{"id":14209,"date":"2026-05-29T02:00:00","date_gmt":"2026-05-29T06:00:00","guid":{"rendered":"https:\/\/www.both.org\/?p=14209"},"modified":"2026-05-19T12:33:16","modified_gmt":"2026-05-19T16:33:16","slug":"yes-dos-filenames-can-have-spaces","status":"publish","type":"post","link":"http:\/\/www.both.org\/?p=14209","title":{"rendered":"Yes, DOS filenames can have spaces"},"content":{"rendered":"
\r\n
\r\n \r\n <\/i>\r\n <\/a>\r\n <\/span>\r\n<\/div><\/div>\n

Someone asked me recently if FreeDOS supports spaces in filenames. FreeDOS<\/a> is an open source DOS-compatible operating system that you can use to play classic DOS games, run legacy business software, or write new DOS programs. Any program that works on MS-DOS should also run on FreeDOS. And that means FreeDOS comes with the same limitations as classic DOS.<\/p>\n\n\n\n

DOS uses 8.3 filenames<\/a>, which means filenames can only have up to 8 characters for the base name<\/em> and up to 3 characters for the extension<\/em>. Filenames are stored in all-uppercase, but are actually case insensitive. That means if you save as file as MYFILE.TXT<\/code> you can also access it as Myfile.txt<\/code> or MyFile.Txt<\/code> or any other mix of uppercase and lowercase.<\/p>\n\n\n\n

You can use almost any character in a filename, but in practice this is usually letters, numbers, and certain punctuation characters like !<\/code>, #<\/code>, $<\/code>, %<\/code>, (<\/code>, )<\/code>, -<\/code>, _<\/code>, {<\/code>, }<\/code>, _<\/code>, and a few other characters. You cannot use some other characters like quotes, question marks, slashes, square brackets, colon or semicolon, periods, commas, greater-than or less-than (plus a few more), which would get in the way of the shell.<\/p>\n\n\n\n

But space is technically allowed in 8.3 filenames. Although in practice it’s not a good idea to use them, because some applications may not support spaces in filenames in the same way.<\/p>\n\n\n\n

Let’s try it<\/h2>\n\n\n\n

Whenever you have a question about something, like can a filename have a space in it<\/em>, I recommend writing a quick program to test it. So let’s write a test program that creates a new text file with a space in the filename, writes a short message, and saves it. This program does just that, saving the file as A A.TMP<\/code>. Note that the space must be surrounded<\/em> by other valid characters. For example, you can name a file as MY FILE.TXT<\/code> but not MYFILE .TXT<\/code> where the space is at the end of the base name<\/em>.<\/p>\n\n\n\n

