[Richard Suchenwirth] 2002-07-29 - The behavior of some shells (even including cmd.exe!) to complete commands or filenames on <Tab> is occasionally asked from Tcl too. Here is a quick shot of a mini-console with an entry, that does command completion, a label where multiple alternatives are shown, and a text widget where the command and its result (or error message) are displayed when <Return> was hit:
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 proc complete {varName infoName} {
     upvar 1 $varName var
     upvar 1 $infoName info
     if {[llength $var]==1} {
	 set cmds [info commands $var*]
	 if {[llength $cmds]==1} {
	     set var "$cmds " ;# added complementary blank
	 } elseif {[llength $cmds]>1} {
	     set info [lsort $cmds] ;# make choices available for display
             set var [longestCommonPrefix $cmds] ;# partial completion (1)
	 } else bell
     }
 }
# (1): longestCommonPrefix is available on [Additional string functions]
 entry .e -textvar entry
 bind .e <Tab> {complete entry info; %W icursor end; break}
 bind .e <Return> {catch $entry res; .t insert end "%% $entry\n$res\n"}
 label .info -textvar info -anchor w -width 60
 text .t
 pack .e .info  -fill x
 pack .t        -fill both -expand 1 
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Further extensions that one could add:
   * try subcommands for well-known commands like [string], [package], [info], ...
   * if a word starts with $, check [[info vars]] of the rest of string
   * try [glob] on other than first word
   
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[tkcon] has routines for expanding pathnames, command names and variable names (::tkcon::Expand* in the code).  These have also been carried over into the updated console of the Tcl core.


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a variant with instant completion
[Command completion in the iFile console]

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[Arts and crafts of Tcl-Tk programming]