Provided by: tcl8.4-doc_8.4.19-4ubuntu3_all

#### 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).



#### PATHTYPES

       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.



#### PATHSYNTAX

       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.



#### TILDESUBSTITUTION

       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.



#### PORTABILITYISSUES

       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



#### SEEALSO

       file(3tcl), glob(3tcl)