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(autoconf.info)File System Conventions

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File System Conventions
=======================

   While `autoconf' and friends will usually be run on some Unix
variety, it can and will be used on other systems, most notably DOS
variants.  This impacts several assumptions regarding file and path
names.

For example, the following code:

     case $foo_dir in
       /*) # Absolute
          ;;
       *)
          foo_dir=$dots$foo_dir ;;
     esac

will fail to properly detect absolute paths on those systems, because
they can use a drivespec, and will usually use a backslash as directory
separator.  The canonical way to check for absolute paths is:

     case $foo_dir in
       [\\/]* | ?:[\\/]* ) # Absolute
          ;;
       *)
          foo_dir=$dots$foo_dir ;;
     esac

Make sure you quote the brackets if appropriate and keep the backslash
as first character (Note: Limitations of Builtins).

   Also, because the colon is used as part of a drivespec, these
systems don't use it as path separator.  When creating or accessing
paths, use the `PATH_SEPARATOR' output variable instead.  `configure'
sets this to the appropriate value (`:' or `;') when it starts up.

   File names need extra care as well.  While DOS-based environments
that are Unixy enough to run `autoconf' (such as DJGPP) will usually be
able to handle long file names properly, there are still limitations
that can seriously break packages.  Several of these issues can be
easily detected by the doschk(1) package.

   A short overview follows; problems are marked with SFN/LFN to
indicate where they apply: SFN means the issues are only relevant to
plain DOS, not to DOS boxes under Windows, while LFN identifies
problems that exist even under Windows.

No multiple dots (SFN)
     DOS cannot handle multiple dots in filenames.  This is an
     especially important thing to remember when building a portable
     configure script, as `autoconf' uses a .in suffix for template
     files.

     This is perfectly OK on Unices:

          AC_CONFIG_HEADER(config.h)
          AC_CONFIG_FILES([source.c foo.bar])
          AC_OUTPUT

     but it causes problems on DOS, as it requires `config.h.in',
     `source.c.in' and `foo.bar.in'.  To make your package more portable
     to DOS-based environments, you should use this instead:

          AC_CONFIG_HEADER(config.h:config.hin)
          AC_CONFIG_FILES([source.c:source.cin foo.bar:foobar.in])
          AC_OUTPUT

No leading dot (SFN)
     DOS cannot handle filenames that start with a dot.  This is usually
     not a very important issue for `autoconf'.

Case insensitivity (LFN)
     DOS is case insensitive, so you cannot, for example, have both a
     file called `INSTALL' and a directory called `install'.  This also
     affects `make'; if there's a file called `INSTALL' in the
     directory, `make install' will do nothing (unless the `install'
     target is marked as PHONY).

The 8+3 limit (SFN)
     Because the DOS file system only stores the first 8 characters of
     the filename and the first 3 of the extension, those must be
     unique.  That means that `foobar-part1.c', `foobar-part2.c' and
     `foobar-prettybird.c' all resolve to the same filename
     (`FOOBAR-P.C').  The same goes for `foo.bar' and `foo.bartender'.

     Note: This is not usually a problem under Windows, as it uses
     numeric tails in the short version of filenames to make them
     unique.  However, a registry setting can turn this behaviour off.
     While this makes it possible to share file trees containing long
     file names between SFN and LFN environments, it also means the
     above problem applies there as well.

Invalid characters
     Some characters are invalid in DOS filenames, and should therefore
     be avoided. In a LFN environment, these are `/', `\', `?', `*',
     `:', `<', `>', `|' and `"'.  In a SFN environment, other
     characters are also invalid.  These include `+', `,', `[' and `]'.

   ---------- Footnotes ----------

   (1) doschk, <ftp://ftp.gnu.org/gnu/non-gnu/doschk/doschk-1.1.tar.gz>.