I installed cygwin/curl on my machine and from tcl console or tclsh I can call the curl command however if I try to do it in a procedure I get the "invalid command name (name)" error.
e.g.
%curl -o google.html http://www.google.com
works, but
%proc a {} {curl -o google.html http://www.google.com}
%a
gives
invalid command name "curl"
I thought this was a namespace issue or something trivial but surprisingly I couldn't find too much useful information on it.