How to fork an external program and get back it's stdout and stderr without blocking and WITH a timeout!
proc _exec { prog { var "" } { tmpfile "" } { i 0 } { to 5 } } {
if { ! [ regexp {^file\d+$} $prog ] } {
set tmpfile _exec-[ clock seconds ][ clock clicks ]
set tmpfile /tmp/$tmpfile
if { [ catch {
set fid [ open "|$prog 2>$tmpfile" ]
fconfigure $fid -blocking off
fconfigure $fid -buffering full
} err ] } {
file delete -force $tmpfile
return -code error "_exec: $err"
}
} else {
set fid $prog
}
set ret [ read $fid ]
if { ($i / 10) >= $to } {
if { ! [ string length $ret ] } {
set ret timed_out
}
}
if { [ string length $ret ] || [ file size $tmpfile ] } {
set pids [ pid $fid ]
catch { ::close $fid }
foreach pid $pids {
catch { exec kill -KILL $pid }
}
set fid [ open $tmpfile r ]
set err [ read $fid [ file size $tmpfile ] ]
catch { ::close $fid }
file delete -force $tmpfile
if { [ string length $var ] } {
set ::$var [ list $ret $err ]
}
} else {
incr i
after 100 [ list _exec $fid $var $tmpfile $i ]
}
}
Usage example:
# of course, you really want to trace the variable, # not vwait on it! _exec "curl http://www.ligo.caltech.edu" foo vwait ::foo puts $::foo