Tcl is a command based language - everything you do uses a command that starts with a command word such as puts to output information or set to assign a value to a variable. The while command (yes, it really is a command) lets you define a block of code that's to be run repeatedly while a condition is true, and so on.

As well as storing Tcl programs in a file, you can type Tcl commands in at an interactive prompt ... and if you do so, you're allowed to shorten the name of your commands provided they remain non-ambiguous. This is why Tcl will let you pu but not p ....


earth-wind-and-fire:~ grahamellis$ tclsh
% pu daily
daily
% p hourly
ambiguous command name "p": package pid proc puts pwd
% exit
earth-wind-and-fire:~ grahamellis$


Please excuse the - err - lavatorial sense of humour this example shows. It came up (I confess I originated it) on a Tcl Course that I've just completed in Scotland.
(written 2005-06-30, updated 2006-06-05)

 T214 - Tcl/Tk - Other Facilities in Tcl
  [239] What and why for the epoch - (2005-03-08)
  [366] Error handling in Tcl through catch - (2005-07-02)
  [461] Shortened interactive commands - (2005-10-11)
  [748] Getting rid of variables after you have finished with them - (2006-06-06)
  [782] Converting between Hex and Decimal in Tcl - (2006-06-28)
  [1277] AgtInvoke - a command to drive Agilent Tcl software extensions - (2007-07-26)
  [1334] Stable sorting - Tcl, Perl and others - (2007-09-06)
  [1338] Handling Binary data in Tcl (with a note on C) - (2007-09-09)
  [2467] Tcl - catching an error before your program crashes - (2009-10-22)
  [3287] Exceptions - Tcl style - (2011-05-12)
  [3570] Trapping errors in Tcl - the safety net that catch provides - (2012-01-06)
  [3583] Expanding a list of parameters in Tcl - {*} and eval - (2012-01-17)
  [4207] Exception handling in Tcl - (2013-11-14)
  [4523] Catching failed commands and not crashing the program in Tcl - (2015-10-10)
  [4525] What does Tcl do if you try to run a command that is not defined? - (2015-10-10)
  [4762] Coverage map in Tcl - how many times has each proc been called? - (2017-09-28)

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