Tcl/Tk - Tcl Fundamentals

Exercises, examples and other material relating to training module T202. This topic is presented on public courses Learning to program in Tcl, Tcl Programming, Tcl Programming

Starting with a first program ("Hello World" in Tcl), we move on to cover command syntax and grouping with quotes, brackets and braces. Amongst the most important commands covered at this early stage are those that let you read from the keyboard, write to the screen and create, display and perform basic operations on variables.

Related technical and longer articles

Brackets and Braces in Tcl

Articles and tips on this subject		updated
4453	Tcl variable names - no real limits! In Tcl, there are no limits as to what you use as a vaiable name in Tcl, although I would reommend that you stick with "letter, followed by letters, digits, underscores". Here are some examples of thinks you can, but should not, write: % set " " ohdear! ohdear! % ...	2015-03-11
4324	Learning to program - variables and constants Further material from our "learning to program in ...." courses ... an introduction to variables and constants variable basics Information - data - needs to be stored in a program between statements. Or rather it needs to be stored in the computer's memory. At the lowest of levels, that's a binary ...	2014-11-22
3917	BODMAS - the order a computer evaluates arithmetic expressions What order does a computer program use to evaluate expressions? If I write 2 + 3 * 4 + 5 does it start off, left to right ... 2 + 3 is 5 5 * 4 is 20 20 + 5 is 25 No! it does not, even though the newcomer might think that was the most natural way for ...	2012-11-10
782	Converting between Hex and Decimal in Tcl Tcl is much used in the semiconductor industry, so there's a common requirement to use it to convert values back and forth between hexadecimal (base 16) and decimal (base 10). Easily done! The format command can be used to convert from decimal to hexadecimal, and the expr command can be used to convert ...	2011-03-01
1282	Stringing together Tcl scripts If you have a series of Tcl scripts that you want to run in a sequence, you can call all of them up in a master script using a series of source commands. This command switches input from the current script (sources) to the new source given as if the text of the sourced file was copied in to the original ...	2011-03-01
2442	Variable storage - Perl, Tcl and Python compared From Monday to Wednesday, I was teaching Python to a group of delegates at a company where I have previously taught Tcl and Expect and Perl. And this interesting diagram shows just what a contrast there is between the three languages right from the start - in terms of how data is stored into variables! In ...	2009-10-08
1136	Buffering output - why it is done and issues raised in Tcl, Perl, Python and PHP When you go to board a plane at Heathrow, do the ground staff admit the passengers one at a time, ensuring that each is seated before the next boards, and sealing and re-opening the main doors between each? What a stupid and inefficient system that would be!! The same thing applies when you're programming ...	2009-08-31
362	The ireallyreallywanna operator In Tcl, any character (yes - any character) can appear in a variable name, though making use of variable names that contain - for example - spaces adds a needless complexity to your coding. Groups of special characters can be protected from the Tcl interpreter by wrapping them in curly braces, and individual ...	2008-06-07
349	Comments in Tcl It's always a good idea to comment your programs. OK - I know you know that, but I find it's always a good idea to remind people too! In Tcl, you add a comment starting with a # character and really what you're adding is a "do nothing" command .... in other words, the # must appear where a command ...	2008-06-05 (short)
3	Looking for a donkey Why is it that the most common-place of things is hard to find when you need it? I was driving around the countryside early this evening looking for a donkey to photograph .... ...	2008-04-29 (short)
1469	Curley brackets v double quotes - Tcl, Tk, Expect In Tcl, both Curley braces and double quotes can be used to hold a block of program or data together as a single unit / parameter ... but there are differences ... a) Curley braces can stretch over a number of lines, with new lines within the block being simply a part of the block. So they're ideal ...	2007-12-13
1426	Buffering up in Tcl - the empty coke can comparison A comment on buffering in Tcl .... if {1 == 0} { When you finish drinking a can of Coke, you don't call your local recycling plant up straight away and have them send a truck around to collect the empty - that would be inefficient to put it mildly. And in the same way, a computer doesn't always save ...	2007-11-10
210	Joining lists in Tcl. Indirect variables in Tcl. With all programming languages, there seem to be a few things that you end up saying "I'm SURE there's a way to do that" .... yet you can't find out how. Here are two quick solutions in Tcl - a specialist subject, I know, but one of the busiest on our forum. # Two quick solutions in Tcl ... # How ...	2006-06-05

Examples from our training material

anno	A trivial Tcl program with comments
anno2	Comments - inline and continuations
gr2	Double quote substitution in Tcl
greet	Reading from the user in Tcl
gry	Variables in Tcl - first use
hddh	Hexadecimal to decimal, and decimal to hex, in Tcl
pricer	Completed simple application in Tcl - pricing tickets

Pictures

Tcl trainees come from far and wide
Square brackets and braces in Tcl

Background information

Some modules are available for download as a sample of our material or under an Open Training Notes License for free download from [here].

Topics covered in this module

Hello World.
Running environment.
source.
Structure of Tcl Commands.
Running from the command line.
Integration into your system.
Step 1 - First line.
Step 2 - Mark the program as being executable.
Step 3 - Ensure that your program is on the "PATH"..
The comment command and more syntax.
Comments.
More flexible command syntax.
Variables.
Setting up variables.
Referencing variables.
Variable substitution using double quotes.
Reading Input.
fileIds.
Command substitution.
flushing.
The expr command.
Integer v float.

Complete learning

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