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	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  com-
       mands 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 Macin-
		 tosh 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  direc-
		 tory  and the parent of the current directory respectively.  Multiple adjacent slash characters are interpreted as a single sepa-
		 rator.  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 sep-
		 arators  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 \servernamesharenamepathfile, but must at the very  least  contain  the  server  and
		 share	components,  i.e.   \servernamesharename.   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:

		 \Hostshare/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.

		 fooar	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.

KEYWORDS

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

SEE ALSO

       file(n), glob(n)

Tcl									7.5							       filename(n)