#!/usr/bin/wish
#code to make a Marquee
label .student_id_lab
pack .student_id_lab

set str "mysql is a database "
set substr ""

while { true } {

for { set i 0 } { $i < [string length $str] } { incr i } {
    for { set j 0 } { $j < $i } { incr j } {
    set current_char [string index $str $j ]
    set substr "$substr$current_char"
    }
    .student_id_lab configure -text "$substr"
    set substr ""
    update
    after 500
}
.student_id_lab configure -text ""
}