Git-ignoring files with special characters in their names, especially newlines

My actual motivation is to understand the semantics of the .gitignore file syntax in precise detail, for a program which is expected to emulate them as accurately as possible. However, while coming up with test cases I realized an interesting problem.

Suppose, on Linux, I have created a file with a newline in its name:

$ ls fo*
'fo'$'\n''o'

In this example, the actual filename is recorded as 4 bytes long, and the third byte represents a newline in ASCII.

I can't find a way to specify in a .gitignore file to exclude this file from version control. For example, if I use the pattern fo\no, it seems to instead exclude files named fono (even though git status reports the name of the not-ignored file as "fo\no", with the double-quotes). Similarly, if I use fo\\no, it excludes a file that actually have a backslash and lowercase n in the name. Quoting with either single or double quotes doesn't seem to work; it seems to expect those literal symbols in the filename. And of course it will not work to specify the name using an actual newline, because that would just make two separate entries in the file (to match the file fo and the file o).

Do I understand correctly that in the gitignore syntax, a backslash followed by any other character just means the other character (similar to typical regex escaping, rather than string escaping)?

It seems that a gitignore line that ends with a backslash cannot match anything; correct? I tried a foo\ pattern, and it didn't match a file named foo nor the corresponding file with a trailing backslash in the name (which looks like 'foo\' in my shell but "foo\\" in git status output). Why doesn't Git warn about this?

Do I understand correctly that fundamentally, Git treats the patterns as byte-based, at least on Linux? Thus I could specify, say, a filename and a pattern such that neither is valid UTF-8, and it will match byte-by-byte? The documentation seems rather sparse, and naive about the distinction between bytes and text.

I know that Windows doesn't allow newlines (or several other "problematic" characters) in filenames, but I also know that it allows Unicode in filenames by storing them as UTF-16 - and that Windows versions of Git don't require UTF-16 encoding for the .gitignore file. What are the semantics of that?

Most importantly: with the gitignore syntax, is it possible to ignore a specific file (i.e. not via a wildcard) which has an embedded newline in its name? If so, how?

posted about 1 year ago

CC BY-SA 4.0

1y ago

Karl Knechtel‭

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