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What does Tcl do if you try to run a command that is not defined?

In Tcl, if a command doesn't exist within the loaded code the interpretter will look through the commands that can be loaded vis package ifneeded, and failing that will call the unknown proc. And there's nothing to stop you defining unknown for yourself, as I did as a demonstration on Friday afternoon on the Learning to program in Tcl course. Example source code [here]

This example also shows a loop in which a whole load of proces is defined, using names in a variable for the name of the command. Yu may think this is a bit of an odd thing to do, but in effect it's what Tk does as it defines commands for each widget, and also what ITcl ([incr-Tcl]) does for its objects - it's just not a common think in a little demo program.

Finally, the example shows how yo accesss shell environment variables via the array env

(written 2015-10-10)

 
Associated topics are indexed as below, or enter http://melksh.am/nnnn for individual articles
T214 - Tcl/Tk - Other Facilities in Tcl
  [4762] Coverage map in Tcl - how many times has each proc been called? - (2017-09-28)
  [4523] Catching failed commands and not crashing the program in Tcl - (2015-10-10)
  [4207] Exception handling in Tcl - (2013-11-14)
  [3583] Expanding a list of parameters in Tcl - {*} and eval - (2012-01-17)
  [3570] Trapping errors in Tcl - the safety net that catch provides - (2012-01-06)
  [3287] Exceptions - Tcl style - (2011-05-12)
  [2467] Tcl - catching an error before your program crashes - (2009-10-22)
  [1338] Handling Binary data in Tcl (with a note on C) - (2007-09-09)
  [1334] Stable sorting - Tcl, Perl and others - (2007-09-06)
  [1277] AgtInvoke - a command to drive Agilent Tcl software extensions - (2007-07-26)
  [782] Converting between Hex and Decimal in Tcl - (2006-06-28)
  [748] Getting rid of variables after you have finished with them - (2006-06-06)
  [461] Shortened interactive commands - (2005-10-11)
  [366] Error handling in Tcl through catch - (2005-07-02)
  [364] pu daily and p hourly - (2005-06-30)
  [239] What and why for the epoch - (2005-03-08)


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