A scripting language, script language, or extension language is a programming language that allows control of one or more applications. "Scripts" are distinct from the core code of the application, as they are usually written in a different language and are often created or at least modified by the...
John Kenneth Ousterhout is the chairman of Electric Cloud, Inc. and a professor of computer science at Stanford University. He founded Electric Cloud with John Graham-Cumming. Ousterhout previously was a professor of computer science at University of California, Berkeley where he created the Tcl...
. Originally "born out of frustration", according to the author, with programmers devising their own languages intended to be embedded into applications, Tcl gained acceptance on its own. It is commonly used for rapid prototyping
Rapid application development
Rapid application development is a software development methodology that uses minimal planning in favor of rapid prototyping. The "planning" of software developed using RAD is interleaved with writing the software itself...
, scripted applications, GUIs and testing. Tcl is used on embedded systems platforms, both in its full form and in several other small-footprinted versions.
Tk is an open source, cross-platform widget toolkit that provides a library of basic elements for building a graphical user interface in many different programming languages....
In computing, a widget toolkit, widget library, or GUI toolkit is a set of widgets for use in designing applications with graphical user interfaces...
is referred to as Tcl/Tk.
History
The Tcl programming language was created in the spring of 1988 by John Ousterhout
John Ousterhout
John Kenneth Ousterhout is the chairman of Electric Cloud, Inc. and a professor of computer science at Stanford University. He founded Electric Cloud with John Graham-Cumming. Ousterhout previously was a professor of computer science at University of California, Berkeley where he created the Tcl...
Expect is a Unix automation and testing tool, written by Don Libes as an extension to the Tcl scripting language, for interactive applications such as telnet, ftp, passwd, fsck, rlogin, tip, ssh, and others. It uses Unix pseudo terminals to wrap up subprocesses transparently, allowing the...
Tk is an open source, cross-platform widget toolkit that provides a library of basic elements for building a graphical user interface in many different programming languages....
(Winter USENIX).
June 1993
First Tcl/Tk conference (Berkeley). [table] geometry manager (forerunner of [grid]), [incr Tcl], TclDP and Groupkit, announced there.
August 1997
Tcl 8.0 introduced bytecode compiler.
April 1999
Tcl 8.1 introduces full Unicode support.
August 2000
Tcl Core Team formed, moving Tcl to a more community-oriented development model.
In computing, a command is a directive to a computer program acting as an interpreter of some kind, in order to perform a specific task. Most commonly a command is a directive to some kind of command line interface, such as a shell....
, including language structures. They are written in prefix notation.
In computer science, an operator or function is variadic if it can take a varying number of arguments; that is, if its arity is not fixed.For specific articles, see:* Variadic function* Variadic macro in the C preprocessor* Variadic templates...
.
Everything can be dynamically redefined and overridden.
In computer programming, a data type is a classification identifying one of various types of data, such as floating-point, integer, or Boolean, that determines the possible values for that type; the operations that can be done on values of that type; the meaning of the data; and the way values of...
In formal languages, which are used in mathematical logic and theoretical computer science, a string is a finite sequence of symbols that are chosen from a set or alphabet....
In computer science, source code is text written using the format and syntax of the programming language that it is being written in. Such a language is specially designed to facilitate the work of computer programmers, who specify the actions to be performed by a computer mostly by writing source...
In computer programming, event-driven programming or event-based programming is a programming paradigm in which the flow of the program is determined by events—i.e., sensor outputs or user actions or messages from other programs or threads.Event-driven programming can also be defined as an...
In computer networking, an Internet socket or network socket is an endpoint of a bidirectional inter-process communication flow across an Internet Protocol-based computer network, such as the Internet....
A computer file is a block of arbitrary information, or resource for storing information, which is available to a computer program and is usually based on some kind of durable storage. A file is durable in the sense that it remains available for programs to use after the current program has finished...
s. Time-based and user-defined events are also possible.
Variable visibility restricted to lexical (static) scope by default, but uplevel
Uplevel
Uplevel is a command in Tcl that allows a command script to be executed in a scope other than the current innermost scope on the stack. Because the command script may itself call procedures that use the uplevel command, this has the net effect of transforming the call stack into a call tree.It was...
and upvar allowing procs to interact with the enclosing functions' scopes.
All commands defined by Tcl itself generate error messages on incorrect usage.
In software engineering, extensibility is a system design principle where the implementation takes into consideration future growth. It is a systemic measure of the ability to extend a system and the level of effort required to implement the extension...
