filename(1T) Tcl Built-In Commands filename(1T)
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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 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 com-
mands 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.
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 Macin-
tosh 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 direc-
tory and the parent of the current directory respectively. Multiple adjacent slash characters are interpreted as a single sepa-
rator. 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 sep-
arators 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 \servernamesharenamepathfile, but must at the very least contain the server and
share components, i.e. \servernamesharename. 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:
\Hostshare/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 root directory of drive c.
fooar 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.
\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 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 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.
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.
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 normalize'. 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)
ATTRIBUTES
See attributes(5) for descriptions of the following attributes:
+--------------------+-----------------+
| ATTRIBUTE TYPE | ATTRIBUTE VALUE |
+--------------------+-----------------+
|Availability | SUNWTcl |
+--------------------+-----------------+
|Interface Stability | Uncommitted |
+--------------------+-----------------+
NOTES
Source for Tcl is available on http://opensolaris.org.
Tcl 7.5 filename(1T)