Why sh-set-shell insert a space after #!

Why sh-set-shell insert a space after #!

[Leo]

Hello all,

If you M-x sh-set-shell in a buffer it inserts something like:

  #! /bin/bash

I am curious why a space after #!. I read this page:
http://en.wikipedia.org/wiki/Shebang_(Unix). The newsgroup post by
Dennis Ritchie also has a space. But most scripts I have seen do not. So
I am curious ;)

Leo

Re: Why sh-set-shell insert a space after #!

[Thierry Volpiatto]

Leo <sdl.web@gmail.com> writes:

> Hello all,
>
> If you M-x sh-set-shell in a buffer it inserts something like:
>
>   #! /bin/bash
>
> I am curious why a space after #!. I read this page:
> http://en.wikipedia.org/wiki/Shebang_(Unix). The newsgroup post by
> Dennis Ritchie also has a space. But most scripts I have seen do not. So
> I am curious ;)
Seems that this is wrong:
http://en.wikipedia.org/wiki/Shebang_%28Unix%29#Magic_number
http://www.in-ulm.de/~mascheck/various/shebang/#details


-- 
  Thierry
Get my Gnupg key:
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Re: Why sh-set-shell insert a space after #!

[Leo]

On 2012-08-17 13:22 +0800, Thierry Volpiatto wrote:
> Seems that this is wrong:
> http://en.wikipedia.org/wiki/Shebang_%28Unix%29#Magic_number
> http://www.in-ulm.de/~mascheck/various/shebang/#details

Have I just discovered one of the oldest bugs? ;)

Leo

Re: Why sh-set-shell insert a space after #!

[Leo]

On 2012-08-17 14:54 +0800, Leo wrote:
>> Seems that this is wrong:
>> http://en.wikipedia.org/wiki/Shebang_%28Unix%29#Magic_number
>> http://www.in-ulm.de/~mascheck/various/shebang/#details
>
> Have I just discovered one of the oldest bugs? ;)

Hello Yidong,

Any objection to installing this tiny patch in emacs-24?

diff --git a/lisp/progmodes/executable.el b/lisp/progmodes/executable.el
index c44f1d73..201b4797 100644
--- a/lisp/progmodes/executable.el
+++ b/lisp/progmodes/executable.el
@@ -84,8 +84,9 @@ (defcustom executable-magicless-file-regexp "/[Mm]akefile$\\|/\\.\\(z?profile\\|
   :group 'executable)
 
 
-(defcustom executable-prefix "#! "
+(defcustom executable-prefix "#!"
   "*Interpreter magic number prefix inserted when there was no magic number."
+  :version "24.2"
   :type 'string
   :group 'executable)
 

Why sh-set-shell insert a space after #!

[Stephen J. Turnbull]

Leo writes:
 > Hello all,
 > 
 > If you M-x sh-set-shell in a buffer it inserts something like:
 > 
 >   #! /bin/bash
 > 
 > I am curious why a space after #!. I read this page:
 > http://en.wikipedia.org/wiki/Shebang_(Unix). The newsgroup post by
 > Dennis Ritchie also has a space. But most scripts I have seen do not. So
 > I am curious ;)

IIRC, POSIX allows but doesn't require the space.  However, some
historical mostly-compatible shells had problems if there was no
space.  Since it never hurts with fully conforming shells, and
sometimes helps, it's a definite portability win.  (AFAIK there was no
particular correlation between this kind of non-conformance and other,
more important, non-conformance.)

Although it's not needed for bash, you can argue for it from
simplicity of sh-mode implementation (you don't need to detect the
shell and maintain a list of which shells care to decide whether to
insert the space) and consistency of style.

Re: Why sh-set-shell insert a space after #!

[Andreas Schwab]

"Stephen J. Turnbull" <stephen@xemacs.org> writes:

> IIRC, POSIX allows but doesn't require the space.  However, some
> historical mostly-compatible shells had problems if there was no
> space.

There is some background information in
<http://www.in-ulm.de/~mascheck/various/shebang/#blankrequired>.

Andreas.

-- 
Andreas Schwab, schwab@linux-m68k.org
GPG Key fingerprint = 58CA 54C7 6D53 942B 1756  01D3 44D5 214B 8276 4ED5
"And now for something completely different."

Re: Why sh-set-shell insert a space after #!

[Leo]

On 2012-08-17 15:18 +0800, Stephen J. Turnbull wrote:
> IIRC, POSIX allows but doesn't require the space.  However, some
> historical mostly-compatible shells had problems if there was no
> space.  Since it never hurts with fully conforming shells, and
> sometimes helps, it's a definite portability win.  (AFAIK there was no
> particular correlation between this kind of non-conformance and other,
> more important, non-conformance.)

From my reading of the two links, separation #! and the path with a
space is abnormal and evidenced by all scripts I can find. So I think
the better default for executable-prefix is "#!", not "#! ".

Leo

Re: Why sh-set-shell insert a space after #!

[Thierry Volpiatto]

Leo <sdl.web@gmail.com> writes:

> On 2012-08-17 15:18 +0800, Stephen J. Turnbull wrote:
>> IIRC, POSIX allows but doesn't require the space.  However, some
>> historical mostly-compatible shells had problems if there was no
>> space.  Since it never hurts with fully conforming shells, and
>> sometimes helps, it's a definite portability win.  (AFAIK there was no
>> particular correlation between this kind of non-conformance and other,
>> more important, non-conformance.)
>
> From my reading of the two links, separation #! and the path with a
> space is abnormal and evidenced by all scripts I can find. So I think
> the better default for executable-prefix is "#!", not "#! ".
Agree, also in all books, manuals I found , it is described like "#!/bin/bash"
and never "#! /bin/bash", same for python.

-- 
  Thierry
Get my Gnupg key:
gpg --keyserver pgp.mit.edu --recv-keys 59F29997 

Re: Why sh-set-shell insert a space after #!

[Bastien]

Leo <sdl.web@gmail.com> writes:

> Any objection to installing this tiny patch in emacs-24?

I read the links and I also think the default should be "#!".

I just applied Leo's patch.

-- 
 Bastien

Re: Why sh-set-shell insert a space after #!

[Leo]

On 2012-08-23 01:17 +0800, Bastien wrote:
> I just applied Leo's patch.

Thanks. I wonder if a :version "24.3" is needed? ;)

Leo

Re: Why sh-set-shell insert a space after #!

[Bastien]

Leo <sdl.web@gmail.com> writes:

> On 2012-08-23 01:17 +0800, Bastien wrote:
>> I just applied Leo's patch.
>
> Thanks. I wonder if a :version "24.3" is needed? ;)

Yep.  Already done.

-- 
 Bastien

Re: Why sh-set-shell insert a space after #!

[Aurélien Aptel]

On Fri, Aug 17, 2012 at 7:22 AM, Thierry Volpiatto
<thierry.volpiatto@gmail.com> wrote:
> Seems that this is wrong:
> http://en.wikipedia.org/wiki/Shebang_%28Unix%29#Magic_number
> http://www.in-ulm.de/~mascheck/various/shebang/#details

That was an interesting read, thank you.