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split and join in tcl and expect

Split and join in most languages convert strings of text into arrays / lists / collections of other sorts. But in Tcl, all variables are held as strings, so are split and join actually needed?

If you're working with a collection of single words - no embedded spaces, no special characters, space delimited, then running split and join in Tcl will return you a string that's identical to the one you sent to them ... but if you do have special characters involved, it's another matter:

Dorothy-2:tcl grahamellis$ tclsh
% set places [list Calne Devizes Melksham Corsham Bradford-on-Avon]
Calne Devizes Melksham Corsham Bradford-on-Avon
% join $places
Calne Devizes Melksham Corsham Bradford-on-Avon
% split [join $places]
Calne Devizes Melksham Corsham Bradford-on-Avon
% Dorothy-2:tcl grahamellis$


Dorothy-2:tcl grahamellis$ tclsh
% set places [list "404, The Spa" {"Well House Manor"} Bristol]
{404, The Spa} {"Well House Manor"} Bristol
% join $places
404, The Spa "Well House Manor" Bristol
% split [join $places]
404, The Spa {"Well} House Manor\" Bristol
% Dorothy-2:tcl grahamellis$

Because they're so often 'null' in their effect, you should test any code that uses lists very carefully, and with special characters too when you're working in Tcl.

I've added an example from this week's Tcl course here, and there are further string manipulation examples here and here. A further example here shows a case of handling a string as a list where you don't need to use split or join.
(written 2009-10-23)

Associated topics are indexed as below, or enter http://melksh.am/nnnn for individual articles
T205 - Tcl/Tk - String Handling in Tcl
  [4455] Working out distance between places, using OS grid references and a program in Tcl - (2015-03-11)
  [4454] Everything is a string - even a list - (2015-03-11)
  [4205] Regular Expression Substitution - Tcl - (2013-11-12)
  [3576] Tcl - apparently odd behaviour of string trimleft - (2012-01-13)
  [3285] Extracting data from a string / line from file - Tcl - (2011-05-10)
  [3192] Tcl - Some example of HOW TO in handling data files and formats - (2011-03-04)
  [1601] Replacing the last comma with an and - (2008-04-04)
  [1410] Tcl / regsub - changing a string and using interesting bits - (2007-10-27)
  [1403] Square Bracket protection in Tcl - (2007-10-23)
  [943] Matching within multiline strings, and ignoring case in regular expressions - (2006-11-25)
  [779] The fragility of pancakes - and better structures - (2006-06-26)
  [404] How to check that a string contains a number in Tcl - (2005-08-06)

T206 - Tcl/Tk - Lists
  [4209] Lists in Tcl - fundamentals in a commented source code example - (2013-11-16)
  [3618] lists and struct::list in Tcl - Introduction to struct::list and examples - (2012-02-18)
  [3583] Expanding a list of parameters in Tcl - {*} and eval - (2012-01-17)
  [3582] Tcl collections - lists, dicts and array - (2012-01-16)
  [3415] User defined sorting and other uses of callbacks in Tcl and Tk - (2011-09-02)
  [3394] The difference between lists and strings - Tcl - (2011-08-16)
  [2468] What are Tcl lists? - (2009-10-22)
  [1405] Sorting in Tcl - lists and arrays - (2007-10-24)
  [1402] Tcl - append v lappend v concat - (2007-10-23)
  [1334] Stable sorting - Tcl, Perl and others - (2007-09-06)
  [1283] Generating traffic for network testing - (2007-07-29)
  [1282] Stringing together Tcl scripts - (2007-07-29)
  [781] Tcl - lappend v concat - (2006-06-27)
  [463] Splitting the difference - (2005-10-13)
  [144] Tcl sandwich - lists in Tcl - (2004-12-08)

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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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