set test {
       On the Future!-how it tells
       Of the rapture that impells
      To the swinging and the ringing
       Of the bells, bells, bells-
    Of the bells, bells, bells, bells, 
              Bells, bells, bells-
 To the rhyming and the chiming of the bells!
 }

 proc concordance {text} {
     set n 0
     foreach line [split $text \n] {
        if {$line==""} continue
        regsub -all {[^a-z]} [string tolower $line] " " line2
        incr n
        foreach word $line2 {
            if [string length $word]>=3 {lappend A($word) $n}
        }
        puts [format "%10d %s" $n $line]
     }
     puts ""
     foreach word [lsort [array names A]] {
        puts [format "%-15s %s" $word [join [luniq $A($word)] ", "]]
     }
 }
 proc luniq list {
    set res {}
    foreach i $list {
        if {[lsearch $res $i]<0} {lappend res $i}
    }
    set res
 }

 concordance $test

        1        On the Future!-how it tells
        2        Of the rapture that impells
        3       To the swinging and the ringing
        4        Of the bells, bells, bells-
        5     Of the bells, bells, bells, bells, 
        6               Bells, bells, bells-
        7  To the rhyming and the chiming of the bells!

and             3, 7
bells           4, 5, 6, 7
chiming         7
future          1
how             1
impells         2
rapture         2
rhyming         7
ringing         3
swinging        3
tells           1
that            2
the             1, 2, 3, 4, 5, 7