filename(3tcl)						       Tcl Built-In Commands						    filename(3tcl)

__________________________________________________________________________________________________________________________________________________

NAME

       filename - File name conventions supported by Tcl commands
_________________________________________________________________

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):

       Unix	 On  Unix and Apple MacOS X platforms, Tcl uses path names where the components are separated by slashes.  Path names may be rela-
		 tive 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 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 //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.

		 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.  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  other-
       wise 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

Tcl									7.5							    filename(3tcl)