filename(n) Tcl (7.5) filename(n)
_________________________________________________________________
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 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_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.
Page 1 (printed 2/19/99)
filename(n) Tcl (7.5) filename(n)
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.
Page 2 (printed 2/19/99)
filename(n) Tcl (7.5) filename(n)
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. 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.
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.
Page 3 (printed 2/19/99)
filename(n) Tcl (7.5) filename(n)
\foo Volume-relative path to a file foo
in the root directory of the
current volume.
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. File names that have a tilde
without a user name will be 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.
KEYWORDS
current directory, absolute file name, relative file name,
volume-relative file name, portability
Page 4 (printed 2/19/99)
