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Q&A

Comments on Are there any legitimate uses for newlines in filenames?

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Are there any legitimate uses for newlines in filenames?

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Unix is very permissive with filenames, and this can sometimes lead to a bunch of annoying corner cases when printing files. A well known example is when you put a newline in a filename, and it breaks naive parsing of a file list later in the pipeline.

There's not much mystery around why Unix decided to be permissive with filenames, so I'm not asking why newlines are allowed in filenames.

However, are there any situations where it is useful (or necessary, or desirable...) to have newlines in filenames? Hypothetical is okay, but "in the wild" would be even better.

I've only seen it when someone is deliberately trying to set up a trap (hacking, pranks) or by accident (programmer forgot to add a whitespace normalizer to their filename generator).

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3 comment threads

A related question (opinion based) is are there practical cases where a very long file name is useful... (2 comments)
About newlines and other problems with filenames (2 comments)
Fun fact: comparison of allowed characters (1 comment)
About newlines and other problems with filenames
Kamil Maciorowski‭ wrote over 1 year ago

There is this article Fixing Unix/Linux/POSIX Filenames: Control Characters (such as Newline), Leading Dashes, and Other Problems by David A. Wheeler. Users who find the question interesting will probably find the article interesting as well.

alx‭ wrote about 1 year ago

To add a bit more to this:

POSIX.1-202x (Issue 8) is considering outlawing \n (actually, characters 1 through 31) in filenames.

See https://www.austingroupbugs.net/view.php?id=251.

And the POSIX portable filename character set already limits the characters that one should want to use in file names: https://pubs.opengroup.org/onlinepubs/9699919799/basedefs/V1_chap03.html#tag_03_282.