Tcl Built-In Commands filename(1T)
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 plat-
form. In addition, on all platforms, Tcl supports a Unix-
like syntax intended to provide a convenient way of con-
structing 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: abso-
lute, 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 rela-
tive to the root directory on the current volume, or rela-
tive 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 tclplatform(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 char-
acter 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.
Tcl Last change: 7.5 1
Tcl Built-In Commands filename(1T)
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 direc-
tory. 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.
Tcl Last change: 7.5 2
Tcl Built-In Commands filename(1T)
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 direc-
tory.
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 com-
ponents, 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
Tcl Last change: 7.5 3
Tcl Built-In Commands filename(1T)
root directory of drive c.
foo\bar Relative path to a file bar in the
foo directory in the current direc-
tory 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 vari-
able 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 substitu-
tion.
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 try-
ing to interpret them is the same as on Unix. File names
that have a tilde without a user name will be correctly sub-
stituted using the $HOME environment variable, just like for
Unix.
PORTABILITY ISUES
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.
Tcl Last change: 7.5 4
Tcl Built-In Commands filename(1T)
On Windows platforms there are file and path length restric-
tions. 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 nor-
malize'. Furthermore, a file name consisting only of dots
'.........' or dots with trailing characters '.....abc' is
illegal.
KEYWORDS
current directory, absolute file name, relative file name,
volume-relative file name, portability
SEE ALSO
file(1T), glob(1T)
ATRIBUTES
See attributes(5) for descriptions of the following attri-
butes:
ATRIBUTE TYPE ATRIBUTE VALUE
Availability SUNWTcl
Interface Stability Uncommitted
NOTES
Source for Tcl is available on http:/opensolaris.org.
Tcl Last change: 7.5 5
|
