filename

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
       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
       platform element of the tcl_platform array:

       Unix      On Unix and Apple MacOS X 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.  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 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.  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 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.  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(n), glob(n)

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



Tcl                                   7.5                          filename(n)