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NAME

       filename - File name conventions supported by Tcl commands
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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(platform):

       mac       On Apple Macintosh systems, Tcl supports two forms of path  names.   The  normal
                 Mac  style  names  use  colons  as  path  separators.   Paths may be relative or
                 absolute, and file names may contain any character other than colon.  A  leading
                 colon  causes  the  rest  of  the path to be interpreted relative to the current
                 directory.  If a path contains a colon that is not at the  beginning,  then  the
                 path  is  interpreted  as  an  absolute  path.   Sequences of two or more colons
                 anywhere in the path are used to construct relative paths where :: refers to the
                 parent  of the current directory, ::: refers to the parent of the parent, and so
                 forth.

                 In addition to Macintosh style names, Tcl also supports a  subset  of  Unix-like
                 names.   If  a path contains no colons, then it is interpreted like a Unix path.
                 Slash is used as the path separator.  The file name  .  refers  to  the  current
                 directory,  and .. refers to the parent of the current directory.  However, some
                 names like / or /.. have no mapping, and are interpreted as Macintosh names.  In
                 general,  commands  that  generate file names will return Macintosh style names,
                 but commands that accept file names will  take  both  Macintosh  and  Unix-style
                 names.

                 The following examples illustrate various forms of path names:

                 :              Relative path to the current folder.

                 MyFile         Relative path to a file named MyFile in the current folder.

                 MyDisk:MyFile  Absolute path to a file named MyFile on the device named MyDisk.

                 :MyDir:MyFile  Relative  path  to  a file name MyFile in a folder named MyDir in
                                the current folder.

                 ::MyFile       Relative path to a file named MyFile  in  the  folder  above  the
                                current folder.

                 :::MyFile      Relative  path  to  a  file named MyFile in the folder two levels
                                above the current folder.

                 /MyDisk/MyFile Absolute path to a file named MyFile on the device named MyDisk.

                 ../MyFile      Relative path to a file named MyFile  in  the  folder  above  the
                                current folder.

       unix      On  Unix  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
                 character  other  than  slash.  The file names . and .. are special and refer to
                 the current directory and the parent  of  the  current  directory  respectively.
                 Multiple  adjacent  slash characters are interpreted as a single separator.  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 contain 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 volume.

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

       The  Macintosh  and  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 behaviour  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.  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 normalize'.  Furthermore, a file name consisting only of
       dots '.........' or dots with trailing characters '.....abc' is illegal.

KEYWORDS

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

SEE ALSO

       file(3tcl), glob(3tcl)