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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):

       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 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.  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 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.  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 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.   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 normalize.  Furthermore, a file name consisting  only  of
       dots “.........”  or dots with trailing characters “.....abc” is illegal.

SEE ALSO

       file(3tcl), glob(3tcl)

KEYWORDS

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