#!/bin/bash
# Default command anyterm will run.
# Simply prompt the user for a username and 
# ssh locally as that user

while : ; do
    echo -n "Username: "
    read U
    # Make sure it does not start with a "-" and only contains valid
    # username characters.
    if [[ "$U" =~ "^[A-Za-z0-9_][A-Za-z0-9_-]*\$" ]]; then
      ssh "$U@localhost"
    else
      echo "Bad username."
    fi
done