Jos Decoster <decoster@retarget.com> wrote in [the comp.lang.tcl newsgroup]:

When not using canvas widgets, I sometimes use the following to change the fonts of a running application:

 # Put your favourite fonts here
 set font(Button)      {Helvetica -12 bold}
 set font(Checkbutton) {Helvetica -12 bold}
 set font(Radiobutton) {Helvetica -12 bold}
 set font(Label)       {Helvetica -12 bold}
 set font(Entry)       {Helvetica -12}
 set font(Listbox)     {Helvetica -12 bold}
 set font(Menuentry)   {Helvetica -12 bold}
 set font(Menu)        {Helvetica -12 bold}
 set font(Menubutton)  {Helvetica -12 bold}
 set font(Message)     {Helvetica -12 bold}
 set font(Scale)       {Helvetica -12 bold}
 set font(Text)        {Courier   -12}

 proc refont_tree { path } {
    global font

    foreach child [winfo children $path] {
        set childtype [winfo class $child]
        if { [info exists font($childtype)] } {
            if {[catch {$child configure -font $font($childtype)} msg] } {
                puts stderr "$child ($childtype) ERROR: $msg"
            }
        }
        refont_tree $child
    }
 }

 refont_tree .
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[Arts and crafts of Tcl-Tk programming]