Ubuntu Manpage: filename - File name conventions supported by Tcl commands

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 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  Windows  platform  does 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