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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 file from which the source was run at that same point.

Can it be that easy? Not quite - you may have to deal with debris left from previous commands. Although Tcl will not (in most circumstances) let you use a variable that does not exist, there are a few exceptions and if these exceptions are used by the sourced file, you could be in trouble by not starting from a clean sheet. Some of the commands you need to watch are:

append This command will create a new variable if it does not exist, but alter an existing variable if it does exist. If your sourced file uses an append on a variable that is assumed to be initially empty, then a series of calls to that file can cause a buildup of data which you do not want to happen.

lappend This command will create a new variable if it does not exist, but alter an existing variable if it does exist. If your sourced file uses a lappend on a variable that is assumed to be initially empty, then a series of calls to that file can cause a buildup of data which you do not want to happen.

info exists If you check whether a variable exists as a part of your script to see whether it's just started, bear in mind that with a series of sourced files, it may actually exist from something you've previously pulled in.

array names If you have an array set up in one sourced file and then use that same array in a second sourced file, assuming it to start empty, then commands such as array names will reveal the old information to the new sourced file.

open You should close files once you open them. I know that files do get closed at the end of a script run, but if you source a series of files you can end up with a build-up of open files. This can be a particular issue if one sources file writes to a file, then the next opens it to read it back. Run as two separate Tcl commands, it will all work fine as the file is flushed and closed, but with two files of Tcl sourced from within a single script, it's another matter.

(written 2007-07-29, updated 2011-03-01)

 
Associated topics are indexed as below, or enter http://melksh.am/nnnn for individual articles
T208 - Tcl/Tk - Arrays and dicts
  [122] Passing arrays to procs in Tcl - (2004-11-18)
  [779] The fragility of pancakes - and better structures - (2006-06-26)
  [1283] Generating traffic for network testing - (2007-07-29)
  [1405] Sorting in Tcl - lists and arrays - (2007-10-24)
  [1427] Arrays in Tcl - a demonstration - (2007-11-10)
  [1614] When an array is not an array - (2008-04-17)
  [2466] Tcl - passing arrays and strings in and back out of procs - (2009-10-22)
  [3192] Tcl - Some example of HOW TO in handling data files and formats - (2011-03-04)
  [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)
  [3614] Tcl - dicts - a tutorial and examples - (2012-02-14)
  [3638] Sorting dicts and arrays in Tcl - (2012-03-04)

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)
  [1334] Stable sorting - Tcl, Perl and others - (2007-09-06)
  [1402] Tcl - append v lappend v concat - (2007-10-23)
  [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)
  [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)
  [4454] Everything is a string - even a list - (2015-03-11)
  [4455] Working out distance between places, using OS grid references and a program in Tcl - (2015-03-11)

T202 - Tcl/Tk - Tcl Fundamentals
  [3] Looking for a donkey - (2004-08-05)
  [210] Joining lists in Tcl. Indirect variables in Tcl. - (2005-02-12)
  [328] Making programs easy for any user to start - (2005-05-29)
  [349] Comments in Tcl - (2005-06-16)
  [362] The ireallyreallywanna operator - (2005-06-28)
  [782] Converting between Hex and Decimal in Tcl - (2006-06-28)
  [1136] Buffering output - why it is done and issues raised in Tcl, Perl, Python and PHP - (2007-04-06)
  [1426] Buffering up in Tcl - the empty coke can comparison - (2007-11-10)
  [1469] Curley brackets v double quotes - Tcl, Tk, Expect - (2007-12-12)
  [2442] Variable storage - Perl, Tcl and Python compared - (2009-10-08)
  [3917] BODMAS - the order a computer evaluates arithmetic expressions - (2012-11-09)
  [4324] Learning to program - variables and constants - (2014-11-22)
  [4453] Tcl variable names - no real limits! - (2015-03-10)


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A wasted evening?
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Latercomer to the technology
West Wilts - no longer Wet Wilts - show
The Gdansk fireball
West Wilts Show
AgtInvoke - a command to drive Agilent Tcl software extensions
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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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