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I would like to know if an empty string is a legal file name in any of the commonly used operating and file systems.

I guess not - but I can only guess.

Context: If the empty string is a universally illegal filename, it would be a simple to use test case for non-existent files. However, tests may err if there are situations where the empty string is a valid file name.

fabianegli
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  • The inspiration for this question came from a comment by [Olvin Roght](https://stackoverflow.com/users/10824407/olvin-roght) to my question about testing Python IO code: https://stackoverflow.com/q/68516544/6018688 – fabianegli Jul 26 '21 at 14:32

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Perhaps unfortunately for you, it depends! Different filesystems firmly disagree about what is a "legal file name"! (a frequent source of confusion is that some are case-insensitive)

I suspect that some filesystem you will encounter will support it, but that case may not really matter for you

Your best bet would be to explicitly prevent silly names in your program (see below) or to try testing on a subset of filesystems with known versions

Some helpful information

However, for program design, I would instead try to follow these rules

  • regulate filenames to exact sets of characters (perhaps with a regex)
  • explicitly prevent empty or blank strings and reserved names ( , \0, localhost, null..)
  • store whatever "name" users cook up to trouble your programs and filesystem in a field in a meta-file or database you control
    name the file or entry yourself (perhaps with a uuid to guarantee uniqueness everywhere .. this could also or instead be a SQLite db entry or some config in a new directory for their work) .. here you are effectively creating your own filesystem with whatever rules you like
ti7
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