filename(n) Tcl Built-In Commands filename(n)
filename - File name conventions supported by Tcl commands
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 plat-
forms, Tcl supports a Unix-like syntax intended to provide a convenient way of construct-
ing 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
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.
The rules for native names depend on the value reported in the Tcl array element tcl_plat-
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 abso-
lute, 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 any-
where 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
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
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 cur-
:::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 cur-
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. 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
../foo Relative path to the file foo in the directory above the current
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 abso-
lute or relative path. UNC paths follow the general form \\servername\share-
name\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:
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
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
In addition to the file name rules described above, Tcl also supports csh-style tilde sub-
stitution. 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 separa-
tor are taken as a user name, which is used to retrieve the user's home directory for sub-
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 substi-
tuted using the $HOME environment variable, just like for Unix.
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 char-
acters 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.
current directory, absolute file name, relative file name, volume-relative file name,
Tcl 7.5 filename(n)