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For 2023 (and 2024 ...) - we are now fully retired from IT training.
We have made many, many friends over 25 years of teaching about Python, Tcl, Perl, PHP, Lua, Java, C and C++ - and MySQL, Linux and Solaris/SunOS too. Our training notes are now very much out of date, but due to upward compatability most of our examples remain operational and even relevant ad you are welcome to make us if them "as seen" and at your own risk.

Lisa and I (Graham) now live in what was our training centre in Melksham - happy to meet with former delegates here - but do check ahead before coming round. We are far from inactive - rather, enjoying the times that we are retired but still healthy enough in mind and body to be active!

I am also active in many other area and still look after a lot of web sites - you can find an index ((here))
Everything is a string - even a list

Almost all variables in Tcl are held as strings ... if you use integers and stirings in calculations such as expr and incr. the strings are converted back and forth intergally. Lists, too, are held as strings of characters in which chunks of string are counted / taken out as being elements in the list. Here's an example setting up a list ... and then reporting the length as a list (where it contains two values), and as a string (where it contains 15 letters).

  % set daze "Monday Chewsday"
  Monday Chewsday
  % puts daze
  daze
  % puts $daze
  Monday Chewsday
  % put [string length $daze]
  15
  % put [llength $daze]
  2
  %


Note my use of almost - Tcl's arrays are NOT held as simple strings - and that does make a difference (later in Tcl course we'll take a look at this)
(written 2015-03-11)

 
Associated topics are indexed as below, or enter http://melksh.am/nnnn for individual articles
T206 - Tcl/Tk - Lists
  [144] Tcl sandwich - lists in Tcl - (2004-12-08)
  [463] Splitting the difference - (2005-10-13)
  [781] Tcl - lappend v concat - (2006-06-27)
  [1282] Stringing together Tcl scripts - (2007-07-29)
  [1283] Generating traffic for network testing - (2007-07-29)
  [1334] Stable sorting - Tcl, Perl and others - (2007-09-06)
  [1402] Tcl - append v lappend v concat - (2007-10-23)
  [1405] Sorting in Tcl - lists and arrays - (2007-10-24)
  [1601] Replacing the last comma with an and - (2008-04-04)
  [2468] What are Tcl lists? - (2009-10-22)
  [2472] split and join in tcl and expect - (2009-10-23)
  [3285] Extracting data from a string / line from file - Tcl - (2011-05-10)
  [3394] The difference between lists and strings - Tcl - (2011-08-16)
  [3415] User defined sorting and other uses of callbacks in Tcl and Tk - (2011-09-02)
  [3582] Tcl collections - lists, dicts and array - (2012-01-16)
  [3583] Expanding a list of parameters in Tcl - {*} and eval - (2012-01-17)
  [3618] lists and struct::list in Tcl - Introduction to struct::list and examples - (2012-02-18)
  [4209] Lists in Tcl - fundamentals in a commented source code example - (2013-11-16)
  [4455] Working out distance between places, using OS grid references and a program in Tcl - (2015-03-11)

T205 - Tcl/Tk - String Handling in Tcl
  [404] How to check that a string contains a number in Tcl - (2005-08-06)
  [779] The fragility of pancakes - and better structures - (2006-06-26)
  [943] Matching within multiline strings, and ignoring case in regular expressions - (2006-11-25)
  [1403] Square Bracket protection in Tcl - (2007-10-23)
  [1410] Tcl / regsub - changing a string and using interesting bits - (2007-10-27)
  [3192] Tcl - Some example of HOW TO in handling data files and formats - (2011-03-04)
  [3576] Tcl - apparently odd behaviour of string trimleft - (2012-01-13)
  [4205] Regular Expression Substitution - Tcl - (2013-11-12)


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Tcl variable names - no real limits!
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Forward to
Working out distance between places, using OS grid references and a program in Tcl
Some other Articles
A new Tcl/tk example - a window to show system status
Test framework for TCL - Tcltest - some examples
Objects in Tcl - iTcl - updated first steps example
Everything is a string - even a list
Tcl variable names - no real limits!
Binary data handling - Python and Perl
Running an operating system command from your Python program - the new way with the subprocess module
Deciding whether to use parameters, conditional statements or subclasses
Spike solution, refactoring into encapsulated object methods - good design practise
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This is a page archived from The Horse's Mouth at http://www.wellho.net/horse/ - the diary and writings of Graham Ellis. Every attempt was made to provide current information at the time the page was written, but things do move forward in our business - new software releases, price changes, new techniques. Please check back via our main site for current courses, prices, versions, etc - any mention of a price in "The Horse's Mouth" cannot be taken as an offer to supply at that price.

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