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Comment by warbiscuit | Hacker News Reader

This is cribbing from source of a filename sanitizer in one of my company's internal libraries. The function is a little... paranoid... so I'm not positive all of these are actually forbidden.

/ and 0x00 for unix

:?"<>/|\* and chars 0x00 .. 0x31 for windows

'~!#$&%^; if there's a chance of filename being passed to shell w/o proper escaping.

Windows also forbids a bunch of filenames matching regex "CON|AUX|PRN|NUL|COM[1-9]|LPT[1-9]"

Also, ending filenames with space or period really messes up windows. File explorer can see it, but can't delete or rename it.

edit: fixed markup

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> Also, ending filenames with space or period really messes up windows. File explorer can see it, but can't delete or rename it.

As a related tip, if you need to name a file something like .foo in explorer, it rejects it as "not having a file name". But if you type .foo. then it accepts the name and silently strips the trailing period.

That should be NUL (one L). Interestingly, when I tried it in Powershell, 'type NUL' reports that the file does not exist, but in CMD, 'type NUL' outputs nothing (it's the DOS equivalent of UNIX's /dev/null). So apparently some APIs will allow you to use those as filenames while others will choke on them.

It is likely that the .NET base class libraries block NUL and the other special file names that Win32 supports. This would explain why PowerShell (which is written in C#) behaves differently from cmd (which is written in C).

Thanks, corrected that. Shows what I get for transcribing wrong :)

Yeah, windows is kinda crazy inconsistent for some of these. I had a file (created under Linux) which ended in a space... drove windows nuts. Could list it, open it in some programs, but couldn't even open/rename by shortname under DOS or python.

Yes the reserved file names based on device names can be a tricky issue for portability. We ran into a problem where a source code file was named Con.java and it was impossible to use that repository on Windows. Had to rename it as Con_.java to make it work.

  `echo missed one`

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