filename
filename(n) Tcl Built-In Commands 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 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 separa-
tors. 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 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 inter-
preted as a single separator. The following examples illus-
trate 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-rela-
tive and UNC style names. Both / and \ may be used as direc-
tory 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\sharename\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:
\\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 cur-
rent directory on drive c.
c:/foo Absolute path to a file foo in the root direc-
tory of drive c.
foo\bar Relative path to a file bar in the foo direc-
tory 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 environ-
ment 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 alphanu-
meric 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.
KEYWORDS
current directory, absolute file name, relative file name, volume-rela-
tive file name, portability
SEE ALSO
file(n), glob(n)
Tcl 7.5 filename(n)
