## Pathlists: How Paths Are Named

Whenever a path is established (or “opened”), OS-9 must be given a description of the “routing” of the path. This description is given in the form of a character string called a “pathlist”. It specifies a particular mass-storage file, directory file, or any other I/O device. OS-9 “pathlists” are similar to “filenames” used by other operating systems.

The name “pathlist” is used instead of “pathname” or “filename” because in many cases it is a list consisting of more than one name to specify a particular I/O device or file. In order to convey all the information required, a pathlist may include a device name, one or more directory file names and a data file name. Each name within a pathlist is separated by slash “/” characters.

Names are used to describe three kinds of things:

- Names of Physical I/O Devices

- Names of Regular Files

- Names of Directory Files

Names can have one to 29 characters, all of which are used for matching. They must begin with an upper- or lower-case letter followed by any combination of the following characters:

uppercase letters: A - Z
lowercase letters: a - z
decimal digits: 0 - 9
underscore: _
period: .

Here are examples of legal names:

raw.data.2 | projectreview.backup
reconciliation.report | X042953
RJJones | search.bin

Here are examples of illegal names:

22November | (does not start with a letter)
max*min | (* is not a legal character)
.data | (does not start with a letter)
open orders | (cannot contain a space)
this.name.obviously.has.more.than.29.characters | (too long)