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The Worm has Turned again - part 8 of 1 2 3 4 5 6 7 8

by Mike McNamee Published 01/10/2009

#6. If you intend to transmit files over the internet (especially as an email attachment) multiple periods such as 'filename.tif.zip' will often get the file killed in transit. This is because IT systems that see files with 'multiple extensions' as a risk since the true nature of the file may be 'masked' so that a worm/virus can inflict damage. See also the notes on

#9 below - more than one period in a path (whether folder or filename) may be intepreted by a well-secured web server as an illegal path (possible hacking attempt) and the file at the path won't be served.

#7. Windows convention is for three letter extensions but more or fewer characters are not unknown, e.g. 'logo.ai' (Illustrator) 'page.html' (some HTML editors' output). The point of this rule is not to insist extensions of 3 characters but to flag up odd - normally Mac created names - that might have problems on Windows computers.

#8. Illegal path characters: as above minus, backslash and colon.

#9. Periods, though allowed in filenames, are deprecated as they aren't supported in stricter ISO9660 versions (without Joliet) and on some older systems such as VMS.

#9. For web use, periods in filenames are deprecated as some web servers (especially IIS), when fully security patched, will not serve content if the URL has any folder names containing a period (effectively the underlying server 'rule' being applied is to check the path for > one period, assuming the filename at the end of the path contains a single period).

#10/11. You are well advised not to use commas as a starting or finishing character - they are likely to get missed when reading by eye.

#12. See also MSDN. 'Null.txt' is allowed but 'nul.txt', 'NUL' or 'nul' are not.

#13. Consider being case-insensitive when naming. In a large archive it can be tempting fate to rely on case to distinguish a file from another; thus ideally 'Filename.jpg' and 'FILENAME.JPG' should resolve to be the same file. In addition, 'Filename.jpg' is arguably not unique. So regardless of whether your primary OS is case-sensitive, it is a good idea to (a) treat all case variations of a name as one for uniqueness of naming but (b) use only ever use one variant of the name (as if the OS were case-sensitive).

#14. Unix system command line calls usually involve a program command with a series of hyphen-prefixed letter(s), or 'flags', that alter that program's behaviour. Starting a filename with a hyphen on such systems could cause the filename to be misinterpreted in command lines as a concatenated set of flags and thus not processed as a filename as intended.

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1st Published 01/10/2009
last update 09/12/2022 14:59:51

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