C is a general-purpose computer programming language developed between 1969 and 1973 by Dennis Ritchie at the Bell Telephone Laboratories for use with the Unix operating system....
C++ is a statically typed, free-form, multi-paradigm, compiled, general-purpose programming language. It is regarded as an intermediate-level language, as it comprises a combination of both high-level and low-level language features. It was developed by Bjarne Stroustrup starting in 1979 at Bell...
Java is a programming language originally developed by James Gosling at Sun Microsystems and released in 1995 as a core component of Sun Microsystems' Java platform. The language derives much of its syntax from C and C++ but has a simpler object model and fewer low-level facilities...
Interpreted language is a programming language in which programs are 'indirectly' executed by an interpreter program. This can be contrasted with a compiled language which is converted into machine code and then 'directly' executed by the host CPU...
Bytecode, also known as p-code , is a term which has been used to denote various forms of instruction sets designed for efficient execution by a software interpreter as well as being suitable for further compilation into machine code...
Unicode is a computing industry standard for the consistent encoding, representation and handling of text expressed in most of the world's writing systems...
In computing, cross-platform, or multi-platform, is an attribute conferred to computer software or computing methods and concepts that are implemented and inter-operate on multiple computer platforms...
The Windows API, informally WinAPI, is Microsoft's core set of application programming interfaces available in the Microsoft Windows operating systems. It was formerly called the Win32 API; however, the name "Windows API" more accurately reflects its roots in 16-bit Windows and its support on...
Unix is a multitasking, multi-user computer operating system originally developed in 1969 by a group of AT&T employees at Bell Labs, including Ken Thompson, Dennis Ritchie, Brian Kernighan, Douglas McIlroy, and Joe Ossanna...
Linux is a Unix-like computer operating system assembled under the model of free and open source software development and distribution. The defining component of any Linux system is the Linux kernel, an operating system kernel first released October 5, 1991 by Linus Torvalds...
The Macintosh , or Mac, is a series of several lines of personal computers designed, developed, and marketed by Apple Inc. The first Macintosh was introduced by Apple's then-chairman Steve Jobs on January 24, 1984; it was the first commercially successful personal computer to feature a mouse and a...
Gui or guee is a generic term to refer to grilled dishes in Korean cuisine. These most commonly have meat or fish as their primary ingredient, but may in some cases also comprise grilled vegetables or other vegetarian ingredients. The term derives from the verb, "gupda" in Korean, which literally...
Tk is an open source, cross-platform widget toolkit that provides a library of basic elements for building a graphical user interface in many different programming languages....
.
Multiple distribution mechanisms exist:
Full development version (e.g., ActiveState Tcl)
tclkit (kind of single-file runtime, only about 1 megabyte in size)
starpack (single-file executable of a script/program, derived from the tclkit technology)
freewrapTCLSH turns TCL scripts into single-file binary executable programs.
BSD licenses are a family of permissive free software licenses. The original license was used for the Berkeley Software Distribution , a Unix-like operating system after which it is named....
Object-oriented programming is a programming paradigm using "objects" – data structures consisting of data fields and methods together with their interactions – to design applications and computer programs. Programming techniques may include features such as data abstraction,...
XOTcl is an object-oriented extension for the Tool Command Language created by Gustaf Neumann and Uwe Zdun. It is an extension of the MIT OTcl. XOTcl supports metaclasses. Class and method definitions are completely dynamic...
. Even purely scripted OO packages exist, such as Snit
Snit
Snit is an object-oriented extension to the Tcl programming language. Snit is a recursive acronym that stands for "Snit's Not Incr Tcl." Snit is a pure Tcl object and megawidget system. It is unique among Tcl object systems in that it is based not on inheritance but on delegation...
and STOOOP (simple tcl-only object-oriented programming).
Safe-Tcl is a subset of TCL that has restricted features. File system access is limited and arbitrary system commands are prevented from execution. It uses a dual interpreter model with the "untrusted interpreter" running code in an untrusted script. It was designed by Nathaniel Borenstein and Marshall Rose to include active messages in e-mail. Safe-Tcl can be included in e-mail when the application/safe-tcl and multipart/enabled-mail are supported. The functionality of Safe-Tcl has since been incorporated as part of the standard Tcl/Tk releases.
Syntax and fundamental semantics
A Tcl script consists of several command invocations. A command invocation is a list of words separated by whitespace and terminated by a newline or semicolon.
word0 word1 word2 ... wordN
The first word is the name of a command, which is not built into the language, but which is in the library. The following words are arguments. So we have:
commandName argument1 argument2 ... argumentN
Practical example, using the puts command which outputs a string, adding a trailing newline, by default to the stdout channel:
puts "Hello, world!"
