List Box in tcl/tk

#!/bin/sh
# chk_btnn.tcl \
exec tclsh "$0" ${1+"$@"}
# Graphical User Interface :ListBox

proc insert_to_list {} {

#take the input of the entry

set input [ .ent get ]

#if { $input =""} {return}

#put input on the end of all listbox items

.lst insert end "$input"
}
proc delete_from_list {} {

#to delete the current selection

set selected_index [ .lst curselection]
if { $selected_index ==""} { return }
.lst delete $selected_index
.lst activate 0
}


listbox .lst -selectmode single ; # select mode can be single browse multiple or extend; the default value is browse


.lst insert end "student " "Teacher" "clerk" "Business Man"  "Common Man" "Computer Expert" "Others"


.lst configure -activestyle underline

.lst activate 1
entry .ent -textvariable text_ent
button .but1 -text "insert to list" -command "insert_to_list"
button .but2 -text "delete from list" -command "delete_from_list"
pack .lst
pack .ent
pack .but1
pack .but2