Tool Command Language

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What Does Tool Command Language Mean?

Tool command language (Tcl) is a powerful scripting language with programming features. It is available across Unix, Windows and Mac OS platforms. Tcl is used for Web and desktop applications, networking, administration, testing, rapid prototyping, scripted applications and graphical user interfaces (GUI).


Techopedia Explains Tool Command Language

Introduced in 1988 by John Ousterhout, Tcl is used for common gateway interface (CGI) scripting and serves as the Eggdrop bot scripting language. Tcl/Tk refers to a combination of Tcl and the Tk GUI toolkit.

Tcl features include:

  • Complete Unicode and cross-platform usage
  • Extensibility through Java and C++
  • Integration with Windows GUI toolkit
  • Data types, including source code, may be manipulated as strings.
  • Event-driven interface to sockets and files
  • Variadic function commands and interpreted language with bytecode
  • Error message generation on incorrect usage by Tcl commands.
  • FreeWrap TCLSH
  • Berkeley Software Distribution (BSD) license
  • Full development version

Tcl interfaces with the C language. Arrays of values that describe command arguments are passed to the command implementation functions. Digital logic simulators also include a Tcl scripting interface for Verilog, VHSIC hardware description language (VHDL) and SystemVerilog hardware language simulation. Tools like Simplified Wrapper and Interface Generator (SWIG) and ffidl automatically generate the code required to connect arbitrary C functions and Tcl runtime. Tcl scripts house command invocations as a list of words separated by whitespace and terminated by a newline or semicolon.

Major substitutions supported by Tcl are command substitution, variable substitution and backslash substitution. Additionally, there is a database access interface for Tcl scripts that supports access drivers for MySQL, Open Database Connectivity (ODBC), PostgreSQL and SQLite databases.

Tcl supports extension packages for additional functionality, including GUI, terminal-based application automation and database access.


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Margaret Rouse
Technology Expert
Margaret Rouse
Technology Expert

Margaret is an award-winning technical writer and teacher known for her ability to explain complex technical subjects to a non-technical business audience. Over the past twenty years, her IT definitions have been published by Que in an encyclopedia of technology terms and cited in articles by the New York Times, Time Magazine, USA Today, ZDNet, PC Magazine, and Discovery Magazine. She joined Techopedia in 2011. Margaret's idea of a fun day is helping IT and business professionals learn to speak each other’s highly specialized languages.