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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.

tcl course delegateCan 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
T202 - Tcl/Tk - Tcl Fundamentals
  [3917] BODMAS - the order a computer evaluates arithmetic expressions - (2012-11-09)
  [2442] Variable storage - Perl, Tcl and Python compared - (2009-10-08)
  [1469] Curley brackets v double quotes - Tcl, Tk, Expect - (2007-12-12)
  [1426] Buffering up in Tcl - the empty coke can comparison - (2007-11-10)
  [1136] Buffering output - why it is done and issues raised in Tcl, Perl, Python and PHP - (2007-04-06)
  [782] Converting between Hex and Decimal in Tcl - (2006-06-28)
  [362] The ireallyreallywanna operator - (2005-06-28)
  [349] Comments in Tcl - (2005-06-16)
  [328] Making programs easy for any user to start - (2005-05-29)
  [210] Joining lists in Tcl. Indirect variables in Tcl. - (2005-02-12)
  [3] Looking for a donkey - (2004-08-05)

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)
  [3285] Extracting data from a string / line from file - Tcl - (2011-05-10)
  [2472] split and join in tcl and expect - (2009-10-23)
  [2468] What are Tcl lists? - (2009-10-22)
  [1601] Replacing the last comma with an and - (2008-04-04)
  [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)
  [781] Tcl - lappend v concat - (2006-06-27)
  [463] Splitting the difference - (2005-10-13)
  [144] Tcl sandwich - lists in Tcl - (2004-12-08)

T208 - Tcl/Tk - Arrays and dicts
  [3638] Sorting dicts and arrays in Tcl - (2012-03-04)
  [3614] Tcl - dicts - a tutorial and examples - (2012-02-14)
  [3192] Tcl - Some example of HOW TO in handling data files and formats - (2011-03-04)
  [2466] Tcl - passing arrays and strings in and back out of procs - (2009-10-22)
  [1614] When an array is not an array - (2008-04-17)
  [1427] Arrays in Tcl - a demonstration - (2007-11-10)
  [779] The fragility of pancakes - and better structures - (2006-06-26)
  [122] Passing arrays to procs in Tcl - (2004-11-18)


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