The source code for Tcl is managed by fossil. Tcl developers coordinate all changes to the Tcl source code at

Tcl Source Code

Release Tcl 9.0.1 arises from the check-in with tag core-9-0-1.

Changes since Tcl 9.0.0

• zlib-8.8, zlib-8.16 fail on Fedora 40, gcc 14.1.1
• regression in tzdata, %z instead of offset TZ-name
• Tcl will not start properly if there is an init.tcl file in the current dir
• clock scan "24:00", ISO-8601 compatibility
• install registry and dde in $INSTALL_DIRlib always
• cannot build .chm help file (Windows)
• TIP 701 - Tcl_FSTildeExpand C API
• buffer overwrite for non-BMP characters in utf-16
• Temporary folder with file "tcl9registry13.dll" remains after "exit"
• load library (dll) from zipfs-library causes a leak in temporary folder

Release Tcl 9.0.0 arises from the check-in with tag core-9-0-0.

Highlighted differences between Tcl 9.0 and Tcl 8.6 are summarized below, with focus on changes important to programmers using the Tcl library and writing Tcl scripts.

Major Features

64-bit capacity: Data values larger than 2Gb

• Strings can be any length (that fits in your available memory)
• Lists and dictionaries can have very large numbers of elements

Internationalization of text

• Full Unicode range of codepoints
• New encodings: utf-16/utf-32/ucs-2(le|be), CESU-8, etc.
• encoding options -profile, -failindex manage encoding of I/O.
• msgcat supports custom locale search list
• source defaults to -encoding utf-8

Zip filesystems and attached archives.

• Packaging of the Tcl script library with the Tcl binary library, meaning that the TCL_LIBRARY environment variable is usually not required.
• Packaging of an application into a virtual filesystem is now a supported core Tcl feature.

Unix notifiers available using epoll() or kqueue()

• This relieves limits on file descriptors imposed by legacy select() and fixes a performance bottleneck.

Incompatibilities

Notable incompatibilities

• Unqualified varnames resolved in current namespace, not global. Note that in almost all cases where this causes a change, the change is actually the removal of a latent bug.
• No --disable-threads build option. Always thread-enabled.
• I/O malencoding default response: raise error (-profile strict)
• Windows platform needs Windows 7 or Windows Server 2008 R2 or later
• Ended interpretation of ~ as home directory in pathnames. (See file home and file tildeexpand for replacements when you need them.)
• Removed the identity encoding. (There were only ever very few valid use cases for this; almost all uses were systematically wrong.)
• Removed the encoding alias binary to iso8859-1.
• $::tcl_precision no longer controls string generation of doubles. (If you need a particular precision, use format.)
• Removed pre-Tcl 8 legacies: case, puts and read variant syntaxes.
• Removed subcommands [trace variable|vdelete|vinfo]
• Removed -eofchar option for write channels.
• On Windows 10+ (Version 1903 or higher), system encoding is always utf-8.
• %b/%d/%o/%x format modifiers (without size modifier) for format and scan always truncate to 32-bits on all platforms.
• %L size modifier for scan no longer truncates to 64-bit.
• Removed command ::tcl::unsupported::inject. (See coroinject and coroprobe for supported commands with significantly more comprehensible semantics.)

Incompatibilities in C public interface

• Extensions built against Tcl 8.6 and before will not work with Tcl 9.0; ABI compatibility was a non-goal for 9.0. In most cases, rebuilding against Tcl 9.0 should work except when a removed API function is used.
• Many arguments expanded type from int to Tcl_Size, a signed integer type large enough to support 64-bit sized memory objects. The constant TCL_AUTO_LENGTH is a value of that type that indicates that the length should be obtained using an appropriate function (typically strlen() for char * values).
• Ended support for Tcl_ChannelTypeVersion less than 5
• Introduced versioning of the Tcl_ObjType struct
• Removed macros CONST*: Tcl 9 support means dropping Tcl 8.3 support. (Replaced with standard C const keyword going forward.)
• Removed registration of several Tcl_ObjTypes.

• Removed API functions:

  Tcl_Backslash(), Tcl_*VA(), Tcl_*MathFunc*(), Tcl_MakeSafe(), Tcl_(Save|Restore|Discard|Free)Result(), Tcl_EvalTokens(), Tcl_(Get|Set)DefaultEncodingDir(), Tcl_UniCharN(case)cmp(), Tcl_UniCharCaseMatch()

• Revised many internals; beware reliance on undocumented behaviors.

New Features

New commands

• array default — Specify default values for arrays (note that this alters the behaviour of append, incr, lappend).
• array for — Cheap iteration over an array's contents.
• chan isbinary — Test if a channel is configured to work with binary data.
• coroinject, coroprobe — Interact with paused coroutines.
• clock add weekdays — Clock arithmetic with week days.
• const, info const* — Commands for defining constants (variables that can't be modified).
• dict getwithdefault — Define a fallback value to use when dict get would otherwise fail.
• file home — Get the user home directory.
• file tempdir — Create a temporary directory.
• file tildeexpand — Expand a file path containing a ~.
• info commandtype — Introspection for the kinds of commands.
• ledit — Equivalent to lreplace but on a list in a variable.
• lpop — Remove an item from a list in a variable.
• lremove — Remove a sublist from a list in a variable.
• lseq — Generate a list of numbers in a sequence.
• package files — Describe the contents of a package.
• string insert — Insert a string as a substring of another string.
• string is dict — Test whether a string is a dictionary.
• tcl::process — Commands for working with subprocesses.
• *::build-info — Obtain information about the build of Tcl.
• readFile, writeFile, foreachLine — Simple procedures for basic working with files.
• tcl::idna::* — Commands for working with encoded DNS names.

New command options

• chan configure ... -inputmode ... — Support for raw terminal input and reading passwords.
• clock scan ... -validate ...
• info loaded ... ?prefix?
• lsearch ... -stride ... — Search a list by groups of items.
• regsub ... -command ... — Generate the replacement for a regular expression by calling a command.
• socket ... -nodelay ... -keepalive ...
• vwait controlled by several new options
• expr string comparators lt, gt, le, ge
• expr supports comments inside expressions

Numbers

• 0NNN format is no longer octal interpretation. Use 0oNNN.
• 0dNNNN format to compel decimal interpretation.
• NN_NNN_NNN, underscores in numbers for optional readability
• Functions: isinf(), isnan(), isnormal(), issubnormal(), isunordered()
• Command: fpclassify
• Function int() no longer truncates to word size

TclOO facilities

• private variables and methods
• class variables and methods
• abstract and singleton classes
• configurable properties
• method -export, method -unexport

Known bugs

• changed behaviour wrt command names, namespaces and resolution
• windows dos device paths inconsistencies and missing functionality
• lsearch -stride with -subindices and -inline -all gives unexpected result
• lsearch -sorted -inline -subindices incorrect result
• "No error" when load fails due to a missing secondary DLL