filename(n) Tcl Built-In Commands 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(plat-form): tcl_platform(platform):
form):
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 par-ent parent
ent 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 cur-rent current
rent 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 par-ent parent
ent of the current directory respectively. Multiple adjacent slash characters are inter-preted interpreted
preted 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 absolute or relative path. UNC paths
follow the general form \\servername\sharename\path\file, but must at the very least con-tain contain
tain 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 /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 vol-ume. volume.
ume.
\\foo Volume-relative path to a file foo in the root directory of the current vol-ume. volume.
ume. 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 imme-diately immediately
diately 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 envi-ronment environment
ronment 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)
|