printing - TCL - How to print on the screen th messages that where printed during execution of exec command? -

say have want execute script or , executable file printing runtime output of execution.

when do:

set log [exec ./executable_file] puts $log 

then waits long time , prints @ once. want runtime printing. how can this?

not perfect (as require writing external file):

set log [exec executable_file | tee log.txt >@stdout] 

the output displayed immediately, @ same time, saved 'log.txt'. if don't care saving output:

set log [exec executable_file >@stdout]