Tcl facts for kids

Quick facts for kids
Tcl

Paradigm	multi-paradigm: object-oriented, functional, procedural, event-driven programming, imperative
Designed by	John Ousterhout
Developer	Tcl Core Team
First appeared	1988; 36 years ago (1988)
Stable release	8.6.8 (Dec, 22 2017) / December 22, 2017; 6 years ago (2017-12-22)
Typing discipline	dynamic typing, everything can be treated as a string
License	BSD-style
Filename extensions	.tcl, .tbc
Major implementations
ActiveTcl Androwish
Dialects
Jim
Influenced by
AWK, Lisp
Influenced
PHP, Tea, PowerShell

Tcl (pronounced "tickle" or tee cee ell) or Tool Command Language is a High-level programming language which can be used for many things. Tcl was made to be easy to use, but able to do many things. Tcl's language is based on commands which tell the computer what to do or how to save a variable. Tcl is able to do object-oriented, imperative, functional, or procedural styles.

Tcl is used a lot to in C to create prototypes quickly. There are interpreters available for many operating systems. This means many different kinds of computers are able to run Tcl code. Tcl is a very small language which means it is good to use as embedded systems.

Tcl is sometimes combined with Tk. When it is, it is called Tcl/Tk. Tcl/Tk is a part of the normal Python installation.

History

Tcl was created by John Ousterhout at University of California, Berkeley. Ousterhout won a ACM Software System Award in 1997 for making Tcl/Tk.

Safe-Tcl is a form of Tcl that has certain parts turned off so it can't hurt the computer which is running it. Nathaniel Borenstein and Marshall Rose created Safe-Tcl. Safe-Tcl can only work on some files including email messages.

Examples

In Tcl programming, empty whitespace separates words. Commands are ended by going to a new line or a semicolon:

word0 word1 word2 ... wordN

The first word is always a command which comes from Tcl's library:

commandName arg1 arg2 ... argN

For example, the commmand puts makes the computer display something:

puts "Hello, World!"

In that example, "Hello, World!" is called a string. Tcl adds a special character which can't be seen at the end of a line. This character tells the computer to go a new line after the command is complete.

Tcl is able to do math and many other things using variables. In order to use a variable, the programmer must set their value:

set variableA 1
set variableB 2

After a variable is set, it can be used in other parts of the program or set to something different. Variables can be used to perform math:

set x 2
set y 4
set ans [expr $x+$y]
puts "The answer is $ans." # The computer would show: "The answer is 6."

The command expr tells the computer to solve the "expression" or, in this case, an equation.

Easy commands

• set saves numbers, words, or letters, to a variable. It can also be used to change what is in a variable.
• proc tells the computer what a new command will do (procedure).
• if tells the computer to do what is written only if something is true.
• while tells the computer to do what is written as long as something is true.
• foreach tells the computer to something for each item in a list of variables.
• break stops the command from running. This is good to use to get out of a loop.
• continue stops the active command, but allows the loop to continue. If the loop is a while loop, it will start over. It will let foreach and for go to the next step in the program.
• return stops the active command and loop, then goes back to the procedure with a value.

Related pages

• Eggdrop
• TclX
• List of programming languages

Images for kids

• 

  A Tcl file being edited in the Eclipse IDE

See also

In Spanish: Tcl para niños