Tcl Source Code

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	Tcl is maintained, enhanced, and distributed freely as a
	service to the Tcl community by Scriptics Corporation.

RCS: @(#) $Id: README,v 1999/03/17 21:29:56 stanton Exp $

    1. Introduction
    2. Documentation
    3. Compiling and installing Tcl
    4. Summary of changes in Tcl 8.1
    5. Development tools
    6. Tcl newsgroup
    7. Tcl contributed archive
    8. Tcl Resource Center
    9. Mailing lists
    10. Support and bug fixes
    11. Tcl version numbers

1. Introduction

Tcl provides a powerful platform for creating integration
applications that tie together diverse applications, protocols,
devices, and frameworks.  When paired with the Tk toolkit, Tcl
provides the fastest and most powerful way to create GUI applications
that run on PCs, Unix, and the Macintosh.  Tcl can also be used for a
variety of web-related tasks and for creating powerful command
languages for applications.

This directory contains the sources and documentation for Tcl.  The
information here corresponds to release 8.1b3, which is the third
beta release for Tcl 8.1.  This release is mostly feature complete but
may have bugs and be missing some minor features.  This release is for
early adopters who are willing to help us find and fix problems.
Please let us know about any problems you uncover.

Tcl 8.1 includes four major new features: Unicode support (all internal
strings are now stored in UTF-8 form), a new regular expression matcher
with most of the Perl features, support for multithreading, and a new
message catalog package.  For details on features, incompatibilities, and
potential problems with this release, see the Tcl/Tk 8.1 Web page at or refer to the "changes" file
in this directory, which contains a historical record of all changes to

Tcl is a freely available open source package.  You can do virtually
anything you like with it, such as modifying it, redistributing it,
and selling it either in whole or in part.  See the file
"license.terms" for complete information.

2. Documentation

The best way to get started with Tcl is to read about Tcl on the
Scriptics Web site at:

Another good way to get started with Tcl is to read one of the
introductory books on Tcl:

    Practical Programming in Tcl and Tk, 2nd Edition, by Brent Welch,
    Prentice-Hall, 1997, ISBN 0-13-616830-2

    Tcl and the Tk Toolkit, by John Ousterhout,
    Addison-Wesley, 1994, ISBN 0-201-63337-X

    Exploring Expect, by Don Libes,
    O'Reilly and Associates, 1995, ISBN 1-56592-090-2

Other books are listed at

There is also an official home for Tcl and Tk on the Scriptics Web site:

These Web pages include information about the latest releases, products
related to Tcl and Tk, reports on bug fixes and porting issues, HTML
versions of the manual pages, and pointers to many other Tcl/Tk Web
pages at other sites.  Check them out!

2a. Unix Documentation

The "doc" subdirectory in this release contains a complete set of
reference manual entries for Tcl.  Files with extension ".1" are for
programs (for example, tclsh.1); files with extension ".3" are for C
library procedures; and files with extension ".n" describe Tcl
commands.  The file "doc/Tcl.n" gives a quick summary of the Tcl
language syntax.  To print any of the man pages on Unix, cd to the
"doc" directory and invoke your favorite variant of troff using the
normal -man macros, for example

		ditroff -man Tcl.n

to print Tcl.n.  If Tcl has been installed correctly and your "man"
program supports it, you should be able to access the Tcl manual entries
using the normal "man" mechanisms, such as

		man Tcl

2b. Windows Documentation

The "doc/help" subdirectory in this release contains a complete set of
Windows help files for TclPro.  Once you install this Tcl release, a
shortcut to the Windows help Tcl documentation will appear in the
"Start" menu:

	Start | Programs | Tcl | Tcl Help

3. Compiling and installing Tcl

This release contains everything you should need to compile and run
Tcl under UNIX, PCs (either Windows NT, Windows 95, or Win 3.1 with
Win32s), and Macintoshes.

Before trying to compile Tcl you should do the following things:

    (a) Check for a binary release.  Pre-compiled binary releases are
        available now for PCs, Macintoshes, and several flavors of UNIX.
        Binary releases are much easier to install than source releases.
        To find out whether a binary release is available for your
        platform, check the Scriptics Tcl Resource Center
        (  Also, check in
        the FTP directory from which you retrieved the base

    (b) Make sure you have the most recent patch release.  Look in the
	FTP directory from which you retrieved this distribution to see
	if it has been updated with patches.  Patch releases fix bugs
	without changing any features, so you should normally use the
	latest patch release for the version of Tcl that you want. 

Once you've done this, change to the "unix" subdirectory if you're
compiling under UNIX, "win" if you're compiling under Windows, or
"mac" if you're compiling on a Macintosh.  Then follow the instructions
in the README file in that directory for compiling Tcl, installing it,
and running the test suite.

4. Summary of changes in Tcl 8.1

Here are the most significant changes in Tcl 8.1.  In addition to these
changes, there are several smaller changes and bug fixes.  See the file
"changes" for a complete list of all changes.

