What characters are forbidden in Windows and Linux directory names

Question

I know that   is illegal in Linux  and the following are illegal in Windows  I think                         What else am I missing     I need a comprehensive guide  however  and one that takes into account double-byte characters  Linking to outside resources is fine with me   I need to first create a directory on the filesystem using a name that may contain forbidden characters  so I plan to replace those characters with underscores  I then need to write this directory and its contents to a zip file  using Java   so any additional advice concerning the names of zip directories would be appreciated

User · Answer

The easy way to get Windows to tell you the answer is to attempt to rename a file via Explorer and type in / for the new name. Windows will popup a message box telling you the list of illegal characters.

A filename cannot contain any of the following characters:
    \ / : * ? " < > |

https://support.microsoft.com/en-us/kb/177506

User · Answer

I always assumed that banned characters in Windows filenames meant that all exotic characters would also be outlawed  The inability to use      and   in particular irked me  One day I discovered that it was virtually only those chars which were banned  Other Unicode characters may be used  So the nearest Unicode characters to the banned ones I could find were identified and MS Word macros were made for them as Alt-   Alt-  etc  Now I form the filename in Word  using the substitute chars  and copy it to the Windows filename  So far I have had no problems  Here are the substitute chars  Alt - the decimal Unicode         Alt-8432      Alt-8260       Alt-8421      Alt-8739     Alt-11622     Alt-11162      Alt-8253      Alt 4961      Alt-8246      Alt-8243 As a test I formed a filename using all of those chars and Windows accepted it

User · Answer

When creating internet shortcuts in Windows  to create the file name  it skips illegal characters  except for forward slash  which is converted to minus

User · Answer

For Windows you can check it using PowerShell   PathInvalidChars    System IO Path   GetInvalidPathChars    36 chars   To display UTF-8 codes you can convert   enc    system Text Encoding   UTF8  PathInvalidChars   foreach    enc GetBytes         FileNameInvalidChars    System IO Path   GetInvalidFileNameChars    41 chars   FileOnlyInvalidChars                               5 chars - as a difference

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Under Linux and other Unix-related systems  there are only two characters that cannot appear in the name of a file or directory  and those are NUL   0  and slash       The slash  of course  can appear in a path name  separating directory components   Rumour1 has it that Steven Bourne  of  shell  fame  had a directory containing 254 files  one for every single letter  character code  that can appear in a file name  excluding      0   the name   was the current directory  of course    It was used to test the Bourne shell and routinely wrought havoc on unwary programs such as backup programs   Other people have covered the Windows rules   Note that MacOS X has a case-insensitive file system    1 It was Kernighan  amp  Pike in The Practice of Programming who said as much in Chapter 6  Testing    6 5 Stress Tests      When Steve Bourne was writing his Unix shell  which came to be known as the Bourne shell   he made a directory of 254 files with one-character names  one for each byte value except   0  and slash  the two characters that cannot appear in Unix file names  He used that directory for all manner of tests of pattern-matching and tokenization   The test directory was of course created by a program   For years afterwards  that directory was the bane of file-tree-walking programs  it tested them to destruction    Note that the directory must have contained entries   and     so it was arguably 253 files  and 2 directories   or 255 name entries  rather than 254 files  This doesn t affect the effectiveness of the anecdote  or the careful testing it describes

User · Answer

Instead of creating a blacklist of characters  you could use a whitelist  All things considered  the range of characters that make sense in a file or directory name context is quite short  and unless you have some very specific naming requirements your users will not hold it against your application if they cannot use the whole ASCII table   It does not solve the problem of reserved names in the target file system  but with a whitelist it is easier to mitigate the risks at the source   In that spirit  this is a range of characters that can be considered safe    Letters  a-z A-Z  - Unicode characters as well  if needed Digits  0-9  Underscore      Hyphen  -   Space  Dot       And any additional safe characters you wish to allow  Beyond this  you just have to enforce some additional rules regarding spaces and dots  This is usually sufficient    Name must contain at least one letter or number  to avoid only dots spaces  Name must start with a letter or number  to avoid leading dots spaces  Name may not end with a dot or space  simply trim those if present  like Explorer does    This already allows quite complex and nonsensical names  For example  these names would be possible with these rules  and be valid file names in Windows Linux    A           ext B    - -    ext   In essence  even with so few whitelisted characters you should still decide what actually makes sense  and validate adjust the name accordingly  In one of my applications  I used the same rules as above but stripped any duplicate dots and spaces

User · Answer

I had the same need and was looking for recommendation or standard references and came across this thread   My current blacklist of characters that should be avoided in file and directory names are    CharactersInvalidForFileName          pound  - gt            left angle bracket  - gt    lt         dollar sign  - gt            plus sign  - gt            percent  - gt            right angle bracket  - gt    gt         exclamation point  - gt            backtick  - gt            ampersand  - gt    amp         asterisk  - gt            single quotes  - gt              pipe  - gt            left bracket  - gt            question mark  - gt            double quotes  - gt              equal sign  - gt            right bracket  - gt            forward slash  - gt            colon  - gt            back slash  - gt             lank spaces  - gt   b        at sign  - gt

