Invalid characters for Windows filenames

ntfs-filenames.txt

Information from https://docs.microsoft.com/en-us/windows/win32/fileio/naming-a-file :

    Use any character in the current code page for a name, including Unicode
    characters and characters in the extended character set (128–255), except
    for the following:

    - The following reserved characters:

        < (less than)
        > (greater than)
        : (colon)
        " (double quote)
        / (forward slash)
        \ (backslash)
        | (vertical bar or pipe)
        ? (question mark)
        * (asterisk)

    - Integer value zero, sometimes referred to as the ASCII NUL character.
    - Characters whose integer representations are in the range from 1 through
      31, except for alternate data streams where these characters are
      allowed. For more information about file streams, see File Streams.
    - Any other character that the target file system does not allow.
    
    - Do not use the following reserved names for the name of a file:
        
        CON, PRN, AUX, NUL, COM1, COM2, COM3, COM4, COM5, COM6, COM7, COM8,
        COM9, LPT1, LPT2, LPT3, LPT4, LPT5, LPT6, LPT7, LPT8, and LPT9.
        
        Also avoid these names followed immediately by an extension; for
        example, NUL.txt is not recommended.

    - Do not end a file or directory name with a space or a period. Although
      the underlying file system may support such names, the Windows shell and
      user interface does not. However, it is acceptable to specify a period
      as the first character of a name. For example, ".temp".

---

Handy list to copy/paste:

<>:"/\|?*

---

Note: Other OSs and file systems may vary; but in general, the only forbidden characters
in filenames on Unix-like systems appear to be the forward slash (/) and the null byte.

Microsoft's documentation neglects to mention COM0 and LPT0 which explorer.exe has trouble with (even on Windows 10 20H2), possibly because of a bug.

function filenameValidator(fname, { replacement = "�" } = {}) {
    // https://stackoverflow.com/a/31976060
    // https://gist.github.com/doctaphred/d01d05291546186941e1b7ddc02034d3

    const fname_original = fname;

    // resolve multi-line, whitespace trimming
    fname = fname.split(/[\r\n]/).map(s => s.trim()).filter(s => s.length).join("  ");
    
    // forbidden characters
    // (after multi-line, because new-line-chars are themselves forbidden characters)
    fname = fname.replaceAll(/[<>:"\/\\\|?*\x00-\x1F]/g, replacement);

    // advanced trim
    fname = fname.replace(/\.$/, "");

    // empty filename
    if (!fname.length) {
        fname = '_';
    }
    
    // forbidden filenames
    if (fname.match(/^(CON|PRN|AUX|NUL|COM1|COM2|COM3|COM4|COM5|COM6|COM7|COM8|COM9|LPT1|LPT2|LPT3|LPT4|LPT5|LPT6|LPT7|LPT8|LPT9)(\..+)?$/)) {
        fname = `_${fname}`;
    }
    
    return {
        fname,
        isOriginal: (fname === fname_original),
    };
}

For .Net, there is https://docs.microsoft.com/en-us/dotnet/api/system.io.path.getinvalidpathchars?view=net-5.0: name?.IndexOfAny(Path.GetInvalidFileNameChars()) == -1 or name?.IndexOfAny(Path.GetInvalidPathChars()) == -1 depending if you want to validate a file name or a full path.

It will still not catch issues with file names like NUL or COM on FAT or NTFS.

For Python3:
import re
re.sub(r'[<>:/\|?*"]+',"",filename)

Can a filename have space under windows?

Yes it can, you can verify by creating one yourself

Python3 :

def cleanFilename(sourcestring,  removestring ="\"|%:/,.\\[]<>*?") :
    return ''.join([c for c in sourcestring if c not in removestring])

If you know of a good GitHub Action that detect (or replace) those filenames automatically, I'm looking for one.

I'd like to rename a filename with a "-" (hyphen) suffix but windows (7) refuses.
Do you guys think this is forbidden only at the end of filenames?