    1. Internationalization. Tcl has undergone a major revision to
    support international character sets:

    All strings in Tcl are now represented in UTF-8 instead of ASCII,
    so that Tcl now supports the full Unicode character set.  The
    representation of ASCII characters is unchanged (in UTF-8 anything
    that looks like an ASCII character is an ASCII character), but
    characters with the high-order bit set, such as those in ISO-8859,
    are represented with multi-byte sequences, as are all Unicode
    characters with values greater than 127.  This change does not
    affect Tcl scripts but it does affect C code that parses strings.
    Tcl automatically translates between UTF-8 and the normal encoding
    for the platform during interactions with the system.

    In Tcl scripts the backslash sequence \u can be used to enter
    16-bit Unicode characters.  \o and \x generate only 8-bit
    characters as before.

    There is a new "encoding" command that allows scripts to determine
    what encodings are available as well as to convert strings between
    different encodings.  The fconfigure command now supports a
    -encoding option for specifying the encoding of an open file or
    socket.  Tcl will automatically translate between the specified
    encoding and UTF-8 during I/O.

    There are several new C APIs that support UTF-8 and various
    encodings.  See the manual entry Utf.3 for procedures that
    translate between Unicode and UTF-8 and manipulate UTF-8 strings.
    See Encoding.3 for procedures that create new encodings and
    translate between encodings.  See ToUpper.3 for procedures that
    perform case conversions on UTF-8 strings.

    2. Binary data.  Binary data is handled differently in Tcl 8.1
    than in Tcl 8.0.  Tcl 8.1 uses the UTF-8 facilities to represent
    binary data: the character value zero is represented with a
    multi-byte sequence, so that (once again) strings in Tcl 8.1 never
    contain null bytes.  This means that binary data is now accepted
    everywhere in Tcl and Tk (in Tcl 8.0 the support for binary data
    was incomplete).  If you have C code that needs to manipulate the
    bytes of binary data (as opposed to just passing the data through)
    you should use a new object type called "byte array".  See the
    manual entry ByteArrObj.3 for information about procedures such as

    3. Regular expressions.  Tcl 8.1 contains a brand new
    implementation of regular expressions from Henry Spencer.  The
    regular expression syntax has been greatly expanded to include
    most of the features in Perl.  In addition, the regexp engine
    supports Unicode and binary data.  See the doc/regexp.n manual
    entry for more details.

    4. Threads.  If configured with the --enable-threads flag, Tcl can
    now be compiled for use in a multi-threaded application.
    Individual threads are allowed to use one or more interpreters as
    long as each interpreter (and any slave interpreters) is only
    accessed by one thread.  Each thread runs its own event loop, and
    you can post events to other threads. There are new C APIs for
    mutexes, condition variables, and thread local storage.  See the
    doc/Thread.3 manual entry for more details.  Tk 8.1 is not yet
    multi-thread safe.  There is not yet support for tcl level use of
    threading except for a test command. (Compile tcltest and try

    5. Message catalog. There is a new message catalog package which makes
    it easy to localize the strings in a script.  See the doc/msgcat.n
    manual entry for more details.

    6. Stubbs library for building extensions.  There is now a new
    way to build extensions for Tcl.  Instead of linking with the
    tcl shared library you can now link to a stubs library that gets
    built in this release.  By linking with the stubs library it
    is possible to use dynamically loaded extensions in staticlly
    built applications.  It will also be possible for some extensions
    to work for both Tcl 8.0 & 8.1 with out having to recompile.

5. Development tools

A high quality set of commercial development tools is now available to
accelerate your Tcl application development.  Scriptics' TclPro
product provides a debugger, static code checker, packaging utility,
and bytecode compiler.  Visit the Scriptics Web site at:

for more information on TclPro and for a free 30-day evaluation

6. Tcl newsgroup

There is a network news group "comp.lang.tcl" intended for the
exchange of information about Tcl, Tk, and related applications.  The
newsgroup is a greata place to ask general information questions.  For
bug reports, please see the "Support and bug fixes" section below.

7. Tcl contributed archive

Many people have created exciting packages and applications based on Tcl
and/or Tk and made them freely available to the Tcl community.  An archive
of these contributions is kept on the machine  You
can access the archive using anonymous FTP;  the Tcl contributed archive is
in the directory "/pub/tcl".  The archive also contains several FAQ
("frequently asked questions") documents that provide solutions to problems
that are commonly encountered by TCL newcomers.

8. Tcl Resource Center

Visit to see an annotated index of
many Tcl resources available on the World Wide Web.  This includes
papers, books, and FAQs, as well as development tools, extensions,
applications, binary releases, and patches.  You can also recommend
additional URLs for the resource center using the forms labeled "Add a

9. Mailing lists

A couple of  Mailing List have been set up to discuss Macintosh or
Windows related Tcl issues.  To subscribe send a message to:
	[email protected]
	[email protected]
In the body of the message (the subject will be ignored) put:
	subscribe mactcl Joe Smith
Replacing Joe Smith with your real name, of course.  (Use wintcl
instead of mactcl if your interested in the Windows list.)  If you
would just like to receive more information about the list without
subscribing put the line:

	information mactcl
in the body instead (or wintcl).