Variables and the results of other commands can be substituted inside strings too, such as in this example where we use set and expr to store a calculation result in a variable, and puts to print the result together with some explanatory text:
Good style would put the expression (1+2+3+4+5, in this case) inside {curly braces}
set sum [expr 1+2+3+4+5]
puts "The sum of the numbers 1..5 is $sum."
expr function will be evaluated faster if curly braces are added on the equation.
set sum [expr {1+2+3+4+5}]
puts "The sum of the numbers 1..5 is $sum."
Formally, words are either written as-is, with double-quotes around them (allowing whitespace characters to be embedded), or with curly-brace characters around them, which suppresses all substitutions inside (except for backslash-newline elimination). In bare and double-quoted words, three types of substitution occur (once, in a single left-to-right scan through the word):
Command substitution replaces the contents of balanced square brackets with the result of evaluating the script contained inside. For example, “[expr 1+2+3]” is replaced with the result of evaluating the contained expression (i.e. 6) since that's what the expr command does.
Variable substitution replaces a dollar-sign followed by the name of a variable with the contents of the variable. For example, “$foo” is replaced with the contents of the variable called “foo”. The variable name may be surrounded in curly braces so as to delimit what is and isn't the variable name in otherwise ambiguous cases.
Backslash substitution replaces a backslash followed by a letter with another character. For example, “\n” is replaced with a newline.
From Tcl 8.5 onwards, any word may be prefixed by “{*}” to cause that word to be split apart into its constituent sub-words for the purposes of building the command invocation (similar to the “,@” sequence of Lisp's quasiquote feature).
As a consequence of these rules, the result of any command may be used as an argument to any other command. Also, there is no operator or command for string concatenation, as the language concatenates directly. Note that, unlike in Unix command shells
Bourne shell
The Bourne shell, or sh, was the default Unix shell of Unix Version 7 and most Unix-like systems continue to have /bin/sh - which will be the Bourne shell, or a symbolic link or hard link to a compatible shell - even when more modern shells are used by most users.Developed by Stephen Bourne at AT&T...
, Tcl does not reparse any string unless explicitly directed to do so, which makes interactive use more cumbersome but scripted use more predictable (e.g. the presence of spaces in filenames does not cause difficulties).
To summarize: there is one basic construct (the command) and a set of simple substitution rules. The single equality sign (=) for example is not used at all, and the double equality sign is the test for equality, and even then only in expression contexts such as the expr command or the first argument to if. (Both of those commands are just part of the standard library; they have no particularly special place in the library and can be replaced if so desired.)
The majority of Tcl commands, especially in the standard library, are variadic
Variadic function
In computer programming, a variadic function is a function of indefinite arity, i.e., one which accepts a variable number of arguments. Support for variadic functions differs widely among programming languages....
, and the proc (the constructor for scripted command procedures) supports the definition of both default values for arguments and a catch-all argument to allow the code to process arbitrary numbers of arguments.
Tcl is not statically typed: each variable may contain integers, floats, strings, lists, command names, dictionaries, or any other value; values are reinterpreted (subject to syntactic constraints) as other types on demand. However, values are immutable
Immutable object
In object-oriented and functional programming, an immutable object is an object whose state cannot be modified after it is created. This is in contrast to a mutable object, which can be modified after it is created...
and operations that appear to change them actually just return a new value instead.
Interfacing with other languages
Tcl interfaces natively with the C
C (programming language)
C is a general-purpose computer programming language developed between 1969 and 1973 by Dennis Ritchie at the Bell Telephone Laboratories for use with the Unix operating system....
language.
This is because it was originally written to be a framework for providing a syntactic front-end to commands written in C, and all commands in the language (including things that might otherwise be keyword
Keyword (computer programming)
In computer programming, a keyword is a word or identifier that has a particular meaning to the programming language. The meaning of keywords — and, indeed, the meaning of the notion of keyword — differs widely from language to language....
s, such as if or while) are implemented this way. Each command implementation function
Subroutine
In computer science, a subroutine is a portion of code within a larger program that performs a specific task and is relatively independent of the remaining code....
is passed an array of values that describe the (already substituted) arguments to the command, and is free to interpret those values as it sees fit.
Logic simulation is the use of a computer program to simulate the operation of a digital circuit. Logic simulation is the primary tool used for verifying the logical correctness of a hardware design. In many cases logic simulation is the first activity performed in the process of taking a hardware...
often include a Tcl scripting interface for simulating Verilog
Verilog
In the semiconductor and electronic design industry, Verilog is a hardware description language used to model electronic systems. Verilog HDL, not to be confused with VHDL , is most commonly used in the design, verification, and implementation of digital logic chips at the register-transfer level...
