Messages in this thread | | | Date | Tue, 6 Mar 2001 10:17:33 -0800 | Subject | Re: binfmt_script and ^M (historical note) | From | Don Dugger <> |
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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? > > - > To unsubscribe from this list: send the line "unsubscribe linux-kernel" in > the body of a message to majordomo@vger.kernel.org > More majordomo info at http://vger.kernel.org/majordomo-info.html > Please read the FAQ at http://www.tux.org/lkml/
-- Don Dugger "Censeo Toto nos in Kansa esse decisse." - D. Gale n0ano@valinux.com Ph: 303/938-9838 - To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
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