The differences between the Expectk and Expect environment follows.
The send command is Tk's. Expect's send command can be invoked by the name send_spawn. (For compatibility, Expect allows either send or send_spawn to be used.)
Scripts may be invoked implicitly on systems which support the #! notation by marking the script executable, and making the first line in your script:
#!/usr/local/bin/expectk -f
Of course, the path must accurately describe where Expectk lives. /usr/local/bin is just an example.