In electronics, a hardware description language or HDL is any language from a class of computer languages, specification languages, or modeling languages for formal description and design of electronic circuits, and most-commonly, digital logic...
SWIG is an open source software tool used to connect computer programs or libraries written in C or C++ with scripting languages such as Lua, Perl, PHP, Python, R, Ruby, Tcl, and other languages like C#, Java, Modula-3, Objective Caml, Octave, and Scheme...
, ffidl) to automatically generate the necessary code to connect arbitrary C functions and the Tcl runtime, and Critcl does the reverse, allowing embedding of arbitrary C code inside a Tcl script and compiling it at runtime into a DLL
Dynamic-link library
Dynamic-link library , or DLL, is Microsoft's implementation of the shared library concept in the Microsoft Windows and OS/2 operating systems...
.
Extension packages
The Tcl language has always supported extension packages, which provide additional functionality, such as a GUI, terminal-based application automation, database access, etc.
Tk is an open source, cross-platform widget toolkit that provides a library of basic elements for building a graphical user interface in many different programming languages....
In computing, a graphical user interface is a type of user interface that allows users to interact with electronic devices with images rather than text commands. GUIs can be used in computers, hand-held devices such as MP3 players, portable media players or gaming devices, household appliances and...
An operating system is a set of programs that manage computer hardware resources and provide common services for application software. The operating system is the most important type of system software in a computer system...
s. Each GUI consists of one or more frames. Each frame has a layout manager.
Expect
One of the other very popular Tcl extensions is Expect
Expect
Expect is a Unix automation and testing tool, written by Don Libes as an extension to the Tcl scripting language, for interactive applications such as telnet, ftp, passwd, fsck, rlogin, tip, ssh, and others. It uses Unix pseudo terminals to wrap up subprocesses transparently, allowing the...
extension. The early close relationship of Expect with Tcl is largely responsible for the popularity of Tcl in prolific areas of use such as in Unix testing, where Expect was (and still is today) employed very successfully to automate telnet, ssh, and serial sessions to perform many repetitive tasks (i.e., scripting of formerly interactive-only applications). Tcl was the only way to run Expect, so Tcl skyrocketed in popularity in these areas of industry.
Tile/Ttk
Tile/Ttk is a styles and theming widget collection which can replace most of the widgets in Tk with variants which are truly platform native through calls to an operating system
Operating system
An operating system is a set of programs that manage computer hardware resources and provide common services for application software. The operating system is the most important type of system software in a computer system...
Windows XP is an operating system produced by Microsoft for use on personal computers, including home and business desktops, laptops and media centers. First released to computer manufacturers on August 24, 2001, it is the second most popular version of Windows, based on installed user base...
Qt is a cross-platform application framework that is widely used for developing application software with a graphical user interface , and also used for developing non-GUI programs such as command-line tools and consoles for servers...
KDE is an international free software community producing an integrated set of cross-platform applications designed to run on Linux, FreeBSD, Microsoft Windows, Solaris and Mac OS X systems...
Aqua is the GUI and primary visual theme of Apple Inc.'s Mac OS X operating system. It is based around the theme of water, as its name suggests, with droplet-like elements and liberal use of translucency and reflection effects...
(Mac OS X). A theme can also be constructed without these calls using widget definitions supplemented with image pixmaps. Themes created this way include Classic Tk, Step, Alt/Revitalized, Plastik and Keramik.
Under Tcl 8.4, this package is known as Tile, while in Tcl 8.5 it has been folded into the core distribution of Tk (as Ttk).
Tix
Tix, the Tk Interface eXtension, is a set of user interface components that expand the capabilities of Tcl/Tk and Python applications. It is an open source software package maintained by volunteers in the Tix Project Group and released under a BSD-style license.
incr Tcl is a set of object-oriented extensions for the Tcl programming language. It is widely used among the Tcl community, and is generally regarded as industrial strength...
is an object system for Tcl, and is normally named as [incr Tcl] (that being the way to increment in Tcl, similar in fashion to the name C++).
Tcllib is a collection of packages available for the Tcl programming language. Tcllib is distributed in both source code as well as pre-compiled binary formats...
is a set of scripted packages for Tcl that can be used with no compilation steps.
The User Datagram Protocol is one of the core members of the Internet Protocol Suite, the set of network protocols used for the Internet. With UDP, computer applications can send messages, in this case referred to as datagrams, to other hosts on an Internet Protocol network without requiring...