User · Answer

Though the only illegal Unix chars might be   and NULL  although some consideration for command line interpretation should be included   For example  while it might be legal to name a file 1 gt  amp 2 or 2 gt  amp 1 in Unix  file names such as this might be misinterpreted when used on a command line   Similarly it might be possible to name a file  PATH  but when trying to access it from the command line  the shell will translate  PATH to its variable value

User · Answer

A    comprehensive guide    of forbidden filename characters is not going to work on Windows because it reserves filenames as well as characters  Yes  characters like       and others are forbidden  but there are a infinite number of names composed only of valid characters that are forbidden  For example  spaces and dots are valid filename characters  but names composed only of those characters are forbidden   Windows does not distinguish between upper-case and lower-case characters  so you cannot create a folder named A if one named a already exists  Worse  seemingly-allowed names like PRN and CON  and many others  are reserved and not allowed  Windows also has several length restrictions  a filename valid in one folder may become invalid if moved to another folder  The rules for naming files and folders are on the Microsoft docs   You cannot  in general  use user-generated text to create Windows directory names  If you want to allow users to name anything they want  you have to create safe names like A  AB  A2 et al   store user-generated names and their path equivalents in an application data file  and perform path mapping in your application   If you absolutely must allow user-generated folder names  the only way to tell if they are invalid is to catch exceptions and assume the name is invalid  Even that is fraught with peril  as the exceptions thrown for denied access  offline drives  and out of drive space overlap with those that can be thrown for invalid names  You are opening up one huge can of hurt

User · Answer

As of 18 04 2017  no simple black or white list of characters and filenames is evident among the answers to this topic - and there are many replies   The best suggestion I could come up with was to let the user name the file however he likes  Using an error handler when the application tries to save the file  catch any exceptions  assume the filename is to blame  obviously after making sure the save path was ok as well   and prompt the user for a new file name  For best results  place this checking procedure within a loop that continues until either the user gets it right or gives up  Worked best for me  at least in VBA

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Difficulties with defining  what s legal and not were already adressed and whitelists were suggested  But Windows supports more-than-8-bit characters  Wikipedia states  that  for example  the  modifier letter colon   See 7  below  is  sometimes used in Windows filenames as it is identical to the colon in the Segoe UI font used for filenames  The  inherited ASCII  colon itself is not permitted   Therefore  I want to present a much more liberal approach using Unicode characters to replace the  quot illegal quot  ones  I found the result in my comparable use-case by far more readable  Plus you can even restore the original content from the replacements  Possible choices and research are provided in the following list   Instead of    U 002A   ASTERISK   you can use one of the many listed  for example U 2217    ASTERISK OPERATOR  or the Full Width Asterisk   U FF0A    Instead of    you can use one of these  for example      U 22C5 dot operator Instead of  quot   you can use      U 201C  english leftdoublequotemark  Alternatives see here  Instead of       SOLIDUS     U 002F    you can use     DIVISION SLASH  U 2215   others here  Instead of      U 005C Reverse solidus   you can use   U 29F5 Reverse solidus operator   more  Instead of    U 005B     Left square bracket  and    U 005D     Right square bracket   you can use for example U FF3B  FULLWIDTH LEFT SQUARE BRACKET and U FF3D  FULLWIDTH RIGHT SQUARE BRACKET  from here  more possibilities here  Instead of    you can use U 2236   RATIO  for mathematical usage  or U A789   MODIFIER LETTER COLON   see colon  letter   sometimes used in Windows filenames as it is identical to the colon in the Segoe UI font used for filenames  The colon itself is not permitted   See here  Instead of    you can use U 037E   GREEK QUESTION MARK  see here  For    there are some good substitutes such as  U 0964   DEVANAGARI DANDA  U 2223   DIVIDES or U 01C0   LATIN LETTER DENTAL CLICK  Wikipedia   Also the box drawing characters contain various other options  Instead of      U 002C COMMA   you can use for example     U 201A SINGLE LOW-9 QUOTATION MARK  see here  For    U 003F   QUESTION MARK   these are good candidates  U FF1F   FULLWIDTH QUESTION MARK or U FE56   SMALL QUESTION MARK  from here  two more from Dingbats Block  search for  quot question quot    For additional ideas  you can also look for example into this block  In Windows  these special characters should theoretically be able to be typed by using an alt-code  but I only found a solution to insert it in Microsoft Office in this Microsoft article using ALT   X  It can of course still be copied instead of typed

