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# OpenDarwin 7.2.1 - man page for filename (opendarwin section n)

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

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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 plat-
forms, Tcl supports a Unix-like syntax intended to provide a convenient way of  construct-
ing  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_plat-
form(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 abso-
lute, 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 any-
where 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 cur-
rent 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 cur-
rent 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 abso-
lute or relative path.  UNC paths follow the  general	form  \\servername\share-
name\path\file,  but  must at the very least contain the server and share compo-
nents, 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 direc-
tory 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 /fB//Host/fR.

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 sub-
stitution.  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  $HOME environment variable is substituted. Otherwise the characters between the tilde and the next separa- tor are taken as a user name, which is used to retrieve the user's home directory for sub- stitution. The Macintosh and Windows platforms do not support tilde substitution when a user name follows the tilde. On these platforms, attempts to use a tilde followed by a user name will generate an error that the user does not exist when Tcl attempts to interpret that part of the path or otherwise access the file. The behaviour of these paths when not try- ing to interpret them is the same as on Unix. File names that have a tilde without a user name will be correctly substituted using the$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 char-
acters 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 file-
names longer than about 260 characters will lead to errors in most file operations.

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

Tcl					       7.5				      filename(n)