Re: binfmt_script and ^M (historical note)

[Don Dugger <n0ano@valinux.com>]

Paul-

Minor historical note.  The `#!' processing was never done by the
shell, this was always done in the kernel.  Think about about it,
the `#' character denotes a comment line, the shell ignores that
line.  `#!' was used to create a way for the kernel to execute
a shell script directly.  Since the kernel recognized the type of
executable based on a 16-bit magic number `#!' became a new magic
number that meant "break the remainder of the line into `program'
and `args' and then execute `program' with `args'".

A nice side effect of this is that it became a way to create shell
scripts that worked no matter what shell a user was running.  For
efficiency, most shells just read and execute a shell script so
releasing a Bourne shell script to a group of CSH users created
problems.  At the expense of a `fork' and `exec' the `#!' magic
number solved this problem.

On Tue, Mar 06, 2001 at 12:33:49PM +0000, Paul Flinders wrote:
> Andreas Schwab wrote:
> 
> > Paul Flinders <paul@dawa.demon.co.uk> writes:
> >
> > |> Andreas Schwab wrote:
> > |>
> > |> > This [isspace('\r') == 1] has no significance here.  The right thing to
> > |>
> > |> > look at is $IFS, which does not contain \r by default.  The shell only splits
> > |>
> > |> > words by "IFS whitespace", and the kernel should be consistent with it:
> > |> >
> > |> > $ echo -e 'ls foo\r' | sh
> > |> > ls: foo: No such file or directory
> > |>
> > |> The problem with that argument is that #!<interpreter> can be applied
> > |> to more than just shells which understand $IFS, so which environment
> > |> variable does the kernel pick?
> >
> > The kernel should use the same default value of IFS as the Bourne shell,
> > ie. the same value you'll get with /bin/sh -c 'echo "$IFS"'.  This is
> > independent of any settings in the environment.
> >
> > |> It's a difficult one - logically white space should terminate the interpreter
> >
> > No, IFS-whitespace delimits arguments in the Bourne shell.
> 
> Way back whenever processing #! was moved from the
> shell to the kernel** this argument would have made sense -
> today I'm not so sure.
> 
> But I'm quite happy for the kernel to use just space and
> tab if it wishes, or anything else for that matter but it _is_
> confusing that the error code doesn't distinguish problems
> with the script from problems with the interpreter.
> 
> **Did linux ever rely on the shell for this?
> 
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-- 
Don Dugger
"Censeo Toto nos in Kansa esse decisse." - D. Gale
n0ano@valinux.com
Ph: 303/938-9838