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 plat-
form, Tcl supports file names in the standard forms(s) for
that platform. In addition, on all platforms, Tcl sup-
ports 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 par-
ticular form for file names. Instead, portable scripts
must use the file split and file join commands to manipu-
late 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 rela-
tive 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. Vol-
ume-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 speci-
fied 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 par-
ent, 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 separa-
tor. 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 gen-
erate 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. The following examples illustrate
various forms of path names:
/ Absolute path to the root direc-
tory.
/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 con-
sist of an optional drive specifier followed by
an absolute 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 direc-
tory 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.
\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 charac-
ters and an extension of no more than 3 characters.
KEYWORDS
current directory, absolute file name, relative file name,
volume-relative file name, portability