Re: file extensions in text

Subject: Re: file extensions in text
From: Gary Merrill <merrill -at- HYPERION -dot- PDIAL -dot- INTERPATH -dot- NET>
Date: Sat, 6 Jan 1996 22:48:15 GMT

> Kevin Sporleder <kevinsp -at- crt -dot- com> writes:
> When including references to file extensions in text, should the period
before
> the extension be included. For example:

> "You must include the .Pconfig extension with blah blah blah."
> or
> "You must include the Pconfig extension with blah blah blah."

One of the points that has been ignored in the various responses to this
question is that the notion of "file name extension" is quite dependent upon
the operating system. These replies seem to assume that the OS in question
is either UNIX , or DOS, or Windows. In DOS and Windows there is indeed
a somewhat formally entrenched concept of file name extension with the '.'
indicating the extension. Note, for example, that in DOS when you give
the 'dir' command the file names are displayed in the format

basename extension

*without* any '.'. In the Windows file manager, however, the '.' is displayed.
And in both of these environments, you cannot create a directory whose
name is of the form

x.y.z

(Because of the formal notion of extension used, there would of course be
some ambiguity here as to whether the extension is '.y.z' or '.z'.)

On UNIX, the concept of file name extension is *much* looser. In fact,
there is no such formal concept. Most (but not all) C compilers require C
source
files to end in '.c'. But this is merely a convention. More generally, it is
merely
a historical convention that the '.' marks the beginning of the "extension" at
all. On UNIX, "extension" just means "ends in". In fact, it is common to
have
file names that look like.

mytool.process_id.month.day.year

Which is the "extension"? A UNIX program can as easily use '_C' as an extension
as it can use '.c'. For this reason, at least on UNIX it is a good idea to make
the
'.' explicit. On DOS and Windows this is not so important (because of the
formal
connection between the '.' and the concept of file name extension), but I feel
that
in general it is a good idea to make the '.' explicit there as well. Other
operating
systems must be considered in the light of their own conventions or
requirements,
and so I think there is no truly general answer to the original question --
except
that it is probably wise to be as explicit as possible.

Note that a similar question pertains to whether file names should be specified
in upper or lower case. DOS and Windows fold to upper case, but as a user
or programmer you may use lower case (or mixed case) to specify a file name
(it's just that the OS won't distinguish between two names based on case).
In UNIX, such distinctions are made -- and in fact you can even have file names
with *unprintable* characters in them (some programs depend upon this feature
to make certain of their files relatively untouchable).

----------
Gary Merrill


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