27.4 Limitations on File Names

Automake attempts to support all kinds of file names, even those that contain unusual characters or are unusually long. However, some limitations are imposed by the underlying operating system and tools.

Most operating systems prohibit the use of the null byte in file names, and reserve ‘/’ as a directory separator. Also, they require that file names are properly encoded for the user’s locale. Automake is subject to these limits.

Portable packages should limit themselves to POSIX file names. These can contain ASCII letters and digits, ‘_’, ‘.’, and ‘-’. File names consist of components separated by ‘/’. File name components cannot begin with ‘-’.

Portable POSIX file names cannot contain components that exceed a 14-byte limit, but nowadays it’s normally safe to assume the more-generous XOPEN limit of 255 bytes. POSIX limits file names to 255 bytes (XOPEN allows 1023 bytes), but you may want to limit a source tarball to file names of 99 bytes to avoid interoperability problems with old versions of tar.

If you depart from these rules (e.g., by using non-ASCII characters in file names, or by using lengthy file names), your installers may have problems for reasons unrelated to Automake. However, if this does not concern you, you should know about the limitations imposed by Automake itself. These limitations are undesirable, but some of them seem to be inherent to underlying tools like Autoconf, Make, M4, and the shell. They fall into three categories: install directories, build directories, and file names.

The following characters:

newline " # $ ' `

should not appear in the names of install directories. For example, the operand of configure’s --prefix option should not contain these characters.

Build directories suffer the same limitations as install directories, and in addition should not contain the following characters:

& @ \

For example, the full name of the directory containing the source files should not contain these characters.

Source and installation file names like main.c are limited even further: they should conform to the POSIX/XOPEN rules described above. In addition, if you plan to port to non-POSIX environments, you should avoid file names that differ only in case (e.g., makefile and Makefile). Nowadays it is no longer worth worrying about the 8.3 limits of DOS file systems.