How to suppress a proc's return value in tcl prompt -

i'm relatively new in tcl, in tcl prompt, when invoke proc return value, proc's return value echoed tcl. there way stop (without affecting puts or similar functionality) example

bash$ tclsh % proc {} { puts  "hello"; return 34; } % hello 34 % 

now how suppress 34 coming screen? appreciated.

update: proc part of tool, earlier did not have return value, conditionally can return value. can called script , there won't problem (as bryan pointed out). , can called interactive prompt, after necessary outputs, return value getting printed unnecessarily. 1) don't have facility of changing user's tclshrc 2) existing scripts should continue work. , seems strange every time proc called, after necessary outputs, number gets printed. user, needless information unless has caught value , wants something. wanted value delivered user, without getting printed prompt/ui (hope i'm clear )

the interactive shell code in tclsh , wish print non-empty result. nothing printed, have have last command on “line” produce empty result. command use?

many commands produce empty result:

if 1 {} subst "" format "" 

however, shortest probably:

list 

thus, write code like:

a;list 

of course, becomes useful when command actually produces large result don't want see. in cases, find useful use measures size of result, such as:

set tmp [something_which_produces a_gigantic result]; string length $tmp 

the useful commands find string length, llength , dict size.

---

if absolutely must not print result of command, have write own interactive loop. there 2 ways this, depending on whether running inside event loop or not:

without event loop

this simplistic version checks see if command name in user typed. it's not idea arbitrarily throw away results otherwise!

set accum "" while {[gets stdin line] >= 0} {     append accum $line "\n"     if {[info complete $accum]} {         if {[catch $accum msg]} {             puts stderr $msg         } elseif {$msg ne "" && ![string match *thespecialcommand* $accum]} {             puts $msg         }         set accum ""     } } 

with event loop

this handling blocking io case; that's correct thing when input cooked terminal (i.e., default)

fileevent stdin readable handleinput set accum "" proc handleinput {} {     global accum     if {[gets stdin line] < 0} {         exit; # or whatever     }     append accum $line "\n"     if {[info complete $accum]} {         if {[catch {uplevel "#0" $accum} msg]} {             puts stderr $msg         } elseif {$msg ne "" && ![string match *thespecialcommand* $accum]} {             puts $msg         }         set accum ""     } } vwait forever; # assuming you're not in wish or have other event loop... 

how detect command being executed

the code above uses ![string match *thespecialcommand* $accum] decide whether throw away command results, ugly. more elegant approach leverages tcl's own built-in hooks use execution trace detect whether command has been called (i'll show non-event-loop version here, brevity). other advantage of is simple extend suppressing output multiple commands: add trace each of them.

trace add execution thespecialcommand enter suppressoutput proc suppressoutput args {     # important; not suppress when called inside command     if {[info level] == 1} {         set ::suppresstheoutput 1     } }  # similar here on set accum "" while {[gets stdin line] >= 0} {     append accum $line "\n"     if {[info complete $accum]} {         set suppresstheoutput 0;                       # <<<<<< note this!         if {[catch $accum msg]} {             puts stderr $msg         } elseif {$msg ne "" && !$suppresstheoutput} { # <<<<<< note this!             puts $msg         }         set accum ""     } } 

to clear, wouldn't ever in own code! i'd suppress output manually if mattered.