<\/a>#include <stdio.h>\n<\/a>\n<\/a>int main()\n<\/a>{\n<\/a>  FILE *f;\n<\/a>\n<\/a>  f = fopen(\"A A.TMP\", \"w\");\n<\/a>  if (f==NULL) {\n<\/a>    puts(\"error, cannot open file\");\n<\/a>    return 1;\n<\/a>  }\n<\/a>\n<\/a>  fputs(\"Hello world\\n\", f);\n<\/a>  fclose(f);\n<\/a>\n<\/a>  puts(\"Ok\");\n<\/a>  return 0;\n<\/a>}<\/code><\/pre>\n\n\n\n
There’s not much going on inside this program, because it’s meant to test a specific thing. The fopen<\/code> line opens a file called A A.TMP<\/code> for w<\/strong>riting. The if<\/code> statement after that checks if the file could be opened; if it could not, the program prints an error and immediately quits. Otherwise, the program writes Hello world<\/code> to the file, then closes it before printing an “Ok” message and returning to the operating system.<\/p>\n\n\n\n
If you’ve written this program on FreeDOS, you can compile it with any C compiler. We include several C compilers on the FreeDOS distribution, including Open Watcom C, an IA-16 version of GCC, and BCC. I saved this program as aa.c<\/code> and compiled it with Open Watcom C. (Open Watcom prints a lot of messages as it goes, but I’ve made it q<\/strong>uiet with the -q<\/code> option. I also prevented the DOS4G extender from printing a message by setting the DOS4G<\/code> environment variable to quiet<\/code>.)<\/p>\n\n\n\n
D:\\SRC>set DOS4G=quiet\nD:\\SRC>wcl -q aa.c<\/code><\/pre>\n\n\n\n
Just run the program, and you’ll see that it creates a new file called A A.TMP<\/code> (there’s a space in between the two A<\/strong>‘s).<\/p>\n\n\n\n
D:\\SRC>dir \/b *.tmp\nFile not found.\n\nD:\\SRC>aa.exe\nOk\n\nD:\\SRC>dir \/b *.tmp\nA A.TMP<\/code><\/pre>\n\n\n\n
You can access the file using quotes on the command line. But because the filename has TMP<\/code> for the extension, you can also use a wildcard for other actions such as deleting the file:<\/p>\n\n\n\n
D:\\SRC>type \"A A.TMP\"\nHello world\n\nD:\\SRC>del *.tmp\none file removed.<\/code><\/pre>\n\n\n\n
A caution<\/h2>\n\n\n\n
This is a valid C program and it will compile using any standard C compiler. However, note that some C compilers may alter the behavior because of spaces in the filename. Notably, the runtime library in BCC (Bruce’s C Compiler) prevents spaces in filenames, replacing them with underscore characters. So if you compile this program with BCC and run it, you will get slightly different behavior.<\/p>\n\n\n\n
D:\\SRC>bcc -o aa.com aa.c<\/code><\/pre>\n\n\n\n
Now run the program and you will instead get a file called A_A.TMP<\/code> (with an underscore instead of a space).<\/p>\n\n\n\n
D:\\SRC>aa.com\nOk\n\nD:\\SRC>dir \/b *.tmp\nA_A.TMP\n\nD:\\SRC>type A_A.TMP\nHello world<\/code><\/pre>\n","protected":false},"excerpt":{"rendered":"
A short program to demonstrate that yes, DOS filenames can have spaces in them<\/p>\n","protected":false},"author":33,"featured_media":7678,"comment_status":"open","ping_status":"closed","sticky":false,"template":"","format":"standard","meta":{"_lmt_disableupdate":"","_lmt_disable":"","footnotes":""},"categories":[340,150],"tags":[267,152],"class_list":["post-14209","post","type-post","status-publish","format-standard","has-post-thumbnail","hentry","category-freedos","category-programming","tag-freedos","tag-programming"],"modified_by":"Jim Hall","_links":{"self":[{"href":"http:\/\/www.both.org\/index.php?rest_route=\/wp\/v2\/posts\/14209","targetHints":{"allow":["GET"]}}],"collection":[{"href":"http:\/\/www.both.org\/index.php?rest_route=\/wp\/v2\/posts"}],"about":[{"href":"http:\/\/www.both.org\/index.php?rest_route=\/wp\/v2\/types\/post"}],"author":[{"embeddable":true,"href":"http:\/\/www.both.org\/index.php?rest_route=\/wp\/v2\/users\/33"}],"replies":[{"embeddable":true,"href":"http:\/\/www.both.org\/index.php?rest_route=%2Fwp%2Fv2%2Fcomments&post=14209"}],"version-history":[{"count":1,"href":"http:\/\/www.both.org\/index.php?rest_route=\/wp\/v2\/posts\/14209\/revisions"}],"predecessor-version":[{"id":14210,"href":"http:\/\/www.both.org\/index.php?rest_route=\/wp\/v2\/posts\/14209\/revisions\/14210"}],"wp:featuredmedia":[{"embeddable":true,"href":"http:\/\/www.both.org\/index.php?rest_route=\/wp\/v2\/media\/7678"}],"wp:attachment":[{"href":"http:\/\/www.both.org\/index.php?rest_route=%2Fwp%2Fv2%2Fmedia&parent=14209"}],"wp:term":[{"taxonomy":"category","embeddable":true,"href":"http:\/\/www.both.org\/index.php?rest_route=%2Fwp%2Fv2%2Fcategories&post=14209"},{"taxonomy":"post_tag","embeddable":true,"href":"http:\/\/www.both.org\/index.php?rest_route=%2Fwp%2Fv2%2Ftags&post=14209"}],"curies":[{"name":"wp","href":"https:\/\/api.w.org\/{rel}","templated":true}]}}