(UDP) sockets in Tcl.
Databases
Tcl Database Connectivity (TDBC), part of Tcl 8.6, is a common database access interface for Tcl scripts. It currently supports drivers for accessing MySQL
MySQL
MySQL officially, but also commonly "My Sequel") is a relational database management system that runs as a server providing multi-user access to a number of databases. It is named after developer Michael Widenius' daughter, My...
PostgreSQL, often simply Postgres, is an object-relational database management system available for many platforms including Linux, FreeBSD, Solaris, MS Windows and Mac OS X. It is released under the PostgreSQL License, which is an MIT-style license, and is thus free and open source software...
SQLite is an ACID-compliant embedded relational database management system contained in a relatively small C programming library. The source code for SQLite is in the public domain and implements most of the SQL standard...
databases. More are planned for the future.
Access to databases is also supported through database-specific extensions, of which there are many available.
Metakit is an embedded database library with a small footprint. It fills the gap between flat-file, relational, object-oriented, and tree-structured databases, supporting relational joins, serialization, nested structures, and instant schema evolution...
SQLite is an ACID-compliant embedded relational database management system contained in a relatively small C programming library. The source code for SQLite is in the public domain and implements most of the SQL standard...
aMSN is a free Windows Live Messenger clone. aMSN attempts to emulate the look and feel of Windows Live Messenger, and supports many of its features...
Expect is a Unix automation and testing tool, written by Don Libes as an extension to the Tcl scripting language, for interactive applications such as telnet, ftp, passwd, fsck, rlogin, tip, ssh, and others. It uses Unix pseudo terminals to wrap up subprocesses transparently, allowing the...
InstallJammer is a Microsoft Windows-style installer creator written in Tcl which creates self-extracting files that display an installation wizard. It is also able to generate installers for Windows 98, ME, 2000, XP, 2003, Vista, 2008, FreeBSD, Solaris, HP-UX and AIX .As of August 16th, 2011,...
MacPorts, formerly called DarwinPorts, is a package management system that simplifies the installation of software on the Mac OS X and Darwin operating systems. It is a free/open source software project to simplify installation of other free/open source software...
The Open Architecture Community System is an open-source web application framework licensed under the terms of the GNU GPL.The Open Architecture Community System provides:...
TclMon is a network monitoring system, written in platform-independent language Tcl. TclMon consists of a server that gathers and processes data received from network devices, and the client that provides data visualization, called Netstate.- Overview :...
Tkabber is a GPL instant messaging client for the XMPP protocol which uses the Tk toolkit for the GUI. It runs on anything to which Tcl/Tk is ported: almost any X-based system , Microsoft Windows, and Mac OS X....
OpenSees, the Open System for Earthquake Engineering Simulation, is an object-oriented, open source software framework created at the -sponsored Pacific Earthquake Engineering...
Expect is a Unix automation and testing tool, written by Don Libes as an extension to the Tcl scripting language, for interactive applications such as telnet, ftp, passwd, fsck, rlogin, tip, ssh, and others. It uses Unix pseudo terminals to wrap up subprocesses transparently, allowing the...
The IMG file format is one of the following files:# A CD or DVD image file, essentially equivalent to an ISO file. On such a file, simply changing the extension from IMG to ISO can make it usable as the latter by most programs....
Snit is an object-oriented extension to the Tcl programming language. Snit is a recursive acronym that stands for "Snit's Not Incr Tcl." Snit is a pure Tcl object and megawidget system. It is unique among Tcl object systems in that it is based not on inheritance but on delegation...
Tcllib is a collection of packages available for the Tcl programming language. Tcllib is distributed in both source code as well as pre-compiled binary formats...
TclX, an abbreviation for extended Tcl, was one of the first freely available Tcl extensions to the Tcl programming language, providing new operating system interface commands, extended file controls, time and date manipulation, scanning and status commands and many others...
Tk is an open source, cross-platform widget toolkit that provides a library of basic elements for building a graphical user interface in many different programming languages....
TRF may refer to:*The Rugby Forum, an online forum dedicated to Rugby union and Rugby league.*Thief River Falls, Minnesota*Sandefjord Airport, Torp, its IATA airport code, located near Oslo, Norway*Texas Renaissance Festival*Tactical Recognition Flash...
Further reading
Tcl/Tk 8.5 Programming Cookbook: A practical, comprehensive cookbook to master the depths and breadths of Tcl/Tk 8.5 programming, published by Packt Publishing. Written by Bert Wheeler.
