What characters allowed in file names on Android?

Question

What special characters are allowed for file names on Android?

~!@#$%^&*()_+/\.,

Also, can I save file with Unicode name?

Dunning

Do you mean on the SD card (or equivalent) ? – Mar

superuser.com/a/693819/687273 – Aggrade

On Unix (and thus Android), it’s simply NULL (0x00) and / which are invalid. For interoperability, though, you may be interested in the Windows list from the answers below. – Shafting

Answer 1

1. On Android (at least by default) the file names encoded as UTF-8.

2. Looks like reserved file name characters depend on filesystem mounted (http://en.wikipedia.org/wiki/Filename).

I considered as reserved:

private static final String ReservedChars = "|\\?*<\":>+[]/'";

Dunning

'+[] are not reserved – Kirbykirch

Without '+[] (as @Kirbykirch noted), this is actually the Windows set. But it describes the invalid printable characters only. The control characters 0x00-0x1f and 0x7f are also invalid on Windows. For interoperability, all this may be useful. But on Unix (and thus Android) alone, the only invalid characters are NULL (0x00) and /. – Shafting

Came here researching firefox downloads on android. For some reason firefox thinks the plus sign makes for an invalid filename. – Lachus

Answer 2

From android.os.FileUtils

    private static boolean isValidFatFilenameChar(char c) {
        if ((0x00 <= c && c <= 0x1f)) {
            return false;
        }
        switch (c) {
            case '"':
            case '*':
            case '/':
            case ':':
            case '<':
            case '>':
            case '?':
            case '\\':
            case '|':
            case 0x7F:
                return false;
            default:
                return true;
        }
    }

    private static boolean isValidExtFilenameChar(char c) {
        switch (c) {
            case '\0':
            case '/':
                return false;
            default:
                return true;
        }
    }

Note: FileUtils are hidden APIs (not for apps; for AOSP usage). Use as a reference (or by reflection at one's own risk)

Broaddus

Answer 3

According to wiki and assuming that you are using external data storage which has FAT32.

Allowable characters in directory entries

are

Any byte except for values 0-31, 127 (DEL) and: " * / : < > ? \ | + , . ; = [] (lowcase a-z are stored as A-Z). With VFAT LFN any Unicode except NUL

Pancreatin

"; , . = " are allowed for file names in android – Sparkle

Is it true on both external and internal storage? Are all of the rest of the characters allowed? Do lowercard=uppercase as the text is showing here (meaning I can't have "Hello.txt" and "hello.txt" on the same folder, for example) ? – Waldemar

Answer 4

final String[] ReservedChars = {"|", "\\", "?", "*", "<", "\"", ":", ">"};

for(String c :ReservedChars){
    System.out.println(dd.indexOf(c));
    dd.indexOf(c);
}

Providence

Answer 5

This is correct InputFilter for File Names in Android:

    InputFilter filter = new InputFilter()
    {
        public CharSequence filter(CharSequence source, int start, int end, Spanned dest, int dstart, int dend) 
        { 
            if (source.length() < 1) return null;
            char last = source.charAt(source.length() - 1);
            String reservedChars = "?:\"*|/\\<>";
            if(reservedChars.indexOf(last) > -1) return source.subSequence(0, source.length() - 1);
            return null;
        }  
    };

Priggery

Good idea, poor implementation. As it is it will only filter properly when entering characters one by one. If you paste something in chances are it won't be filtered properly. – Disaccord

Answer 6

This is clearly filesystem and Android operating system dependent. On my oneplus/oxygenOS, the only characters in the accepted answer

private static final String ReservedChars = "|\\?*<\":>+[]/'";

that I could not use to rename a file were / and *

However, Android wide, the list above would seem to be sensible.

Familiar

Answer 7

I tested this quickly on my Galaxy Note 8 on Android 4.4.2. The default My Files app helpfully greys out invalid characters which are as follows:

? : " * | / \ < >

I put all the other special chars available into a filename and it saved. This may not be consistent across all Android versions so maybe it's best to be conservative and replace them with similarly meaningful characters.

Gerhard

What is a Galaxy Note 8? Especially in 2014. – Simony

From Samsung's website: Note Tablet – Gerhard

Answer 8

On Android as suggested there you can use an input filter to prevent user entering invalid characters, here is a better implementation of it:

/**
 * An input filter which can be attached to an EditText widget to filter out invalid filename characters
 */
class FileNameInputFilter: InputFilter
{
override fun filter(source: CharSequence?, start: Int, end: Int, dest: Spanned?, dstart: Int, dend: Int): CharSequence? {
    if (source.isNullOrBlank()) {
        return null
    }

    val reservedChars = "?:\"*|/\\<>\u0000"
    // Extract actual source
    val actualSource = source.subSequence(start, end)
    // Filter out unsupported characters
    val filtered = actualSource.filter { c -> reservedChars.indexOf(c) == -1 }
    // Check if something was filtered out
    return if (actualSource.length != filtered.length) {
        // Something was caught by our filter, provide visual feedback
            if (actualSource.length - filtered.length == 1) {
                // A single character was removed
                BrowserApp.instance.applicationContext.toast(R.string.invalid_character_removed)
            } else {
                // Multiple characters were removed                    
     BrowserApp.instance.applicationContext.toast(R.string.invalid_characters_removed)
                }
            // Provide filtered results then
            filtered
        } else {
            // Nothing was caught in our filter
            null
        }
    }
}

Disaccord

Answer 9

In Android every single symbol that appears on a standard keyboard is allowed 𝘦𝘹𝘤𝘦𝘱𝘵 𝘧𝘰𝘳 𝘰𝘯𝘦: the forward slash (" / ").

That means that the following five symbols, in particular, all of which are 𝘥𝘪𝘴allowed in Windows...

⁠      *  ?  "  :  \

..are allowed to be used in Android filenames. Only the forward slash will generate an error.

That said, it's not impossible that certain Android apps may balk at opening/saving files whose names contain some of the allowed symbols.

Fancywork