[oclug] OT: tcl question

[Patrick Smith]

Joe Burpee wrote:
> I think `concat' would have a similar effect and make the
> `eval' relatively safe.  It strips off at most one level of nesting so
> it preserves the args as separate words.
> 
> eval exec [concat ls -l $dirs]

But concat doesn't process the elements of the lists that are its 
arguments.  So how is the above different from

	eval exec ls -l $dirs

?

For example:

% set dirs "a ; b"
a ; b
% concat ls -l $dirs
ls -l a ; b

On the other hand, lappend does escape list elements.  So to make an 
arbitrary list safe for eval you could do something like this:

 > touch a \; b
 > tclsh
% set dirs "a ; b"
a ; b
% set args {}
% foreach d $dirs {lappend args $d}
% set args
a {;} b
% eval exec ls -l $args
-rw-r--r--    1 pat      pat             0 Mar 16 12:19 ;
-rw-r--r--    1 pat      pat             0 Mar 16 12:19 a
-rw-r--r--    1 pat      pat             0 Mar 16 12:19 b

-- 
patsmith at pobox.com