Naming files

A file name can be up to 255 characters long. To be portable, the file name should use only the characters in the POSIX portable file name character set:

Uppercase or lowercase A to Z
Numbers 0 to 9
Period (.)
Underscore (_)
Hyphen (-)

Do not include any nulls or slash characters in a file name.

Start of change The POSIX portable file name character set (see The POSIX portable file name character set) is a subset of the POSIX portable character set, which is listed in The POSIX portable character set. End of change

Start of change The POSIX portable character set (see The POSIX portable character set) is a complete list of all valid characters for a file name. End of change

Restriction: Double-byte characters are not supported in a file name and are treated as single-byte data. Using double-byte characters in a file name might cause problems. For instance, if you use a double-byte character in which one of the bytes is a . (dot) or / (slash), the file system treats this as a special delimiter in the path name.

The shells are case-sensitive, and distinguish characters as either uppercase or lowercase. Therefore, FILE1 is not the same as file1.

A file name can include a suffix, or extension, that indicates its file type. An extension consists of a period (.) and several characters. For example, files that are C code could have the extension .c, as in the file name dbmod3.c. Having groups of files with identical suffixes makes it easier to run commands against many files at once.