tail -f example

#!/usr/bin/tclsh

proc multitail {args} {
    foreach fn $args {
        set chan [open "|tail -f $fn" r]
        fconfigure $chan -blocking 0
        fileevent $chan readable [list readable $fn $chan]
    }
}

proc readable {fn chan} {
    if {[gets $chan line] <= 0} {
        if {[eof $chan]} {
            puts "EOF on $fn"
            close $chan
        }
    } else {
        puts "$fn:$line"
    }
}

exec touch a.txt b.txt
multitail a.txt b.txt

vwait forever