That's what test2.tcl in this
[http://www.itworld.com/AppDev/4061/swol-1218-regex/]
"Regular Expressions" [http://www.regularexpressions.com] column does.

Also see the  [fileevent] page.  


The sample chapter 22 from [Brent Welch]s book can be downloaded from his home page and ( "TK Examples", or "TK by Example" ) [http://www.beedub.com/book/3rd/Tkexampl.pdf] also gives an example of this.  

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[Category GUI]