Autoconf uses shell-script processing extensively, so the file names that it processes should not contain characters that are special to the shell. Special characters include space, tab, newline, nul, and the following:
" # $ & ' ( ) * ; < = > ? [ \ ` |
Also, file names should not begin with ‘~’ or ‘-’, and should contain neither ‘-’ immediately after ‘/’ nor ‘~’ immediately after ‘:’. On Posix-like platforms, directory names should not contain ‘:’, as this runs afoul of ‘:’ used as the path separator.
These restrictions apply not only to the files that you distribute, but also to the absolute file names of your source, build, and destination directories.
On some Posix-like platforms, ‘!’ and ‘^’ are special too, so they should be avoided.
Posix lets implementations treat leading // specially, but requires leading /// and beyond to be equivalent to /. Most Unix variants treat // like /. However, some treat // as a “super-root” that can provide access to files that are not otherwise reachable from /. The super-root tradition began with Apollo Domain/OS, which died out long ago, but unfortunately Cygwin has revived it.
While autoconf and friends are usually run on some Posix variety, they can be used on other systems, most notably DOS variants. This impacts several assumptions regarding file names.
For example, the following code:
case $foo_dir in /*) # Absolute ;; *) foo_dir=$dots$foo_dir ;; esac
fails to properly detect absolute file names on those systems, because they can use a drivespec, and usually use a backslash as directory separator. If you want to be portable to DOS variants (at the price of rejecting valid but oddball Posix file names like a:\b), you can check for absolute file names like this:
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 (see 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, you can 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 variants that are Posixy enough to run autoconf (such as DJGPP) are usually 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 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 under Microsoft Windows variants, while lfn identifies problems that exist even under Microsoft Windows variants.
This is perfectly OK on Posix variants:
AC_CONFIG_HEADERS([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_HEADERS([config.h:config.hin]) AC_CONFIG_FILES([source.c:source.cin foo.bar:foobar.in]) AC_OUTPUT
The 8+3 limit is not usually a problem under Microsoft Windows, as it
tails in the short version of file names to make them unique. However, a
registry setting can turn this behavior 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