Function: sh-set-shell

Set this buffer's shell to SHELL (a string).
When used interactively, insert the proper starting #!-line,
and make the visited file executable via `executable-set-magic',
perhaps querying depending on the value of `executable-query'.

When this function is called noninteractively, INSERT-FLAG (the third
argument) controls whether to insert a #!-line and think about making
the visited file executable, and NO-QUERY-FLAG (the second argument)
controls whether to query about making the visited file executable.

Calls the value of `sh-set-shell-hook' if set.