2) Child + fileevent (channel)
 
proc wasis {arg} {
  global jobFinished
  puts "Still at $arg"
    if {![eof $arg]} {
        gets $arg data
      if [eof $arg] {
          set jobFinished 1
          catch {close $arg}
          puts "EOF reached"
          return
    }}}    
 
set f [open "|calc " r]
fconfigure $f
   -buffering none -blocking no
fileevent $f readable "wasis $f"
vwait jobFinished
exit