sh-shell-arg

sh-shell-arg is a variable defined in `sh-script.el'.
Its value is

((bash)
 (csh . "-f")
 (pdksh)
 (ksh88)
 (rc . "-p")
 (wksh)
 (zsh . "-f"))

Documentation:
Single argument string for the magic number. See `sh-feature'.

You can customize this variable.