Skip to main content

Slash and backslash (#1033)

Topics/tags: Language, short, rants

When you say slash, most people [1] envision the / character. Some folks may also refer to that character as forward slash. When you say backslash [2], most people [3] envision the \ character. In the land of computers, slashes [4] have been used for a wide variety of situations, such as to represent division in mathematical expressions or in pairs to preface one-line comments in some variants of the C programming language. But one of the most important uses is in URLs [5]. Consider, for example, the URL. [7]

I would pronounce that as

aitch tee tee pee ess colon slash slash dub dub dub dot grinnell dot ee dee you slash admission slash visit.

Of course, most people write it without the leading https://. In that case, the pronunciation becomes somewhat shorter,

dub dub dub dot grinnell dot ee dee you slash admission slash visit.

or even

grinnell dot ee dee you slash admission slash visit.

Seems simple enough, doesn’t it?

So why do I keep hearing people refer to things like grinnell dot ee-dee-you backslash admission backslash visit [8]?. That phrase describes\admission\visit, which is not the same thing, even though on some systems it will redirect to the correct URL. I’ve heard folks on NPR use the wrong term. I’ve heard administrators at Grinnell use it. But why?

As far as I can tell, it’s because Microsoft decided to use backslashes to separate directories in hierarchical file systems, originally on MS-DOS and now on MS-winDOwS, and the mis-speakers have heard technical people say backslash when describing file locations and think they should be using that term when they speak computer-ese.

Given that Microsoft uses backslashes, why does the Web use slashes? Presumably, because the Web was built on Unix systems and Unix uses forward slashes.

Given that Microsoft uses backslashes, why does Unix use forward slashes?

That’s the wrong question. Hierarchical file systems in Unix came before hierarchical file systems in MS-DOS. More precisely, Unix (with hierarchical file systems) came before any form of MS-DOS, and flat file systems on MS-DOS came before hierarchical file systems on MS-DOS.

So the better question is: Given that Unix uses forward slashes, why does Microsoft use backslashes? To answer that question, I turned to the Interweb. Eventually, I ended up on a ’blog post from Larry Osterman at Microsoft from 2005 entitled Why is the DOS path character ""? [9,11]. The answer is fairly straightforward: Some MS-DOS tools, developed by IBM, used a slash character for command-line flags. It appears that VMS had made the same decision. Since slash meant flag, Microsoft chose backslash for their separator. I’m pretty sure that the original Macintosh System used colons.

In the end, none of that should matter to the matter at hand. The ways in which the use of the slash and backslash have evolved are of interest to some [12], but not all. However, everyone should care that we use a correct and unambiguous name for characters, and backslash is not the correct name for /. Use slash.

Postscript: Finding the Larry Osterman ’blog post was an interesting adventure. The first page I found about the use of backslashes in MS-DOS took most of its information from the Osterman post. It gives the URL for that post. Unfortunately, Microsoft does not seem to consider it worthwhile to ensure that links remain consistent. That link redirects to It took a bit of searching to find the right page, particularly because I was doing it on my cell phone and because the word backslash does not appear in the article. The final link I found it at was, which bears little resemblance to the original URL.

Postscript: Can you find the missing right brace in the Osterman piece?

Postscript: Slash fiction is a genre of fanfic named for the slash that appears between two character names, usually of the same gender, as in Kirk/Spock slash fiction. I don’t think I’ve ever heard anyone refer to it as backslash fiction. Now I wonder if there is some form of backlash fiction that one could hybridize with slash fiction to make backslash fiction. Something like that.

[1] Or at least most Americans in the twenty-first century.

[2] Or back slash, to match the spacing of forward slash.

[3] See the prior endnote.

[4] Forward slashes.

[5] I’ve normally pronounced that as You-are-els. I suppose some might refer to them as Earls or Hurls, but with a silent H.

[6] Aitch.

[7] I fell like I know the student who appears on that page.

[8] No, I have not heard that particular phrase. But you know what I mean. At least I hope that you do.

[9] Aren’t you impressed that I found a way to avoid smart quotes [10] in that title?

[10] One of my colleagues would insist that I call those quotation marks rather than quotes.

[11] Are you surprised that there’s no backslash in the title? I am. I assume it has to do with the wonder of Web formatting. But there wasn’t one in the original, so I’m not including one here.

[12] Including me.

Version 1.0 of 2020-03-19.