How to detect unused tokens

Do not know if there is a better way, but this script was created to help detect unused tokens in source:

lassign $argv head
while { [gets stdin line] >= 0 } {
    lappend fileLines $line
    foreach word [regexp -all -inline {[A-Za-z0-9]+} $line] {
        dict incr wordcount [string tolower $word]

set fp [open "freq1.html" w]
    puts $fp "<html>"
    puts $fp "<head>"
    puts $fp "    <title>Singletons are highlighted</title>"
    puts $fp "    <meta charset=\"utf-8\">"
    puts $fp "</head><body>"
    foreach line $fileLines {
        set text "<pre>"
        set strLength [string length $line]
        for {set i 0} {$i < $strLength} {} {
            if {![string is alnum [string index $line $i]]} {
                append text [string index $line $i]
                incr i
            } else {
                set word [regexp -inline {[A-Za-z0-9]+} [string range $line $i end]]
                if {[dict exists $wordcount $word] && [dict get $wordcount $word] == 1} {
                    append text "<span style=background-color:yellow>" $word "</span>"
                } else {
                    append text $word
                incr i [string length $word]
        append text "</pre>"
        puts $fp $text
    puts $fp "</body>"
    puts $fp "</html>"
close $fp

execute with "tclsh freq1.tcl < draftCode.tcl" and all singleton tokens will appear highlighted in context.