Filename character mapping
When dealing with "foreign" media formats, such as zip files, DOS or Unix
disks and images, etc., filenames can be encountered that contain characters
that are not allowed on BBC filing systems, or have different meanings. The
most common occurance is Unix, URLs and Zip files use / as a
directory seperator whereas the BBC uses ., and the converse
mapping of . and / as an extension seperator.
Other than DOS/Windows using \ directory seperators and
Unix/URL/ZIP using / seperators, all non-BBC filename
characters have the same meanings. The following tables show how different
special characters are mapped between BBC and non-BBC platforms.
Non-BBC to BBC
The following characters are legal in DOS/Windows or Unix/URL/ZIP filenames, but are illegal or have special meanings in BBC filenames:
Non-BBC Non-BBC BBC Replace Non-BBC BBC
Character Meaning Meaning with Example Example Notes
---------------------------------------------------------------------------------
# - wildcard ? part#3 part?3
$ - root dir < TEMP.$$$ TEMP/<<<
% - lib dir ; TEMP.%%% TEMP/;;; see notes
& - user dir + one&two one+two see notes
* wildcard wildcard * info* info*
. extension directory / help.txt help/txt
. current dir directory @ ./file @.file .\file on DOS
.. parent dir directory ^ ../menu ^.menu ..\file on DOS
: drive drive : A:file :A.file
? wildcard - # page?? page##
@ - current dir = TEMP.@@@ TEMP/=== see notes
^ - parent dir > TEMP.^^^ TEMP/>>>
/ Unix directory extension . or $ /dir/file $.dir.file
\ DOS directory - . or $ \dir\file $.dir.file
/ DOS - extension \ one/two one\two
The simplest bidirectional mapping is:
Non-BBC BBC DOS BBC Unix BBC
-----------------------------------------------
# <-> ? . -> / . <-> /
$ <-> < / -> \
^ <-> > \ -> .
BBC to Non-BBC
The following characters are legal in BBC filenames, but are illegal or have special meanings in DOS/Windows or Unix/URL/Zip filenames:
BBC BBC Non-BBC Replace BBC Non-BBC
Character Meaning Meaning with Example Example Notes
--------------------------------------------------------------------------------------
# wildcard - ? part#3 part?3
$ root dir - \ $.user \user or /unix
% lib dir - %.blib see notes
& user dir - &.mymail see notes
* wildcard wildcard * info* info*
: drive drive : :A.file A:file
< - redirection $ TEMP/<<< TEMP.$$$
> - redirection ^ TEMP/>>> TEMP.^^^
? - wildcard # why? why#
@ current dir - . @.file .\file or ./file
^ parent dir - .. ^.file ..\file or ../file
/ extension Unix directory . help/txt help.txt
. directory Unix extension / dir.file dir/file
. directory DOS extension \ dir.file dir\file
/ extension DOS - . help/txt help.txt
\ - DOS directory / one\two one/two
The simplest bidirectional mapping is:
BBC Non-BBC BBC DOS BBC Unix
-----------------------------------------------
? <-> # . -> \ . <-> /
< <-> $ \ -> /
> <-> ^ / -> .
DOS to/from UNIX
Included for completeness is mapping between DOS/Windows and Unix/URL/ZIP
filenames. Both use the same characters other than DOS/Windows using
\ for directories and UNIX/URL/ZIP using /.
DOS Unix DOS Replace DOS Unix Character Meaning Meaning with Example Example -------------------------------------------------------------------------------------- / directory - \ \dir\file.txt /dir/file.txt \ - directory / one/two.txt one\two.txt
The bidirection mapping is:
DOS Unix
---------------------
/ <-> \
Notes
- BBC
&and%would be mapped to something like$HOMEDIR$and$PATH$.
- The mapping of non-BBC
%,&and@to BBC;,+and=means that BBC;,+and=have a one-to-two non-reversable mapping.
Implementations
- RISC OS DOSFS translates bidirectionally between DOS
%,&,@and BBC;=,;~,;=. However, BBC%,&,;are also mapped to DOS%,&,;, creating a non-reversable two-to-one mapping.
- BBC DOSFS has not yet been tested.
- SparkFS Zip only maps bidirectionally between
.and/. All other mapping is Zip to BBC only, eg a Zip#is extracted as a?, but a?is stored back in a Zip unchanged as a?.
- BBCZip performs all four bidirectional character mappings
#<->?,$<-><,^<->>,.<->/.
- Other Zip implementations have not yet been tested.
