Insert shebang #! with Emacs

howto-shebang

#!/usr/bin/tail -n+2
Don't chmod that file! Don't type a shebang! Edit an executable script
in Emacs and invoke

    M-x executable-set-magic

This is a self-displaying file made with `executable-self-display'. If
you have had a stroke and forgotten how to make a script executable by
hand, just insert the following form as the first line of the script

    #!/path/to/shell [optional-argument]

Then change the mode of the script

    chmod u+x script