you haven't seen in elsewhere _because_ it is now forever taken for the world's most popular OS?

celoyd2• 14 years ago

Why is - and -- used as a switch character if it is used in dates (and even quite common in normal text, names)

Those uses rarely have it next to whitespace, and almost never immediately after whitespace.

If someone’s named Jean-Claude, it is not customary to refer to them as -Claude for short, and if I refer to items dated 2012-03-19 and 2012-03-20, it is not customary to call one of them -20.

But that last example shows something that Unixy switches do conflict with: negative numbers.

mixmastamyk3• 14 years ago

In addition to the other reasons listed here,

/ is easier to type than \

pjmlp4• 14 years ago

On which country?

archangel_one• 14 years ago

Of course, Windows bans the use of both / and \ (along with : and other useful things) in filenames anyway so you still can't enter dates in that format. I guess back when they made the decision on the path separator the max path length in DOS was so short it may not have seemed relevant.

fanf2• 14 years ago

It seems from http://cm.bell-labs.com/who/dmr/hist.html that Multics used > as the path separator. Unix decided to use < and > for redirection (in the PDP7 era), so something else was chosen for pathnames when they were introduced later on the PDP11.

alanh2• 14 years ago

Argh, second word of second paragraph is “answer’s”, an attempted pluralization of “answer”?

Argh!

Will continue reading anyway, and will lose karma for this, but shit, does no one even read their shit after publishing anymore?

alanh2• 14 years ago

Relevant to this, one of the most popular posts I’ve ever written: http://alanhogan.com/tips/php/directory-separator-not-necess...

Why is the DOS path character "\"?

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