This is a script to automate writing shebang at the top of the file. You can add any extension to 'case' statement.

shebang.sh

#!/bin/sh
#set this script as alias of editor like
#alias vim='/path/shebang.sh'

if [ "${1}" = "" ]; then
  vim
fi
filename=${1}
if [ -e $filename ]; then
  vim $filename
else
  case $filename in
    *\.rb) touch $filename
           echo '#!'`which ruby` > $filename
           vim $filename;;
    *\.py) touch $filename
           echo '#!'`which python` > $filename
           vim $filename;;
    *\.sh) touch $filename
           echo '#!'`which sh` > $filename
           vim $filename;;
    *) vim $filename;;
  esac
fi