User · Answer

In Unix shells  you can quote almost every character in single quotes    Except the single quote itself  and you can t express control characters  because   is not expanded   Accessing the single quote itself from within a quoted string is possible  because you can concatenate strings with single and double quotes  like  I     m  which can be used to access a file called  I m   double quote also possible here    So you should avoid all control characters  because they are too difficult to enter in the shell   The rest still is funny  especially files starting with a dash  because most commands read those as options unless you have two dashes -- before  or you specify them with     which also hides the starting -   If you want to be nice  don t use any of the characters the shell and typical commands use as syntactical elements  sometimes position dependent  so e g  you can still use -  but not as first character  same with    you can use it as first character only when you mean it   hidden file     When you are mean  your file names are VT100 escape sequences  -   so that an ls garbles the output

User · Answer

Let s keep it simple and answer the question  first    The forbidden printable ASCII characters are    Linux Unix      forward slash   Windows    lt   less than   gt   greater than     colon - sometimes works  but is actually NTFS Alternate Data Streams     double quote     forward slash     backslash     vertical bar or pipe     question mark     asterisk    Non-printable characters  If your data comes from a source that would permit non-printable characters then there is more to check for    Linux Unix   0  NULL byte   Windows   0-31  ASCII control characters     Note  While it is legal under Linux Unix file systems to create files with control characters in the filename  it might be a nightmare for the users to deal with such files  Reserved file names  The following filenames are reserved    Windows   CON  PRN  AUX  NUL  COM1  COM2  COM3  COM4  COM5  COM6  COM7  COM8  COM9 LPT1  LPT2  LPT3  LPT4  LPT5  LPT6  LPT7  LPT8  LPT9    both on their own and with arbitrary file extensions  e g  LPT1 txt    Other rules   Windows   Filenames cannot end in a space or dot

User · Answer

Well  if only for research purposes  then your best bet is to look at this Wikipedia entry on Filenames    If you want to write a portable function to validate user input and create filenames based on that  the short answer is don t  Take a look at a portable module like Perl s File  Spec to have a glimpse to all the hops needed to accomplish such a  simple  task

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The  NET Framework System IO provides the following functions for invalid file system characters   Path GetInvalidFileNameChars Path GetInvalidPathChars  Those functions should return appropriate results depending on the platform the  NET runtime is running in

User · Answer

For anyone looking for a regex  const BLACKLIST      lt  gt   quot          g

User · Answer

In Windows 10  2019   the following characters are forbidden by an error when you try to type them   A file name can t contain any of the following characters             quot   lt   gt

User · Answer

Here s a c  implementation for windows based on Christopher Oezbek s answer  It was made more complex by the containsFolder boolean  but hopefully covers everything       lt summary gt      This will replace invalid chars with underscores  there are also some reserved words that it adds underscore to      lt  summary gt       lt remarks gt      https   stackoverflow com questions 1976007 what-characters-are-forbidden-in-windows-and-linux-directory-names      lt  remarks gt       lt param name  containsFolder  gt Pass in true if filename represents a folder file  passing true will allow slash  lt  param gt  public static string EscapeFilename Windows string filename  bool containsFolder   false        StringBuilder builder   new StringBuilder filename Length   12        int index   0          Allow colon if it s part of the drive letter     if  containsFolder                Match match   Regex Match filename      s  A-Z       RegexOptions IgnoreCase           if  match Success                        builder Append match Value               index   match Length                          Character substitutions     for  int cntr   index  cntr  lt  filename Length  cntr                  char c   filename cntr            switch  c                        case   u0000               case   u0001               case   u0002               case   u0003               case   u0004               case   u0005               case   u0006               case   u0007               case   u0008               case   u0009               case   u000A               case   u000B               case   u000C               case   u000D               case   u000E               case   u000F               case   u0010               case   u0011               case   u0012               case   u0013               case   u0014               case   u0015               case   u0016               case   u0017               case   u0018               case   u0019               case   u001A               case   u001B               case   u001C               case   u001D               case   u001E               case   u001F                case   lt                case   gt                case                  case                  case                  case                  case                  case                      builder Append                       break               case                       builder Append containsFolder   c                         break               default                  builder Append c                   break                       string built   builder ToString         if  built                      return                 if  built EndsWith         built EndsWith                     built   built Substring 0  built Length - 1                       These are reserved names  in either the folder or file name  but they are fine if following a dot        CON  PRN  AUX  NUL  COM0    COM9  LPT0    LPT9     builder   new StringBuilder built Length   12       index   0      foreach  Match match in Regex Matches built           s    lt bad gt CON PRN AUX NUL COM d LPT d  s             RegexOptions IgnoreCase                 Group group   match Groups  bad            if  group Index  gt  index                        builder Append built Substring index  match Index - index   1                       builder Append group Value           builder Append                 putting an underscore after this keyword is enough to make it acceptable          index   group Index   group Length             if  index    0                return built             if  index  lt  built Length - 1                builder Append built Substring index               return builder ToString

[windows] What characters are forbidden in Windows and Linux directory names?

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