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filename(n)                                 Tcl Built-In Commands                                filename(n)



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NAME
       filename - File name conventions supported by Tcl commands
____________________________________________________________________________________________________________

INTRODUCTION
       All  Tcl  commands  and C procedures that take file names as arguments expect the file names to be in
       one of three forms, depending on the current platform.  On each platform, Tcl supports file names  in
       the  standard  forms(s)  for  that platform.  In addition, on all platforms, Tcl supports a Unix-like
       syntax intended to provide a convenient way of constructing simple file names.  However, scripts that
       are  intended  to  be portable should not assume a particular form for file names.  Instead, portable
       scripts must use the file split and file join commands to manipulate file names (see the file  manual
       entry for more details).

PATH TYPES
       File  names  are  grouped  into  three general types based on the starting point for the path used to
       specify the file: absolute, relative, and volume-relative.  Absolute names are completely  qualified,
       giving  a  path  to  the  file relative to a particular volume and the root directory on that volume.
       Relative names are unqualified, giving a path to the file relative to the current working  directory.
       Volume-relative  names are partially qualified, either giving the path relative to the root directory
       on the current volume, or relative to the current  directory  of  the  specified  volume.   The  file
       pathtype command can be used to determine the type of a given path.

PATH SYNTAX
       The  rules  for native names depend on the value reported in the Tcl array element tcl_platform(plat-form): tcl_platform(platform):
       form):

       Unix      On Unix and Apple MacOS X platforms, Tcl uses path names where the components are separated
                 by slashes.  Path names may be relative or absolute, and file names may contain any charac-ter character
                 ter other than slash.  The file names . and .. are special and refer to the current  direc-tory directory
                 tory and the parent of the current directory respectively.  Multiple adjacent slash charac-ters characters
                 ters are interpreted as a single separator.  Any number of trailing slash characters at the
                 end  of  a path are simply ignored, so the paths foo, foo/ and foo// are all identical, and
                 in particular foo/ does not necessarily mean a directory is being referred.

                 The following examples illustrate various forms of path names:

                 /              Absolute path to the root directory.

                 /etc/passwd    Absolute path to the file named passwd in the  directory  etc  in  the  root
                                directory.

                 .              Relative path to the current directory.

                 foo            Relative path to the file foo in the current directory.

                 foo/bar        Relative path to the file bar in the directory foo in the current directory.

                 ../foo         Relative path to the file foo in the directory above the current  directory.

       Windows   On Microsoft Windows platforms, Tcl supports both drive-relative and UNC style names.  Both
                 / and \ may be used as directory separators in either type of name.   Drive-relative  names
                 consist of an optional drive specifier followed by an absolute or relative path.  UNC paths
                 follow the general form \\servername\sharename\path\file, but must at the very  least  con-tain contain
                 tain  the  server  and  share components, i.e.  \\servername\sharename.  In both forms, the
                 file names . and .. are special and refer to the current directory and the  parent  of  the
                 current  directory  respectively.   The following examples illustrate various forms of path
                 names:

                 \\Host\share/file
                                Absolute UNC path to a file called file in the root directory of the  export
                                point  share  on  the  host Host.  Note that repeated use of file dirname on
                                this path will give //Host/share, and will never give just //Host.

                 c:foo          Volume-relative path to a file foo in the current directory on drive c.

                 c:/foo         Absolute path to a file foo in the root directory of drive c.

                 foo\bar        Relative path to a file bar in the foo directory in the current directory on
                                the current volume.

                 \foo           Volume-relative path to a file foo in the root directory of the current vol-ume. volume.
                                ume.

                 \\foo          Volume-relative path to a file foo in the root directory of the current vol-ume. volume.
                                ume.   This  is  not  a  valid UNC path, so the assumption is that the extra
                                backslashes are superfluous.

TILDE SUBSTITUTION
       In addition to the file name rules described above, Tcl also supports csh-style  tilde  substitution.
       If a file name starts with a tilde, then the file name will be interpreted as if the first element is
       replaced with the location of the home directory for the given user.  If the tilde is followed  imme-diately immediately
       diately by a separator, then the $HOME environment variable is substituted.  Otherwise the characters
       between the tilde and the next separator are taken as a user name, which  is  used  to  retrieve  the
       user's  home  directory  for  substitution.  This works on Unix, MacOS X and Windows (except very old
       releases).

       Old Windows platforms do not support tilde substitution when a user name follows the tilde.  On these
       platforms,  attempts to use a tilde followed by a user name will generate an error that the user does
       not exist when Tcl attempts to interpret that part of the path or otherwise access the file.  The be-haviour behaviour
       haviour  of  these  paths  when not trying to interpret them is the same as on Unix.  File names that
       have a tilde without a user name will be correctly substituted using the $HOME environment  variable,
       just like for Unix.

PORTABILITY ISSUES
       Not  all  file  systems  are case sensitive, so scripts should avoid code that depends on the case of
       characters in a file name.  In addition, the character sets allowed on different devices may  differ,
       so  scripts  should  choose  file  names  that do not contain special characters like: <>:?"/\|.  The
       safest approach is to use names consisting of alphanumeric characters only.   Care  should  be  taken
       with  filenames which contain spaces (common on Windows systems) and filenames where the backslash is
       the directory separator (Windows native path names).  Also Windows 3.1 only supports file names  with
       a root of no more than 8 characters and an extension of no more than 3 characters.

       On Windows platforms there are file and path length restrictions.  Complete paths or filenames longer
       than about 260 characters will lead to errors in most file operations.

       Another Windows peculiarity is that any number  of  trailing  dots  "."   in  filenames  are  totally
       ignored,  so,  for example, attempts to create a file or directory with a name "foo."  will result in
       the creation of a file/directory with name "foo".  This fact is reflected in the results of file nor-malize. normalize.
       malize.   Furthermore, a file name consisting only of dots "........."  or dots with trailing charac-ters characters
       ters ".....abc" is illegal.

SEE ALSO
       file(n), glob(n)

KEYWORDS
       current directory, absolute file name, relative file name, volume-relative file name, portability



Tcl                                                  7.5                                         filename(n)