[Richard Suchenwirth] 2005-10-04 - "Ellipsis" is Greek for "left out". More specifically,
it's the name of the character(s) "..." (three ASCII periods, or fancier the Unicode \u2026) 
indicating that something was left out. 
When a string is truncated to fit into a given length, the following proc adds an ellipsis where necessary:

 proc string'limit {str length} {
   expr {[string length $str]>$length? 
	"[string range $str 0 [incr length -4]]..."
   : $str}
 }
 % string'limit hello 10
 hello
 string'limit "hello long string" 10
 hello l...
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''[escargo] 4 Oct 2005'' - There are typographic rules for the use of ellipsis that make its use
less than straightforward [http://graphicdesign.about.com/od/typesetting/a/ellipsis.htm].
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[JH] - The '''string replace''' command is designed to do the ellipsis without otherwise modifying the string.  Just use:

 set str [string replace $str $length end ...]

If the string is already shorter than $length, it will not be touched.

''There is the end case where [[string length $str]] > $length, but [[string length $str]] < $length + 3.
Adding the ellipsis might make the string longer.''
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[JMN] - the little [overtype] package also supports the ellipsis.

 %package require overtype
 %set field1 [string repeat " " 5]
 %puts [overtype::left -ellipsis 1 $field1 1234567]nextfieldstring
 12...nextfieldstring

It too has an edge case where if the field is shorter than an ellipsis the result will contain just the ellipsis or part thereof.
 
 %set field1 [string repeat " " 2]
 %puts [overtype::left -ellipsis 1 $field1 1234567]nextfieldstring
 ..nextfieldstring
 
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