10. Support and bug fixes

Scriptics is very interested in receiving bug reports, patches, and
suggestions for improvements.  We prefer that you send this
information to us via the bug form on the Scriptics Web site, rather
than emailing us directly.  The bug form is at:

The bug form was designed to give uniform structure to bug reports as
well as to solicit enough information to minimize followup questions.
The bug form also includes an option to automatically post your report
on comp.lang.tcl.  We strongly recommend that you select this option
because someone else who reads comp.lang.tcl may be able to offer a

When reporting bugs, please provide full information about the Tcl/Tk
version and the platform on which you are running Tcl/Tk.  Also,
please include a short tclsh script that we can use to reproduce the
bug.  Make sure that the script runs with a bare-bones tclsh and
doesn't depend on any extensions or other programs, particularly those
that exist only at your site.  Also, please include three additional
pieces of information with the script:

    (a) how do we use the script to make the problem happen (e.g.
	what things do we click on, in what order)?
    (b) what happens when you do these things (presumably this is
    (c) what did you expect to happen instead?

We will log and follow-up on each bug, although we cannot promise a
specific turn-around time.  Enhancements may take longer and may not
happen at all unless there is widespread support for them (we're
trying to slow the rate at which Tcl/Tk turns into a kitchen sink).
It's very difficult to make incompatible changes to Tcl/Tk at this
point, due to the size of the installed base.

The Tcl community is too large for us to provide much individual
support for users.  If you need help we suggest that you post
questions to comp.lang.tcl.  We read the newsgroup and will attempt to
answer esoteric questions for which no-one else is likely to know the
answer.  In addition, Tcl/Tk support and training are available
commercially from Scriptics at:

Also see the following Web site for links to other organizations that
offer Tcl/Tk training:

11. Tcl version numbers

You can test the current version of Tcl by examining the
tcl_version and tcl_patchLevel variables.  The tcl_patchLevel
variable follows the naming rules outlined below (e.g., 8.0.5).
The tcl_version just has the major.minor numbers in it (e.g., 8.0)

Each Tcl release is identified by two numbers separated by a dot, e.g.
6.7 or 7.0.  If a new release contains changes that are likely to break
existing C code or Tcl scripts then the major release number increments
and the minor number resets to zero: 6.0, 7.0, etc.  If a new release
contains only bug fixes and compatible changes, then the minor number
increments without changing the major number, e.g. 7.1, 7.2, etc.  If
you have C code or Tcl scripts that work with release X.Y, then they
should also work with any release X.Z as long as Z > Y.

Alpha and beta releases have an additional suffix of the form a2 or b1.
For example, Tcl 7.0b1 is the first beta release of Tcl version 7.0,
Tcl 7.0b2 is the second beta release, and so on.  A beta release is an
initial version of a new release, used to fix bugs and bad features before
declaring the release stable.  An alpha release is like a beta release,
except it's likely to need even more work before it's "ready for prime
time".  New releases are normally preceded by one or more alpha and beta
releases.  We hope that lots of people will try out the alpha and beta
releases and report problems.  We'll make new alpha/beta releases to fix
the problems, until eventually there is a beta release that appears to
be stable.  Once this occurs we'll make the final release.

We can't promise to maintain compatibility among alpha and beta releases.
For example, release 7.1b2 may not be backward compatible with 7.1b1, even
though the final 7.1 release will be backward compatible with 7.0.  This
allows us to change new features as we find problems during beta testing.
We'll try to minimize incompatibilities between beta releases, but if
a major problem turns up then we'll fix it even if it introduces an
incompatibility.  Once the official release is made then there won't
be any more incompatibilities until the next release with a new major
version number.

(Note: This compatibility is true for Tcl scripts, but historically
the Tcl C APIs have changed enough between releases that you may need
to work a bit to upgrade extensions.)

Patch releases now have a suffix such as ".4" or ".5".  Prior to
version 8.0.3, patch releases had the suffix "p1" or "p2".  So, the
8.0 release went to 8.0p1, 8.0p2, 8.0.3, 8.0.4, and 8.0.5.  The alphas
and betas continue to use the 'a' and 'b' letters in their
tcl_patchLevel.  Patch releases normally contain bug fixes only.  A
patch release (e.g Tcl 8.0.5) should be completely compatible with the
base release from which it is derived (e.g. Tcl 8.0), and you should
normally use the highest available patch release.

12. Thank You

We'd like to express our thanks to the Tcl community for all the
helpful suggestions, bug reports, and patches we have received.
Tcl/Tk has improved vastly and will continue to do so with your help.