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Tcl/Tk module T202
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 subjectupdated
3917BODMAS - 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
 
782Converting 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
 
1282Stringing 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
 
2442Variable 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
 
1136Buffering 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
 
362The 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
 
349Comments 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)
3Looking 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)
1469Curley 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
 
1426Buffering 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
 
328Making programs easy for any user to start
If you write a program in Perl, your colleague writes a program in Tcl/Tk and your company runs an open source program that's written in Python, how do your users ensure that they get the right interpretter to run the program? You certainly don't want them to have to remember to type something like: perl ...
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 http://www.training-notes.co.uk.
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
If you are looking for a complete course and not just a information on a single subject, visit our Listing and schedule page.

Well House Consultants specialise in training courses in Tcl/Tk, Expect,Python, Perl, PHP, and MySQL. We run Private Courses throughout the UK (and beyond for longer courses), and Public Courses at our training centre in Melksham, Wiltshire, England. It's surprisingly cost effective to come on our public courses - even if you live in a different country or continent to us.

We have a technical library of over 700 books on the subjects on which we teach. These books are available for reference at our training centre. Also available is the Opentalk Forum for discussion of technical questions.


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