== A _bash_ irritation: the incompatible _exec_

There are a reasonable number of good things about _bash_ (and the
general GNU program attitude of which it is a standards-bearer). But
[[every so often MutableBashHistory]] it does something that causes me
to grind my teeth. This time around the irritation is what _bash_ has
done to the innocent _exec_ command.

What they've done is simple: they've made _exec_ take options.

The easiest way to explain the problem with this is in illustrated
form. So:

> _sh$ exec -rc_ \\
> <... program runs ...>
>  
> _bash$ exec -rc_ \\
> _bash: exec: -r: invalid option_ \\
> _exec: usage: exec [-cl] [-a name] file [redirection ...]_ \\
> _bash$ exec -- -rc_\\
> <... program runs ...>
>
>  sh$ exec -- -rc
>  exec: --: not found

Oops.

Since bash's _exec_ takes options, it must complain about invalid
options.  This makes it reject valid programs that happen to start with
a dash, so it needs a way around that, but the way is not compatible
with other Bourne shells because, of course, _exec_ does not take
options so there is no need to support an option to ignore things that
look like options.

(As a bonus irritation bash does this *all the time*, not just when
invoked as _bash_. So much for compatibility.)

If you are in this situation, it may be helpful to know that one way
of checking to see if you are in _bash_ is to look for the presence of
a (($BASH_VERSINFO)) environment variable. There are probably better
ways, but this one works well enough for me and I could spot it in the
_bash_ manpage.

(I stubbed my toe on this today because Ubuntu 8.04 changed _/bin/sh_
from _bash_ to another, more strictly Bourne compatible shell, which
made my previous slapdash workaround stop working so I had to actually
pay attention to this issue.)