playing with pipes

foreach {0r 0w} [chan pipe] break
foreach {1r 1w} [chan pipe] break
foreach {2r 2w} [chan pipe] break

fconfigure stdin -blocking no
fconfigure $1r -blocking no
fconfigure $2r -blocking no
fconfigure $0w -buffering none


set cmd {grep-v {error}}

fileevent stdin readable [list {*}$cmd stdin $0w]
fileevent $1r   readable [list {*}$cmd $1r stdout]
fileevent $2r   readable [list {*}$cmd $2r stderr]

proc cat {in out {cond {}}} {
    set s [read $in]
    if {$s ne {}} {
        if {$cond eq {} || [uplevel 1 $cond [list $s]]} {
            puts -nonewline $out $s
        }
    } elseif {[eof $in]} {
        incr ::eof
    }
}

proc not {args} {expr ![uplevel 1 $args]}

proc grep {s in out} {cat $in $out [list regexp $s]}
proc grep-v {s in out} {cat $in $out [list not regexp $s]}

exec {*}$argv <@$0r >@$1w 2>@$2w &
vwait eof