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filename(3tcl) Tcl Built-In Commands filename(3tcl) 





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 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
    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: 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
    platform element of the tcl_platform array:



  

  
On Unix and Apple MacOS X 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. Any
      number of trailing slash characters at the end of a path are simply
      ignored, so the paths foo, foo/ and foo// are all
      identical, and in particular foo/ does not necessarily mean a
      directory is being referred.






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.

  

  
Relative path to the file foo in the current directory.

  

  
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.







  

  
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 components, 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:







  

  
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.

  

  
Volume-relative path to a file foo in the current directory on
      drive c.

  

  
Absolute path to a file foo in the root directory of drive
      c.

  

  
Relative path to a file bar in the foo directory in the
      current directory on the current volume.

  

  
Volume-relative path to a file foo in the root directory of the
      current volume.

  

  
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. This works on Unix,
    MacOS X and Windows (except very old releases).


Old 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. Care should be taken with filenames which
    contain spaces (common on Windows systems) and filenames where the backslash
    is the directory separator (Windows native path names).


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.






SEE ALSO


file(3tcl), glob(3tcl)






KEYWORDS


current directory, absolute file name, relative file name,
    volume-relative file name, portability







  

    7.5
    Tcl